IDENTIFICATION OF G-PROTEIN-COUPLED RECEPTORS POTENTLY STIMULATING MIGRATION OF HUMAN TRANSITIONAL-CELL CARCINOMA-CELLS

The expression of G protein-coupled receptors inducing calcium mobiliz ation and stimulating cell migration was examined in human transitiona l-cell carcinoma (J82) cells. Measurements of cytoplasmic Ca2+ concent ration ([Ca2+](i)) and phospholipase C activity indicated that these c ells express several calcium-mobilizing receptors, including those for lysophosphatidic acid (LPA), thrombin, bradykinin, bombesin and hista mine, of which only the LPA response was sensitive (similar to 50%) to pertussis toxin (PTX). Migration of J82 cells was strongly stimulated by LPA and thrombin, by 5- to 20-fold, whereas bradykinin, bombesin a nd histamine were ineffective. Migration induced by either LPA or thro mbin was inhibited by the actin cytoskeleton-disrupting agent, cytocha lasin B, by the Rho protein-inactivating Clostridium difficile toxin B , by preventing [Ca2+](i) transients with an intracellular cal cium-ch elating agent, and by the phorbol ester, phorbol 12-myristate 13-aceta te, which also blocked the LPA- and thrombin-induced [Ca2+](i) increas es. On the other hand, ADP-ribosylation of G(i) type G proteins by PTX abrogated the migratory response to LPA, without affecting the thromb in effect. Similarly, raising cAMP levels inhibited, by about 50%, the LPA- but not the thrombin-induced J82 cell migration. In conclusion, human transitional-cell carcinoma (J82) cells express various G protei n-coupled, calcium-mobilizing receptors, out of which only those for L PA and thrombin stimulate cell migration, indicating that phospholipas e C-derived second messengers per se are not sufficient for initiating this response. The complex signal transduction processes leading to L PA- and thrombin-stimulated motility of these human carcinoma cells ap parently involve several common, essential factors, such as [Ca2+](i) changes and Rho protein-regulated reorganization of the cytoskeleton, as well as some distinct components, most notably distinct subtypes of heterotrimeric G proteins and apparently also distinct cAMP-sensitive targets.