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Enhanced expression and activation of Ca(2+)/calmodulin-dependent protein kinase IV in hepatocellular carcinoma
1Department of Oral and Maxillofacial Surgery, Faculty of Medicine, Kagawa Medical University, Kagawa, Japan.
Background:
Ca(2+)/calmodulin-dependent protein kinase IV (CaM-kinase IV) is a multifunctional protein kinase that is expressed abundantly in the central nervous system and, to a lesser degree, in nonneuronal tissues such as the liver. In the current study, the authors demonstrated the expression of CaM-kinase IV in hepatocytes from hepatocellular carcinoma (HCC) in both humans and rats.
Methods:
Immunoblotting and immunohistochemical analysis were performed to confirm the expression of CaM-kinase IV and CaM-kinase kinase in HCC occurring in both humans and rats. The kinase activity of CaM-kinase IV in the lysate of each of these liver supernatant fluids was measured using a specific substrate (peptide gamma) for this enzyme before and after phosphorylation by exogenously added CaM-kinase kinase.
Results:
Marked positive staining of HCC hepatocytes was found and the subcellular staining pattern mainly was cytosolic. One immunoreactive band with a molecular weight of 64 kilodaltons, which was identical to an isoform of rat cerebellum CaM-kinase IV, was demonstrated by immunoblotting. Ca(2+)/calmodulin-dependent CaM-kinase IV activity was high in HCC and showed almost no difference in activity in specimens with and without CaM-kinase kinase phosphorylation.
Conclusions:
CaM-kinase IV was found to be expressed in HCC and might have been involved in the development of HCC. CaM-kinase IV that was expressed in cancerous hepatocytes was phosphorylated mainly by CaM-kinase kinase that also was expressed in tumor cells.