The POZ/BTB protein NAC1 interacts with two different histone deacetylases in neuronal-like cultures

NAC1 is a cocaine-regulated POZ/BTB (Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad complex) protein. NAC1 is increased by cocaine selectively in the nucleus accumbens, a CNS region important for drug addiction. NAC1's role in the cell, however, is not known. Each of the two NAC1 isoforms, sNAC1 (short NAC1) and INAC1 (long NAC1), may serve as corepressors for other POZ/BTB proteins. This study investigated whether sNAC1 and INAC1 demonstrated protein-protein interactions with other corepressors. Histone deacetylase (HDAC) inhibition reversed sNAC1 and INAC1 repression of Gal4 luciferase, but only in neuronal-like cultures. Because these inhibitors do not distinguish among histone deacetylases, two histone deacetylases were selected for further study. HDAC 3 and 4 both demonstrated protein-protein interactions with sNAC1 and INAC1. This was shown using coimmunoprecipitations, glutathione-S-transferase (GST) pullclowns and mammalian two-hybrids. Importantly, either the POZ domain or NAC1 without the POZ domain can bind these two HDACs. Other corepressors, specifically NCoR (nuclear receptor corepressor), SMRT (silencing mediator for retinoid and thyroid hormone receptor) and mSin3a, do not exhibit protein-protein interactions with sNAC1 and INAC1. None showed protein-protein interactions in GST pullclowns or mammalian two-hybrids. Taken together, the results of these experiments indicate sNAC1 and INAC1 recruit histone deacetylases for transcriptional repression, further enhancing POZ/BTB protein mediated repression.