Overexpression of caveolin‐1 induces alteration of multidrug resistance in Hs578T breast adenocarcinoma cells

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Abstract
Caveolin-1 is a major caveolae-coat protein involved in a variety of cell signaling processes. Some studies have suggested that the level of caveolin-1 expression positively correlates with multi-drug resistance in cancer cells. We demonstrated for the first time that Hs578T doxorubicin resistant cells (Hs578T/Doxo), which contain low levels of endogenous caveolin-1 and high levels of P-glycoprotein, are rendered drug-sensitive by overexpression of exogenous caveolin-1. MTT assays showed that after overexpressing caveolin-1, the drug resistance of Hs578T/Doxo cells to doxorubicin and cisplatin was reduced from 25.4 ± 1.5 and 65.3 ± 2.5 μg/ml to 0.8 ± 0.15 and 23.2 ± 2.1 μg/ml, respectively (i.e. reduced by 97% and 64%, respectively). Furthermore, using rhodamine-123 efflux assays, we observed a significant decrease in P-glycoprotein activity in caveolin-1 overexpressing cells, similar to that observed with 5 μM cyclosporine A or 10 μM verapamil, 2 inhibitors of P-glycoprotein activity. Using confocal microscopy, subcellular fractionation and co-immunoprecipitation assays, a possible physical interaction between caveolin-1 and P-glycoprotein in the caveolae membrane was observed in Hs578T/Doxo cells overexpressing caveolin-1. These results suggest that overexpression of caveolin-1 changes the state of the cells from drug-resistant to drug-sensitive by inhibiting P-glycoprotein transport activity.