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Objective: Connective tissue activating protein-III (CTAP-III), with molecular weight 9278 Da and isoforms including CTAP-III des 1-15 (neutrophil activating peptide-2, NAP-2) and other amino terminal deletion isoforms, has been isolated from human platelets and characterized. Platelets have also been shown to possess significant heparin/heparanase activity. We investigated whether human platelet heparin/heparanase activity derives from CTAP-III., Methods: Radial immunodiffusion measurement showed substantial amounts of CTAP-III in plasma from outdated platelet packs. A convenient method for measurement of heparin/heparanase activity is described, and with this method platelet associated plasma was investigated for heparin/heparanase activity assayed against 3H-heparin and 35S-heparan sulfate., Results: Removal of CTAP-III from platelet associated plasma with an immunospecific immunoaffinity column did not remove the heparin/heparanase activity from the plasma. Highly purified CTAP-III eluted from an immunospecific affinity column lacked heparin/heparanase activity., Conclusion: Human platelet heparin/heparanase activity resides not in CTAP-III but in a protein or proteins with molecular weight >/= 55 kDa.

Objective: To determine the origin, distribution, and biologic fate of platelet-derived connective tissue activating peptide-III (CTAP-III), to define the relative amounts of the antigen forms (CTAP-III, beta-thromboglobulin [beta-TG], neutrophil activating peptide-2 [NAP-2]) in plasma of normal persons and those with rheumatic or end-stage renal disease, and to define the isoforms of CTAP-III in platelets, plasma, transudates, and tissue deposits., Methods: CTAP-III in plasma was measured by enzyme-linked immunosorbent assay, and growth promoting activity of CTAP-III isoforms was tested in synovial and peritoneal cell cultures by measuring increased synthesis of 14C-glycosaminoglycan (14C-GAG) and 3H-DNA. Isolated CTAP-III was characterized by Western blotting, microsequencing, and mass spectrometry., Results: CTAP-III was the primary isoform of this antigen family in normal platelets and platelet-rich plasma; beta-TG and NAP-2 accounted for < 1% of CTAP-III isoforms. Previously undescribed isoforms, i.e., CTAP-III des 1, des 1-2, des 1-3, and a phosphate adduct of CTAP-III, were observed in varying amounts. Elevated plasma levels of CTAP-III antigen were found in a substantial fraction of rheumatic disease patients: 24% of those with rheumatoid arthritis, 36% of those with systemic sclerosis, and 15% of those with systemic lupus erythematosus. All 10 patients with end-stage kidney disease had marked elevations of plasma CTAP-III levels, which stimulated DNA and GAG synthesis by peritoneal cells in culture. Only large isoforms (such as CTAP-III) were detected in venous plasma of normal subjects, rheumatic disease patients, and patients receiving long-term dialysis. Normal human spleen and kidney contained substantial (micrograms/gm) amounts of CTAP-III and traces of an isoform with the electrophoretic mobility of CTAP-III des 1-15/NAP-2. Liver, lung, and urine contained lesser (ng/gm) amounts of CTAP-III., Conclusion: These data show that, among the 10 known isoforms, intact CTAP-III itself was the major circulating isoform (> 90%), and beta-TG was the most rare (0-1%). Deposition of CTAP-III in tissues, such as synovium, spleen, and kidney, is associated with partial processing to NAP-2-like isoforms and the potential to induce neutrophil and fibroblast activation in patients with rheumatic or end-stage renal disease.

