Receptors induce chemotaxis by releasing the βγ subunit of G(i), not by activating G(q) or G(s)

Many chemoattractants cause chemotaxis of leukocytes by stimulating a structurally distinct class of G protein-coupled receptors. To identify receptor functions required for chemotaxis, we studied chemotaxis in HEK293 cells transfected with receptors for nonchemokine ligands or for interleukin 8 (IL-8), a classical chemokine. In gradients of the appropriate agonist, three nonchemokine G(i)-coupled receptors (the D(2) dopamine receptor and opioid μ and δ receptors) mediated chemotaxis; the β(2)-adrenoreceptor and the M3-muscarinic receptor, which couple respectively to G(s) and G(q), did not mediate chemotaxis. A mutation deleting 31 C-terminal amino acids from the IL-8 receptor type B quantitatively impaired chemotaxis and agonist-induced receptor internalization, but not inhibition of adenylyl cyclase or stimulation of mitogen-activated protein kinase. To probe the possible relation between receptor internalization and chemotaxis, we used two agonists of the μ-opioid receptor. Morphine and etorphine elicited quantitatively similar chemotaxis, but only etorphine induced receptor internalization. Overexpression of two βγ sequestering proteins (βARK-ct and α(t)) prevented IL-8 receptor type B-mediated chemotaxis but did not affect inhibition of adenylyl cyclase by IL-8. We conclude that: (i) Nonchemokine G(i)-coupled receptors can mediate chemotaxis. (ii) G(i) activation is necessary but probably not sufficient for chemotaxis. (iii) Chemotaxis does not require receptor internalization. (iv) Chemotaxis requires the release of free βγ subunits.