Bi-directional regulation of Ser-985 phosphorylation of c-met via protein kinase C and protein phosphatase 2A involves c-Met activation and cellular responsiveness to hepatocyte growth factor.
Previous studies indicated that treatment of cells with 12-O-tetradecanoylphorbol-13-acetate induced phosphorylation of Ser-985 at the juxtamembrane of c-Met, the receptor tyrosine kinase for hepatocyte growth factor (HGF), and this was associated with decreased tyrosine phosphorylation of c-Met. However, the regulatory mechanisms and the biological significance of the Ser-985 phosphorylation in c-Met remain unknown. When A549 human lung cancer cells were exposed to oxidative stress with H(2)O(2), H(2)O(2) treatment induced phosphorylation of Ser-985, but this was abrogated by an inhibitor for protein kinase C (PKC). Likewise, treatment of cells with NaF (an inhibitor of protein phosphatases) allowed for phosphorylation of Ser-985, and a protein phosphatase responsible for dephosphorylation of Ser-985 was identified to be protein phosphatase 2A (PP2A). The effects of PKC inhibitors revealed that PKCdelta and -epsilon were responsible for the Ser-985 phosphorylation of c-Met, and pull-down analysis indicated that associations of PKCdelta and -epsilon with c-Met may be involved in the regulation of Ser-985 phosphorylation of c-Met. Instead, PP2A was constitutively associated with c-Met, whereas its activity to dephosphorylate Ser-985 of c-Met was decreased when cells were exposed to H(2)O(2). Addition of HGF to A549 cells in culture induced c-Met tyrosine phosphorylation, the result being mitogenic response and cell scattering. In contrast, in the presence of H(2)O(2) stress, HGF-dependent tyrosine phosphorylation of c-Met was largely suppressed with a reciprocal relationship to Ser-985 phosphorylation, and this event was associated with abrogation of cellular responsiveness to HGF. These results indicate that Ser-985 phosphorylation of c-Met is bi-directionally regulated through PKC and PP2A, and the Ser-985 phosphorylation status may provide a unique mechanism that confers cellular responsiveness/unresponsivenss to HGF, depending on extracellular conditions.
Hashigasako
Atsuko
A
Division of Molecular Regenerative Medicine, Course of Advanced Medicine, Osaka University Graduate School of Medicine, Osaka 565-0871, Japan.
Machide
Mitsuru
M
Nakamura
Takahiro
T
Matsumoto
Kunio
K
Nakamura
Toshikazu
T
D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000494:pharmacology; D045744:Cell Line, Tumor; D004396:Coloring Agents / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017228:Hepatocyte Growth Factor / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008954:Models, Biological; D018384:Oxidative Stress; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054648:Protein Phosphatase 2; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism*; D012694:Serine / Q000737:chemistry*; D012969:Sodium Fluoride / Q000494:pharmacology; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism
D004396:Coloring Agents; D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D014443:Tyrosine; D012694:Serine; D017228:Hepatocyte Growth Factor; D012969:Sodium Fluoride; D006861:Hydrogen Peroxide; D019859:Proto-Oncogene Proteins c-met; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D001973:Bromodeoxyuridine