Objective: To determine whether extracts of unincubated osteoarthritis (OA) and rheumatoid arthritis (RA) synovial tissue contain connective tissue activating peptide-III (CTAP-III) isoforms and prostaglandin E2 (PGE2), and whether such extracts have growth-promoting activity, and to determine whether binary combinations of CTAP-III with other cytokines reported to be present in synovial tissue lead to synergistic, additive, or inhibitory effects on growth., Methods: Acid-ethanol extracts of human synovium were examined for growth-promoting activity by measuring formation of 14C-glycosaminoglycan (14C-GAG) and 3H-DNA in synovial cell cultures; PGE2 was measured by enzyme immunoassay, and CTAP-III isoforms were identified by Western blotting of extracted proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Growth-promoting activity of CTAP-III and other cytokines was tested in synovial cultures treated with the agonists singly and in binary combination, by measuring changes in synthesis of 14C-GAG and 3H-DNA., Results: Platelet-derived CTAP-III and a cleavage isoform with the electrophoretic mobility of CTAP-III-des 1-15/neutrophil-activating peptide-2 (NAP-2) and PGE2 were found in biologically active extracts of synovial samples from patients with RA and OA. Five growth factors (recombinant epidermal growth factor [rEGF], recombinant interleukin-1 beta [rIL-1 beta], basic fibroblast growth factor [bFGF], PGE1, and PGE2) in binary combination with CTAP-III showed synergism in stimulating GAG synthesis; two (recombinant platelet-derived growth factor type BB [rPDGE-BB] and recombinant transforming growth factor beta [rTGF beta]) had an additive effect. In combination with CTAP-III, rEGF and rPDGF-BB had a synergistic effect in promoting DNA synthesis, rTGF beta and rbFGF had an additive effect, and rIL-1 beta, PGE1, and PGE2 were antagonistic., Conclusions: The results suggest that, in addition to endogenous factors, CTAP-III and other platelet-derived cytokines may play roles in regulating synovial cell metabolism in RA and OA, and that combinations of growth factors may be more significant than single agents in amplification or suppression of important cell functions.

Connective tissue-activating peptide-III (CTAP-III) is a 9 kd platelet alpha-granule-derived growth factor. It stimulates the synthesis of DNA, hyaluronic acid, glycosaminoglycans, and proteoglycan core protein in human fibroblasts. Human mononuclear cell-derived proteases have been previously demonstrated to digest the N-terminal 15 residues of CTAP-III (total, 85 residues) to produce neutrophil-activating peptide-2 (NAP-2). CTAP-III and NAP-2 belong to a class of proteins (platelet factor 4, interleukin-8/NAP-1, etc.) associated with inflammation and wound repair. In our efforts to purify human mononuclear cells and platelet-derived histamine-releasing factors, we had previously discovered that mixtures of CTAP-III and NAP-2 released histamine from human basophils. We have now developed simple protocols for the purification of CTAP-III and NAP-2, independently, from calcium ionophore (A23187)-stimulated platelet supernatants by affinity chromatography and have established their identity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and N-terminal sequence analysis. Each of these related histamine between 2 and 10 micrograms/ml, a range identical to that obtained with CTAP-III/NAP-2 mixtures that we reported earlier. Thus, our data suggest that CTAP-III and NAP-2 independently release histamine from human basophils in dose ranges similar to ranges required for fibroblast stimulation by each.

Neutrophil attractant/activation protein-1 (NAP-1) has sequence similarity to platelet factor-4 (PF-4) and to NAP-2 (a truncated from of connective tissue activating protein-III [CTAP-III(des 1-15)]. We compared chemotactic activity for neutrophils of these related proteins. We also included for comparison CTAP-III, CTAP-III(des 1-13), the C-terminal dodecapeptide of PF-4 [PF-4(59-70)], and C5a. Chemotactic potency (EC50) was highest for NAP-1 and C5a. Although chemotactic efficacy (peak percentage of neutrophils migrating) was comparable for C5a, NAP-1, and NAP-2, the NAP-2 response occurred only at concentrations 100-fold higher than the NAP-1 EC50 of 10(8) M. Data for the CTAP-III proteins confirmed that CTAP-III is not an attractant and that chemotactic activity appears as a result of cleavage of residues at the N-terminus to make CTAP-III(des 1-13) or NAP-2 [CTAP-III(des 1-15)]. Chemotactic activity of PF-4 was low and variable, with no significant response by neutrophils from six of nine subjects. In contrast, PF-4(59-70) regularly induced high chemotactic responses, although the EC50 of 1.6 x 10(5)M was 1,000-fold greater than that of NAP-1. The binding of fluoresceinated NAP-1 to neutrophils was inhibited by unlabeled NAP-1 or NAP-2 but not by PF-4 or PF-4 (59-70). This suggests that NAP-2 interacts with the neutrophil NAP-1 receptor. Despite the low chemotactic potency of NAP-2, it is a potential attractant at sites of injury because of the relatively large amounts of the parent CTAP-III released from platelets, as indicated by a serum concentration of approximately 10(-6) M.

Microheterogeneity of connective tissue activation peptide III (CTAP-III) was revealed by preparative and analytical isoelectric focusing. Proteolytic activities in human platelet preparations resulted in four cleavage products of platelet-derived CTAP-III. Three isoforms (CTAP-III des 1-13, des 1-14, and des 1-15/NAP-2) stimulate [14C]glycosaminoglycan synthesis; two isoforms also promote [3H]DNA synthesis in human fibroblast cultures. Elastase (from porcine pancreas) cleavage of human platelet-derived CTAP-III and rCTAP-III-Leu-21 to the des 1-15 isoforms was associated with either preservation of specific anabolic biologic activity or an actual increase in specific activity. Nonenzymatic glycosylation of lysyl residues and deamination of the NH2-terminal asparagine of platelet-derived CTAP-III were commonly present, but did not correlate with the biologic activities that were measured. Protein sequence homology shows CTAP-III and its isoforms to be members of a family of proteins (including NAP-1/II-8, MGSA, and platelet factor-4) known to be associated with growth, wound repair, inflammation, and neoplasia. The consequences of proteolytic processing reported here for CTAP-III may be characteristic of the other proteins in this group.

Connective tissue activating peptide III (CTAP-III) is an 85-residue peptide which has been purified from platelets and shown to possess mitogenic activity toward a variety of fibroblastic cell lines. beta-Thromboglobulin (beta TG) is an 81-residue peptide which is derived from CTAP-III by cleavage of the N-terminal tetrapeptide Asn-Leu-Ala-Lys which results in the loss of mitogenic activity. The near-UV CD spectra for the two proteins indicated that the conformations as well as the electronic environments of the two disulfide bonds, and also of the single aromatic tyrosine residue, were similar in CTAP-III and beta TG. However, differences in the far-UV CD spectra of these proteins indicated a substantial decrease in alpha-helical content for beta TG (29%) as compared to CTAP-III (38%). Structure prediction analysis also suggested that the longer N-terminal segment of CTAP-III may form an alpha-helix. The N-terminal region of beta TG, which lacks this tetrapeptide, was predicted to be in an unordered, or possibly a turn, conformation. This predicted structural difference appears to be due to the high helix-forming potential of the N-terminal tetrapeptide Asn-Leu-Ala-Lys in CTAP-III. These results suggest a possible structural role for the N-terminal region of CTAP-III in the expression of the biologic activities of this protein. On the basis of these studies, a reasonable hypothesis to account for the difference in mitogenic activity between beta TG and CTAP-III is that the N-terminal region must be helical for receptor binding to occur.

