Involvement of the p38 mitogen-activated protein kinase cascade in hepatocellular carcinoma.
BACKGROUND
The mitogen-activated protein kinase (MAPK) cascade is activated in response to various extracellular stimuli. The authors investigated the involvement of the p38 MAPK, a member of the MAPK superfamily, cascade in hepatoma cell lines and in human hepatocellular carcinoma (HCC) tissue specimens.


METHODS
Constitutively active mutant of MAPK kinase 6 (MKK6), which is upstream of p38 MAPK, was transfected into the HepG2 and HuH7 human hepatoma cell lines. The constitutive active mutant was constructed by replacing Ser-189 and Thr-193 with Glu. The growth and death of mutant MKK6-transfected hepatoma cells were analyzed by the WST-1 and sub-G1 assays. The surgically resected livers of 20 HCC patients were divided histologically into tumorous (T) and nontumorous (NT) lesions. p38 MAPK activity was analyzed using in vitro kinase assay and MKK6 activity was measured using Western blot analysis.


RESULTS
Mutant MKK6 transfection increased p38 MAPK activity, cytochrome c release from the mitochondria to the cytosol, and caspase-3 activity, accompanied by apoptosis. In contrast, SB203580, a p38 MAPK-specific inhibitor, prevented MKK6-induced apoptosis in hepatoma cell lines. In the T lesions of 20 HCC parients, p38 MAPK and MKK6 activities were significantly lower compared with NT lesions (P < 0.05). There was a significant positive correlation between p38 MAPK and MKK6 activity (r = 0.507, P < 0.05). Larger tumors (> 20 mm) exhibited lower levels of p38 MAPK and MKK6 activity than did smaller tumors (P < 0.05).


CONCLUSIONS
These findings suggested that reduction of the p38 MAPK cascade may account, in part, for the resistance to apoptosis, leading to the unrestricted cell growth of human HCC.
Iyoda
Kenya
K
Department of Molecular Therapeutics, Osaka University Graduate School of Medicine, Osaka, Japan.
Sasaki
Yutaka
Y
Horimoto
Masayoshi
M
Toyama
Takashi
T
Yakushijin
Takayuki
T
Sakakibara
Mitsuru
M
Takehara
Tetsuo
T
Fujimoto
Jiro
J
Hori
Masatsugu
M
Wands
Jack R
JR
Hayashi
Norio
N
D017209:Apoptosis; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D048669:MAP Kinase Kinase 6; D020935:MAP Kinase Signaling System; D008297:Male; D014407:Tumor Cells, Cultured
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048669:MAP Kinase Kinase 6; C482566:MAP2K6 protein, human