Exploring Possible Roles Of Organic Anion-Transporting Polypeptides In Invadopodia Function

Drug resistant, invasive tumors are among the most devastating cancers. It is the goal of this project to explore the potential relationships between these two phenotypes in a variety of tissue culture model systems. Invadopodia are actin-rich protrusions of the cellular membrane involved in extracellular matrix remodeling that allow cancer cells to invade other tissues during metastasis. Organic anion transporting-polypeptides (OATPs) mediate xenobiotic exchange across the cellular membrane and are believed to colocalize with lipid raft domains (LRDs) and caveolin-1 in humans, two factors that are also required for invadopodia function in breast cancer and melanoma cells. These transporters are thought to contribute to the multi-drug resistance phenotype of stubborn tumors and are upregulated in multiple cancer cell lines. To determine if functional OATPs are present in invadopodia-competent cells, fluorescence transport assays were performed on human prostate (PC3, LNCaP) and breast (MDA-MB-231) cancer cells as well as a murine fibroblast (NIH-3T3) cell line overexpressing constitutively active Src (Src-3T3). All cell lines exhibited robust uptake of rhodamine-123 (Rh-123), a fluorescent substrate of OATP1A2. Furthermore, the uptake of Rh-123 by MDA-MB-231 and PC3 cells was likely protein-mediated as the fluorescence signals were reduced by 67% and 68% respectively when the transport assays were performed on ice. In addition, an inhibition assay indicated that OATP1A2 might be responsible for the observed uptake of Rh-123 by LNCaP cells grown in androgen-depleted conditions. These inhibition studies are ongoing, and future experiments will explore the ultimate downstream effects of OATP substrates on invadopodia morphology and function. If OATPs play a role in invadopodia activity, they may contribute to the enhanced invasive phenotype of certain cancers and therefore serve as viable therapeutic targets.