Abstract 5162: Phosphatidylinositol 4-Kinase type IIIa (PI4KA) expression in prostate cancer
Authors: Sbrissa Diego , Semaan Louie , Yanfeng Li , Shisheva Assia , Chinni Sreenivasa R. 
Published: August 2015

Advanced prostatic carcinoma (PC) is a progressive disease characterized by a high rate of recurrence and death even after traditional pharmacological androgen deprivation therapy. Phosphatidylinositol 4-kinases (PI4K’s) and the counteracting Sac1 phosphatase, which generates and turns over phosphoinositide phosphatidylinositol 4-phosphate [PtdIns4P], respectively, are required for maintenance and functioning of the Golgi apparatus. Intriguingly, both enzymes have been recently identified as cellular factors associated with prostate cancer. These findings support the hypothesis that modulation in PtdIns4P levels and ER-Golgi and Golgi-PM trafficking activities regulated by PI4K's and the Sac1 phosphatase, can alter the membrane trafficking flux to meet the proliferative demands of cancer-cell growth. Targeting these enzymes with drugs could potentially reduce the proliferation/invasion phenotype and prolong patient survival. The goal of our study was to demonstrate the expression of PI4KA and Sac1 in prostate cancer cells and correlate their expression with CXCR4 status.

CXCR4 overexpression and knockdown were performed with PC-3 cells using lentiviral infections. Stable isotope labeling by amino acids in cell culture (SILAC) proteomics analysis was performed on lipid raft membrane micro-domains isolated from PC-3 CXCR4 knockdown and overexpressing cells. Reverse transcription, quantitative real-time PCR (RT-qPCR) was used to quantitate PI4KA mRNA; Western blotting (WB), for PI4KA and Sac1 protein expression levels and immunoprecipitation followed by lipid kinase activity assays were used to determine the PI4KA activity.

SILAC analysis of lipid raft membrane microdomains in CXCR4 knockdown and overexpressing cells reveal alterations in G-protein coupled receptor signaling and endocytic vesicular traffic pathways. PI4KA is one of the proteins highly associated with CXCR4 overexpressing cells. PI4KA protein expression was 2.4 to 3.5-fold more abundant in CXCR4-overexpressing vs. control PC3 cell line. A similar finding was made for the C2-4B compared to its progenitor line LnCap, ranging from 1.2 to 2.7-fold higher. PI4KA activity measured by lipid kinase assay in CXCR4-overexpressing cells reflected these enhanced expression levels, showing increases by ∼2 fold. This upregulation may correlate with both PC cell-migration/invasion. This correlation confirmed initial proteomics analysis of CXCR4 association with PI4KA and Sac1 in lipid raft membrane microdomains.

Our findings suggest that PI4KA mRNA could be used as a new molecular marker to improve established prognostic models for PC. These findings also indicate possible new lines of research for the development of innovative therapeutic approaches targeting PI4KA in PC, whereby reductions in PI4KA levels would be expected to reduce its severity/recurrence and improve patient survival.

Citation Format: Diego Sbrissa, Louie Semaan, Li Yanfeng, Assia Shisheva, Sreenivasa R. Chinni. Phosphatidylinositol 4-Kinase type IIIa (PI4KA) expression in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5162. doi:10.1158/1538-7445.AM2015-5162