Identification of casein kinase Iα 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 CKIa interacting proteins including RCC1, high mobility group proteins 1 and 2 (HMG1, HMG2), Erf, centaurin-alpha(1), synaptotagmin IX and CPI-17 that were isolated from brain as CKIalpha co-purifying proteins. Actin, importin-alpha(1), importin-beta, PP2Ac, centaurin-alpha(1), and HMGI were identified by affinity chromatography using a peptide column comprising residues 214-233 of CKIalpha We have previously shown that centaurin-alpha(1) represents a CKIalpha partner both in Vitro and in vivo. The nuclear protein regulator of chromosome condensation 1 (RCC1) is a guanosine nucleotide exchange factor for Ran which is involved in nuclear transport and mitotic spindle formation. Here we show that CKIalpha and RCC1 interact in brain and in cultured cells. However, the interaction does not involve residues 217-233 of CKIalpha which are proposed from X-ray structures to represent an anchoring site for CKI partners. Formation of the RCC1/CKIalpha complex is consistent with the association of the kinase with mitotic spindles. In conclusion, we have identified a number of novel CKIalpha protein partners and their relations to CKI are discussed. (C) 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.