ACTIVATION OF G-PROTEINS WITH ALF4--MEDIATED INDUCES LFA-I-MEDIATED ADHESION OF T-CELL HYBRIDOMA CELLS TO ICAM-1 BY SIGNAL PATHWAYS THAT DIFFER FROM PHORBOL ESTER-INDUCED AND MANGANESE-INDUCED ADHESION

T-cell hybridomas metastasize widely, and the extent of dissemination correlates with invasiveness in fibroblast cultures. Previously, we pr ovided evidence that both metastasis and in vitro invasion require act ivation of LFA-1, induced by G-protein-transduced signals triggered by as yet unidentified factors. We show here that LFA-P-mediated adhesio n of TAM2D2 T-cell hybridoma cells to ICAM-1 can in fact be induced by direct activation of G-proteins using AlF4-, to the same extent as by using PMA or Mn2+. We assessed effects of protein kinase C (PKC), tyr osine kinase (TK), PI3-kinase (PI3K), and phospholipase C (PLC) inhibi tors. Both AlF4--induced adhesion and invasion were completely blocked by the TK inhibitor genistein and partially blocked by the PI3K inhib itor wortmannin, but not influenced by PKC inhibitor GF109203X. Downre gulation of PKC did not affect invasion or adhesion induced by AlF4- e ither. In contrast, GF109203X and PKC downregulation blocked PMA-induc ed adhesion, but genistein and wortmannin had no effect. Invasion and both AlF4- and PMA-induced adhesion were completely blocked by the PLC inhibitor U73122. Mn2+-induced adhesion, which was not or was only pa rtially blocked by the other inhibitors, was delayed by U73122, and sp reading of Mn2+-treated cells was completely prevented by U73122. Howe ver, PLC activity during adhesion was not detected, We conclude that s ignals required for invasion and G-protein-induced adhesion are simila r and are distinct from PKC-induced adhesion, and that in all eases PL C is likely to be activated, but is probably too local and/or transien t to be detected. (C) 1997 Academic Press.