R1, a novel repressor of the human monoamine oxidase A

Monoamine Oxidase catalyzes the oxidative deamination of a number of neurotransmitters. A deficiency in Monoamine Oxidase A results in aggressive behavior in both humans and mice. Studies on the regulation of Monoamine Oxidase A gene expression have shown that the Sp1 family is important for Monoamine Oxidase A expression. To search for novel transcription factors, the sequences of three Sp1 sites in the Monoamine Oxidase A core promoter were used in the yeast one-hybrid system to screen a human cDNA library. A novel repressor, R1 (RAM2), has been cloned. The R1 cDNA encodes a protein with 454 Amino acids and an open reading frame at the 5'-end. The transfection of R1 in a human neuroblastoma cell line, SK-N-BE (2)-C, inhibited the Monoamine Oxidase A promoter and enzymatic activity. The degree of inhibition of Monoamine Oxidase A by R1 correlated with the level of R1 protein expression. R1 was also found to repress Monoamine Oxidase A promoter activity within a natural chromatin environment. A gel-shift assay indicated that the endogenous R1 protein in SK-N-BE (2)-C cells interacted with the R1 binding sequence. R1 also bound directly to the natural Monoamine Oxidase A promoter in vivo as shown by chromatin immunoprecipitation assay. Immunocytochemical analysis showed that R1 was expressed in both cytosol and nucleus, which suggested a role for R1 in transcriptional regulation. Northern blot analysis revealed the presence of endogenous R1 mRNA in human brain and peripheral tissues. Taken together, this study shows that R1 is a novel repressor that inhibits Monoamine Oxidase A gene expression.