Increase of brain-derived neurotrophic factor gene expression in NG108-15 cells by the nuclear isoforms of Ca2+/calmodulin-dependent protein kinase II

We have reported that the delta 3 isoform of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) is abundant in the nucleus in cerebellar granule cells. To examine the possibility that the nuclear isoforms of (CaM kinase II are involved in the expression of brain-derived neurotrophic factor (BDNF), we transiently overexpressed the delta 3 isoform in NG108-15 cells. The quantitative RT-PCR analysis revealed that rat cerebellum and NG108-15 cells expressed the exon IV-containing mRNA of BDNF (exon IV-BDNF mRNA) more than the exon III-BDNF mRNA. Treatment of NG108-15 cells with Bay K 8644 increased both exon III- and exon IV-BDNF mRNAs, and overexpression of the delta 3 isoform potentiated the expression of the exon IV-BDNF mRNA. The potentiation was not observed in the cells that were overexpressed with either the delta 1 isoform, a nonnuclear isoform, or the inactive mutant of the delta 3 isoform. We constructed the luciferase reporter gene following the promoter upstream of exon IV and confirmed that overexpression of the delta 3 isoform increased luciferase gene expression. Double-immunostaining of NG108-15 cells with the antibodies to CaM kinase II and BDNF clearly showed that BDNF was highly expressed in the cells that were overexpressed with the delta 3 isoform or the alpha B isoform, another nuclear isoform of CaM kinase II. These results suggest that the nuclear isoforms of CaM kinase II are involved in the expression of BDNF.