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Background: Preclinical data show that belinostat (Bel) is synergistic with carboplatin and paclitaxel in ovarian cancer. To further evaluate the clinical activity of belinostat, carboplatin, and paclitaxel (BelCaP), a phase 1b/2 study was performed, with an exploratory phase 2 expansion planned specifically for women with recurrent epithelial ovarian cancer (EOC)., Methods: Thirty-five women were treated on the phase 2 expansion cohort. BelCap was given as follows: belinostat, 1000 mg/m² daily for 5 days with carboplatin, AUC 5; and paclitaxel, 175 mg/m² given on day 3 of a 21-day cycle. The primary end point was overall response rate (ORR), using a Simon 2 stage design., Results: The median age was 60 years (range, 39-80 years), and patients had received a median of 3 prior regimens (range, 1-4). Fifty-four percent had received more than two prior platinum-based combinations, sixteen patients (46%) had primary platinum-resistant disease, whereas 19 patients (54%) recurred within 6 months of their most recent platinum treatment. The median number of cycles of BelCaP administered was 6 (range, 1-23). Three patients had a complete response, and 12 had a partial response, for an ORR of 43% (95% confidence interval, 26%-61%). When stratified by primary platinum status, the ORR was 44% among resistant patients and 63% among sensitive patients. The most common drug-related adverse events related to BelCaP were nausea (83%), fatigue (74%), vomiting (63%), alopecia (57%), and diarrhea (37%). With a median follow-up of 4 months (range, 0-23.3 months), 6-month progression-free survival is 48% (95% confidence interval, 31%-66%). Median overall survival was not reached during study follow-up., Conclusions: Belinostat, carboplatin, and paclitaxel combined was reasonably well tolerated and demonstrated clinical benefit in heavily-pretreated patients with EOC. The addition of belinostat to this platinum-based regimen represents a novel approach to EOC therapy and warrants further exploration.

Purpose: Histone deacetylases (HDAC) are involved in the regulation of gene transcription. Aberrant HDAC activity has been associated with tumorigenesis, and, therefore, HDACs are potential targets for the treatment of cancers, including tumors of the central nervous system (CNS). Belinostat is a novel, potent, pan-HDAC inhibitor with antiproliferative activity on a wide variety of tumor cell lines. We studied the cerebrospinal fluid (CSF) penetration of intravenous (IV) belinostat in a non-human primate model as a surrogate for blood:brain barrier penetration., Design: Five adult rhesus monkeys received increasing doses of belinostat (10-60 mg/kg) as a 30-min IV infusion. Serial blood and CSF samples were collected over 48 h. Plasma and CSF concentrations of belinostat were quantified with an LC/MS/MS assay. Pharmacokinetic parameters were calculated using non-compartmental methods, and CSF penetration is expressed as the ratio of the area under the concentration-time curve (AUC) in CSF to the AUC in plasma., Results: Belinostat was cleared rapidly from plasma with a half-life of 1.0 h, a mean residence time of 0.47 h, and a clearance of 425 ml/min/m(2). CSF penetration of belinostat was limited. CSF drug exposure was <1% of plasma drug exposure and <10% of free (non-protein bound) plasma drug exposure., Conclusion: IV belinostat is rapidly cleared from plasma and has limited penetration into the CSF.

Histone deacetylase inhibitors (HDACi) represent a promising new class of anticancer agents. In the current investigation, we examined the activity of the HDACi belinostat in preclinical models of prostate cancer. In vitro proliferation assays demonstrated that belinostat potently inhibited the growth of prostate cancer cell lines (IC(50) < 1.0 microM) and was cytotoxic to these cells. Washout experiments indicated that exposure to belinostat for relatively short periods of time (<12 hr) induced suboptimal growth-inhibition and that cells exposed to 1.0 microM belinostat for 48 hr retained the capacity for regrowth following drug withdrawal, while cells exposed to 4.0 microM belinostat were irreversibly growth-inhibited. Cell cycle analyses demonstrated that belinostat induced G2/M arrest and increased the percentage of cells with subG1 DNA content, thus confirming the growth-inhibitory and cytotoxic effects of this compound. Normal prostate epithelial cells were generally less susceptible to the effects of belinostat than were prostate cancer cells. In an orthotopic prostate cancer tumor model, belinostat inhibited tumor growth by up to 43%. Moreover, metastatic lung lesions were present in 47% of vehicle-treated animals but in none of the animals administered belinostat. Consistent with its observed antimetastatic activity, belinostat inhibited the migration of prostate tumor cells and increased the production of tissue inhibitor of metalloproteinase-1 (TIMP-1) by these cells, the latter effect being replicated by siRNA knockdown of HDAC3. Belinostat also increased the expression of p21 and decreased the expression of potentially oncogenic proteins (mutant p53 and ERG). These results support the clinical evaluation of belinostat for the treatment of prostate cancer., ((c) 2007 Wiley-Liss, Inc.)

The human HDAC (histone deacetylase) family, a well-validated anticancer target, plays a key role in the control of gene expression through regulation of transcription. While HDACs can be subdivided into three main classes, the class I, class II and class III HDACs (sirtuins), it is presently unclear whether inhibiting multiple HDACs using pan-HDAC inhibitors, or targeting specific isoforms that show aberrant levels in tumours, will prove more effective as an anticancer strategy in the clinic. To address the above issues, we have tested a number of clinically relevant HDACis (HDAC inhibitors) against a panel of rhHDAC (recombinant human HDAC) isoforms. Eight rhHDACs were expressed using a baculoviral system, and a Fluor de Lystrade mark (Biomol International) HDAC assay was optimized for each purified isoform. The potency and selectivity of ten HDACs on class I isoforms (rhHDAC1, rhHDAC2, rhHDAC3 and rhHDAC8) and class II HDAC isoforms (rhHDAC4, rhHDAC6, rhHDAC7 and rhHDAC9) was determined. MS-275 was HDAC1-selective, MGCD0103 was HDAC1- and HDAC2-selective, apicidin was HDAC2- and HDAC3-selective and valproic acid was a specific inhibitor of class I HDACs. The hydroxamic acid-derived compounds (trichostatin A, NVP-LAQ824, panobinostat, ITF2357, vorinostat and belinostat) were potent pan-HDAC inhibitors. The growth-inhibitory effect of the HDACis on HeLa cells showed that both pan-HDAC and class-I-specific inhibitors inhibited cell growth. The results also showed that both pan-HDAC and class-I-specific inhibitor treatment resulted in increased acetylation of histones, but only pan-HDAC inhibitor treatment resulted in increased tubulin acetylation, which is in agreement with their activity towards the HDAC6 isoform.

