Ganglioside GD1a inhibits HGF-induced motility and scattering of cancer cells through suppression of tyrosine phosphorylation of c-Met

We previously reported that ganglioside GD1a, which is highly expressed in poorly metastatic FBJ-SI cells, inhibits the serum-induced motility of FBJ- LL cells and that the metastatic potential of FBJ-LL cells is completely su ppressed by by enforced GD1a expression (Hyuga et al., Int J Cancer 1999; 8 3:685-91). We recently discovered that hepatocyte growth factor (HGF) induc es FBJ-LL cell motility. In the present study, the HGF-induced motility of FBJ-SI cells was found to be one-thirtieth that of FBJ-LL cells. This motil ity of GD1a-expressing transfectants, which were produced by transfection o f FBJ-LL cells with GM2/GD2 synthase cDNA, decreased with increases in thei r GD1a expression and HGF induced almost no motility in GD1a-pretreated FBJ -LL cells, indicating that GD1a inhibits the HGF-induced motility of FBJ-LL cells. The expression of the HGF receptor c-Met on FBJ-SI cells, FBJ-LL ce lls, transfectants and a mock-transfectant was almost the same. The level o f tyrosine phosphorylation of c-Met after HGF stimulation in FBJ-SI cells, GD1a-pretreated FBJ-LL cells and a GD1a-expressing transfectant was signifi cantly lower than in FBJ-LL cells and a mock-transfectant. These findings s uggested that GD1a inhibits the HGF-induced motility of FBJ-LL cells throug h suppression of tyrosine phosphorylation of c-Met. HepG2 cells, a human he patoma cell line, were used to investigate whether GD1a interferes with oth er cancer cells expressing c-Met. HepG2 cells did not express GD1a. HGF ind uced cell scattering of HepG2 cells and the scattering was inhibited by pre treating the cells with GD1a. The c-Met in the cells was autophosphorylated by stimulation with HGF, but after treating the cells with GD1a, the HGF-i nduced autophosphorylation of c-Met was suppressed. These results suggest t hat GD1a acts as a negative regulator of c-Met in cancer cells. (C) 2001 Wi ley-Liss, Inc.