CHEMOTAXIS IN A LYMPHOCYTE CELL-LINE TRANSFECTED WITH C-C CHEMOKINE RECEPTOR 2B - EVIDENCE THAT DIRECTED MIGRATION IS MEDIATED BY BETA-GAMMA DIMERS RELEASED BY ACTIVATION OF G(ALPHA-I)-COUPLED RECEPTORS

Chemotaxis is mediated by activation of seven-transmembrane domain, G protein-coupled receptors, but the signal transduction pathways leadin g to chemotaxis are poorly understood. To identify G proteins that sig nal the directed migration of cells, we stably transfected a lymphocyt e cell line (300-19) with G protein-coupled receptors that couple excl usively to G(alpha q) (the m3 muscarinic receptor), G(alpha i) (the ka ppa-opioid receptor), and G(alpha s) (the beta-adrenergic receptor), a s well as the human thrombin receptor (PAR-1) and the C-C chemokine re ceptor 2B. Cells expressing receptors that coupled to G(alpha i), but not to G(alpha q) or G(alpha s), migrated in response to a concentrati on gradient of the appropriate agonist. Overexpression of G(alpha) tra nsducin, which binds to and inactivates free G(beta gamma) dimers, com pletely blocked chemotaxis although having little or no effect on intr acellular calcium mobilization or other measures of cell signaling. Th e identification of G(beta gamma) dimers as a crucial intermediate in the chemotaxis signaling pathway provides further evidence that chemot axis of mammalian cells has important similarities to polarized respon ses in yeast. We conclude that chemotaxis is dependent on activation o f G(alpha i) and the release of G(beta gamma) dimers, and that G(alpha i)-coupled receptors not traditionally associated with chemotaxis can mediate directed migration when they are expressed in hematopoietic c ells.