Analyzing the interactome of human CK2 beta in prostate carcinoma cells reveals HSP70-1 and Rho guanin nucleotide exchange factor 12 as novel interaction partners

CK2 beta is the non-catalytic modulating part of the S/T-protein kinase CK2. However, the overall function of CK2 beta is poorly understood. Here, we report on the identification of 38 new interaction partners of the human CK2 beta from lysates of DU145 prostate cancer cells using photo-crosslinking and mass spectrometry, whereby HSP70-1 was identified with high abundance. The K-D value of its interaction with CK2 beta was determined as 0.57 mu M by microscale thermophoresis, this being the first time, to our knowledge, that a K-D value of CK2 beta with another protein than CK2 alpha or CK2 alpha ' was quantified. Phosphorylation studies excluded HSP70-1 as a substrate or activity modulator of CK2, suggesting a CK2 activity independent interaction of HSP70-1 with CK2 beta. Co-immunoprecipitation experiments in three different cancer cell lines confirmed the interaction of HSP70-1 with CK2 beta in vivo. A second identified CK2 beta interaction partner was Rho guanin nucleotide exchange factor 12, indicating an involvement of CK2 beta in the Rho-GTPase signal pathway, described here for the first time to our knowledge. This points to a role of CK2 beta in the interaction network affecting the organization of the cytoskeleton.