Valproic Acid as a Histone Deacetylase Inhibitor Induces ABCB1 Overexpression and De Novo ABCB5 Expression in HeLa Cells.

Histone deacetylase inhibitors (HDACis) induce the expression of multidrug resistance (MDR) pumps and can even display the MDR phenotype in cell lines. This is the first report to include the profiles of ATP-binding cassette (ABC) transporters in intrinsically expressed HeLa cells as well as those acquired due to a 5 mM valproic acid (VPA) treatment. Expression of ABC transporters related to the MDR phenotype was analyzed by RT-PCR in untreated HeLa cells and HeLa cells treated with 5 mM VPA. The ABCB5 protein was identified in HeLa cells by immunocytochemistry. HeLa cell treatment with 5 mM VPA increased ABCB1 expression and triggered the de novo expression of ABCB5 in mRNA and protein. Despite the expression of ABCB5 and the overexpression of ABCB1, VPA reduced the growth rate by 20%, delayed doubling time by 25%, and decreased the number of living cells per well to 50% after 72 h. Pretreatment with VPA for 24 h followed by cotreatment with doxorubicin (DOX) sensitized HeLa cells to DOX. However, for the de novo expression of ABCB5, HeLa cells did not acquire the MDR phenotype from the 5 mM VPA treatment. The ABCB5 isoform induced by VPA treatment probably lacks MDR activity.