Abstract

Chemotaxis is a cellular response that directs cell migration toward a chemical gradient and is fundamental to a variety of cellular processes. The receptors for most known chemokines belong to the seven transmembrane-spanning superfamily and signal through members of the G_αi family. β-Arrestins, in addition to regulating desensitization, have emerged as potential mediators of G-protein-independent signaling pathways and have been implicated in several chemotactic pathways. Here, we report a system wherein chemotaxis is stimulated in a β-arrestin 2-dependent and apparently G-protein-independent manner. Human embryonic kidney 293 cells with stable expression of the angiotensin II (Ang II) receptor type 1A (AT_1AR) undergo chemotaxis in response to Ang II. An Ang II peptide analog S¹I⁴I⁸ Ang II that is unable to activate G-protein-mediated responses induces chemotaxis in these cells that is unaffected by pertussis toxin-mediated suppression of G_αi. Suppression of β-arrestin 2 expression using small interfering RNA (siRNA) essentially eliminated AT_1AR-mediated chemotaxis induced by either Ang II or the S¹I⁴I⁸ Ang II peptide but had no effect on epidermal growth factor (EGF)-induced chemotaxis. It also abolished chemotaxis induced by lysophosphatidic acid (LPA), which was completely sensitive to pertussis toxin. In contrast, reduction of G_αq/11 through siRNA and inhibition of protein kinase C, extracellular signal-regulated kinases 1 and 2, or phosphatidylinositol-3-kinase did not diminish AT_1AR-mediated chemotaxis. Inhibiting p38 mitogen-activated protein kinase decreased AT_1AR-mediated chemotaxis and eliminated EGF-mediated chemotaxis, suggesting that p38 plays a role in chemotaxis that is not specific to the AT_1AR in this system. These data suggest that β-arrestin 2 can mediate chemotaxis through mechanisms which may be G-protein-independent (Ang II receptors) or -dependent (LPA receptors).