{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n CXCR1, a high‐affinity G‐protein–coupled receptor for interleukin‐8 (IL-8/CXCL8), mediates a broad range of cellular responses that bridge inflammatory signaling, innate immunity, and tumor biology. It is expressed on diverse cell types—including endothelial cells, neutrophils, osteoclast precursors, monocytes, and certain cancer cells—and transduces IL-8 signals that promote proliferation, survival, chemotaxis, and differentiation. For example, in endothelial cells, engagement of CXCR1 (along with CXCR2) by IL-8 directly enhances cell proliferation, survival, and matrix metalloproteinase production, thereby facilitating angiogenesis and tumor progression."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " Structural studies performed under physiological conditions in lipid bilayers have revealed key domains and conformational features essential for G-protein activation and downstream signaling."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "2"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n In bone, IL-8 acting via CXCR1 promotes osteoclast differentiation and activity; this mechanism has been linked to bone resorption associated with metastatic breast cancer."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": " In the innate immune system, CXCR1 plays a central role in mediating neutrophil responses. Its activation by IL-8 enhances bacterial killing, a vital function that is compromised in conditions such as cystic fibrosis when CXCR1 is cleaved by proteases."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Moreover, in prostate cancer cells, IL-8 signals through CXCR1 to drive androgen-independent proliferation, invasiveness, and chemoresistance, making it an attractive target for therapeutic intervention."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " Regulation of CXCR1 is also crucial for controlling inflammatory cell trafficking; for instance, alterations in its membrane expression—as seen in α-1 antitrypsin deficiency—affect neutrophil chemotaxis and contribute to dysregulated immune responses in lung and liver diseases."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Finally, functional studies reveal that IL-8 activates CXCR1 with distinctive kinetics compared to its counterpart CXCR2. The IL-8 monomer, for example, induces more rapid receptor phosphorylation, desensitization, and internalization via CXCR1, underscoring discrete signaling outcomes from closely related chemokine receptors."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Collectively, these findings position CXCR1 as a critical mediator of IL-8–driven processes—including angiogenesis, immune defense, and cancer cell survival—that warrant further exploration as a potential therapeutic target.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Aihua Li, Seema Dubey, Michelle L Varney, et al. 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