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Background  TCR and CXCR4-mediated signaling appears to be reciprocally regulated pathways. TCR activation dampens the chemotactic response towards the CXCR4 ligand CXCL12, while T cells exposed to CXCL12 are less prone to subsequent TCR-activation. The heterotrimeric G proteins G αq  and G αi2  have been implicated in CXCR4-signaling and we have recently also reported the possible involvement of G αq  in TCR-dependent activation of Lck (Ngai et al., Eur. J. Immunol., 2008, 38: 32083218). Here we examined the role of G αq  in migration and TCR activation.    Results  Pre-treatment of T cells with CXCL12 led to significantly reduced Lck Y394 phosphorylation upon TCR triggering indicating heterologous desensitization. We show that knockdown of G αq  significantly enhanced basal migration in T cells and reduced CXCL12-induced SHP-1 phosphorylation whereas G αi2  knockdown inhibited CXCL12-induced migration.    Conclusion  Our data suggest that G αi2  confers migration signals in the presence of CXCL12 whereas G αq  exerts a tonic inhibition on both basal and stimulated migrational responses. This is compatible with the notion that the level of G αq  activation contributes to determining the commitment of the T cell either to migration or activation through the TCR.

Interplay between the heterotrimeric G-protein subunits Gαq and Gαi2 sets the threshold for chemotaxis and TCR activation