Role of CK2 in the regulation of ABCC1

Increased expression of the ABC transporter, Multidrug Resistance‐associated Protein ABCC1 (MRP1), is associated with multidrug resistance (MDR) in a wide range of cancers. Our lab has recently shown that yeast homolog of ABCC1, Ycf1p, is regulated by the yeast CK2α homologue, Cka1p, via phosphorylation of S251 within the NTE of Ycf1p. By analogy, we hypothesize that human ABCC1 is regulated by CK2α phosphorylation at the homologous site, T249. In the studies presented here, we show that a synthetic peptide corresponding to the T249 containing CK2 consensus site is phosphorylated by recombinant CK2α. Mutation of the putative CK2 phosphorylation site (T249A) resulted in decreased transporter function in vitro inside‐out vesicle transport assays and in cell survival assays carried out in tissue culture. We generated CK2α knockdowns in both WT and ABCC1 overexpressing cells. Knockdown of CK2α in our ABCC1 overexpressing cells resulted in a dramatic increase in intracellular doxorubicin, indicative of decrease in MRP1‐dependent efflux. Direct interaction of ABCC1 protein and the CK2α kinase was assessed by coimmunoprecipitation. In conclusion, the data presented here strongly suggests that CK2 regulates ABCC1 by phosphorylation at T249. These findings open exciting possibility that MDR patients would greatly benefit from addition of CK2 inhibitors to their treatments. This work was funded by NIH P20RR020171.