Participation of a MEK-independent pathway in MAP kinase activation and modulation of cell growth in mouse hepatoma cell lines.
The mechanism of cell growth was investigated in GIT medium-supplemented in vitro assay using high and low metastatic mouse hepatoma cell sublines, G-5 and G-1, respectively. G-5 cells exhibited high growth rate compared to G-1 cells. The PI3-kinase inhibitor LY294002 and P70 S6 kinase inhibitor rapamycin partially blocked both G-1 and G-5 cell growth, suggesting that these two kinases are involved in hepatoma cell growth. In contrast, the MEK1 inhibitor PD98059 partially blocked G-5 cell growth but not G-1 cell growth. MAP kinases (MAPK) in both G-1 and G-5 cells were indistinguishably phosphorylated, yet MEK-dependent MAPK activation was observed only in G-5 cells. In G-1 cells, MAPK was phosphorylated in a manner not connected to MEK activation. Thus, the low degree of cell growth in G-1 cells was attributable to disruption of the MEK-dependent MAPK cascade. However, the molecular mechanism whereby MAPK phosphorylation does not parallel MAPK activation in G-1 cells remains unknown. Here, we suggest that there may be an as yet unidentified MAPK phosphorylation pathway in malignantly transformed cells, which may affect in vivo cell growth and metastatic capacities of cancers.
Saeki
Y
Y
Department of Immunology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Higashinari-ku, Osaka 537-8511, Japan.
Hazeki
K
K
Hazeki
O
O
Ui
M
M
Itoh
K
K
Matsumoto
M
M
Toyoshima
K
K
Akedo
H
H
Seya
T
T
D000818:Animals; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D016895:Culture Media, Serum-Free; D003720:Densitometry; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006133:Growth Substances / Q000494:pharmacology; D015151:Immunoblotting; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000201:enzymology / Q000473:pathology*; D048728:MAP Kinase Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D020928:Mitogen-Activated Protein Kinases / Q000276:immunology / Q000378:metabolism*; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014407:Tumor Cells, Cultured
D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors; D006133:Growth Substances; D048728:MAP Kinase Kinase Kinase 1; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; C482578:Map3k1 protein, mouse