Isoform-specific Activation and Structural Diversity of Calmodulin Kinase I

Abstract

We earlier confirmed that there are isoforms of Ca2+/calmodulin (CaM)-dependent protein kinase I (CaM kinase I) (CaM kinase Ibeta1 and Igamma) beside CaM kinase Ialpha by cDNA cloning (Yokokura, H., Terada, O., Naito, Y., and Hidaka, H. (1997) Biochim. Biophys. Acta 1338, 8-12). Here, we demonstrate the existence of an isoform-specific activation mechanism of CaM kinase I and alternative splicing specifically regulating CaM kinase I (CaM kinase Ibeta2) in the central nervous system. To cast light on isoform structure-enzyme activity relationships, CaM kinase Ibeta1, Ibeta2, and Ialpha were expressed separately using a baculovirus/Sf9 cell expression system. The novel CaM kinase Ibeta2 isoform demonstrated similar catalytic activity to those of CaM kinase Ibeta1 and Ialpha. Interestingly, CaM kinase Ibeta1 and Ibeta2 both can activate CaM kinase Ialpha activity via phosphorylation at Thr177. Reverse transcribed-polymerase chain reaction analysis showed that CaM kinase Ibeta2 is dominant in the cerebrum and cerebellum, whereas CaM kinase Ibeta1 is present in peripheral tissues such as liver, heart, lung, kidney, spleen, and testis. CaM kinase Ibeta2 was also detected with an anti-CaM kinase Ibeta2 antibody in PC12 cells. The results indicate that alternative splicing is a means for tissue-specific expression of CaM kinase Ibeta. Thus the Thr177 residue of CaM kinase Ialpha is phosphorylated by not only CaM kinase kinase but also CaM kinase Ibeta for activation of the enzyme.

Human Ca2+/Calmodulin-dependent Protein Kinase Kinase β Gene Encodes Multiple Isoforms That Display Distinct Kinase Activity

“…Alternative splicing is a common mechanism that creates a variety of proteins with constant and variable functional domains from a single gene by RNA processing (38). Members of the CaMK family also contain various isoforms by means of alternative splicing (39,40). The rat CaMK I␤ is differentially spliced into two isoforms (designated as ␤1 and ␤2) with distinct C termini (39,41).…”

“…Members of the CaMK family also contain various isoforms by means of alternative splicing (39,40). The rat CaMK I␤ is differentially spliced into two isoforms (designated as ␤1 and ␤2) with distinct C termini (39,41). These isoforms are developmentally regulated, with the ␤1 isoform present in rat embryos from day 18 and the ␤2 isoform present from day 5 postnatally.…”

Molecular Cloning and Characterization of CLICK-III/CaMKIγ, a Novel Membrane-anchored Neuronal Ca2+/Calmodulin-dependent Protein Kinase (CaMK)

“…The ability of the CaMKI isoforms and a related kinase, CKLiK, to phosphorylate neuronal substrates, such as synapsin I and CREB in vitro, has been demonstrated so far (13,17,18). However, little is yet known about the physiological role of CaMKI, although CaMKI␣ and CaMKI␤ have been shown to be expressed both in neural as well as non-neural peripheral tissues (13,(17)(18)(19)(20)(21).…”

Pregnancy-upregulated nonubiquitous calmodulin kinase induces ligand-independent EGFR degradation

“…In addition to synapsin I and II, calmodulin kinase I phosphorylates a wide variety of substrates, such as cAMP response element-binding protein (57), cystic fibrosis transmembrane conductance regulator (51), and the Numb family proteins (Numb and Numb-1) (63). Over the years, two other isoforms of calmodulin kinase I, namely, ␤ and ␥, were reported (71), and, subsequently, a splice variant of calmodulin kinase I␤, called calmodulin kinase I␤ 2 , was discovered (47), which is also known as pregnancy-upregulated nonubiquitous calmodulin kinase (Pnck) (20,21). Pnck is a unique member of the calmodulin kinase I family, being most homologous to calmodulin kinase I within the catalytic domain (21).…”