Nuclear Localization of the δ Subunit of Ca2+/Calmodulin-Dependent Protein Kinase II in Rat Cerebellar Granule Cells

Abstract : To examine the physiological roles of the δ subunit of Ca²⁺/calmodulin-dependent protein kinase ∥ (CaM kinase ∥δ) in brain, we examined the localization of CaM kinase ∥δ in the rat brain. A specific antibody to CaM kinase ∥δ1-δ4 isoforms was prepared by immunizing rabbits with a synthesized peptide corresponding to the unique carboxyl-terminal end of these isoforms. The prepared antibody did not recognize the α, β, and γ subunits, which were each overexpressed in NG108-15 cells. Immunoblot analysis on various regions and the nuclear fractions from rat brains suggested that some isoforms of CaM kinase ∥δ1-δ4 were abundant in the nucleus in the cerebellum. Total RNA from the cerebellum was analyzed by RT-PCR with a primer pair from variable domain 1 to variable domain 2. We detected the three PCR products δ3.1, δ3.4, and δ3 that contained the nuclear localization signal. These CaM kinase ∥δ3 isoforms were localized in the nuclei in transfected NG108-15 cells. Immunohistochemical study suggested the existence of these isoforms in the nuclei in cerebellar granule cells. These results suggest that CaM kinase ∥δ3 isoforms are involved in nuclear Ca²⁺ signaling in cerebellar granule cells.