Calcium/calmodulin-dependent protein kinase II inhibitor protein: Localization of isoforms in rat brain

A second isoform of Ca2+/calmodulin-dependent-kinase II inhibitor protein (CaM-KIIN) has been identified using the yeast two-hybrid screen. The 1.8 kb message encodes a 78 residue CaM-KIIN alpha that is 65% identical in its putative open-reading frame and 95% identical in its inhibitory domain to the previously characterized CaM-KIIN beta. CaM-KIIN alpha exhibits inhibitory properties towards recombinant mouse CaM-kinase II alpha indistinguishable from CaM-KIIN beta. The 27 amino acid inhibitory peptide (CaM-KIINtide) derived from CaM-KIIN has the ability to inhibit brain CaM-kinase II activity from multiple organisms including rat, Drosophila and goldfish. Northern analysis of various rat tissues indicates that CaM-KIIN alpha is specific to brain whereas CaM-KIIN beta message is also present in testis. In situ hybridization shows a general distribution of both isoforms in rat brain with stronger localization of CaM-KIIN beta in cerebellum and hindbrain and CaM-KIIN alpha in frontal cortex, hippocampus and inferior colliculus. An antibody that recognizes both isoforms shows a distribution of CaM-KIIN in rat brain that correlates with immunoreactivity of CaM-kinase II. In cultured mature hippocampal neurons, CaM-KIIN is present in cell bodies and dendrites but, unlike CaM-kinase II, does not display punctate staining at synapses. These results suggest a localized function for CaM-KIIN in inhibiting specialized pools of CaM-kinase II. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.