Transcriptional corepressor. Corepressor of MTG8 transcriptional repression. Has some intrinsic repression activity which is independent of the number of the poly-Q repeats (By similarity). Recruits NR2E1 to repress transcription. Promotes vascular smooth cell (VSMC) migration and orientation. Interacts with BAIAP2, WWP1, WWP2, WWP3 and RERE. Interacts (via its N-terminus) with MTG8; the interaction enhances transcriptional repression of MTG8. Interacts with PQBP1 (By similarity). Interacts with NR2E1; the interaction represses the transcriptional activity of NR2E1. Interacts with FAT1 (via a C-terminal domain). Shuttles between nucleus and cytoplasm. Colocalizes with FAT1 in the perinuclear area, at cell-cell junctions and leading edges of cells. Colocalizes with MTG8 in discrete nuclear dots (By similarity). Widely expressed. Most abundant in the brain. Expressed as early as 5 days and thereafter shows little variation throughout 17 days. In vascular smooth muscle, induced by angiotensin II, FGF; PGF and IL1B. Phosphorylated in vitro by MAPK8/JNK1 on Ser-724. The poly-Gln region of Atn1 is polymorphic (3 to 8 repeats). The mouse model of DRPLA with 129 CAG repeats (Q129) exhibited severe neurological defects similar to those of juvenile-onset DRPLA patients including age-dependent and region-specific presynaptic dysfunction in the globus pallidus and cerebellum. Progressive shrinkage of distal dendrites of Purkinje cells and decreased currents through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and gamma-aminobutyrate type A receptors in CA1 neurons was observed. There is progressive brain atrophy.