Purpose: PEDF (pigment epithelium-derived factor) promotes the differentiation and survival of neuronal cells, and expands the adult neuronal stem cell niche. In the prostate PEDF is suppressed by androgen with unclear physiological consequences. We report that PEDF induced the neuroendocrine differentiation of prostate cancer cells, which was accompanied by neurite outgrowth and chromogranin A expression.
Materials and methods: We performed neuroendocrine differentiation assay, Western blot analysis, immunostaining and reverse transcriptase-polymerase chain reaction in the human prostate cancer cell lines LNCaP, PC-3 and DU145, and the prostate epithelial strain RWPE-1 (ATCC).
Results: Ectopic and endogenous PEDF caused neuroendocrine differentiation of prostate cancer cells, as manifested by neurite-like outgrowths and chromogranin A expression. The transdifferentiated cells expressed axonal and dendritic markers, as ascertained by immunoblotting for specific markers. Neuroendocrine cells formed multiple synaptophysin positive protrusions resembling dendritic spines and vesicles containing serotonin, pointing to possible synapse formation. The known transdifferentiating agent interleukin-6 induced PEDF secretion. Moreover, PEDF neutralizing antibodies abolished the transdifferentiation of interleukin-6 treated cells, suggesting an autocrine loop. Neurogenic events were independent of cyclic adenosine monophosphate. Instead, PEDF activated in this order RhoA, nuclear factor kappaB and Stat3. Inhibitors of the Rho, nuclear factor kappaB and STAT pathways abolished differentiation and synapse formation. Additionally, nuclear factor kappaB activation caused interleukin-6 expression.
Conclusions: We discovered that nuclear factor kappaB controls the formation of neuronal communications in the prostate due to PEDF. We defined a feed-forward loop, in which nuclear factor kappaB induction elicits Stat3 activation and pro-differentiating interleukin-6 expression causes the further expansion of neuroendocrine communications. Our findings point to the role of nuclear factor kappaB and PEDF in coordinated prostate development.