Purpose: To investigate the pharmacological properties of the CR011-vcMMAE fully human antibody-drug conjugate (ADC), such as dose titrations, quantitation of the time (days) to complete regression, pharmacokinetics, and schedule dependency. Our prior study characterized a fully human antibody to GPNMB covalently linked to monomethylauristatin E, CR011-vcMMAE, and further demonstrated cell surface staining of melanoma lines susceptible to the immunoconjugate's cytotoxicity (Clin Cancer Res 2005; 12(4): 1373-1382)., Methods: The human SK-MEL-2 and SK-MEL-5 melanoma xenografts were used in athymic mice to assess anti-tumor efficacy. After s.c. implantation, tumors became established (60-100 mg), and treatment commenced by i.v. injection of the immunoconjugate or vinblastine or paclitaxel. Short-term anti-tumor effects (inhibition of tumor growth) and long-term effects (complete regression) were observed., Results: CR011-vcMMAE induced regression of established human SK-MEL-2 and SK-MEL-5 xenografts at doses from 1.25 to 80 mg/kg treatment when administered intravenously every 4 days (4 treatments); strikingly, regressions were not associated with re-growth during the observation period (200 days). The disappearance rate of implants was dose dependent (minimum time, 18.5 days). Detectable serum CR011-vcMMAE >or=1 microg/mL (approximately 0.01 microM) was observed for >30 days post-dose; CR011-vcMMAE showed an elimination half-life of 10.3 days. A low volume of distribution suggested that CR011-vcMMAE was confined to blood and interstitial fluid. CR011-vcMMAE could be delivered by either a single bolus dose or by intermittent dosing (i.e., every 1, 2, 4, 8, or 16 days) with no discernible differences in the proportion of tumor-free survivors, indicating a lack of schedule dependency. The antibody-drug conjugate produced complete regressions, but the equivalent doses of free monomethylauristatin E or unconjugated antibody did not show anti-tumor effects. In addition, decreases in plasma tumor-derived human interleukin-8 coincided with tumor nodule disappearance., Conclusions: Short-term anti-tumor effects and long-term effects (complete regression) were observed with CR011-vcMMAE, but not with the reference agents. These results suggest that CR011-vcMMAE may provide therapeutic benefit in malignant melanoma.

Histone deacetylase inhibitors represent a promising new class of anticancer agents. In the current investigation, we examined the activity of PXD101, a potent histone deacetylase inhibitor, used alone or in combination with clinically relevant chemotherapeutics (docetaxel, paclitaxel, and carboplatin), in preclinical in vitro and in vivo models of ovarian cancer. In vitro activity was examined in ovarian cancer and multidrug-resistant cell lines grown in monolayer culture, and in primary clinical ovarian cancer specimens grown in three-dimensional organoid culture. PXD101 was found to inhibit in vitro cancer cell growth at sub- to low micromolar IC(50) potency, exhibited synergistic activity when used in combination with relevant chemotherapeutics, and effectively inhibited the growth of multidrug-resistant cells. In vivo, PXD101 displayed single-agent antitumor activity on human A2780 ovarian cancer s.c. xenografts which was enhanced via combination therapy with carboplatin. In support of these findings, PXD101 was shown to increase the acetylation of alpha-tubulin induced by docetaxel and the phosphorylation of H2AX induced by carboplatin. Taken together, these results support the clinical evaluation of PXD101 used alone or in combination therapy for the treatment of ovarian cancer.

Platelet-derived growth factor (PDGF)-BB and PDGF-DD mediate mesangial cell proliferation in vitro and in vivo. While PDGF-BB is a ligand for the PDGF alpha- and beta-receptor chains, PDGF-DD binds more selectively to the beta-chain, suggesting potential differences in the biological activities. Signal transduction and regulation of gene expression induced by PDGF-BB and -DD were compared in primary human mesangial cells (HMCs), which expressed PDGF alpha- and beta-receptor subunits. The growth factor concentrations used were chosen based on their equipotency in inducing HMCs proliferation and binding to the betabeta-receptor. Both growth factors, albeit at different concentrations induced phosphorylation and activation of extracellular signal-regulated kinase 1 (ERK1) and ERK2. In addition, PDGFs led to the phosphorylation and activation of signal transducers and activators of transcription 1 (STAT1) and STAT3. HMCs proliferation induced by either PDGF-BB or -DD could be blocked by signal transduction inhibitors of the mitogen-activated protein kinase-, Janus kinase (JAK)/STAT-, or phosphatidyl-inositol 3-kinase pathways. Using a gene chip array and subsequent verification by real-time reverse transcriptase (RT)-polymerase chain reaction, we found that in HMC genes for matrix metalloproteinase 13 (MMP-13) and MMP-14 and, to a low extent, cytochrome B5 and cathepsin L were exclusively regulated by PDGF-BB, whereas no exclusive gene regulation was detected by PDGF-DD. However, at the protein level, both MMP-13 and -14 were equally induced by PDGF-BB and -DD. PDGF-BB and -DD effect similar biological responses in HMCs albeit at different potencies. Rare apparently differential gene regulation did not result in different protein expression, suggesting that in HMCs both PDGFs exert their biological activity almost exclusively via the PDGF beta-receptor.

Purpose: Advanced melanoma is a highly drug-refractory neoplasm representing a significant unmet medical need. We sought to identify melanoma-associated cell surface molecules and to develop as well as preclinically test immunotherapeutic reagents designed to exploit such targets., Experimental Design and Results: By transcript profiling, we identified glycoprotein NMB (GPNMB) as a gene that is expressed by most metastatic melanoma samples examined. GPNMB is predicted to be a transmembrane protein, thus making it a potential immunotherapeutic target in the treatment of this disease. A fully human monoclonal antibody, designated CR011, was generated to the extracellular domain of GPNMB and characterized for growth-inhibitory activity against melanoma. The CR011 monoclonal antibody showed surface staining of most melanoma cell lines by flow cytometry and reacted with a majority of metastatic melanoma specimens by immunohistochemistry. CR011 alone did not inhibit the growth of melanoma cells. However, when linked to the cytotoxic agent monomethylauristatin E (MMAE) to generate the CR011-vcMMAE antibody-drug conjugate, this reagent now potently and specifically inhibited the growth of GPNMB-positive melanoma cells in vitro. Ectopic overexpression and small interfering RNA transfection studies showed that GPNMB expression is both necessary and sufficient for sensitivity to low concentrations of CR011-vcMMAE. In a melanoma xenograft model, CR011-vcMMAE induced significant dose-proportional antitumor effects, including complete regressions, at doses as low as 1.25 mg/kg., Conclusion: These preclinical results support the continued evaluation of CR011-vcMMAE for the treatment of melanoma.

