Identification of cytoskeletal [14C]carboplatin-binding proteins reveals reduced expression and disorganization of actin and filamin in cisplatin-resistant cell lines

Cisplatin resistant (CP-r) cells often show decreased uptake of cisplatin in association with reduced cell surface proteins and decreased endocytosis. In this report, two major [C-14] carboplatin-binding proteins were identified as filamin and actin by photoaffinity labeling and mass spectrometry. Decreased expression of these two proteins was found in two different human CP-r cell lines (KB-CP20 and 7404-CP20), in comparison with their parental cell lines (KB-3-1 and BEL-7404), respectively. Disorganization of beta-actin and filamin 250 and 90 was also detected in these CP-r cells by confocal microscopy. Transfection of a wild-type actin-enhanced green fluorescent protein (EGFP) expression vector into 7404-CP20 cells resulted in a nonfilamentous actin-EGFP distribution compared with a normal distribution in the cisplatin-sensitive BEL-7404 cells, suggesting that cytoskeletal organization is disturbed in the CP-r cells. The identification of actin and filamin as [C-14] carboplatin-binding proteins and decreased expression and disorganization of several cytoskeletal proteins in CP-r cells provide a molecular and cellular basis for the known defect in endocytosis in these cells.