Adiponectin receptor 1 interacts with both subunits of protein kinase CK2

Adiponectin is an adipose tissue-derived hormone that is involved in the inhibition of metabolic syndrome, protection of hypertension, and suppression of atherosclerosis. Since these effects are not understood in detail, adiponectin signaling has to be clarified for therapeutic applications. Adiponectin activities are mediated by its two receptors adiponectin receptor 1 and adiponectin receptor 2, which consist of seven transmembrane helices. Previous studies revealed the beta subunit of protein kinase CK2 as an interaction partner of the adiponectin receptor 1 N-terminus using a yeast-two-hybrid screen, co-immunoprecipitation, ELISA experiments, and co-localization studies. Inhibition of CK2 activity by 2-dimethylamino-4,5,6,7-tetrabromo-1H-benz-imidazole led to a decrease of ACC phosphorylation and indicates an important role of CK2 in adiponectin signaling. CK2 is characterized as a heterotetramer that consists of two regulatory beta and two catalytic alpha subunits, but a holoenzyme-independent role for both subunits is described as well. Therefore, we analyzed the role of the catalytic subunit in this interaction by co-immunoprecipitation and bimolecular fluorescence complementation studies and found CK2 alpha as an interaction partner of the receptor. Treatment with full-length adiponectin resulted in no dissociation of the catalytic alpha subunit. Consequently, our data suggest an interaction of the adiponectin receptor 1 with the tetrameric complex and identified protein kinase CK2 as a key player in adiponectin signaling.