Autocatalytic tyrosine-phosphorylation of protein kinase CK2 alpha and alpha' subunits: implication of Tyr182.

CK2 is a pleiotropic and constitutively active serine/threonine protein kinase composed of two catalytic (alpha and/or alpha') and two regulatory beta-subunits, whose mechanism of modulation is still obscure. Here we show that CK2 alpha/alpha' subunits undergo intermolecular (trans) tyrosine-autophosphorylation, which is dependent on intrinsic catalytic activity and is suppressed by the individual mutation of Tyr182, a crucial residue of the activation loop, to phenylalanine. At variance with serine-autophosphorylation, tyrosine-autophosphorylation of CK2alpha is reversed by ADP and GDP and is counteracted by the beta-subunit and by a peptide reproducing the activation loop of CK2alpha/alpha' (amino acids 175-201). These results disclose new perspectives about the mode of regulation of CK2 catalytic subunits.