Fatty Acid Synthase (FAS), a major lipogenic enzyme, and Caveolin-1 (Cav-1), a membrane protein that transports cholesterol and regulates signal transduction, are both over-expressed in human and animal models of prostate cancer (PCa). Both proteins exert an oncogenic function in PCa cells. Now, for the first time, we have acquired preliminary results demonstrating that FAS and Cav-1 interact in PCa cells and that FAS, a cytosolic protein, can be induced to associate with cholesterol-rich, lipid raft membranes. Further data show that complex formation between the two proteins is impaired in a Cav-1 mutant deficient in palmitoylation. We also have evidence suggesting that Cav-1 palmitoylation may play a role in signal transduction and that EGFR activation of aggressive PCa cells results in rapid formation of membrane vesicles that contain lipid raft components as well as membrane Cav-1. Because Cav-1 is a circulating marker for aggressive PCa, these secreted vesicles may be linked to metastatic dissemination. Finally, we have acquired evidence indicating that Cav-1 and FAS inhabit similar subcellular locations in human tumors, allowing for cooperation between the two proteins in vivo. In the experiments outlined in this project, we will challenge the following overall hypothesis: Cav-1 and FAS collaborate to alter the lipid raft compartment, contributing to a membrane environment that is richer in cholesterol and saturated fatty acids. These changes in cell membranes may exert important functional consequences on tumor cell survival, growth and other malignant behaviors. Cav-1 and FAS colocalization might also be a useful prognostic indicator.
The specific aims of the study are:
Aim 1 : Determine whether Fatty Acid Synthase and Caveolin-1 collaborate to alter membrane composition and membrane dynamics in PCa cells. We will test the hypotheses that: (i) Activation of c-Src determines FAS localization at the membrane, and FAS and Cav-1 co-localize at the plasma membrane and/or at other cellular membranes, (ii) FAS and Cav-1 alter membrane composition and dynamics, (iii) FAS plays a role in protein palmitoylation.
Aim 2 : Determine the biological significance of Fatty Acid Synthase and Caveolin-1 colocalization at cell membranes in PCa. We will test the hypotheses that: (i) FAS localization at the membrane is oncogenic. (ii) FAS and Cav-1 co-localization stratifies human tumors with respect to biological behavior, (iii) FAS and Cav-1 collaborate to mediate the secretion of Cav-1-containing vesicles. We believe these experiments will provide new insights into the role of Cav-1 and FAS in PCa and will expand our understanding of the nature, the extent, and the biological significance of membrane lipid changes relevant to oncogenesis in PCa and possibly other malignancies.
