Association of CPI-17 with protein kinase C and casein kinase I.

The protein kinase C-potentiated inhibitor protein of 17kDa, called CPI-17, specifically inhibits myosin light chain phosphatase (MLCP). Phosphorylation of Thr-38 in vivo highly potentiates the ability of CPI-17 to inhibit MLCP. Thr-38 has been shown to be phosphorylated in vitro by a number of protein kinases including protein kinase C (PKC), Rho-associated coiled-coil kinase (ROCK), and protein kinase N (PKN).

Centaurin-alpha(1) associates with and is phosphorylated by isoforms of protein kinase C.

Centaurin-alpha(1) is a member of the family of ADP-ribosylation factors (ARF) GTPase activating proteins (GAPs), although ARF GAP activity has not yet been demonstrated. The human homologue, centaurin-alpha(1) functionally complements the ARF GAP activity of Gcs1 in yeast. Although Gcs1 is involved in the formation of actin filaments in vivo, the function of centaurin remains elusive.

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.

Centaurin-alpha 1 associates in vitro and in vivo with nucleolin.

Centaurin-alpha(1) was originally described as a binding partner for phosphoinositides. In spite of the presence of a putative ADP-ribosylation factor (ARF) GTPase-activating protein (GAP) domain, no ARF-GAP activity has been attributed to centaurin-alpha(1) so far. Thus the function of this protein remains to be determined.

Identification of casein kinase Ialpha interacting protein partners.

Casein kinase Ialpha (CKIalpha) belongs to a family of serine/threonine protein kinases involved in membrane trafficking, RNA processing, mitotic spindle formation and cell cycle progression. In this report, we identified several CKIalpha interacting proteins including RCC1, high mobility group proteins 1 and 2 (HMG1, HMG2), Erf, centaurin-alpha1, synaptotagmin IX and CPI-17 that were isolated from brain as CKIalpha co-purifying proteins. Actin, importin-alpha(1), importin-beta, PP2Ac, centaurin-alpha1, and HMG1 were identified by affinity chromatography using a peptide column comprising residues 214-233 of CKIalpha.