Differential involvement of Gα16 in CC chemokine-induced stimulation of phospholipase Cβ, ERK, and chemotaxis

Chemokines are known to regulate the chemotaxis of leukocytes and play an important role in immunological processes. Chemokine receptors are widely distributed in hematopoietic cells and are often co-localized with the hematopoietic-specific G16 and its close relative, G14. Yet, many chemokine receptors utilize pertussis toxin-sensitive Gi proteins for signaling. Given that both G16 and G14 are capable of linking Gi-coupled receptors to the stimulation of phospholipase Cβ, we examined the capacity of six CC chemokine receptors (CCR1, CCR2a, CCR2b, CCR3, CCR5 and CCR7) to interact with G14 and G16 in a heterologous expression system. Among the CC chemokine receptors tested, CCR1, CCR2b, and CCR3 were capable of mediating chemokine-induced stimulation of phospholipase Cβ via either G14 or G16. The G14/G16-mediated responses exhibited CC chemokine dose-dependency and were resistant to pertussis toxin (PTX) treatment. In contrast, CCR2a, CCR5 and CCR7 were unable to interact with G14 and G16. Under identical experimental conditions, all six CC chemokine receptors were fully capable of inhibiting adenylyl cyclase via Gi as well as stimulating phospholipase Cβ via 16z44, a G16/z chimera that possesses increased promiscuity toward Gi-coupled receptors. Moreover, CCR1-mediated ERK1/2 phosphorylation was largely PTX-insensitive in THP-1 monocytic cells that endogenously express Gα16. In addition, CCR1 agonist was less efficacious in mediating chemotaxis of THP-1 cells following the knockdown of Gα16 by overexpressing siRNA, indicating the participation of Gα16 in CCR1-induced cell migration. These results show that different CC chemokine receptors can discriminate against G14 and G16 for signal transduction.