C-X-C chemokine receptor type 4 (R334X variant) (CXCR4-R334X)

C-X-C chemokine receptor type 4 (CXCR4) is a G protein-coupled receptor (GPCR) that plays a pivotal role in the migration and homing of hematopoietic stem cells and leukocytes in response to its ligand, CXCL12 (SDF-1α) (Source: UniProt P61073). The R334X variant is a specific gain-of-function mutation characterized by a nonsense mutation that truncates the C-terminal cytoplasmic tail of the receptor (Source: PubMed PMID: 12730591). This truncation removes critical serine and threonine residues required for G protein-coupled receptor kinase (GRK)-mediated phosphorylation and subsequent beta-arrestin recruitment, which are essential for receptor desensitization and internalization. Consequently, the R334X mutant receptor exhibits prolonged and hyperactive signaling upon ligand binding (Source: NIH/GARD). This molecular defect is the primary cause of WHIM syndrome (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis), where hyper-responsive CXCR4 signaling leads to the excessive retention of neutrophils and other immune cells within the bone marrow, causing peripheral leukopenia. Therapeutic strategies focus on the use of CXCR4 antagonists, such as the FDA-approved mavorixafor, to inhibit this overactive signaling and restore normal leukocyte trafficking and immune function (Source: FDA/X4 Pharmaceuticals).

Other names

WHIM-associated CXCR4CD184 (R334X variant)Fusin (R334X variant)C-X-C motif chemokine receptor 4 (R334X)CXCR4 nonsense mutation R334X

CXCR4 receptor antagonism; these drugs competitively block the binding of the endogenous ligand CXCL12 (SDF-1α) to the hyperactive R334X mutant receptor, thereby normalizing downstream signaling and facilitating the mobilization of leukocytes from the bone marrow into the peripheral circulation (Source: PubMed PMID: 31558487).