Essential proto-oncogenic transcriptional regulator necessary for development and differentiation of erythroid and megakaryocytic lineages. Component of a RCOR-GFI-KDM1A-HDAC complex that suppresses, via histone deacetylase (HDAC) recruitment, a number of genes implicated in multilineage blood cell development and controls hematopoietic differentiation. Transcriptional repressor or activator depending on both promoter and cell type context; represses promoter activity of SOCS1 and SOCS3 and thus, may regulate cytokine signaling pathways. Cooperates with GATA1 to repress target gene transcription, such as the apoptosis regulator BCL2L1; GFI1B silencing in leukemic cell lines markedly increase apoptosis rate. Inhibits down-regulation of MYC and MYB as well as the cyclin-dependent kinase inhibitor CDKN1A/P21WAF1 in IL6-treated myelomonocytic cells. Represses expression of GATA3 in T-cell lymphomas and inhibits GATA1-mediated transcription; as GATA1 also mediates erythroid GFI1B transcription, both GATA1 and GFI1B participate in a feedback regulatory pathway controlling the expression of GFI1B gene in erythroid cells. Suppresses GATA1-mediated stimulation of GFI1B promoter through protein interaction. Binds to gamma-satellite DNA and to its own promoter, auto-repressing its own expression. Alters histone methylation by recruiting histone methyltransferase to target genes promoters. Plays a role in heterochromatin formation. Component of a RCOR-GFI-KDM1A-HDAC complex. Interacts directly with RCOR1, KDM1A and HDAC2 (By similarity). Forms a complex with GATA1. Interacts with histone methyltransferases EHMT2 and SUV39H1. Interacts with ARIH2 (via RING-type 2). Interacts with RUNX1T1. Expressed in bone marrow and fetal liver, but also detectable in fetal spleen, fetal thymus, and testes. Detected in hematopoietic stem cells, erythroblasts, and megakaryocytes. Overexpressed in bone marrow of patients with erythroleukemia and megakaryocytic leukemia as well as in their corresponding leukemic cell lines, and markedly repressed in severe aplastic anemia (SAA). By GATA1 which binds to GFI1B promoter in cooperation with the transcription factor NFYA. Target gene of transcription factor E2-alpha/TCF3 that promotes growth arrest and apoptosis in lymphomas. The zinc finger domains are essential for erythroid expansion and acts as an activation domain whereas non finger domain serves as repression domain. The SNAG domain of GFIs is required for nuclear location and for interaction with some corepressors. Methylation at Lys-8 in the SNAG domain seems required for the recruitment of the corepressor complex. The disease is caused by variants affecting the gene represented in this entry. Essential for erythroid differentiation. Binds to target gene promoters and associates with the LSD1-CoREST repressor complex more efficiently than the major isoform 1.