Molecular and cellular biological study about the abnormal neurite outgrowth and protein phosphorylation in temporal lobe epilepsy

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A morphological characteristic of temporal lobe epilepsy consists of the abnormal neurite outgrowth of the hippocampal dentate granule cells. Some isoforms of Ca^<2+>/calmodulin-dependent protein kinase II (CaM kinase II) may be related to this abnormal neurite outgrowth. Among CaM kinase II, four subunits and several isoforms have been identified from brain. In order to investigate the pathophysiological roles of each isoform of CaM kinase II in temporal lobe epilepsy, we studied about the structures and functions of CaM kinase II isoforms mainly about the delta subunit of CaM kinase II (CaM kinase IIdelta). 1) We prepared the antibody against CaM kinase IIdelta and examined the localization of the subunit in brain. 2) We obtained the cDNAs of 6 isoforms of CaM kinase IIdelta from rat brain. Among these isoforms, delta3 was localized in the nuclei in transfected NG1O8-15 cells. 3) Overexpression of delta3 in NG1O8- 15 cells induced the gene expression of brain-derived neurotrophic factor (BDNF) which promotes survival and differentiation of specific populations of neurons in the brain. 4) We found that the major isoform of CaM kinase II in PC12 cells and NG108-15 cells was delta2. And delta2 appeared to be mainly localized in Golgi's apparatus.5) Other isoforms were localized in the cytoplasm in NG 108-15 cells. Therefore, these isoforms may be involved in the regulation of neurite outgrowth via phosphorylation of cytoskeletal proteins such as microtubule-associated protein 2.These results suggest that each isoform is localized in the specific site in neurons to play some important roles in neuronal functions.