Transcriptional coregulator (By similarity). Involved in control of the cell cycle (PubMed:9087427). Also antagonizes transactivation by ZBTB17 and GABP2; represses ZBTB17 activation of the p15(INK4b) promoter and inhibits its ability to recruit p300 (By similarity). Coactivator for EGR2 and GABP2 (By similarity). Tethers the chromatin modifying Set1/Ash2 histone H3 'Lys-4' methyltransferase (H3K4me) and Sin3 histone deacetylase (HDAC) complexes (involved in the activation and repression of transcription respectively) together (By similarity). As part of the NSL complex it may be involved in acetylation of nucleosomal histone H4 on several lysine residues (By similarity). Recruits KMT2E to E2F1 responsive promoters promoting transcriptional activation and thereby facilitates G1 to S phase transition (By similarity). Modulates expression of homeobox protein PDX1, perhaps acting in concert with transcription factor E2F1, thereby regulating pancreatic beta-cell growth and glucose-stimulated insulin secretion (By similarity). May negatively modulate transcriptional activity of FOXO3 (By similarity). Composed predominantly of six polypeptides ranging from 110 to 150 kDa and a minor 300 kDa polypeptide. The majority of N- and C-terminal cleavage products remain tightly, albeit non-covalently, associated. Interacts with POU2F1, CREB3, ZBTB17, EGR2, E2F4, CREBZF, SP1, GABP2, Sin3 HDAC complex (SIN3A, HDAC1, HDAC2, SUDS3), SAP30, SIN3B and FHL2. Component of a MLL1 complex, composed of at least the core components KMT2A/MLL1, ASH2L, HCFC1, WDR5 and RBBP5, as well as the facultative components BAP18, CHD8, DPY30, E2F6, HCFC2, HSP70, INO80C, KANSL1, LAS1L, MAX, MCRS1, MEN1, MGA, KAT8, PELP1, PHF20, PRP31, RING2, RUVBL1, RUVBL2, SENP3, TAF1, TAF4, TAF6, TAF7, TAF9 and TEX10. Component of a THAP1/THAP3-HCFC1-OGT complex that is required for the regulation of the transcriptional activity of RRM1. Interacts directly with THAP3 (via its HBM). Interacts (via the Kelch-repeat domain) with THAP1 (via the HBM); the interaction recruits HCHC1 to the RRM1. Interacts directly with OGT; the interaction, which requires the HCFC1 cleavage site domain, glycosylates and promotes the proteolytic processing of HCFC1 and retains OGT in the nucleus. Component of the SET1 complex, at least composed of the catalytic subunit (SETD1A or SETD1B), WDR5, WDR82, RBBP5, ASH2L, CXXC1, HCFC1 and DPY30. Component of the NSL complex at least composed of MOF/KAT8, KANSL1, KANSL2, KANSL3, MCRS1, PHF20, OGT1/OGT, WDR5 and HCFC1. Component of a complex at least composed of ZNF335, HCFC1, CCAR2, EMSY, MKI67, RBBP5, ASH2L and WDR5; the complex is formed as a result of interactions between components of a nuclear receptor-mediated transcription complex and a histone methylation complex (By similarity). Within the complex interacts with ZNF335 (By similarity). Interacts with TET2 and TET3. Interacts with HCFC1R1. Interacts with THAP11. Interacts (via Kelch domain) with KMT2E (via HBM motif). Interacts with E2F1. HCFC1R1 modulates its subcellular localization and overexpression of HCFC1R1 leads to accumulation of HCFC1 in the cytoplasm. Non-processed HCFC1 associates with chromatin. Colocalizes with CREB3 and CANX in the ER. The HCF repeat is a highly specific proteolytic cleavage signal. The kelch repeats fold into a 6-bladed kelch beta-propeller called the beta-propeller domain which mediates interaction with HCFC1R1. Proteolytically cleaved at one or several PPCE--THET sites within the HCF repeats. Cleavage is promoted by O-glycosylation (By similarity). Further cleavage of the primary N- and C-terminal chains results in a 'trimming' and accumulation of the smaller chains (By similarity). Cleavage is promoted by O-glycosylation (By similarity). O-glycosylated. GlcNAcylation by OGT promotes proteolytic processing. Ubiquitinated. Lys-1862 and Lys-1863 are ubiquitinated both via 'Lys-48'- and 'Lys-63'-linked polyubiquitin chains. BAP1 mediated deubiquitination of 'Lys-48'-linked polyubiquitin chains; deubiquitination by BAP1 does not seem to stabilize the protein.