摘要：

Protein Kinase C epsilon (PKC∈), a member of the PKC family of phorbol ester/diacylglycerol receptors, has been shown to be up-regulated in human prostate cancer specimens. As PKC∈ plays an important role in prostate cancer cell survival and cooperates with other oncogenic insults, we hypothesized that PKC∈ may regulate NF-κB signaling pathway, known to be highly dysregulated during prostate tumorigenesis. Similar to human tumors, we observed high PKC∈ overexpression in prostate cancer cell lines compared to normal immortalized RWPE-1 cells. PKC∈ depletion using siRNA or its pharmacological inhibition in LNCaP cells resulted in decreased TNFα-induced IκBα phosphorylation and degradation, as well as decreased NF-κB nuclear translocation and transactivation of NF-κB reporter activity. Conversely, significant enhancements in these TNFα-induced responses were observed in LNCaP cells upon PKC∈ overexpression using an adenoviral approach. Interestingly, TNFα treatment led to activation of PKC∈ in LNCaP cells, as analyzed by enhanced translocation from cytosolic to membrane fractions. Furthermore, TNFα-mediated PKC∈ translocation and IκBα phosphorylation were found to be dependent on phosphatidylcholine- but not phosphatidylinositol-specific phospholipase C. As determined by co-immunoprecipitation, PKC∈ associates with TNF receptor-1 (TNFR1) in response to TNFα and has important regulatory consequences in the assembly of TNFR-1 signaling complex. PKC∈ depletion by siRNA decreased the TNFα- mediated recruitment of receptor interacting protein (RIP) and TNFR-associated factor-2 (TRAF2), which are both known to mediate NF-κB activation. In accordance with the co-immunoprecipitation results, siRNA-mediated PKC∈ depletion inhibits TNFR1, TRADD, TRAF2, IKK-β- mediated NF-κB reporter activity. Furthermore, effects of PKC∈ overexpression on NF-κB transcriptional activity correlated well with the increased mRNA levels of known NF-κB regulated genes involved in cell survival, inflammation, invasion and angiogenesis (Cox2, VEGF, MMP9, and IL8). Finally, we found that in preneoplastic lesions from transgenic mice overexpressing PKC∈ in the prostate there is enhanced NF-κB activation. In summary, our study established a molecular link between PKC∈ and NF-κB in prostate cancer and suggests a prominent role for this pathway in prostate cancer cell survival.

展开