ISX (intestine-specific homeobox) is a transcription factor that regulates gene expression in intestinal tissues and plays critical roles in both normal physiology and disease pathogenesis. Primary Function: ISX functions as an IL-6-inducible transcription factor that binds sequence-specific DNA elements to regulate RNA polymerase II-mediated transcription 1. In normal intestinal physiology, ISX regulates carotenoid metabolism by controlling BCO2 expression and SR-B1 regulation in enterocytes, serving as a gatekeeper for dietary carotenoid bioavailability 2. Additionally, ISX influences enteroendocrine cell differentiation pathways 3. Mechanism: ISX mediates transcriptional regulation through protein acetylation-dependent mechanisms; PCAF-mediated acetylation of ISX at lysine 69 recruits BRD4 to promoters of target genes, initiating chr22 remodeling and histone acetylation 4. Disease Relevance: ISX is implicated in multiple malignancies. In hepatocellular carcinoma, ISX orchestrates a feed-forward loop integrating inflammation, tryptophan catabolism, and immune suppression via IDO1-kynurenine-AHR signaling, promoting PD-L1-mediated CD8+ T-cell suppression 15. ISX drives proliferation through cyclin D1 induction 5 and regulates epithelial-mesenchymal transition, promoting metastasis 4. In pancreatic ductal adenocarcinoma and gastric carcinoma, ISX correlates with poor survival and promotes invasiveness and cell proliferation 67. Clinical Significance: ISX expression negatively correlates with patient survival across multiple cancer types and represents a potential therapeutic target 16.