S1Ping in Two Directions

Science's STKE  25 Feb 2003:
Vol. 2003, Issue 171, pp. tw81-TW81
DOI: 10.1126/stke.2003.171.tw81

Sugimoto et al. investigated sphingosine-1-phosphate (S1P)-mediated effects on cell motility and discovered evidence for simultaneous activation of opposing signals mediated through individual S1P receptor isotypes. S1P acts through guanine-nucleotide-binding protein (G protein)-coupled receptors (GPCRs) to stimulate or inhibit cell migration. Two GPCR isotypes, S1P1 and S1P3, stimulate migration through Gi-dependent activation of the small guanosine triphosphatase Rac, whereas S1P2 blocks chemotaxis by inhibiting Rac. Both S1P2 and S1P3 stimulate RhoA. Aluminum fluoride (AlF4-), which activates G proteins, mimicked S1P in stimulating Rho but inhibiting Rac and chemotaxis in Chinese hamster ovary (CHO) cells expressing S1P2. The authors used pharmacological analysis, combined with transient expression of COOH-terminal peptides of G protein α subunits (Gα), to implicate Gα12 and Gα13 in S1P2-mediated inhibition of cell migration, inhibition of Rac, and stimulation of RhoA. S1P2 coimmunoprecipitated with Gα12 and Gα13. CHO cells expressing mutant receptors consisting of Gα sequences fused to the S1P2 COOH-terminal showed S1P-dependent inhibition of Rac activation, inhibition of chemotaxis, and activation of RhoA. Pharmacological analysis combined with expression of Rho mutants implicated Rho in S1P2-mediated inhibition of chemotaxis and of Rac. Whereas overexpressing Gα12 and Gα13 potentiated inhibition of chemotaxis mediated by AlF4- and S1P, overexpressing Gαi countered S1P-dependent inhibition of Rac and cell migration. In CHO cells expressing S1P1 or S1P3, S1P stimulated chemotaxis and Rac. After inactivation of Gi with pertussis toxin, however, S1P inhibited Rac and chemotaxis. Thus, both classes of S1P receptor activate distinct signaling pathways with opposing effects on Rac and on cell migration that are integrated into the overall response.

N. Sugimoto, N. Takuwa, H. Okamoto, S. Sakurada, Y. Takuwa, Inhibitory and stimulatory regulation of Rac and cell motility by the G12/13-Rho and Gi pathways integrated downstream of a single G protein-coupled sphingosine-1-phosphate receptor isoform. Mol. Cell. Biol. 23, 1534-1545 (2003). [Abstract] [Full Text]