Novel in vitro and in vivo phosphorylation sites on protein phosphatase 1 inhibitor CPI-17.
CPI-17 is a protein phosphatase 1 (PP1) inhibitor that has been shown to act on the myosin light chain phosphatase. CPI-17 is phosphorylated on Thr-38 in vivo, thus enhancing its ability to inhibit PP1. Thr-38 has been shown to be the target of several protein kinases in vitro. Originally, the expression of CPI-17 was proposed to be smooth muscle specific. However, it has recently been found in platelets and we show in this report that it is endogenously phosphorylated in brain on Ser-128 in a domain unique to CPI-17. Ser-128 is within a consensus phosphorylation site for protein kinase A (PKA) and calcium calmodulin kinase II. However, these two kinases do not phosphorylate Ser-128 in vitro but phosphorylate Ser-130 and Thr-38, respectively. The kinase responsible for Ser-128 phosphorylation remains to be identified. CPI-17 has strong sequence similarity with PHI-1 (which is also a phosphatase inhibitor) and LimK-2 kinase. The novel in vivo and in vitro phosphorylation sites (serines 128 and 130) are in a region/domain unique to CPI-17, suggesting a specific interaction domain that is regulated by phosphorylation.
Dubois
Thierry
T
Division of Biomedical and Clinical Laboratory Sciences, University of Edinburgh, UK.
Howell
Steven
S
Zemlickova
Eva
E
Learmonth
Michele
M
Cronshaw
Andy
A
Aitken
Alastair
A
D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism
D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; C107507:PPP1R14A protein, human; D010750:Phosphoproteins; D013912:Threonine; D012694:Serine; D017868:Cyclic AMP-Dependent Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1