Search

The intestinal epithelium has a high rate of turnover, and dysregulation of pathways that regulate regeneration can lead to tumor development; however, the negative regulators of oncogenic events in the intestinal epithelium are not fully understood. Here we identified a feedback loop between the epidermal growth factor receptor (EGFR), a known mediator of proliferation, and the transient receptor potential cation channel, subfamily V, member 1 (TRPV1), in intestinal epithelial cells (IECs). We found that TRPV1 was expressed by IECs and was intrinsically activated upon EGFR stimulation. Subsequently, TRPV1 activation inhibited EGFR-induced epithelial cell proliferation via activation of [Ca.sup.2+]/calpain and resulting activation of protein tyrosine phosphatase 1B (PTP1B). In a murine model of multiple intestinal neoplasia ([Apc.sup.Min/+] mice), TRPV1 deficiency increased adenoma formation, and treatment of these animals with an EGFR kinase inhibitor reversed protumorigenic phenotypes, supporting a functional association between TRPV1 and EGFR signaling in IECs. Administration of a TRPV1 agonist suppressed intestinal tumorigenesis in [Apc.sup.Min/+] mice, similar to--as well as in conjunction with--a cyclooxygenase-2 (COX-2) inhibitor, which suggests that targeting both TRPV1 and COX-2 has potential as a therapeutic approach for tumor prevention. Our findings implicate TRPV1 as a regulator of growth factor signaling in the intestinal epithelium through activation of PTP1B and subsequent suppression of intestinal tumorigenesis., Introduction The mammalian intestinal epithelium reveals a complex interplay among intestinal stem cell (ISC) self-renewal in the crypts of Lieberkuhn, progenitor cell proliferation, differentiation, and, ultimately, apoptosis (1). The high [...]

Toll-like receptor (TLR) signaling is essential for intestinal tumorigenesis in [Apc.sup.min/+] mice, but the mechanisms by which Apc enhances tumor growth are unknown. Here we show that microflora-MyD88-ERK signaling in intestinal epithelial cells (IECs) promotes tumorigenesis by increasing the stability of the c-Myc oncoprotein. Activation of ERK (extracellular signal--related kinase) phosphorylates c-Myc, preventing its ubiquitination and subsequent proteasomal degradation. Accordingly, [Apc.sup.min/+]/[Myd88.sup.-1-] mice have lower phospho-ERK (p-ERK) levels and fewer and smaller IEC tumors than [Apc.sup.min/+] mice. MyD88 (myeloid differentiation primary response gene 88)-independent activation of ERK by epidermal growth factor (EGF) increased p-ERK and c-Myc and restored the multiple intestinal neoplasia (Min) phenotype in [Apc.sup.min/+]/[Myd88.sup.-1-] mice. Administration of an ERK inhibitor suppressed intestinal tumorigenesis in EGF-treated [Apc.sup.min/+]/[Myd88.sup.-/-] and [Apc.sup.min/+] mice and increased their survival. Our data reveal a new facet of oncogene-environment interaction, in which microflora-induced TLR activation regulates oncogene expression and related IEC tumor growth in a susceptible host., The gastrointestinal tract is constantly exposed to vast numbers of commensal bacteria and their inflammatory products. Essential to intestinal homeostasis are pattern recognition receptors (PRRs) such as TLRs (1). Engagement [...]

TLRs sense various microbial products. Their function has been best characterized in DCs and macrophages, where they act as important mediators of innate immunity. TLR4 is also expressed on [CD4.sup.+] T cells, but its physiological function on these cells remains unknown. Here, we have shown that TLR4 triggering on [CD4.sup.+] T cells affects their phenotype and their ability to provoke intestinal inflammation. In a model of spontaneous colitis, [Il10.sup.[-/-]] [Tlr4.sup.[-/-]] mice displayed accelerated development of disease, with signs of overt colitis as early as 8 weeks of age, when compared with [Il10.sup.[-/-]] and [Il10.sup.[-/-]][Tlr9.sup.[-/-]] mice, which did not develop colitis by 8 months. Similar results were obtained in a second model of colitis in which transfer of naive [Il10.sup.[-/-]] [Tlr4.sup.[-/-]] [CD4.sup.4] T cells into [Rag1.sup.[-/-]]recipients sufficient for both IL-10 and TLR4 induced more aggressive colitis than the transfer of naive [Il10.sup.[-/-]] [CD4.sup.+] T cells. Mechanistically, LPS stimulation of TLR4-bearing [CD4.sup.+] T cells inhibited ERK1/2 activation upon subsequent TCR stimulation via the induction of MAPK phosphatase 3 (MKP-3). Our data therefore reveal a tonic inhibitory role for TLR4 signaling on subsequent TCR-dependent [CD4.sup.+] T cell responses., Introduction IL-10 is an antiinflammatory cytokine that regulates T cell proliferation and functions (1). [Il10.sup.[-/-]] mice develop spontaneous chronic enterocolitis with mucosal infiltration of lymphocytes, macrophages, and neutrophils (2) similarly [...]

