Chemotaxis in a lymphocyte cell line transfected with C-C chemokine receptor 2B: Evidence that directed migration is mediated by βγ dimers released by activation of G(αi)-coupled receptors

Chemotaxis is mediated by activation of seven-transmembrane domain, G protein-coupled receptors, but the signal transduction pathways leading to chemotaxis are poorly understood. To identify G proteins that signal the directed migration of cells, we stably transfected a lymphocyte cell line (300-19) with G protein-coupled receptors that couple exclusively to G(αq) (the m3 muscarinic receptor), G(αi) (the κ-opioid receptor), and G(αs) (the β-adrenergic receptor), as well as the human thrombin receptor (PAR-1) and the C-C chemokine receptor 2B. Cells expressing receptors that coupled to G(αi), but not to G(αq) or G(αs), migrated in response to a concentration gradient of the appropriate agonist. Overexpression of G(α) transducin, which binds to and inactivates free G(βγ) dimers, completely blocked chemotaxis although having little or no effect on intracellular calcium mobilization or other measures of cell signaling. The identification of G(βγ) dimers as a crucial intermediate in the chemotaxis signaling pathway provides further evidence that chemotaxis of mammalian cells has important similarities to polarized responses in yeast. We conclude that chemotaxis is dependent on activation of G(αi) and the release of G(βγ) dimers, and that G(αi)-coupled receptors not traditionally associated with chemotaxis can mediate directed migration when they are expressed in hematopoietic cells.