RESUMO
BACKGROUND: Multidrug resistance (MDR) phenotype of malignant cells is the major problem in the chemotherapy of neoplasia. The treatment of leukemia with retinoids is aimed on the induction of leukemic cells differentiation. However the interconnections between retinoid regulated differentiation of leukemic cells and regulation of MDR remains unclear. METHODS: Four lines of cultured leukemic cells of diverse types of differentiation were infected with RARalpha gene and stable transfectants were isolated. We investigated the differentiation of these cells as well as the expression of RARalpha and MDR1 genes and P-glycoprotein (Pgp, MDR protein) functional activity in these cells. RESULTS: All RARalpha transfected sublines demonstrated the increase in the quantity of RARalpha mRNA. All these sublines became more differentiated. Intrinsic activity of MDR1 gene (but not Pgp functional activity) was increased in one of the transfectants. All-trans-retinoic acid (ATRA) induced Pgp activity in two of three infectants to a larger extent than in parental cells. CONCLUSION: The data show that RARalpha regulates MDR1/ Pgp activity in human leukemic cells, in the first place, Pgp activity induced by ATRA. These results show that RARalpha overexpression in leukemic cells could result in MDR.
