The function of CXCR4 (C-X-C motif chemokine receptor 4, ENSG00000121966) is as follows. Receptor for the C-X-C chemokine CXCL12/SDF-1 that transduces a signal by increasing intracellular calcium ion levels and enhancing MAPK1/MAPK3 activation (PubMed:10074102, PubMed:10452968, PubMed:10644702, PubMed:10825158, PubMed:18799424, PubMed:20048153, PubMed:20505072, PubMed:24912431, PubMed:28978524, PubMed:8752280, PubMed:8752281). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors, such as adenylate cyclase (PubMed:16725153, PubMed:17197449, PubMed:18799424, PubMed:39093700). CXCR4 is coupled to G(i) G alpha proteins and mediates inhibition of adenylate cyclase (PubMed:17197449, PubMed:39093700). Involved in the AKT signaling cascade (PubMed:24912431). Plays a role in regulation of cell migration, e.g. during wound healing (PubMed:28978524). Also acts as a receptor for extracellular ubiquitin; leading to enhanced intracellular calcium ions and reduced cellular cAMP levels (PubMed:20228059). Binds bacterial lipopolysaccharide (LPS) et mediates LPS-induced inflammatory response, including TNF secretion by monocytes (PubMed:11276205). Involved in hematopoiesis and in cardiac ventricular septum formation (By similarity). Also plays an essential role in vascularization of the gastrointestinal tract, probably by regulating vascular branching and/or remodeling processes in endothelial cells (By similarity). Involved in cerebellar development; in the CNS, could mediate hippocampal-neuron surviva (By similarity). {ECO:0000250|UniProtKB:P70658, ECO:0000269|PubMed:10074102, ECO:0000269|PubMed:10452968, ECO:0000269|PubMed:10644702, ECO:0000269|PubMed:10825158, ECO:0000269|PubMed:11276205, ECO:0000269|PubMed:16725153, ECO:0000269|PubMed:17197449, ECO:0000269|PubMed:18799424, ECO:0000269|PubMed:20048153, ECO:0000269|PubMed:20228059, ECO:0000269|PubMed:20505072, ECO:0000269|PubMed:24912431, ECO:0000269|PubMed:28978524, ECO:0000269|PubMed:39093700, ECO:0000269|PubMed:8752280, ECO:0000269|PubMed:8752281}. (Microbial infection) Acts as a coreceptor (CD4 being the primary receptor) for human immunodeficiency virus-1/HIV-1 X4 isolates and as a primary receptor for some HIV-2 isolates. Promotes Env- mediated fusion of the virus (PubMed:10074122, PubMed:10756055, PubMed:8849450, PubMed:8929542, PubMed:9427609). {ECO:0000269|PubMed:10074122, ECO:0000269|PubMed:10756055, ECO:0000269|PubMed:8849450, ECO:0000269|PubMed:8929542, ECO:0000269|PubMed:9427609}.