The process of angiogenesis plays a pivotal role in embryogenesis, wound healing, and tumorigenesis through the growth of new blood vessels from pre-existing vasculature. Among the angiogenic factors recently identified as specific for vascular endothelium are the angiopoietins. In depth characterization of the angiopoietins has allowed investigators to better understand the molecular basis of blood vessel formation and vascular endothelial cell function. In this review, we describe angiopoietins and related family members, with particular emphasis on a recently identified protein known as angioarrestin. Our investigations clearly demonstrate that angioarrestin is an anti-angiogenic molecule. The effects of angioarrestin on tumor cell progression and specific aspects of the angiogenic cascade in in vitro models are further discussed.

The Semaphorins are a large family of transmembrane, GPI-anchored and secreted proteins that play an important role in neuronal and endothelial cell guidance. A human gene related to the class 6 Semaphorin family, Semaphorin 6A-1 (Sema 6A-1) was identified by homology-based genomic mining. Recent implication of Sema 3 family members in tumor angiogenesis and our expression analysis of Sema 6A-1 suggested that class 6 Semaphorin might effect tumor neovascularization. The mRNA expression of Sema 6A-1 was elevated in several renal tumor tissue samples relative to adjacent nontumor tissue samples from the same patient. Sema 6A-1 transcript was also expressed in the majority of renal clear cell carcinoma (RCC) cell lines and to a lesser extent in endothelial cells. To test the role of Sema 6A-1 in tumor angiogenesis, we engineered, expressed and purified the Sema 6A-1 soluble extracellular domain (Sema-ECD). The purified Sema-ECD was screened in a variety of endothelial cell-based assays both in vitro and in vivo. In vitro, Sema-ECD blocked VEGF-mediated endothelial cell migration. These effects were explained in part by our observation in endothelial cells that Sema-ECD inhibited VEGF-mediated Src, FAK and ERK phosphorylation. In vivo, mouse Matrigel assays demonstrated that the intraperitoneal administration of recombinant Sema-ECD inhibited both bFGF/VEGF and tumor cell line-induced neovascularization. These findings reveal a novel therapeutic utility for Sema 6A-1 (Sema-ECD) as an inhibitor of growth factor as well as tumor-induced angiogenesis.

PDGF-B is of central importance in mesangioproliferative diseases. PDGF-D, a new PDGF isoform, like PDGF-B, signals through the PDGF betabeta-receptor. The present study first determined that PDGF-D is mitogenic for rat mesangial cells and is not inhibited by a PDGF-B antagonist. Low levels of PDGF-D mRNA were detected in normal rat glomeruli. After induction of mesangioproliferative nephritis in rats by anti-Thy 1.1 mAb, glomerular PDGF-D mRNA and protein expression increased significantly from days 4 to 9 in comparison with nonnephritic rats. Peak expression of PDGF-D mRNA occurred 2 d later than peak PDGF-B mRNA expression. In addition, PDGF-D serum levels increased significantly in the nephritic animals on day 7. For investigating the functional role of PDGF-D, neutralizing fully human mAb were generated using the XenoMouse technology. Rats with anti-Thy 1.1-induced nephritis were treated on days 3 and 5 with different amounts of a fully human PDGF-DD-specific neutralizing mAb (CR002), equal amounts of irrelevant control mAb, or PBS by intraperitoneal injection. Specific antagonism of PDGF-D led to a dose-dependent (up to 67%) reduction of glomerular cell proliferation. As judged by double immunostaining for 5-bromo-2'-deoxyuridine and alpha-smooth muscle actin, glomerular mesangial cell proliferation was reduced by up to 57%. Reduction of glomerular cell proliferation in the rats that received CR002 was not associated with reduced glomerular expression of PDGF-B mRNA. PDGF-D antagonism also led to reduced glomerular infiltration of monocytes/macrophages (day 5) and reduced accumulation of fibronectin (day 8). In contrast, no effect was noted in normal rats that received an injection of CR002. These data show that PDGF-D is overexpressed in mesangioproliferative states and can act as an auto-, para-, or even endocrine glomerular cell mitogen, indicating that antagonism of PDGF-D may represent a novel therapeutic approach to mesangioproliferative glomerulonephritides.

Purpose: The purpose of this study was to evaluate the activity of CG53135 (FGF-20), a protein with in vitro mitogenic activity on epithelial and mesenchymal cells, in two in vivo models of oral mucositis (OM)., Experimental Design: Radiation or concomitant chemotherapy/radiation-induced OM was elicited in hamsters. Activity of CG53135 was assessed at different doses and regimens in the models. Bromodeoxyuridine (BrdUrd) incorporation and pharmacokinetic studies were also performed to correlate in vivo activity of CG53135 with exposure., Results: In the hamster radiation model, administration of CG53135 (600 or 1200 micro g/day, i.p.) on days 3-15 resulted in a statistically significant (P < 0.001) reduction in days spent with severe mucositis. CG53135 administered at 12 mg/kg, i.p. (days 1-2 or 1-8) in the concomitant chemotherapy/radiation model resulted in a statistically significant (P < 0.001) reduction in severe mucositis. Maximal BrdUrd incorporation was observed in cheek pouch and jejunal tissues at 8 h, and peak plasma levels of CG53135 were reached 1 h after administration., Conclusions: CG53135 demonstrates potent, regimen-dependent activity in hamster models of OM. The activity was regimen dependent. BrdUrd incorporation studies confirmed that CG53135 had proliferative activity in vivo with a favorable pharmacokinetic profile. Based in part on work described herein, CG53135 has received approval from the United States Food and Drug Administration to be evaluated in a Phase I clinical trial of cancer patients at risk for developing OM.

