Access Type

Open Access Dissertation

Date of Award

January 2022

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Pathology

First Advisor

Sreenivasa Chinni

Abstract

The CXCR4-CXCL12 chemokine signaling axis plays a key role in migration and bone metastasis in prostate cancer (PC). Androgens regulate CXCR4 expression and its receptor activation in lipid-raft micro domains of PC cells, resulting in higher protease expression and invasion. In order to identify some novel CXCR4 co-regulators associated within the lipid-raft, a SILAC (Stable isotope labeling using amino acid in cell culture)-based proteomic analysis was performed with PC3 stable cell-lines over-expressing or knocking-down CXCR4. Phosphatidylinositol 4-kinase III alpha (PI4KIIIα or PI4KA) and SAC1 lipid phosphatase were identified as candidate proteins enriched in CXCR4 expressing cells. PI4KA is an evolutionarily conserved mammalian kinase that converts PI to PI4P; and SAC1 dephosphorylates PI4P to PI. PI4K is required for the maintenance and functioning of the plasma-membrane and vesicular trafficking in the Golgi apparatus. PI4KA is also needed to maintain a steady pool of PI(4,5)P2 in the plasma-membrane, to be utilized in various signaling pathways. We show that CXCR4 interacts with PI4KA through its adaptor proteins EFR3B and TTC7B, recruiting it to the plasma-membrane for PI4P generation. Similarly, PI4KA was closely linked to CXCR4 induced PC cell invasion, and knockdown of PI4KA in CXCR4 over-expressing PC3 cell lines reduced cell invasion. Also, localized productions of PI4P was evident in invasive projections of CXCR4 over-expressing cell lines through immunofluorescence microscopy. PC tumor microarray data show increased PI4K expression in metastatic PC tissue vs localized or normal adjacent tissue. These data suggest a novel interaction between PI4KA and CXCR4, promoting tumor cell invasion and metastasis. Pharmacological targeting of PI4KA, its adaptor proteins or its signaling-related proteins might prove therapeutically beneficial and enhance survival in PC patients.

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