We have previously reported purification of three forms of histamine-releasing factors (HRFs) from mixtures of streptokinase-streptodornase stimulated human mononuclear cells and platelets with apparent molecular masses of 10-12, 15-17, and 40-41 kD (1989. J. Clin. Invest. 83:1204-1210). We have also prepared mouse MAbs against the 10-12-kD HRF (1989. J. Allergy Clin. Immunol. 83:281). Affinity-purified 10-12-kD HRF appears as a broad band upon polyacrylamide gel electrophoresis in the presence of SDS. We determined the NH2-terminal amino acid sequence of the top and bottom halves of this broad band. Sequence analysis revealed striking homology between this HRF and connective tissue activating peptide-III (CTAP-III), a platelet-derived 8-10-kD protein known to cause mitogenesis and extracellular matrix formation in fibroblast cultures. 19 of 21 NH2-terminal residues in the top half of the HRF band were identical to the NH2-terminal sequence of CTAP-III. 20 of 21 NH2-terminal residues in the bottom half were identical to the NH2-terminal sequence of neutrophil-activating peptide-2, which is derived from CTAP-III by proteolytic cleavage between residues 15 and 16. Purified CTAP-III also released histamine from basophils. Rabbit antiserum raised against either native or recombinant CTAP-III recognized affinity-purified HRF in immunodot blot assays, and MAb against HRF recognized CTAP-III in both dot blot and microtiter plate based immunoassays. These data demonstrate the first structural, functional, and immunologic relationship between one form of human HRF and a previously described cell product.

Connective tissue activating peptide-III (CTAP-III) isolated from human platelets is a potent mitogen for human connective tissue cells in culture in addition to stimulating glycosaminoglycan synthesis, glucose consumption, and lactate formation. The amino acid composition of apparently homogeneous CTAP-III was determined, confirming the presence of two disulfide links and providing a calculated molecular weight of 11,633 daltons. Comparison of the mitogenic activity of serum and plasma-serum suggests that CTAP-III is a major mitogenic component of human serum. Seventeen strains of human connective tissue cells (synovial, cartilage, dermal and thyroid) incorporated [3H]-thymidine at up to 30 times control at levels under the influence of microgram quantities of CTAP-III and caused detectable increases in thymidine incorporation at levels as low as 10-29 ng/ml. Prostaglandin E1 (0.01 microgram/ml) and dibutyryl cyclic AMP (25 microgram/ml) potentiated the glycosaminoglycan stimulating effect of CTAP-III, but not its mitogenic effect. Cycloheximide and actinomycin D blocked the biologic actions of CTAP-III. Cortisol and penicillamine had little effect on the mitogenic activity of CTAP-III, whereas antirheumatic agents such as acetylsalicylic acid and phenylbutazone opposed the mitogenic activity when added to cultures at clinically relevant concentrations. A weak antiheparin factor secreted by platelets, low affinity platelet factor 4 (LA-PF4), was shown to be similar to CTAP-III in biologic actions, electrophoretic mobility, amino acid composition, and antigenic determinants.

The quantitative radiochemical methodology described in this report allows a major increase in information generation, increased experimental flexibility, improved statistical control, and increased diversity of information per culture. Other advantages relate to economies of technical time, supplies, cells, and test materials per individual culture. Microcultures of human synovial cells incorporate [14C]glucosamine into hyaluronic acid that accumulated primarily in the media and to a lesser extent in the cell mass. CTAP-I (from lymphoid cells), CTAP-III (from human platelets), PGE2, dibutyryl cAMP, and poly(I) . poly(C) markedly stimulated hyaluronate synthesis, whereas cortisol, cycloheximide, and tunicamycin inhibited stimulated synthesis. Time studies with cycloheximide indicated that translation, essential for the activation of synovial cells, was completed by 17 h postexposure to CTAP-I. Tunicamycin also seemed to inhibit CTAP-I induced activation primarily by interfering with translation; however, tunicamycin also caused modest post-translation inhibition of hyaluronate synthesis in activated adult human synovial cells.

