Upon sensing chemoattractant signals, leukocytes migrate towards the chemoattractant. If the signal is extravascular, circulating leukocytes roll on the surface of endothelial cells, firmly adhere and migrate through the endothelial monolayer to the inflammation site. Transendothelial migration of leukocytes requires integrins, particularly β2 family of integrins. We previously demonstrated that the heterotrimeric G protein subunit Gα13 interacts with the cytoplasmic domains of certain integrin β subunits including β2. To understand the role of Gα13 in integrin-dependent neutrophil migration, myeloid-specific Gα13 deficient mice have been generated by cross-breeding lysozyme M-cre mice with Gα13-floxed mice. Neutrophil migration was attenuated in myeloid-specific Gα13 knockout mice in a thioglycolate (3%) induced peritonitis model in vivo, and was also attenuated in transendothelial or mouse ICAM-1-coated transwell migration assays ex vivo. In contrast, endothelial cell/ICAM-independent transwell migration was not affected. Importantly, on an ICAM-coated surface, only the speed of migration of Gα13-deficient neutrophils were attenuated but migration directionality was not affected, suggesting that Gα13 plays an important role in motility rather than chemoattractant sensing. To further determine the role of Gα13-β2 integrin interaction in leukocyte migration, we examined the effect of a peptide, MB2mP6, derived from the Gα13 binding site of integrin β2 subunit. Like Gα13 deficiency, MB2mP6 inhibited integrin-dependent neutrophil transendothelial migration, but had minimal effects on leukocyte transwell migration in the absence of endothelial cell monolayer. Gα13 plays dual role in RhoA regulation. GPCR-activated Gα13 binds to and activates RhoGEFs resulting in RhoA activation, but Gα13 binding to integrin cytoplasmic domain is associated inhibition of RhoA. Interestingly, treatment with MB2mP6 enhanced RhoA activity of neutrophils adherent on ICAM1, suggesting that MB2mP6 mainly affects Gα13-β2 interaction. These data suggest that Gα13-integrin interaction plays an important role in the integrin-dependent transendothelial migration. Thus, Gα13-β2 is important in the immune and inflammatory functions of neutrophils.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.