Background & Aims: We recently identified a novel member of the human fibroblast growth factor (FGF) family of signaling molecules, designated FGF-20. In the present study, we examined the activity of this protein in 2 animal models of acute intestinal inflammation and in mechanistic studies in vitro., Methods: In vivo experiments consisted of a murine dextran sulfate sodium (DSS) model of colitis and a rat indomethacin model of small intestinal ulceration/inflammation. Cell growth, restitution, gene expression (cyclooxygenase-2 [COX-2] and intestinal trefoil factor [ITF]), and prostaglandin E2 (PGE2) levels were examined in vitro., Results: In the DSS-colitis model, prophylactic administration of FGF-20 significantly reduced the severity and extent of mucosal damage as indicated by a 55%-93% reduction in luminal blood loss, distal colonic edema, histologic inflammation, and epithelial cell loss relative to animals administered vehicle control. No toxicity was noted during administration of FGF-20 to normal controls. In addition, therapeutic administration of FGF-20 enhanced survival in this model. In the indomethacin-small bowel ulceration/inflammation model, administration of FGF-20 reduced small intestinal weight gain, necrosis, inflammation, and weight loss (36%-53% relative to vehicle control). In vitro studies demonstrated that FGF-20 stimulates growth, restitution, mRNA expression of COX-2 and ITF, and PGE2 levels in human intestinal epithelial cells and enhances the growth of human intestinal fibroblasts., Conclusions: FGF-20, having demonstrated therapeutic activity in 2 experimental models of intestinal inflammation, represents a promising new candidate for the treatment of human inflammatory bowel disease.

The fibroblast growth factor (FGF) family of signalling molecules and its receptors (FGFRs) contribute to normal developmental and physiological processes. However, the subversion of this powerful growth stimulatory pathway has been implicated in the generation of a variety of pathological conditions. This review focuses on the role of FGF/FGFRs in cancer. The case will be made that this signalling pathway is associated with and functionally important for the growth of some human tumours. As such, FGF/FGFRs can be viewed as rational therapeutic oncology targets and strategies used to inhibit these molecules are discussed. The therapeutic exploitation of tumour-associated FGFR expression to deliver toxins or antiproliferative signals to tumour cells is also reviewed, as is the use of FGFs as protein therapeutics to alleviate the side effects of cancer therapy.

The angiopoietins comprise a family of proteins that have pro or antiangiogenic activities. Through a proprietary technology designed to identify transcripts of all expressed genes, we isolated a cDNA encoding an angiopoietin-related protein that we designate angioarrestin. The mRNA expression profile of angioarrestin was striking in that it was down-regulated in many tumor tissues when compared with adjacent nontumor tissue, suggesting a role for this protein in tumor inhibition. To test this hypothesis, we ectopically expressed angioarrestin in HT1080 tumor cells and measured pulmonary tumor nodule formation in nude mice. HT1080 cells expressing angioarrestin showed a marked reduction in the number and size of tumor nodules. In vitro, the recombinant protein was systematically tested in a number of endothelial cell assays and found to block critical processes involved in the angiogenic cascade, such as vascular endothelial growth factor/basic fibroblast growth factor-mediated endothelial cell proliferation, migration, tubular network formation, and adhesion to extracellular matrix proteins. These findings reveal a novel function for angioarrestin as an angiogenesis inhibitor and indicate that the molecule may be a potential cancer therapeutic.

Platelet-derived growth factor (PDGF) has been directly implicated in developmental and physiological processes, as well as in human cancer and other proliferative disorders. We have recently isolated and characterized a novel protease-activated member of the PDGF family, PDGF D. PDGF D has been shown to be proliferative for cells of mesenchymal origin, signaling through PDGF receptors. Comprehensive and systematic PDGF D transcript analysis revealed expression in many cell lines derived from ovarian, renal, and lung cancers, as well as from astrocytomas and medulloblastomas. beta PDGF receptor profiling further suggested autocrine signaling in several brain tumor cell lines. PDGF D transforming ability and tumor formation in SCID mice was further demonstrated. Exploiting a sensitive PDGF D sandwich ELISA using fully human monoclonal antibodies, PDGF D was detected at elevated levels in the sera of ovarian, renal, lung, and brain cancer patients. Immunohistochemical analysis confirmed PDGF D localization to ovarian and lung tumor tissues. Together, these data demonstrate that PDGF D plays a role in certain human cancers.

Platelet-derived growth factor (PDGF) has been directly implicated in developmental and physiological processes, as well as in human cancer, fibrotic diseases and arteriosclerosis. The PDGF family currently consists of at least three gene products, PDGF-A, PDGF-B and PDGF-C, which selectively signal through two PDGF receptors (PDGFRs) to regulate diverse cellular functions. After two decades of searching, PDGF-A and B were the only ligands identified for PDGFRs. Recently, however, database mining has resulted in the discovery of a third member of the PDGF family, PDGF-C, a functional analogue of PDGF-A that requires proteolytic activation. PDGF-A and PDGF-C selectively activate PDGFR-alpha, whereas PDGF-B activates both PDGFR-alpha and PDGFR-beta. Here we identify and characterize a new member of the PDGF family, PDGF D, which also requires proteolytic activation. Recombinant, purified PDGF-D induces DNA synthesis and growth in cells expressing PDGFRs. In cells expressing individual PDGFRs, PDGF-D binds to and activates PDGFR-beta but not PDGFR-alpha. However, in cells expressing both PDGFRs, PDGF-D activates both receptors. This indicates that PDGFR-alpha activation may result from PDGFR-alpha/beta heterodimerization.

The fibroblast growth factor (FGF) family of signaling molecules has been implicated in normal developmental and physiological processes, as well as in human malignancy. Using a homology-based genomic DNA mining process, we identified a human gene encoding a novel member of the FGF family, that we designate FGF-20. The FGF-20 cDNA was isolated, and its sequence confirmed the gene prediction. FGF-20 is expressed in normal brain, particularly the cerebellum, and in some cancer cell lines. Recombinant FGF-20 protein induces DNA synthesis in a variety of cell types and is recognized by multiple FGF receptors. Ectopic expression of FGF-20 in NIH 3T3 cells renders the cells transformed in vitro and tumorigenic in nude mice. These results underscore the utility of mining genomic DNA databases and reveal FGF-20 to be a novel oncogene that may play a role in human cancer.

Neutrophil activation plays an important role in the inflammatory response to Gram-negative bacterial infections. LPS has been shown to be a major mediator of neutrophil activation which is accompanied by an early down-regulation of L-selectin and up-regulation of CD1lb/CD18. In this study, we investigated whether lipoprotein (LP), the most abundant protein in the outer membrane of bacteria from the family Enterobacteriaceae, can activate neutrophils and whether this activation is mediated by mechanisms that differ from those used by LPS or Escherichia coli diphosphoryl lipid A (EcDPLA). Neutrophil activation was assessed by measuring down-regulation of L-selectin and up-regulation of CD11b/CD18. When comparing molar concentrations of LP vs EcDPLA, LP was more potent (four times) at activating neutrophils. In contrast to LPS/EcDPLA, LP activation of neutrophils was serum independent. However, LP activation of neutrophils was enhanced by the addition of soluble CD14 and/or LPS-binding protein. In the presence of serum, LP activation of neutrophils was inhibited by different mAbs to CD14. This inhibition was significantly reduced or absent when performed in the absence of serum. Diphosphoryl lipid A from Rhodobacter spheroides (RaDPLA) completely inhibited LPS/EcDPLA activation of neutrophils but only slightly inhibited LP activation of neutrophils. These results suggest that LP activation of human neutrophils can be mediated by a mechanism that is different from LPS activation and that LP is a potentially important component in the development of diseases caused by Gram-negative bacteria of the family Enterobacteriaceae.

