What’s known on the subject? and What does the study add? We found that resistin, a member of adipokine family, is expressed in human prostate cancers and induces prostate cancer cell proliferation through PI3K/Akt signaling pathways. We are studying the effect of resistin on other urogenital tract diseases besides prostate cancer, and the relationship between other adipokines and the urogenital tract diseases. OBJECTIVES • To determine whether resistin, a novel adipokine, induces prostate cancer cell proliferation. • To identify the mechanisms underlying the activation of prostate cancer cells by resistin. MATERIALS AND METHODS • Semi‐quantitative reverse transcriptase‐polymerase chain reaction and immunohistochemical staining were performed to investigate the intensity of prostate epithelial resistin expression. • Human full‐length resistin gene (RETN) was transfected into the PC‐3 cells using the pEGFP‐N1 vector to assess the effect of overexpression of resistin in prostate cancer cell line PC‐3. • Various concentrations of human recombinant protein resistin were added to the hormone‐insensitive prostate cancer cell lines PC‐3 and DU‐145 for 48 h, and cell proliferation was assessed by a water‐soluble tetrazolium salt assay. RESULTS • Human prostate cancer cell lines PC‐3 and DU‐145 were found to express the human resistin mRNA. • Resistin protein was strongly detected in high‐grade prostate cancer tissue, whereas BPH or low‐grade prostate cancer tissue revealed fainter expression of resistin. • Cell proliferation was stimulated by both the full‐length resistin gene overexpression and resistin treatment. • Akt phosphorylation occurred after addition of resistin to PC‐3 and DU‐145 cells. LY294002, a pharmacological inhibitor of phosphatidylinositol 3‐kinase (PI3K), significantly inhibited PC‐3 and DU‐145 cell proliferation after resistin treatment. CONCLUSIONS • Resistin is expressed in human prostate cancers. • Resistin induces prostate cancer cell proliferation through PI3K/Akt signalling pathways. • The proliferative effect of resistin on prostate cancer cells may account in part for prostate cancer progression.

DDR2 is a receptor tyrosine kinase whose activating ligands are various collagens. DDR2-mediated cellular signaling has been shown to require Src activity. However, the precise mechanism underlying the Src dependence of DDR2 signaling is unknown. Here, using baculoviral co-expression of the DDR2 cytosolic domain and Src, we show that Src targets three tyrosine residues (Tyr-736, Tyr-740, and Tyr-741) in the activation loop of DDR2 for phosphorylation. This phosphorylation by Src stimulates DDR2 cisautophosphorylation of additional tyrosine residues. In vitro Shc binding assays demonstrate that phosphotyrosines resulting from DDR2 autophosphorylation are involved in Shc binding to the DDR2 cytosolic domain. Mutating tyrosine 740 of DDR2 to phenylalanine stimulates autophosphorylation of DDR2 to an extent similar to that resulting from Src phosphorylation of DDR2. In addition, the DDR2 Y740F mutant protein displays collagenindependent, constitutively activated signaling. These findings suggest that tyrosine 740 inhibits DDR2 autophosphorylation. Collectively, our findings are consistent with the following mechanism for Src-dependent DDR2 activation and signaling: 1) ligand binding promotes phosphorylation of Tyr-740 in the DDR2 activation loop by Src; 2) Tyr-740 phosphorylation stimulates intramolecular autophosphorylation of DDR2; 3) DDR2 autophosphorylation generates cytosolic domain phosphotyrosines that promote the formation of DDR2 cytosolic domain-Shc signaling complexes. The discoidin domain receptor (DDR)2 family, including DDR1 and DDR2, belongs to receptor tyrosine kinases (RTKs) family. Its extracellular part, containing the so-called discoidin domain, binds to various collagen proteins as their activating ligands (1-3), and its intracellular part possesses a domain of tyrosine kinase, which shares ϳ50% sequence homology with that of the Trk family of neurotrophin receptors as well as with insulin receptor (4 -6).Involvement of DDR proteins in the proliferation of various cell types has been reported. Increased DDR1 expression is observed in keratinocytes of the skin and smooth muscle cells around blood vessels when the tissues are injured (7,8). DDR1 is also expressed in monocyte-derived cells where it is believed to play a role in collagen binding and cell differentiation (9, 10). DDR2 expression is observed in mesenchymal cells and is involved in bone growth (11). During liver fibrosis, induction and activation of DDR2 occur in liver stellate cells, and its tyrosine kinase activity is necessary for the proliferation of stellate cells and for the increase of collagen and MMP-2 synthesis (12, 13). In rheumatoid arthritis, DDR2 induction is also observed in activated synovial fibroblasts and is thought to stimulate the growth of these cells and MMP-1 synthesis (14). In addition, the induction of DDR proteins is implicated in breast and ovarian cancer, and is correlated with metastasis (15, 16).Autophosphorylation of the cytosolic domain of RTKs is typically a critical event for the activation of RTK-med...

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Ceramide is an important lipid messenger involved in mediating a variety of cell functions including apoptosis. In this study, we show that antisense bax inhibits cytochrome c release, poly(ADP-ribose)polymerase cleavage and cell death induced by ceramide in HL-60 cells. In addition, ceramide induces translocation of Bax to mitochondria. The addition of the broad spectrum caspase inhibitor zVAD-fmk prevented ceramideinduced apoptotic cell death but did not inhibit translocation of Bax and mitochondrial cytochrome c release. Furthermore, ceramide inhibits the expression of the antiapoptotic protein BclxL with an increase in the ratio of Bax to Bcl-xL. These data provide direct evidence that Bax plays an important role in regulating ceramide-induced apoptosis. ß 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.

Ceramide induces cell cycle arrest and apoptotic cell death associated with increased levels of p27(kip1). The aim of this study was to examine the effects of ceramide on p27(kip1) protein levels as a measure of cell cycle arrest and apoptosis. Results showed that ceramide increased p27(kip1) protein levels through activation of protein phosphatase 2A (PP2A) in PC-3 prostate cancer cells. Treatment of cells with the PP2A inhibitor okadaic acid or with PP2A-Cα siRNA inhibited ceramide-induced enhanced p27(kip1) protein expression and Akt dephosphorylation, and prevented Skp2 downregulation. Overexpression of constitutively active Akt attenuated ceramide-induced Skp2 downregulation and p27(kip1) upregulation. In addition, ceramide stimulated binding of the PP2A catalytic subunit PP2A-Cαβ to Akt as assessed by immunoprecipitation experiments, indicating that PP2A is involved in the induction of p27(kip1) via inhibition of Akt pathway. Finally, whether PP2A can regulate p27(kip1) expression independently of Akt pathway was determined. Knockdown of PP2A-Cα with siRNA reduced p27(kip1) levels in the presence of Akt inhibitor. These data reveal that PP2A is a regulator of ceramide-induced p27(kip1) expression via Akt-dependent and Akt-independent pathways.