Regulation of the physiological consequences of neuroendocrine differentiation in prostate cancer by kinase and phosphatase cross talk

Prostate cancer is a leading health concern among Canadian males, with one in seven Canadian men developing the disease in their lifetime and one in 27 dying from it. Localized prostatic disease can be treated with surgery, but once metastasis occurs, clinicians rely on the hormone dependent nature of the tumor for treatment. Androgen withdrawal therapy is very effective at limiting tumor growth; however, progression of the tumor to an androgen independent state is inevitable, and at the present time there is no effective therapy for this form of the disease. Neuroendocrine (NE) cells are post-mitotic, secretory cells found distributed throughout both normal and malignant prostate tissue. Increased NE cell content is associated with hormone refractory disease, and it is suspected that these NE cells play a role in the adaptation of surrounding cells to androgen withdrawal conditions through the secretion of paracrine factors. The research in this thesis was aimed towards understanding the biochemical mechanisms by which trans-differentiation of an adenocarcinoma cell to a NE cell occurs. By understanding the nature of this process, rationally designed therapeutic reagents can be developed that either block transdifferentiation of adenocarcinoma cells and inhibit the increase in NE cell content following androgen withdrawal or block the actions of NE cells that promote tumor progression. I used the Kinetworks™ Phospho-Site Screen KPSS 1.1 as well as the Human Operon Version 3.0 microarray to broadly profile changes in protein kinase regulation and mRNA expression levels occurring during NE differentiation of the human prostate cancer cell line model, LNCaP. I found that agents that induce NE differentiation in LNCaP cells cause a perturbation in the phospho-state of two downstream targets of the mammalian target of rapamycin (mTORC1), the ribosomal S6 kinase S6K1 and Rb, as well as increasing vascular endothelial growth factor (VEGF) mRNA expression. Both of these phenomena appear to involve the cAMP-dependent protein kinase PKA and a protein phosphatase PP2A family member. Since mTORC1 is considered to be a critical component in the control of tumourigenicity, and since increased VEGF is associated with advanced tumor progression, these findings appear to address some of the processes by which transdifferentiation of adenocarcinoma cells to NE cells may regulate prostate cancer progression.Medicine, Faculty ofMedicine, Department ofExperimental Medicine, Division ofGraduat