Objective: To identify the site(s) in tumor necrosis factor (TNFalpha), interleukin-6 (IL-6), and macrophage inflammatory protein-1alpha (MIP-1alpha) biosynthesis that is blocked by SB202190, a selective inhibitor of p38-mitogen activated protein kinase (p38)., Materials: Human blood monocytes isolated by centrifugal elutriation., Methods: Monocytes were stimulated with lipopolysaccharide in the presence of 0, 0.3, 1 and 3 microM SB202190. Induced TNFalpha, IL-6, and MIP-1alpha protein and mRNA were measured by ELISA and quantitative RT-PCR, respectively. The half-lives of cytokine mRNA levels were determined following treatment of cells with actinomycin D or SB202190., Results: SB202190 suppressed >60% of lipopolysaccharide-induced TNFalpha, IL-6, and MIP-1alpha protein and mRNA expression. Suppressed mRNA levels could be attributed to a >2 to 7-fold reduction in cytokine mRNA half-lives. In contrast, SB202190 did not destabilize mRNAs encoding interferon-induced gene 15 protein and glyceraldehyde-3-phosphate dehydrogenase., Conclusions: Specific mRNA destabilization represents an important and novel site of action for the cytokine suppressive effects of p38 inhibitors.

p38 is a proline-directed serine/threonine kinase that is activated by inflammatory cytokines and cellular stress. At present, four isoforms of p38 have been identified and termed alpha, beta, gamma, and delta. We expressed each p38 homolog in Escherichia coli and purified the recombinant isoforms. p38alpha and C-terminal Flag-tagged p38beta were purified by Q-Sepharose fast flow, hydroxyapatite, and Q-Sepharose high-performance chromatography. His-tagged p38gamma was purified using Ni2+-NTA resin followed by Mono Q chromatography. Glutathione S-transferase-Flag p38delta was purified using M2 affinity agarose and gel-filtration chromatography. Upstream activators of p38, constitutively active (ca) MKK3 and MKK6, were also cloned, purified, and used to activate each p38 isoform. p38 alpha, gamma, and delta were phosphorylated by both MKK6 and caMKK3. p38beta was phosphorylated only by MKK6. Mass spectrometry analysis and kinase assays showed that MKK6 was the superior reagent for phosphorylating and activating all p38 isoforms., (Copyright 1998 Academic Press.)

CD14 is a pattern recognition receptor involved in the interaction with multiple ligands, including LPS from gram-negative bacteria and lipoarabinomannan (LAM) from mycobacteria. While the interactions between LPS and soluble CD14 (sCD14) have been analyzed in detail, LAM/CD14 interactions remain uncharacterized due to the lack of suitable functional assays. We describe herein a novel bioassay for the analysis of CD14/ligand interactions. CD14-negative myeloid HL-60 cells up-regulate endogenous CD14 gene expression when stimulated with LPS in the presence of recombinant soluble CD14(1-348). Using the HL-60 bioassay, we showed that sCD14(1-348) confers responsiveness not only to LPS, but also to LAM. The response to LAM, but not that to LPS, was highly dependent on LPS binding protein (LBP). The N-terminal half of CD14 was sufficient to mediate HL-60 responses to LAM, since HL-60 cells responded with similar efficiency when stimulated with LAM and LBP in the presence of sCD14(1-348) or sCD14(1-152). Thus, the N-terminal 152 amino acids of CD14 contain the site(s) involved in the interaction with LAM and LBP, as well as the residues required for LAM-dependent CD14 signaling.

p38 mitogen-activated protein kinases (MAPK) are a family of kinases that are activated by cellular stresses and inflammatory cytokines. Although there are many similarities shared by the isoforms of p38 (alpha, beta, gamma, and delta), p38 delta differs from the others in some respects such as inhibitor sensitivity and substrate specificity. Utilizing in a solution kinase assay, we identified a novel p38 delta substrate as stathmin. Stathmin is a cytoplasmic protein that was previously reported to be a substrate of several intracellular signaling kinases and has recently been linked to regulation of microtubule dynamics. p38 delta has significantly higher in vitro phosphorylating activity against stathmin than other p38 isoforms or related MAPKs. In transient expression studies, we found that in addition to different stimuli osmotic stress activates p38 delta to phosphorylate stathmin. The sites of phosphorylation were mapped to Ser-25 and Ser-38, both in vitro and in cells.

Tumor necrosis factor-alpha (TNF) is initially expressed as a 26-kDa membrane-bound precusor protein (pro-TNF) that is shed proteolytically from the cell surface, releasing soluble 17-kDa TNF. We have identified human ADAM 10 (HuAD10) from THP-1 membrane extracts as a metalloprotease that specifically clips a peptide substrate spanning the authentic cleavage site between Ala76 and Val77 in pro-TNF. To confirm that HuAD10 has TNF processing activity, we cloned, expressed, and purified an active, truncated form of HuAD10. Characterization of recombinant HuAD10 (rHuAD10) suggests that this enzyme has many of the properties (i.e. substrate specificity, metalloprotease activity, cellular location) expected for a physiologically relevant TNF-processing enzyme.

The p38 mitogen-activated protein kinases (MAPK) are activated by cellular stresses and play an important role in regulating gene expression. We have isolated a cDNA encoding a novel protein kinase that has significant homology (57% amino acid identity) to human p38alpha/CSBP. The novel kinase, p38delta, has a nucleotide sequence encoding a protein of 365 amino acids with a putative TGY dual phosphorylation motif. Dot-blot analysis of p38delta mRNA in 50 human tissues revealed a distribution profile of p38delta that differs from p38alpha. p38delta is highly expressed in salivary gland, pituitary gland, and adrenal gland, whereas p38alpha is highly expressed in placenta, cerebellum, bone marrow, thyroid gland, peripheral leukocytes, liver, and spleen. Like p38alpha, p38delta is activated by cellular stress and proinflammatory cytokines. p38delta phosphorylates ATF-2 and PHAS-I, but not MAPK-activated protein kinase-2 and -3, known in vivo and in vitro substrates of p38alpha. We also observed that p38delta was strongly activated by MKK3 and MKK6, while p38alpha was preferentially activated by MKK6. Other experiments showed that a potent p38alpha kinase inhibitor AMG 2372 minimally inhibited the kinase activity of p38delta. Taken together, these data indicate that p38delta is a new member of the p38 MAPK family and that p38delta likely has functions distinct from that of p38alpha.

