Acts as a transcriptional repressor (PubMed:12724404). May function in the assembly and/or enzymatic activity of the Sin3A corepressor complex or in mediating interactions between the complex and other regulatory complexes (PubMed:12724404). Plays a role in the regulation of epigenetic modifications at the PWS/AS imprinting center near the SNRPN promoter, where it might function as part of a complex with RB1 and ARID4A. Involved in spermatogenesis, together with ARID4A, where it functions as a transcriptional coactivator for AR (androgen receptor) and enhances expression of genes required for sperm maturation. Regulates expression of the tight junction protein CLDN3 in the testis, which is important for integrity of the blood-testis barrier. Plays a role in myeloid homeostasis where it regulates the histone methylation state of bone marrow cells and expression of various genes involved in hematopoiesis. May function as a leukemia suppressor (By similarity). Component of a Sin3A corepressor complex consisting of SIN3A, SAP130, SUDS3/SAP45, SAP180, HDAC1 and HDAC2 (PubMed:12724404). Interacts with ARID4A (PubMed:17043311). Interacts with AR (By similarity). Cytoplasmic in breast cancer cells. Highly expressed in the testis and in breast, lung, colon, pancreatic and ovarian cancers. Expressed at low levels in the thymus, prostate and ovary. The C-terminus mediates interaction with mSin3A corepressor complex. The N-terminus is involved in transcriptional repression by HDAC-independent mechanisms. The ARID domain is involved in stabilizing the mSin3A corepressor complex on DNA.