Enhanced expression and activation of Ca(2+)/calmodulin-dependent protein kinase IV in hepatocellular carcinoma.
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.
Tamura
N
N
Department of Oral and Maxillofacial Surgery, Faculty of Medicine, Kagawa Medical University, Kagawa, Japan.
Tai
Y
Y
Sugimoto
K
K
Kobayashi
R
R
Konishi
R
R
Nishioka
M
M
Masaki
T
T
Nagahata
S
S
Tokuda
M
M
D000818:Animals; D015153:Blotting, Western; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology* / Q000473:pathology; D022781:Hepatocytes; D006801:Humans; D007124:Immunoenzyme Techniques; D008107:Liver Diseases / Q000201:enzymology / Q000473:pathology; D008113:Liver Neoplasms / Q000201:enzymology* / Q000473:pathology; D051381:Rats; D020318:Rats, Long-Evans; D017208:Rats, Wistar
C517683:CAMK4 protein, human; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517686:Camk4 protein, rat