Functions as a transcriptional repressor. Isoform 1 is a stronger transcriptional repressor than isoform 2. 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. Homooligomer; mediated by the BTB domain (By similarity). Both isoforms interact with HDAC3 and HDAC4. Interacts (via BTB domain) with CUL3, PSMD7 AND RCOR1. Punctate distribution in nucleus. In differentiated PC12 cells diffusely distributed in the cytoplasm and is dependent on phosphorylation. Highly expressed in the hippocampus, brain cortex, cerebellum and brainstem. Expressed in the nucleus accumbens, olfactory tubercle, the striatum, frontal and parietal cortex and ventral pallidum. Weakly expressed in the heart, liver, kidney, spleen, testis, and skeletal muscle. Isoform 2 is expressed in the brain and liver, less abundantly expressed in the brain than isoform 1. Expressed in the brain at E16, E18, P2, P8 and P90. Expression is increased by cocaine, selectively in the nucleus accumbens. mRNA is present at increased levels in the nucleus accumbens 3 weeks after withdrawal from cocaine self-administration. Phosphorylated by protein kinase C (PKC).