Connective tissue activating peptide III (CTAP III), a human platelet derived growth factor, induced marked stimulation of 2-deoxy[14C]glucose (2dG) uptake in cultures of human synovial cells, chondrocytes, and dermal fibroblasts. Cytochalasin B (2 X 10(-5) M) blocked the mediator-induced increase in 2dG uptake; phlorhizin (8 X 10(-4) M) partially inhibited this process. When cells were exposed to CTAP III (4 X 10(-6) M) for 30 min prior to uptake assay, 2dG uptake was stimulated by 30-110%; greater stimulation (400-800%) occurred following 17-40-h preincubation with the mediator. A 17-h exposure to CTAP III similarly stimulated 3-O-methylglucose uptake by over 400%, suggesting that CTAP III stimulated 2dG uptake is mediated via changes in hexose transport. Cycloheximide clearly prevented the 17-h effects of CTAP III on 2dG uptake. Insulin (3 X 10(-6) M) stimulated 2dG uptake 40-70% after 30-min preincubation with hormone; little effect was seen after 17-h preincubation. These data suggest that CTAP III stimulates glucose transport shortly after addition to target cells; the major stimulation observed after a 17-h incubation is consistent with the synthesis of new glucose transport protein.

We previously identified, in normal urine, a growth factor that stimulated monolayer cultures of human synovial, cartilage, and dermal fibroblasts to synthesize incremental amounts of hyaluronic acid, proteoglycans, and DNA. An isolation procedure guided by bioassays and immunologic methods disclosed 2 anionic bioactive polypeptides with Mr of 28,000 and 16,000, respectively, as judged by single bands with sodium dodecyl sulfate-polyacrylamide gel electrophoresis in reduced and nonreduced samples. Rabbit antibodies raised against each purified protein were shown to react, on immunodiffusion and Western blot, with both antigens. Immunohistochemical and immunobinding studies detected the protein in normal human synovial, dermal, and cartilage fibroblasts and in human saphenous vein endothelial cells. The mesenchymal cell-derived growth factor is now designated connective tissue activating peptide-V (CTAP-V). Monospecific polyclonal anti-CTAP-V antibodies were used in a radial immunodiffusion assay for quantitative determination of the antigen in biologic fluids. In normal human plasma the concentration of CTAP-V was below the limit of detection. The CTAP-V concentration in normal urine was 4.5 +/- 2.0 micrograms/ml, calculated from measurements of 5-18-fold concentrated samples. Joint fluid from patients with rheumatic diseases and normal renal function had CTAP-V levels similar to those found in plasma; 2-15-fold increases were detected in plasma and joint fluid of patients with chronic renal failure. Immunodiffusion or dot-blot analysis revealed a CTAP-V-like material in the plasma or serum of 10 mammalian species. It was not detectable in 2 avian species.

Earlier studies showed that guinea pig lung fibroblasts in cell culture could be "activated" by naturally occurring peptides with a resultant increase in glycolysis and glycosaminoglycan formation. Such connective tissue activation (CTA) in human cell systems (synovial, cartilage, dermal) has proved a useful tool for studying the mechanisms of inflammation and dissecting the efficacy and actions of anti-inflammatory drugs. The present study examined the consequences of treating basal and activated guinea pig lung fibroblasts with glucocorticoids. The data indicate that glucocorticoids minimally suppress glycosaminoglycan (GAG) synthesis in nonactivated cultures. Further, CTA was inhibited to only a minor degree in activated lung fibroblast cultures by steroids, and even markedly supraphysiologic concentrations of glucocorticoids were not notably inhibitory. It was of interest that thiols enhanced suppression of incremental GAG synthesis by some glucocorticoids in activated lung fibroblast cultures.

Alpha- and beta-adrenergic blocking agents and imipramine inhibit the increased hyaluronate synthesis that may be induced in human synovial cultures by connective tissue activating peptide (CTAP). Considerations of drug concentration requirements, actions of analogues, and time studies all indicate that the adrenergic blockers do not act in this circumstance as conventional blockers of alpha or beta receptor sites. It is suggested that the membrane-stabilizing properties of these agents may be the important determinant for their limited "antiactivation" effect. Ethacrynic acid, a potent and more complete inhibitor of connective tissue activation, appears to act via a different mechanism.

