Autocrine activation of the hepatocyte growth factor receptor/met tyrosine kinase induces tumor cell motility by regulating pseudopodial protrusion.
The multiple beta-actin rich pseudopodial protrusions of the invasive variant of Moloney sarcoma virus (MSV)-transformed epithelial MDCK cells (MSV-MDCK-INV) are strongly labeled for phosphotyrosine. Increased tyrosine phosphorylation among a number of proteins was detected in MSV-MDCK-INV cells relative to untransformed and MSV-transformed MDCK cells, especially for the hepatocyte growth factor receptor (HGF-R), otherwise known as c-met proto-oncogene. Cell surface expression of HGF-R was similar in the three cell lines, indicating that HGF-R is constitutively phosphorylated in MSV-MDCK-INV cells. Both the tyrosine kinase inhibitor herbimycin A and the HGFalpha antibody abolished HGF-R phosphorylation, induced retraction of pseudopodial protrusions, and promoted the establishment of cell-cell contacts as well as the apparition of numerous stabilizing stress fibers in MSV-MDCK-INV cells. Furthermore, anti-HGFalpha antibody abolished cell motility among MSV-MDCK-INV cells. Conditioned medium from MSV-MDCK-INV cells induced MDCK cell scattering, indicating that HGF is secreted by MSV-MDCK-INV cells. HGF titration followed by a subsequent washout of the antibodies led to renewed pseudopodial protrusion and cellular movement. We therefore show that activation of the tyrosine kinase activity of HGF-R/Met via an autocrine HGF loop is directly responsible for pseudopodial protrusion, thereby explaining the motile and invasive potential of this model epithelium-derived tumor cell line.
Vadnais
Julie
J
Département de physiologie, Groupe de recherche en transport membranaire, Université de Montréal, Montréal, Québec H3C 3J7, Canada.
Nault
Geneviève
G
Daher
Zeinab
Z
Amraei
Mohammad
M
Dodier
Yolaine
Y
Nabi
Ivan Robert
IR
Noël
Josette
J
D000199:Actins / Q000378:metabolism; D000818:Animals; D002465:Cell Movement / Q000502:physiology*; D004285:Dogs; D010766:Phosphorylation; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism* / Q000502:physiology; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D000199:Actins; D014443:Tyrosine; D019859:Proto-Oncogene Proteins c-met