Protein kinase CK2α is a target for the Abl and Bcr–Abl tyrosine kinases

Abstract

Protein kinase CK2 is a ubiquitous serine-threonine kinase in which a catalytic α subunit often associates with a β subunit. CK2α is required for cell survival in yeast and has been proposed to be involved in cell growth control; however, its regulation in cells remains unclear. Here we present evidence that CK2α may be an associated substrate for the normal and oncogenic forms of the Abl tyrosine kinase. By probing CK2α with anti-phosphotyrosine antibodies, we found that CK2α can be phosphorylated on tyrosine in quiescent cells. In vitro phosphorylation of CK2α-containing immunoprecipitates showed that CK2α is substrate of an associated tyrosine kinase activity. Immunoprecipitation experiments revealed that CK2α is associated with normal c-Abl in mouse NIH3T3 fibroblasts and with the Bcr–Abl fusion protein in K562 human myeloid leukemia cells. Coexpression of Bcr–Abl and CK2α in NIH3T3 cells also leads to the formation of a Bcr–Abl/CK2α complex and to the inhibition of CK2α activity. Bcr–Abl-induced inhibition of CK2α could be reverted by incubating CK2α with a tyrosine phosphatase. These observations clearly support the idea that a signal transduction pathway contributes to CK2 regulation and point to CK2α as a possible mediator of Bcr-Abl effects.