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chromodomain of chromobox homolog 4 CHRomatin Organization Modifier (chromo) domain of chromobox homolog 4 (CBX4), a component of the PcG repressive complex PRC1, one of the two classes of PRCs. PcG proteins form large multiprotein complexes (PcG bodies) which are involved in the stable repression of genes involved in development, signaling or cancer via chromatin-based epigenetic modifications. Mammalian PRC1 includes canonical (cPRC1) and non-canonical complexes; cPRC1, contains four core subunits including one CBX protein (CBX2, CBX4, and CBX6-CBX8) that binds H3K27me3. CBX family members have different affinity for H3K27me3, with CBX7 having the highest binding capability. The human CBX proteins show distinct nuclear localizations and contribute differently to transcriptional repression. Some CBX proteins of the PRC1 complex have been implicated in transcriptional activation as well as in PRC1-independent roles in embryonic stem cells and in somatic cells. In addition to a chromodomain with H3K27me3-binding activity, Cbx4 contains two SUMO-interacting motifs responsible for its small ubiquitin-related modifier (SUMO) E3 ligase activity. CBX proteins may act as an oncogene or tumor suppressor in a cell-type-dependent manner, for example CBX8 promotes proliferation while suppressing metastasis, in colorectal carcinoma progression. CBX4 may serve as a tumor suppressor in colorectal carcinoma, and has been shown to be an oncogene in osteosarcoma and breast cancer. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",