Plasma levels of platelet granule proteins CTAP-III and beta-thromboglobulin (beta-TG) were measured by radioimmunoassay of their common antigen (CTAP-Ag). Healthy adults had 29.4 +r5.8 ng CTAP-Ag/ml plasma while patients with rheumatoid arthritis (RA) had higher levels of the CTAP-Ag (range 23-260 ng/ml, median 43 ng/ml, p less than .006). RA patients with CTAP-Ag levels greater than 50 ng/ml (mean 104.8 ng/ml) were compared to patients having lower CTAP-Ag levels. Patients in the group with elevated plasma CTAP-Ag levels had higher sedimentation rates (p less than .005), and higher platelet counts (p less than .05). Anemia was more common in patients with abnormal CTAP-Ag levels.

This report describes a small basic protein found in human platelets which stimulates hyaluronic acid formation, glucose uptake, and lactate formation in several types of human connective tissue cells. In addition, it stimulates in incorporation of [3H] methyl thymidine into DNA in human synovial cell cultures. This platelet factor (connective tissue activating peptide-II, CTAP-III) clearly differs form CTAP-I, found in human lymphocytes, and may play a role as a mediator of the inflammatory process.

Patients with rheumatoid arthritis frequently have an unexplained thrombocytosis which appears to be related to the severity of the disease process. This report shows that rheumatoid platelets have reduced saline soluble protein per 10(9) platelets, less of a lysosomal enzyme, acid phosphatase, and decreased connective tissue activating peptide (CTAP-III) activity. CTAP-III is a potent connective tissue mitogen, and promotes glycolysis and glycosaminoglycan synthesis, characteristics which make it an interesting candidate for a role as a mediator of inflammation.

Guinea pig lung fibroblasts "activated" in vitro by exposure to connective tissue-activating peptides I and III, and guinea pig tissue extracts showed enhanced glycolysis and accelerated glycosaminoglycan synthesis. Formation of hyaluronic acid, and to a lesser extent, chondroitin 4/6-sulfate was stimulated by these agents.

Evidence for three new isoforms of CTAP-III from human platelets is presented; two NH2-terminal cleavage products were identified, CTAP-III (des 1-13) and CTAP-III (des 1-15). CTAP-III (des 1-13) has a pI of 8.6 and is a relatively stable proteolytic cleavage product that retains the capacity to stimulate [14C]GAG synthesis in human synovial cell cultures. CTAP-III (des 1-15) appears to be an elastase or chymotrypsin cleavage product and identical to NAP-2, an entity thought to have neutrophil activating properties.

The platelet-derived connective tissue activating peptide (CTAP-III) has been shown to be an important factor stimulating the metabolism and proliferation of human connective tissue cell strains, including synovial tissue cells. The quantities of CTAP-III affecting the cellular changes and the amounts of various biologic fluids and tissues are small. The objectives of this study were to develop a radioimmunoassay (RIA) for CTAP-III and to ascertain the specificities of the anti-CTAP-III sera reagents. The antisera were shown not to cross-react with a number of polypeptide hormones. However, two other platelet proteins, beta-thromboglobulin and low affinity platelet factor-4, competed equally as well as CTAP-III for anti-CTAP-III antibodies in the RIA system. Thus, the three platelet proteins are similar or identical with respect to those portions of the molecules constituting the reactive antigenic determinants. The levels of material in normal human platelet-free plasma that inhibited anti-CTAP-III--125I-CTAP-III complex formation were determined to be 34 +/- 13 (S.D.) ng/ml.

CTAP-I from lymphocytes and CTAP-III from platelets markedly stimulated 35SO4= incorporation into chondroitin 4/6 sulfate and dermatan sulfate synthesized by human synovial, dermal, and cartilage connective tissue cells in vitro. These agonists promoted synthesis of the GAG carbon chain as well as sulfate incorporation. Both RNA and protein synthesis were required for these mediators to be effective in stimulating synthesis of connective tissue matrix components. A major part of the capacity of normal serum to stimulate sulfate incorporation into GAG's may reside in CTAP-III.

