Beta-arrestin 2-dependent angiotensin II type 1A receptor-mediated pathway of chemotaxis.
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(alphai) family. Beta-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 beta-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(1A)R) undergo chemotaxis in response to Ang II. An Ang II peptide analog S(1)I(4)I(8) 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(alphai). Suppression of beta-arrestin 2 expression using small interfering RNA (siRNA) essentially eliminated AT(1A)R-mediated chemotaxis induced by either Ang II or the S(1)I(4)I(8) 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(alphaq/11) through siRNA and inhibition of protein kinase C, extracellular signal-regulated kinases 1 and 2, or phosphatidylinositol-3-kinase did not diminish AT(1A)R-mediated chemotaxis. Inhibiting p38 mitogen-activated protein kinase decreased AT(1A)R-mediated chemotaxis and eliminated EGF-mediated chemotaxis, suggesting that p38 plays a role in chemotaxis that is not specific to the AT(1A)R in this system. These data suggest that beta-arrestin 2 can mediate chemotaxis through mechanisms which may be G-protein-independent (Ang II receptors) or -dependent (LPA receptors).
Hunton, DL; Barnes, WG; Kim, J; Ren, X-R; Violin, JD; Reiter, E; Milligan, G; Patel, DD; Lefkowitz, RJ
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