Ser/Thr phosphorylation of hematopoietic specific protein 1 (HS1): implication of protein kinase CK2.
Hematopoietic lineage cell-specific protein 1 (HS1), a tyrosine multiphosphorylated protein implicated in receptor-mediated apoptosis and proliferative responses, is shown here to become Ser/Thr phosphorylated upon incubation of platelets with radiolabeled inorganic phosphate. The in vivo Ser/Thr phosphorylation of HS1 is enhanced by okadaic acid and reduced by specific inhibitors of casein kinase (CK)2. In vitro, HS1 is an excellent substrate for either CK2 alpha subunit alone (Km = 47 nM) or CK2 holoenzyme, tested in the presence of polylysine (Km = 400 nM). Phosphorylation reaches a stoichiometry of about 2 mol phosphate per mol HS1 and occurs mainly at threonyl residue(s), mostly located in the N-terminal region, but also at seryl residue(s) residing in the central core of the molecule (208-402), as judged from experiments with deleted forms of HS1. Ser/Thr phosphorylation of HS1, either induced in vivo by okadaic acid or catalysed in vitro by CK2, potentiates subsequent phosphorylation at tyrosyl residues. These data indicate the possibility that regulation of HS1 may also be under the control of Ser/Thr phosphorylation, and suggest that in quiescent cells CK2 could play a role in inducing constitutive Tyr phosphorylation of HS1 in the absence of stimuli that activate the protein tyrosine kinase pathway.
Ruzzene
M
M
Dipartimento di Chimica Biologica and Centro per lo Studio delle Biomembrane del CNR and CRIBI, University of Padova, Italy.
Brunati
A M
AM
Sarno
S
S
Marin
O
O
Donella-Deana
A
A
Pinna
L A
LA
D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism*; D015153:Blotting, Western; D047390:Casein Kinase II; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D019319:Okadaic Acid / Q000494:pharmacology; D010710:Phosphates / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011107:Polylysine / Q000378:metabolism; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D001798:Blood Proteins; D004791:Enzyme Inhibitors; C061909:HCLS1 protein, human; D010710:Phosphates; D011994:Recombinant Proteins; D019319:Okadaic Acid; D011107:Polylysine; D013912:Threonine; D012694:Serine; D011505:Protein-Tyrosine Kinases; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases