The potentiating effect of HGF/c-Met on IL-6 signaling could be explained by two mechanisms: (i) IL-6 increased the level of c-Met on the cell surface of myeloma cells making cells more sensitive to HGF; and (ii) IL-6 relied on HGF/c-Met to fully activate the Ras-MAPK pathway possibly through Shp2 activation. The gene discussed is HGF; the disease is plasma cell myeloma.