3-Hydroxyanthranilic acid (HAA), a compound generated during tryptophan metabolism initiated by indoleamine 2,3-dioxygenase, is known to induce T cell death, but its molecular target is not known. Here we report that HAA inhibits NF-[kappa]B activation upon T cell antigen receptor engagement by specifically targeting PDK1. Inhibition of NF-[kappa]B by HAA leads to dysfunction and cell death of activated Th2 cells, which in turn suppresses experimental asthma. Inhibition of NF-[kappa]B and induction of apoptosis is specific to CD4 T cells because HAA does not inhibit NF-[kappa]B activation or induce cell death upon Toll-like receptor 4 stimulation in dendritic cells. Thus, HAA is a natural inhibitor that restrains T cell expansion and activation. HAA | indolearnine 2,3-dioxygenase | NF-[kappa]B | tryptophan

We explored the physiological role of conventional dendritic cells (cDCs) in acute colitis induced by a single cycle of dextran sodium sulfate administration. Depending on their mode of activation and independently of T cells, cDCs can enhance or attenuate the severity of dextran sodium sulfate-induced colitis. The latter beneficial effect was achieved, in part, by IFN-1 induced by Toll-like receptor 9-activated cDCs. IFN-1 inhibits colonic inflammation by regulating neutrophil and monocyte trafficking to the inflamed colon and restraining the inflammatory products of tissue macrophages. These data highlight a novel role of cDCs in the regulation of other innate immune cells and position them as major players in acute colonic inflammation. colitis | Toll-like receptor 9 | IFN-1

IFN-[alpha] is used to suppress the replication of hepatitis C virus (HCV) in chronically infected patients with partial success. Here we present evidence showing that a ligand of Toll-like receptor 7 (TLRT) can induce anti-HCV immunity not only by IFN induction, but also through an IFN-independent mechanism. Human hepatocyte line Huh-7 carrying an HCV replicon expressed TLRT, and activation of the receptor induced several antiviral genes including IFN regulatory factor-7. Inhibitors of the enzyme inosine monophosphate dehydrogenase augmented both IFN-dependent and -independent antiviral effect. Prolonged exposure of Huh-7 cells to a TLR7 ligand [SM360320 (9-benzyl-8-hydroxy-2- (2-methoxyethoxy)adenine)], alone or in combination with an inosine monophosphate dehydrogenase inhibitor, reduced HCV levels dose dependently. Immunohistochemical analysis of livers shows that TLR7 is expressed in hepatocytes of normal or HCV-infected people. Because TLR7 agonists can impede HCV infection both via type I IFN and independently of IFN, they may be considered as an alternative treatment of chronic HCV infection, especially in IFN-[alpha]-resistant patients. inosine monophosphate dehydrogenase | IFN regulatory factor

Certain C8-substituted and N7, C8-disubstituted guanine ribonucleosides comprise a class of small molecules with immunostimulatory activity. In a variety of animal models, these agents stimulate both humoral and cellular immune responses. The antiviral actions of these guanosine analogs have been attributed to their ability to induce type I IFNs. However, the molecular mechanisms by which the guanosine analogs potentiate immune responses are not known. Here, we report that several guanosine analogs activate Toll-like receptor 7 (TLR7). 7-Thia-8-oxoguanosine, 7-deazaguanosine, and related guanosine analogs activated mouse immune cells in a manner analogous to known TLR ligands, inducing cytokine production in mouse splenocytes (IL-6 and IL-12, type I and II IFNs), bone marrow-derived macrophages (IL-6 and IL-12), and in human peripheral blood leukocytes (type I IFNs, tumor necrosis factor [alpha] and IL-12). The guanosine congeners also up-regulated costimulatory molecules and MHC I/II in dendritic cells. Genetic complementation studies in human embryonic kidney 293 cells confirmed that the guanosine analogs activate cells exclusively via TLR7. The stimulation of TLR7 by the guanosine analogs in human cells appears to require endosomal maturation because inhibition of this process with chloroquine significantly reduced the downstream activation of NF-[kappa]B. However, TLR8 activation by R-848 and TLR2 activation by {S-[2,3-bis(palmitoyloxy)-(2-RS)-propyl]-N-palmitol-R-Cys-S-Ser-Lys4-OH, trihydrochloride)} were not inhibited by chloroquine, whereas TLR9 activation by CpG oligodeoxynucleotides was abolished. In summary, we present evidence that guanosine analogs activate immune cells via TLR7 by a pathway that requires endosomal maturation. Thus, the B cell-stimulating and antiviral activities of the guanosine analogs may be explained by their TLR7-activating capacity.