gms | German Medical Science

The serine/threonine-specific kinase CK1 delta a member of the CK1 (casein kinase 1) gene family is ubiquitously expressed, is p53 dependently induced in stress situations and plays an important role in various cellular processes, including cell cycle progression, cell proliferation, apoptosis, chromosome segregation, and DNA repair and recombination processes. Alterations in the CK1 delta expression and/or activity level have been shown to contribute to the development and resistance of tumors. The activity of CK1 delta is modulated by several mechanisms, among them subcellular compartimentation, autophosphorylation, dephosphorylation and site-specific cleavage by proteases. In the present study, we identified protein kinase A (PKA) as a major cellular activity that phosphorylates CK1 delta in vitro and vivo. The use of different CK1 delta fragments baring specific amino acid substitutions as substrates coupled with two dimensional phosphopeptide and phosphoamino acid analyses, indicates that PKA phosphorylates predominantly serine residues within the C-terminal regulatory domain. CK1 delta mutants with alanine substitutions at serine residues targeted by PKA exhibited a reduced kinase activity. Furthermore, inhibition or activation of PKA through H89 or forskolin in cell cultures, resulted in changes of the phosphorylation status of CK1 deltaand of its ability to phosphorylate p53 in vitro. These data suggest that PKA plays an important role as a physiological regulator of CK1 delta.