To evaluate the effect of soluble CD14 (sCD14) on human neutrophil response to lipopolysaccharide (LPS), we developed an LPS-priming assay that measures the chemiluminescence response to N-formyl-methionyl-leucyl-phenylalanine stimulation. Priming by 1 ng/mL rough LPS occurred in the presence of either serum or recombinant LPS-binding protein (LBP) only. Priming was completely CD14-dependent because preincubation of the neutrophils with an anti-CD14 monoclonal antibody prevented priming. We hypothesize that sCD14 enhances LPS response in neutrophils, but this response is not as effective as LPS response via membrane CD14 (mCD14). In our experiments sCD14 is present in an excess compared with mCD14. Priming of neutrophils occurs with low LBP, supposedly via sCD14-LPS complexes. With high LBP, addition of sCD14 inhibited LPS-priming of neutrophils. In that case, LPS may be transported to sCD14, preventing a more effective response via mCD14. In this study we demonstrate that the effect of sCD14 on neutrophil response to LPS is a delicate balance between activation and inhibition depending on concentration of serum or LBP.

Well-defined polysaccharides, such as beta1-4-linked D-mannuronic acid (poly[M]) derived from Pseudomonas aeruginosa, induce monocytes to produce tumor necrosis factor (TNF) through a pathway involving membrane CD14. In this study we have investigated the effects of soluble CD14 (sCD14), lipopolysaccharide-binding protein (LBP), and bactericidal/permeability-increasing factor (BPI) on poly(M) binding to monocytes and induction of TNF production. We show that LBP increased the TNF production from monocytes stimulated with poly(M). Addition of sCD14 alone had only minor effects, but when it was added together with LBP, a rise in TNF production was seen. BPI was found to inhibit TNF production from monocytes stimulated with poly(M) in the presence of LBP, LBP-sCD14, or 10% human serum. Binding studies showed that poly(M) bound to LBP- and BPI-coated immunowells, while no significant binding of poly(M) to sCD14-coated wells in the absence of serum was observed. Binding of poly(M) to monocytes was also examined by flow cytometry, and it was shown that the addition of LBP or 10% human serum clearly increased the binding of poly(M) to monocytes. BPI inhibited the binding of poly(M) to monocytes in the presence of LBP, LBP-sCD14, or 10% human serum. Our data demonstrate a role for LBP, LBP-sCD14, and BPI in modulating TNF responses of defined polysaccharides.

Sensitive responses of monocytes, macrophages, and neutrophils to bacterial LPS require membrane-bound CD14 (mCD14) and a plasma protein called LPS-binding protein (LBP). Cells lacking mCD14 respond to complexes of LPS and soluble CD14 (sCD14); these responses do not require LBP. To determine whether LBP is necessary for responses of mCD14-bearing cells to LPS, we measured responses of macrophages and neutrophils to complexes of LPS and sCD14 formed in the absence of LBP. We found that the amount of LPS needed to induce adhesive responses of neutrophils or cytokine production by macrophages was the same whether LPS was added with LBP or as LPS-sCD14 complexes, and was >100-fold less than when LPS was added alone. This result supports the view that LBP transfers LPS to CD14, but is not directly involved in responses of CD14-bearing cells to LPS. Responses of neutrophils to LPS-sCD14 complexes could be inhibited partially by blocking mCD14, suggesting that LPS may move rapidly from sCD14 to mCD14. Additionally, we found that responses of neutrophils to LBP and smooth LPS were made 30 to 100 times more sensitive when sCD14 was added. Our findings show that LBP is not necessary for the activation of CD14-bearing cells with LPS, and suggest that LPS-sCD14 complexes are an important intermediate in the inflammatory responses of leukocytes to LPS.

Mammals mount a rapid inflammatory response to gram-negative bacteria by recognizing lipopolysaccharide (LPS, endotoxin). LPS binds to CD14, and the resulting LPS-CD14 complex induces synthesis of cytokines and up-regulation of adhesion molecules in a variety of cell types. Gram-positive bacteria provoke a very similar inflammatory response, but the molecules that provoke innate responses to these bacteria have not been defined. Here we show that protein-free, phenol extracts of Staphylococcus aureus contain a minor component that stimulates adhesion of neutrophils and cytokine production in monocytes and in the astrocytoma cell line, U373. Responses to this component do not absolutely require CD14, but addition of soluble CD14 enhances sensitivity of U373 cells by up to 100-fold, and blocking CD14 on monocytes decreases sensitivity nearly 1,000-fold. Deletion of residues 57-64 of CD14, which are required for responses to LPS, also eliminates CD14-dependent responses to S. aureus molecules. The stimulatory component of S. aureus binds CD14 and blocks binding of radioactive LPS. Unlike LPS, the activity of S. aureus molecules was neither enhanced by LPS binding protein nor inhibited by bactericidal/permeability increasing protein. The active factor in extracts of S. aureus is also structurally and functionally distinct from the abundant species known as lipoteichoic acid (LTA). Cell-stimulating activity fractionates differently from LTA on a reverse-phase column, pure LTA fails to stimulate cells, and LTA antagonizes the action of LPS in assays of IL-6 production. These studies suggest that mammals may use CD14 in innate responses to both gram-negative and gram-positive bacteria, and that gram-positive bacteria may contain an apparently unique, CD14-binding species that initiates cellular responses.