Connective tissue activating peptide (CTAP-III) is one of the growth factors found in the alpha granules of human platelets. This small cationic platelet protein shows several apparent isoelectric point variants after the preparative isoelectric focusing step in large scale preparations from multiple donors. Analytical isoelectricfocusing techniques under denaturing conditions, coupled with Western blotting and immunodetection, now show that CTAP-III prepared rapidly from single donors also has multiple isoelectric point variants, suggesting that this finding is more likely related to post-translational modification than preparative artifact or genetic polymorphism.

Connective tissue activating peptides (CTAPs) extracted from leukocytes and platelets stimulate glycolysis and synthesis of glycosaminoglycan and DNA in cultured human connective tissue cells. CTAP-III, isolated from fresh or outdated human platelets, is a low molecular weight single-chain protein with an isoelectric point of 8.5 that markedly stimulates DNA synthesis and multiple aspects of glycosaminoglycan and proteoglycan metabolism. This report presents a definitive comparison of CTAP-III prepared by two methods [one designated (A), alternative] with similar platelet proteins described by others, beta-thromboglobulin (beta-TG) and low-affinity platelet factor 4 (LA-PF-4). CTAP-III, CTAP-III(A), LA-PF-4, and beta-TG have common antigenic determinants documented by immunoprecipitation and radioimmunoassay. CTAP-III, CTAP-III(A), and LA-PF-4 are biologically active in that they stimulate DNA and glycosaminoglycan synthesis by human synovial cells; beta-TG is inactive. Carboxyl-terminal digestion gave identical terminal sequences for CTAP-III, CTAP-III(A), and beta-TG. Amino-terminal sequence data indicate that CTAP-III and CTAP-III(A) (also LA-PF-4) are identical and differ from beta-TG only by an additional amino-terminal tetrapeptide (Asn-Leu-Ala-Lys-). The biologically active molecule, CTAP-III, may be proteolytically converted to its inactive degradation product (beta-TG) in the course of platelet aging, platelet storage, release from the platelets, or initiation of biological activity.

Connective tissue-activating peptides (CTAPs) stimulate human synovial cells to exhibit a higher rate of DNA synthesis, glycolysis, and glycosaminoglycan formation. These bioactive peptides have been isolated from human platelets (CTAP-III), lymphocytes, tumor cells, and neutrophilic leukocytes. Several other growth factors, such as somatomedins A and C and nonsuppressible insulin-like activity (soluble), have been shown to be dependent on the circulating levels of pituitary GH. In this study, we examined the human GH (hGH) dependence of CTAP-III. Platelets from children with reduced or absent hGH were examined for the presence of CTAP-III. The peptide was detected qualitatively by polyacrylamide gel electrophoresis and Ouchterlony double diffusion. CTAP-III antigen, measured by RIA, was found in normal amounts in platelet lysates from normal persons and GH-deficient patients. Biological activity of the peptide was suggested by the ability of platelet lysates to stimulate the formation of glycosaminoglycans and increase sulfate incorporation into glycosaminoglycans formed in cell cultures. In addition, normal and hGH-deficient platelet lysates contained potent mitogenic activity which increased thymidine incorporation into DNA. Platelets from GH-deficient patients also released CTAP-III normally on exposure to thrombin.

Connective tissue activating peptide III (CTAP-III) is a platelet factor that induces, in cultured connective tissue cells, activities observed in chronic inflammation. In this study we measured plasminogen activator secretion by synovial fibroblasts after stimulation by CTAP-III. Increased plasminogen activator secretion was observed 24-48 hours after stimulation. Induction was prevented by dexamethasone (10(-9)-10(-7) M), cycloheximide (1 microgram/ml) and, variably, by actinomycin D (0.3 microgram/ml), but not by cytosine arabinoside (10(-4)M). This is the first evidence that CTAP-III induces degradative as well as proliferative activity by connective tissue cells.

