OVEREXPRESSION OF A 40-KDA PROTEIN IN HUMAN MULTIDRUG-RESISTANT CELLS

The use of anticancer drugs in the chemotherapeutic treatment of cance r patients frequently results in the emergence of drug resistant tumor s. Selection of tumor cell lines in vitro has led to the identificatio n of several proteins that mediate drug resistance to anticancer drugs , In this study, an immune-dot blot method was used to isolate a monoc lonal antibody (IPM96) which recognized a 40 kDa protein (or P-40) co- expressed with P-glycoprotein and MRP in several multidrug resistant c ell lines (MCF-7/Adr, SKOV/VLB1.0, H69/Adr, and HL60/AR), Furthermore, P-40 levels dropped significantly in one revertant cell line (H69/PR) derived fi om H69/AR cells, Interestingly, the expression of P-40 was also higher in two tumor cell. lines (SKTax6a and A2780(CP)) that wer e selected with paclitaxel or cisplatin but do not express P-gp or MRP . Immuno-fluorescence staining of cells with IPM96 showed both membran e and cytoplasmic staining. These results were confirmed by Western bl ot analysis of different subcellular fractions from MCF-7/Adr cells. T he membrane bound P-40 was resistant to extraction with high salt, che lating agents, and denaturing agents, but was solubilized with 10 mM C HAPS. Taken together, the overexpression of P-40 in multidrug resistan t cells has not been previously determined and therefore could be impo rtant in the expression of the drugresistance phenotype. (C) 1997 Acad emic Press.