Orphan nuclear receptors as potential transcriptional regulators of the proopiomelanocortin (POMC) gene in the hypothalamus

DE SOUZA FS; LEVI DH; BUMASCHNY VF; MACKENZIE RG; LOW MJ; RUBINSTEIN M

San Diego, California, E. E. U. U.

Congreso; 37th annual meeting of the Society for Neuroscience; 2007

Society for Neuroscience

The prohormone proopiomelanocortin (POMC) gives rise to a series of bioactive peptides and is expressed mainly in the pituitary gland and the arcuate nucleus of the hypothalamus. In the brain, POMC-derived melanocortins and â-endorphin participate in the regulation of energy balance and pain sensitivity. We have recently shown that POMC expression in the mammalian hypothalamus depends on the activity of two enhancers, nPE1 and nPE2, located more than 10 kb upstream of the POMC basal promoter. We have also shown that two 45-bp subregions within nPE2 are essential for enhancer activity in transgenic mice. In the present study, we used critical sequences of nPE2 as baits to isolate transcription factors present in a mouse brain cDNA expression library. Following a yeast one-hybrid screening we identified four different members of the nuclear orphan receptors family. Microarray data performed on a laser-capture microscopy enriched population of POMC arcuate neurons, immunohistochemistry and in situ hybridisation studies indicate that at least one of the factors, COUP-TFII (Nr2f2), is expressed in POMC hypothalamic neurons. Fine mapping of the binding site by gel shift using recombinant proteins revealed that COUP-TFs bind to a 5-bp site present in the middle of nPE2 which matches the consensus for a COUP-TF half-site. Gel shift experiments with nuclear extracts from rat and mouse brain show that proteins present in rodent brain can also bind to this site. Our results strongly suggest that transcription factors of the orphan nuclear receptor family control POMC expression in the mammalian hypothalamus and represent a first step towards elucidating the transcriptional code of POMC in the brain.