GUANINE-NUCLEOTIDE-BINDING PROTEINS MEDIATE THE CHEMOTACTIC SIGNAL OF TRANSFORMING GROWTH-FACTOR-BETA-1 IN RAT IL-2 ACTIVATED NATURAL-KILLER-CELLS

Transforming growth factor (TGF)-beta1 induced rat IL-2-activated natural killer (IANK) cell chemotaxis. Various doses of cholera toxin (CT) or pertussis toxin (PT) inhibited the activity of TGF-beta1 suggesting a role for guanine nucleotide binding (G) proteins. ADP-ribosylation assay showed that rat IANK cell membranes possess a 39 kDa PT substrate and two, 41 and 42 kDa, CT substrates. ADP-ribosylation also showed that incubating IANK cell membranes with TGF-beta1 in the presence of guanosine 5'-O-(3-thiotriphosphate) resulted in the disappearance of the PT substrate. Immunoblot analysis showed that rat IANK cell membranes possess one G(i) (39 kDa), one G0 (39 kDa) and three G(s) (40, 41, and 42 kDa) proteins. Pretreatment of IANK cell membranes with TGF-beta1 in the presence of guanosine-5'-O-(3-thiotriphosphate) reduced the intensity of the 39 kDa G0 and the 40 kDa G(s) but not the 39 kDa G(i) or the 41 kDa or 42 kDa G(s). Furthermore, TGF-beta1 stimulated GTP binding and increased GTPase activity in IANK cell membranes. Both activities were inhibited by PT or CT. This inhibition was associated with the modification of G proteins by the toxins suggesting that bacterial toxin substrates are linked to TGF-beta1 receptors. Our results suggest that G0 and G(s) are involved in mediating the chemotactic signal of TGF-beta1 in rat IANK cells.