Regulation of protein phosphatase-1I by C-TAK1/Cdc25C associated kinase 1 and PFTAIRE protein kinase [Enzymology]

July 15th, 2014 by Platholi, J., Federman, A., Detert, J., Heerdt, P. M., Hemmings, H. C.

Protein phosphatase-1I (PP-1I) is a major endogenous form of protein phosphatase-1(PP-1) that consists of the core catalytic subunit PP-1c and the regulatory subunit inhibitor-2 (I-2). Phosphorylation of the T72 residue of I-2 is required for activation of PP-1I. We studied the effects of two protein kinases previously identified in purified brain PP-1I by mass spectrometry, Cdc25C associated kinase 1 (C-TAK1) and PFTAIRE (PFTK1) kinase, for their ability to regulate PP-1I. Purified C-TAK1 phosphorylated I-2 in reconstituted PP-1I (PP-1c:I-2) on S71,which resulted in partial inhibition of its ATP-dependent phosphatase activity and inhibited subsequent phosphorylation of T72 by the exogenous activating kinase GSK-3. In contrast, purified PFTK1 phosphorylated I-2 at S86, a site known to potentiate T72 phosphorylation and activation of PP-1I phosphatase activity by GSK-3. These findings indicate that brain PP-1I associates with and is regulated by the associated protein kinases C-TAK1 and PFTK1. Multisite phosphorylation of the I-2 regulatory subunit of PP-1I leads to activation or inactivation of PP-1I through bidirectional modulation of T72 phosphorylation, the critical activating residue of I-2.