American journal of physiology. Cell physiology 2017 10 04() ajpcell.00193.2017 doi 10.1152/ajpcell.00193.2017
As an alpha-chemokine receptor specific for stromal-derived-factor-1 (SDF-1, also called CXCL12), CXCR4 plays a vital role in chemotactically attracting lymphocytes during inflammation. CXCR4 also regulates HIV infection due to its role as one of the chemokine co-receptors for HIV entry into CD4+ T cells. Chemokine receptors and their signaling pathways have been shown to be regulated by the process of ubiquitination, a post-translational modification, guided by ubiquitin E3 ligases, which covalently links ubiquitin chains to lysine residues within target substrates. Here we describe a novel mechanism regulating CXCR4 protein levels and subsequent CXCR4/CXCL12 signaling pathway through the ubiquitination and degradation of the receptor in response to ligand stimulation. We identify that an uncharacterized RING finger ubiquitin E3 ligase, RNF113A, directly ubiquitinates CXCR4 in cells, leading to CXCR4 degradation, and therefore disrupts the signaling cascade. We determined that the K331 residue within CXCR4 is essential for RNF113A-mediated ubiquitin conjugation. Overexpression of RNF113A significantly reduces CXCL12-induced kinase activation in HeLa cells, whereas RNF113A knockdown enhances CXCL12-induced downstream signaling. Further, RNF113A expression and silencing directly affects cell motility in a wound healing assay. These results suggest that RNF113A plays an important role in CXCR4 signaling through the ubiquitination and degradation of CXCR4. This mechanistic study might provide new understanding of HIV immunity and neutrophils activation and motility regulated by CXCR4.