{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n CBX4 is a multifunctional Polycomb group protein that integrates epigenetic gene regulation with enzymatic activity as a SUMO E3 ligase to modulate diverse cellular processes. In several cancer models, CBX4 has been shown to enhance oncogenic signaling—for instance, in hepatocellular carcinoma it promotes hypoxia‐induced vascular endothelial growth factor (VEGF) expression by enhancing HIF‐1α sumoylation, with high CBX4 levels (particularly when localized in the cytoplasm) correlating with aggressive tumor behavior and poor patient survival."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " In contrast, in colorectal carcinoma CBX4 functions in a tumor‐suppressive manner by recruiting histone deacetylase 3 (HDAC3) to maintain a deacetylated promoter state of Runx2, thereby repressing its expression and inhibiting cell migration and invasion."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "3"}]}, {"type": "t", "text": " In osteosarcoma, CBX4 promotes metastasis through transcriptional upregulation of Runx2 via recruitment of the acetyltransferase GCN5, with its stability regulated by phosphorylation‐dependent ubiquitination."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Beyond its roles in cancer, CBX4 is critical for maintaining stem cell properties and proper tissue development. In human mesenchymal and epidermal stem cells, CBX4 sustains nucleolar homeostasis and preserves a slow‐cycling, undifferentiated state—thereby protecting against premature senescence."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " Moreover, in the developing thymic epithelium, CBX4 is indispensable for organogenesis, acting in concert with the transcription factor p63 to ensure proper thymic architecture and thymocyte development."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Mechanistically, CBX4 exerts its regulatory functions both as part of PRC1‐mediated chromatin repression and through its SUMO E3 ligase activity. It directly catalyzes the SUMOylation of various substrates, including Dnmt3a—thereby modulating its role in DNA methylation"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "8"}]}, {"type": "t", "text": ", as well as hnRNP K and TP53INP1 to facilitate p53‐dependent transcription and stress responses."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": " In addition, genetic models in which SENP2—a SUMO‐specific protease—is deleted show an accumulation of SUMOylated CBX4 at target gene promoters, underscoring the importance of a balanced SUMO conjugation/deconjugation cycle in controlling its activity."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "11"}]}, {"type": "t", "text": " Finally, genomic studies have revealed focal amplifications of CBX4 in esophageal squamous cell carcinoma, further implying its relevance in tumorigenesis."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "12"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "t", "text": "\n Collectively, these findings underscore that CBX4 functions as a versatile regulator—combining chromatin‐mediated transcriptional repression with SUMOylation of key regulatory proteins—to control cell proliferation, differentiation, senescence, and tumor progression. Its context‐dependent activities highlight CBX4 as a potential therapeutic target in cancer and other aging‐associated disorders.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Jie Li, Ying Xu, Xi-Dai Long, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Cbx4 governs HIF-1α to potentiate angiogenesis of hepatocellular carcinoma by its SUMO E3 ligase activity."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Cancer Cell (2014)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.ccr.2013.12.008"}], "href": "https://doi.org/10.1016/j.ccr.2013.12.008"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "24434214"}], "href": "https://pubmed.ncbi.nlm.nih.gov/24434214"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Boqing Wang, Jianjun Tang, Dan Liao, et al. 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