ACKR3 Regulates Endothelial Cell Function with Non‐canonical Integration of Gαi and β‐arrestin

Abstract

Atypical Chemokine receptor 3 (ACKR3), also known as C‐X‐C chemokine receptor type 7 (CXCR7), is a G protein‐coupled receptor (GPCR) implicated in several physiological processes including leukocyte trafficking, cancer, and angiogenesis. Commonly co‐expressed with C‐X‐C chemokine receptor type 4 (CXCR4), ACKR3 has been shown to be unable to activate G protein pathways and appears to function as a “β‐arrestin‐biased” receptor. Furthermore, ACKR3’s ability to efficiently internalize its ligands, CXCL12 and CXCL11 (which are also ligands for the receptors CXCR4 and CXCR3, respectively), and degrade them, resulting in some of its functions through a “scavenger” or “decoy” mechanism. However, much is still unknown about the bona fide signaling mechanisms by ACKR3 and its implications on cellular physiology. Here we describe ongoing studies to characterize the mechanisms that underlie ACKR3 on endothelial cell function. We demonstrate in vitro and in vivo activity of two ACKR3 specific agonists, WW36 and WW38, that bind ACKR3 with nanomolar affinities, promote β‐arrestin recruitment, and promote proliferation and migration of human umbilical vein endothelial cells (HUVECs). Surprisingly, we found that ACKR3‐promoted proliferation and migration was sensitive to pertussis toxin, suggesting the involvement of Gαi/o proteins at a receptor which does not canonically signal via G proteins. We hypothesize that these results may in part be explained by the recently described coordination of Gαi and β‐arrestin to promote Gαi:βarr complex‐specific downstream signaling. Confirming this potential mechanism, we demonstrate that stimulation of ACKR3 promotes formation of a Gαi:βarr complex in a dose dependent manner. These studies reveal a potentially novel role for Gαi:βarr complexes in mediating ACKR3 function that contribute to endothelial cell biology. Additionally, these findings support an emerging paradigm in which G proteins and β‐arrestins coordinate their signaling downstream of GPCRs.Support or Funding InformationNIH (CYL, SR)