THE ROLE OF G-PROTEIN IN MATRIX-MEDIATED MOTILITY OF HIGHLY AND POORLY INVASIVE MELANOMA CELLS

Membranes from 2 K1735 murine melanoma clones of high invasive capacity show increased amounts of pertussis toxin (PT) substrate when compared to a weakly invasive cellular counterpart. Using a panel of specific G-protein antibodies, we identified Giα2 as the PT-sensitive G-protein uniquely abundant in highly invasive cells. In addition, RNA hybridization results confirm the immunoblot observations that Giα2 is present at higher levels in strongly invasive cells. This result suggests that the elevated expression of Giα2 in highly invasive cells is not entirely due to differences in either translational efficiency or protein degradation but is related to altered RNA transcriptional initiation, processing and/or degradation. ADP-ribosylation of G1 α-subunits by PT inhibited the fi-bronectin, laminin and collagen type-IV-stimulated motility of the 2 highly invasive clones, while PT treatment of cells from a poorly invasive clone resulted in little or no reduction of the fibronectin, laminin or collagen type-IV-stimulated lower motility. Furthermore, PT treatment of highly or poorly invasive KI735 clones does not result in any alteration in cellular cAMP accumulation, suggesting that the PT substrate is not linked with the adenylyl cyclase enzyme complex. The data suggest that a PT-sensitive G-protein, probably Giα2, regulates second messenger pathways that contribute to elevated motility in highly invasive KI735 cells.