Plasma levels of the CTAP-III antigen were measured by radioimmunoassay in 80 patients with rheumatic diseases. Patients with clear evidence of vasculitis usually exhibited increased plasma CTAP-III antigen. In both systemic lupus erythematosus and rheumatoid arthritis, there appeared to be a correlation between pCTAP-III values and other laboratory and clinical parameters of disease activity.

Antisera selectively reactive with the N-terminal tetrapeptide sequence of the platelet-derived connective tissue activating peptide-III mitogen were prepared and characterized. Solid phase synthesized Z-Asn-Leu-Ala-Lys(Z)-OH tetrapeptide representing the N-terminus of the mitogen was used as an immunogen after carbodiimide mediated coupling to methylated bovine serum albumin carrier and subsequent removal of Z groups. Anti-tetrapeptide sera demonstrated cross-reactivity to the mitogen but not beta-thromboglobulin, fibroblast growth factor, or epidermal growth factor, and a limited cross-reactivity to parathyroid hormone. The studies indicate that the N-terminal sequence of the mitogen is accessible for binding with antibody and the antitetrapeptide sera provide a reagent for the selective measurement of biologically active mitogen in the presence of structurally similar beta-thrombo-globulin. In addition, computer analysis of amino acid sequences revealed that few proteins contain the Asn-Leu-Ala-Lys sequence and of those that do, many are retroviral proteins or transforming polyproteins.

Connective tissue activating peptide-V (CTAP-V) is a single-chain, mesenchymal cell-derived anionic protein with large and small molecular forms (Mr of 28,000 and 16,000, respectively), as defined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The proteins have similar specific activities with respect to stimulation of hyaluronic acid and DNA formation in human synovial fibroblast cultures. S-carboxymethylation or removal of sialic acid residues did not modify CTAP-V biologic activity. Rabbit antibodies raised separately against each of the purified CTAP-V proteins reacted, on immunodiffusion and on Western blot, with each antigen and neutralized mitogenic activity. The amino-terminal amino acid sequence of the CTAP-V proteins, determined by 2 laboratories, confirmed their structural similarities. The amino-terminal sequence through 37 residues was demonstrated for the smaller protein. The first 10 residues of CTAP-V (28 kd) were identical to the N-terminal decapeptide of CTAP-V (16 kd). The C-terminal sequence, determined by carboxypeptidase Y digestion, was the same for both CTAP-V molecular species. The 2 CTAP-V peptides had similar amino acid compositions, whether residues were expressed as a percent of the total or were normalized to mannose. Reduction of native CTAP-V protein released sulfhydryl groups in a protein:disulfide ratio of 1:2; this suggests that CTAP-V contains 2 intramolecular disulfide bonds. Clearly, CTAP-V is a glycoprotein. The carbohydrate content of CTAP-V (16 kd) and CTAP-V (28 kd) is 27% and 25%, respectively. CTAP-V may have significance in relation to autocrine mechanisms for growth regulation of connective tissue cells and other cell types.

A protein factor in human urine which has the ability to activate connective tissue cells has been identified and partially purified; it appears to be different from epidermal growth factor and IgG. This urinary connective tissue activating factor (CTAP-U) is nondialyzable, labile to protease, stable to thiols, heat, and acid, and has an acidic isoelectric point. Purified preparations of CTAP-U have biologic activities that cause human connective tissue cells to synthesize incremental amounts of 14C-hyaluronic acid, 35S-proteoglycans, and 3H-DNA in vitro. The cell spectrum responsive to this substance includes human synovial cells, human chondrocytes, and skin fibroblasts. CTAP-U does not react with antisera to connective tissue activating peptide-III or to antibodies against IgG or its Fc and Fab fragments. Furthermore, CTAP-U does not cross-react in a radioreceptor assay for insulin, basic somatomedin, or epidermal growth factor-urogastrone. Utilizing standardized isolation conditions, CTAP-U preparations with these properties have been isolated from the urine of 6 normal individuals.