Proteins that interact with 14-3-3 isoforms are involved in regulation of the cell cycle, intracellular trafficking/targeting, signal transduction, cytoskeletal structure and transcription. Recent novel roles for 14-3-3 isoforms include nuclear trafficking the direct interaction with cruciform DNA and with a number of receptors, small G-proteins and their regulators. Recent findings also show that the mechanism of interaction is also more complex than the initial finding of the novel phosphoserine/threonine motif. Non-phosphorylated binding motifs that can also be of high affinity may show a more isoform-dependent interaction and binding of a protein through two distinct binding motifs to a dimeric 14-3-3 may also be essential for full interaction. Phosphorylation of specific 14-3-3 isoforms can also regulate interactions. In many cases, they show a distinct preference for a particular isoform(s) of 14-3-3. A specific repertoire of dimer formation may influence which of the 14-3-3-interacting proteins could be brought together. Mammalian and yeast 14-3-3 isoforms show a preference for dimerization with specific partners in vivo.

Mammalian casein kinases I (CKI) belong to a family of serine/threonine protein kinases involved in diverse cellular processes including cell cycle progression, membrane trafficking, circadian rhythms, and Wnt signaling. Here we show that CKI␣ co-purifies with centaurin-␣ 1 in brain and that they interact in vitro and form a complex in cells. In addition, we show that the association is direct and occurs through the kinase domain of CKI within a loop comprising residues 217-233. These residues are well conserved in all members of the CKI family, and we show that centaurin-␣ 1 associates in vitro with all mammalian CKI isoforms. To date, CKI␣ represents the first protein partner identified for centaurin-␣ 1 . However, our data suggest that centaurin-␣ 1 is not a substrate for CKI␣ and has no effect on CKI␣ activity. Centaurin-␣ 1 has been identified as a phosphatidylinositol 3,4,5-trisphosphate-binding protein. Centaurin-␣ 1 contains a cysteine-rich domain that is shared by members of a newly identified family of ADPribosylation factor guanosine trisphosphatase-activating proteins. These proteins are involved in membrane trafficking and actin cytoskeleton rearrangement, thus supporting a role for CKI␣ in these biological events.

No abstract

Casein kinase IK K (CKIK K) 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 CKIK K interacting proteins including RCC1, high mobility group proteins 1 and 2 (HMG1, HMG2), Erf, centaurin-K K 1 , synaptotagmin IX and CPI-17 that were isolated from brain as CKIK K co-purifying proteins. Actin, importin-K K 1 , importin-L L, PP2Ac, centaurin-K K 1 , and HMG1 were identified by affinity chromatography using a peptide column comprising residues 214^233 of CKIK K. We have previously shown that centaurin-K K 1 represents a CKIK K 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 CKIK K and RCC1 interact in brain and in cultured cells. However, the interaction does not involve residues 217^233 of CKIK K which are proposed from X-ray structures to represent an anchoring site for CKI partners. Formation of the RCC1/CKIK K complex is consistent with the association of the kinase with mitotic spindles. In conclusion, we have identified a number of novel CKIK K protein partners and their relations to CKI are discussed. ß

No abstract