CD14 is a 55-kDa glycoprotein that binds lipopolysaccharide (LPS) and enables LPS-dependent responses in a variety of cells. Monoclonal antibodies of CD14 such as 3C10 and MEM-18 are known to neutralize biological activity of CD14. Recently, it has been demonstrated that MEM-18 recognizes the LPS-binding site of CD14, between amino acids 57 and 64. It has also been shown that 3C10 recognizes a distinct epitope from that of MEM-18, indicating that 3C10 may yet define another functional domain of CD14. In order to identify the epitope for 3C10, we constructed a series of alanine substitution mutants of soluble CD14 (sCD14). BIAcore analyses showed that regions between amino acids 7 and 10 and between amino acids 11 and 14 are required for 3C10 binding. To assess the effect of altering the 3C10 epitope in CD14, we generated a stable cell line expressing a mutant sCD14 containing alanine substitutions in the region between amino acids 7 and 10, sCD14(7-10)A, and purified this protein to homogeneity. sCD14(7-10)A has impaired ability to mediate LPS-dependent IL-6 up-regulation in U373 cells, integrin activation in neutrophils, and NF-kappa B activation in U373 cells. Purified sCD14(7-10)A was, however, capable of forming a stable complex with LPS in an LPS binding protein-facilitated and LPS binding protein-independent fashion. The ability of sCD14(7-10)A to bind LPS was also demonstrated in assays in which excess sCD14(7-10)A inhibited LPS-mediated tumor necrosis factor-alpha production in whole blood and adhesion of polymorphonuclear leukocytes to fibrinogen. These data strongly suggest that a region recognized by neutralizing monoclonal antibody 3C10 contains a domain required for cellular signaling but not for LPS binding.

In this study we examined the involvement of human serum, recombinant lipopolysaccharide binding protein (rLBP), recombinant (r)CD14, CD14 antibodies and recombinant bactericidal permeability-increasing factor (rBPI) in the induction of TNF by Salmonella minnesota LPS of different polysaccharide chain lengths. Soluble rCD14 and rLBP markedly enhanced LPS 6261 TNF production and to a lesser degree also enhanced TNF production from Re 595 LPS and lipid A DP. Addition of anti-CD14 antibodies resulted in nearly complete inhibition of LPS 6261-induced TNF production and partial inhibition of Re 595 LPS and lipid A DP-induced TNF release. The ability of lipid A MP to induce TNF production increased with addition of rCD14. Addition of rLBP or anti-CD14 antibodies had no detectable effect on lipid A MP-induced TNF production. The effect of rBPI was also tested and the results showed that only the TNF-inducing ability from smooth LPS was completely inhibited by rBPI. Recombinant BPI was considerably less effective in inhibiting Re 595 LPS-induced TNF production, and lipid A DP was not affected by rBPI. Our data suggest that the ability of rLBP, rCD14, CD14 antibodies and rBPI to modulate LPS induced TNF production is strongly dependent on the LPS polysaccharide chain length.

Soluble CD14 (sCD14) is a 55-kDa serum protein that binds lipopolysaccharide (LPS) and mediates LPS-dependent responses in a variety of cells. Using recombinant sCD14 expressed in Chinese hamster ovary (CHO) cells, we examined the structural characteristics of sCD14 and sCD14.LPS complexes. The circular dichroism and fluorescence spectra of the sCD14 indicate that it contains substantial beta-sheet (40%) and a well-defined tertiary structure with the tryptophan residues located in environments with different degrees of hydrophobicity and solvent exposure. The spectra of the sCD14.LPS complex are identical within experimental error to the uncomplexed sCD14. Changes in surface accessibility upon LPS binding were examined using limited proteolysis with endoproteinase Asp-N. This analysis revealed that aspartic acid residues at amino acids 57, 59, and 65 are susceptible to cleavage by Asp-N, while the same residues are protected from proteolytic cleavage in the sCD14.LPS complex. These results suggest that a region including amino acids 57 to 64 is involved in LPS binding by sCD14.

CD14 is a 55-kDa glycoprotein which binds lipopolysaccharide (LPS) and enables LPS-dependent responses in a variety of cells. Recent limited proteolysis studies have implicated a region in CD14 between amino acids 57 and 64 as being involved in LPS interaction. To specifically assess the importance of this region with respect to LPS binding, we constructed a mutant sCD14 (sCD14 delta 57-64) lacking amino acids 57-64. sCD14 delta 57-64 was isolated from the serum-free conditioned medium of this cell line, and, in all assays, the purified protein failed to recognize LPS or enable LPS-dependent responses in cells. We also demonstrated that the region between amino acids 57 and 64 is required for binding of a neutralizing CD14 mAb, MEM-18. Native polyacrylamide gel electrophoresis assays were used to demonstrate that MEM-18 and LPS compete for the same binding site on CD14. These data strongly suggest that the region spanning amino acids 57-64 binds LPS and that formation of sCD14.LPS complex is required in order for sCD14-mediated responses to occur.

Neutrophils roll on P-selectin expressed by activated platelets or endothelial cells under the shear stresses in the microcirculation. P-selectin glycoprotein ligand-1 (PSGL-1) is a high affinity ligand for P-selectin on myeloid cells. However, it has not been demonstrated that PSGL-1 contributes to the rolling of neutrophils on P-selectin. We developed two IgG mAbs, PL1 and PL2, that appear to recognize protein-dependent epitopes on human PSGL-1. The mAbs bound to PSGL-1 on all leukocytes as well as on heterologous cells transfected with PSGL-1 cDNA. PL1, but not PL2, blocked binding of 125-I-PSGL-1 to immobilized P-selectin, binding of fluid-phase P-selectin to myeloid and lymphoid leukocytes, adhesion of neutrophils to immobilized P-selectin under static conditions, and rolling of neutrophils on P-selectin-expressing CHO cells under a range of shear stresses. PSGL-1 was localized to microvilli on neutrophils, a topography that may facilitate its adhesive function. These data indicate that (a) PSGL-1 accounts for the high affinity binding sites for P-selectin on leukocytes, and (b) PSGL-1 must interact with P-selectin in order for neutrophils to roll on P-selectin at physiological shear stresses.

CD14 is a 55-kDa glycoprotein which binds lipopolysaccharide (LPS) and enables LPS-dependent responses in a variety of cells. In order to identify the domains in CD14 required for function, we deleted increasing amounts of CD14 from the C terminus. Truncated CD14 cDNA sequences were transfected into COS-7 cells and serum-free conditioned medium was analyzed for mutant CD14 expression and bioactivity. Mutant CD14s containing as few as 152 amino acids were found to have activity equivalent to full-length sCD14. To further characterize the mutant CD14, we constructed a stable Chinese hamster ovary cell line expressing sCD14(1-152) and purified the protein to homogeneity. sCD14(1-152) bound radioactive LPS, enabled U373 cells to synthesize interleukin 6 in response to LPS, and enabled human neutrophils to respond to smooth LPS. In all of these assays, the behavior of sCD14(1-152) was quantitatively similar to full-length sCD14. We also found that two neutralizing anti-CD14 antibodies (3C10 and MEM-18) bound and neutralized sCD14(1-152). We conclude from these experiments that the N-terminal 152 amino acids of CD14 are sufficient to bind LPS and confer essentially wild-type bioactivity in vitro.

We previously demonstrated that P-selectin binds with high affinity to a trace, homodimeric glycoprotein ligand on human myeloid cells. The ligand carries the sialyl Lewis x (sLe(x)) epitope, a limited number of N-linked glycans, and clustered, sialylated O-linked glycans. In this study we demonstrate that the polypeptide component of this ligand is identical to that of P-selectin glycoprotein ligand-1 (PSGL-1), a molecule recently identified by expression cloning from a human myeloid cell cDNA library. We have examined the effects of glycosidases on purified, radioiodinated PSGL-1 from human neutrophils to further characterize the structure and function of the attached oligosaccharides. We found that PSGL-1 had poly-N-acetyllactosamine, only some of which could be removed with endo-beta-galactosidase. The majority of the Le(x) and sLe(x) structures were on endo-beta-galactosidase-sensitive chains. Peptide:N-glycosidase F (PNGaseF) treatment removed at least two of the three possible N-linked oligosaccharides from PSGL-1. Expression of Le(x) and sLe(x) was not detectably altered by PNGaseF digestion, indicating that these structures were primarily on O-linked poly-N-acetyllactosamine. Endo-beta-galactosidase-treated PSGL-1 retained the ability to bind to P-selectin, suggesting that some of the oligosaccharides recognized by P-selectin were either on enzyme-resistant poly-N-acetyllactosamine or on chains which lack poly-N-acetyllactosamine. PNGaseF treatment did not affect the ability of PSGL-1 to bind to P-selectin, demonstrating that the oligosaccharides required for P-selectin recognition are O-linked. PSGL-1 also bound to E-selectin, but with at least 50-fold lower affinity than to P-selectin. These data suggest that PSGL-1 from human neutrophils displays complex, sialylated, and fucosylated O-linked poly-N-acetyllactosamine that promote high affinity binding to P-selectin, but not to E-selectin.

A novel human serum protein with a molecular mass of 87,000 daltons was purified to homogeneity and subjected to amino acid sequence analyses. These sequences were used to design oligonucleotide primers and to isolate a full-length cDNA. The amino acid sequence encoded by the cDNA shares strong similarity to albumin family members and shares the characteristic pattern of Cys residues observed in this family. In addition, the gene maps to chromosome 4 as do other members of the albumin gene family. Based upon these observations, we conclude that the 87,000-dalton protein, which we designate afamin (AFM), is the fourth member of the albumin family of proteins. Afamin cDNA was stably transfected into Chinese hamster ovary cells and recombinant protein (rAFM) was purified from conditioned medium. Both rAFM and AFM purified from human serum react with a polyclonal antibody that was raised against a synthetic peptide derived from the deduced amino acid sequence of AFM.

CD14 is a 55-kD protein found as a glycosylphosphatidylinositol (GPI)-anchored protein on the surface of monocytes, macrophages, and polymorphonuclear leukocytes, and as a soluble protein in the blood. Both forms of CD14 participate in the serum-dependent responses of cells to bacterial lipopolysaccharide (LPS). While CD14 has been described as a receptor for complexes of LPS with LPS-binding protein (LBP), there has been no direct evidence showing whether a ternary complex of LPS, LBP, and CD14 is formed, or whether CD14 binds LPS directly. Using nondenaturing polyacrylamide gel electrophoresis (native PAGE), we show that recombinant soluble CD14 (rsCD14) binds LPS in the absence of LBP or other proteins. Binding of LPS to CD14 is stable and of low stoichiometry (one or two molecules of LPS per rsCD14). Recombinant LBP (rLBP) does not form detectable ternary complexes with rsCD14 and LPS, but it does accelerate the binding of LPS to rsCD14. rLBP facilitates the interaction of LPS with rsCD14 at substoichiometric concentrations, suggesting that LBP functions catalytically, as a lipid transfer protein. Complexes of LPS and rsCD14 formed in the absence of LBP or other serum proteins strongly stimulate integrin function on PMN and expression of E-selectin on endothelial cells, demonstrating that LBP is not necessary for CD14-dependent stimulation of cells. These results suggest that CD14 acts as a soluble and cell surface receptor for LPS, and that LBP may function primarily to accelerate the binding of LPS to CD14.

The prt gene, encoding a protease (Prt) from Streptomyces lividans TK24, was cloned and sequenced. An S. lividans host with plasmid-borne prt secreted 200 micrograms/ml of a 22-kDa Prt into the culture medium. Prt is classified as a metalloprotease since its activity is significantly inhibited by 1,10-phenanthroline or EDTA. The region upstream from prt codes for an incomplete open reading frame (ORF) oriented opposite to prt. This ORF has a strong similarity to a gene family (lysR) whose members regulate the transcription of structural genes required for either biosynthesis or degradation.

The gene (acm) encoding N-acetylmuramidase M1 (ACM) was cloned of Streptomyces globisporus ATCC No. 21553. The nucleotide sequence of the acm gene was determined and found to code for an ORF of 294 amino acids (aa). Comparison of aa sequence deduced from the acm gene with the N-terminal sequence of the extracellular enzyme suggests that ACM is synthesized with a 77-aa leader peptide. A comparison of the ACM aa sequence with the aa sequences of other proteins in the NBRF data base reveals that ACM has strong similarity to the N-O-diacetylmuramidase secreted by the fungus Chalaropsis.

Catabolite gene activation of the araBAD operon was examined by using catabolite gene activator protein (CAP) site deletion mutants. A high-affinity CAP-binding site between the divergently orientated araBAD and araC operons has been previously identified by DNase I footprinting techniques. Subsequent experiments disagreed as to whether this site is directly involved in stimulating araBAD expression. In this paper, we present data showing that deletions generated by in vitro mutagenesis of the CAP site led to a five- to sixfold reduction in single-copy araBAD promoter activity in vivo. We concluded that catabolite gene activation of araBAD involves this CAP site. The hypothesis that CAP stimulates the araBAD promoter primarily by relieving repression was then tested. The upstream operator araO2 was required for repression, but we observed that the magnitude of CAP stimulation was unaffected by the presence or absence of araO2. We concluded that CAP plays no role in relieving repression. Other experiments showed that when CAP binds it induces a bend in the ara DNA; similar bending has been reported upon CAP binding to lac DNA. This conformational change in the DNA may be essential to the mechanism of CAP activation.