Regulation of casein kinase-2 (CK2) activity by inositol phosphates.
Casein kinase 2 (CK2) was one of the first protein kinases to be discovered and has been suggested to be responsible for as much as one-fifth of the eukaryotic phosphoproteome. Despite being responsible for the phosphorylation of a vast array of proteins central to numerous dynamic cellular processes, the activity of CK2 appears to be unregulated. In the current study, we identified a protein kinase activity in rat liver supernatant that is up-regulated by inositol 1,3,4,5-tetrakisphosphate (IP4) and inositol hexakisphosphate (IP6). The substrate for the inositol phosphate-regulated protein kinase was identified as a phosphatidylcholine transfer protein-like protein. Using the phosphorylation of this substrate in an assay, we purified the inositol phosphate-regulated protein kinase and determined it to be CK2. Bacterially expressed recombinant CK2, however, showed very high basal activity and was only modestly activated by IP6 and not regulated by IP. We found that an endogenous component present in rat liver supernatant was able to inhibit both recombinant and liver-purified CK2 basal activity. Under these conditions, recombinant CK2 catalytic activity could be increased substantially by IP4, inositol 1,3,4,5,6-pentakisphosphate (IP5), and IP6. We concluded that, contrary to the previously held view, CK2 can exist in a state of low constitutive activity allowing for its regulation by inositol phosphates. The ability of the higher inositol phosphates to directly stimulate CK2 catalytic activity provides the first evidence that these signaling molecules can operate via a direct control of protein phosphorylation.
Department of Cell Physiology and Pharmacology, Hodgkin Building, Lancaster Road, University of Leicester, LE1 9HN, UK.
Lev
L
Solyakov
Kelvin
K
Cain
Beryl M
BM
Tracey
Rebekah
R
Jukes
Andrew M
AM
Riley
Barry V L
BV
Potter
Andrew B
AB
Tobin
D000595:Amino Acid Sequence; D000818:Animals; D047390:Casein Kinase II / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism; D007295:Inositol Phosphates / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010833:Phytic Acid / Q000494:pharmacology; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism
D004268:DNA-Binding Proteins; D007295:Inositol Phosphates; D021122:Protein Subunits; D011994:Recombinant Proteins; D010833:Phytic Acid; D047390:Casein Kinase II