ABSTRACT Obesity is linked with greater risk of high-grade prostate cancer (PC), recurrence after therapy, metastases, and PC death. We exploited the link between obesity and aggressive prostate to identify actionable targets. To this end, we performed a shRNA genomic screen in obese mice targeting the entire kinome. Our screen identified Right Open Reading Frame Kinase 2 (RIOK2), as a promising PC target in obese mice and suggests that ribosomal biogenesis plays a role in PC. Our subsequent studies have identified non-ribosomal RIOK2 functions that link Neuropeptide Y (NPY), a neurotransmitter involved in feeding behavior and obesity, with PC cell biology. We found RIOK2 regulates Neuropeptide Y2 Receptor (NYP2R), one of five known mammalian neuropeptide Y receptors designated Y1 through Y5, which bind to NPY. Mechanistically, RIOK2 binds the NPY2R promoter and depletion of RIOK2 significantly reduces NPY2R expression. We found knockdown of NPY2R in PC cells, inhibits proliferation and reduces tumorigenic properties of PC cells in vitro. NPY, the NPY2R ligand, is chiefly produced in hypothalmic neurons, yet the male genital track also expresses NPY secreted from innervation, including in prostate and periprostatic adipocytes. NPY, is further upregulated in PC (~50 fold). In fact, NPY is a reported PC biomarker. Yet, it is unclear if this neurotransmitter plays a biological role in PC development or progression. Adding to the uncertainty, the full length 36 amino acid NPY1–36 is readily cleaved to NPY3–36, making it a selective NPY2R agonist by a dipeptidyl peptidase IV (DPP4), a membrane protease is also highly expressed in PC. Thus, NPY3-36 likely accounts for a large portion of NPY peptides in PC, which may elicit distinct signaling events compared to full length NPY1-36 primarily via NPY2R. However, prostate serum antigen aka kallikerin 3, a prostate serum biomarker is also a peptidase that may act on NPY. Our overarching hypothesis is that NPY is readily cleaved by prostatic peptidases and NPY peptide fragments play a role in PC. Mechanistically, we hypothesize that NPY is cleaved by prostatic DPP4 and/or PSA, and prostatic NPY cleavage peptides have differential downstream signaling cascades and phenotypic effects compared to full length NPY. To test this hypothesis we will (Aim 1) identify and characterize prostatic NPY cleaved peptides and (Aim 2) test if NPY levels alter PC development in vivo and in ex vivo human PCs.

PROJECT NARRATIVE Neuropeptide Y is a prostate cancer biomarker, yet its role or that of its cleaved forms in prostate tumorigenesis is unclear. Herein, we aim to define and characterize Neuropeptide Y prostatic peptide fragments in vitro and human ex vivo prostate cancer specimens. We will determine if prostate cancer associated peptidases, Dipeptidyl peptidase IV and/or prostate serum antigen (aka kallikrein related peptidase 3) cleave NPY. Lastly, we will test if modulating Neuropeptide Y levels in mice alters prostate cancer growth.