Functions as a transcriptional repressor. Seems to function as a transcriptional corepressor in neuronal cells through recruitment of HDAC3 and HDAC4. Contributes to tumor progression, and tumor cell proliferation and survival. This may be mediated at least in part through repressing transcriptional activity of GADD45GIP1. Required for recruiting the proteasome from the nucleus to the cytoplasm and dendritic spines. {ECO:0000269|PubMed:17130457, ECO:0000269|PubMed:17804717}. This is the function of NACC1 (nucleus accumbens associated 1, Ensembl gene identifier ENSG00000160877).