Schafer Christopher T, Chen Qiuyan, Tesmer John J G, Handel Tracy M
Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, USA.
Departments of Biological Sciences and of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, IN, USA.
bioRxiv. 2023 Mar 10:2023.02.25.530029. doi: 10.1101/2023.02.25.530029.
Atypical chemokine receptor 3 (ACKR3) is an arrestin-biased receptor that regulates extracellular chemokine levels through scavenging. The scavenging action mediates the availability of the chemokine CXCL12 for the G protein-coupled receptor (GPCR) CXCR4 and requires phosphorylation of the ACKR3 C-terminus by GPCR kinases (GRKs). ACKR3 is phosphorylated by GRK2 and GRK5, but the mechanisms by which these kinases regulate the receptor are unresolved. Here we mapped the phosphorylation patterns and determined that GRK5 phosphorylation of ACKR3 dominates β-arrestin recruitment and chemokine scavenging over GRK2. Co-activation of CXCR4 significantly enhanced phosphorylation by GRK2 through the liberation of Gβγ. These results suggest that ACKR3 'senses' CXCR4 activation through a GRK2-dependent crosstalk mechanism. Surprisingly, we also found that despite the requirement for phosphorylation, and the fact that most ligands promote β-arrestin recruitment, β-arrestins are dispensable for ACKR3 internalization and scavenging, suggesting a yet to be determined function for these adapter proteins.
非典型趋化因子受体3（ACKR3）是一种偏向β抑制蛋白的受体，通过清除作用调节细胞外趋化因子水平。这种清除作用介导了趋化因子CXCL12对于G蛋白偶联受体（GPCR）CXCR4的可用性，并且需要GPCR激酶（GRK）对ACKR3的C末端进行磷酸化。ACKR3可被GRK2和GRK5磷酸化，但这些激酶调节该受体的机制尚未明确。在此，我们绘制了磷酸化模式，并确定相较于GRK2，ACKR3的GRK5磷酸化在β抑制蛋白募集和趋化因子清除方面占主导地位。CXCR4的共激活通过释放Gβγ显著增强了GRK2介导的磷酸化。这些结果表明，ACKR3通过一种GRK2依赖性的串扰机制“感知”CXCR4的激活。令人惊讶的是，我们还发现，尽管需要磷酸化，且大多数配体可促进β抑制蛋白募集，但β抑制蛋白对于ACKR3的内化和清除并非必需，这表明这些衔接蛋白的功能尚待确定。
