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Title: The Nuclear Transcription Factor RAR Associates with Neuronal RNA Granules and Suppresses Translation

Author
item Onisko, Bruce
item CHEN, NA - UCB
item NAPOLI, JOSEPH - UCB

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2008
Publication Date: 5/21/2008
Citation: Onisko, B.C., Chen, N., Napoli, J. 2008. The Nuclear Transcription Factor RAR Associates with Neuronal RNA Granules and Suppresses Translation. Journal of Biological Chemistry. 283(30):20841-20847.

Interpretive Summary: Prions destroy brain cells and lead to death. The prion protein occurs naturally and is involved in long term memory. In this collaborative research we studied the mechanism of hippocampal brain cell loss due to deficiency in Vitamin A. A novel role for Vitamin A was discovered. It was found to act by preventing translation of messenger RNAs in dendrites of neurons.

Technical Abstract: All-trans-retinoic acid stimulates dendritic growth in hippocampal neurons within minutes by activating mitogen-activated protein kinase and mTOR and increasing dendritic translation of calcium calmodulin-dependent protein kinase II alpha and the alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate receptor subunit GluR1. Hippocampal neurons express RARalpha in dendrites, and knocking down RARalpha prevents all-trans-retinoic acid effects on dendritic growth. Here we show, by liquid chromatography/mass spectrometry analysis of immunoaffinity isolates of hippocampal neurons, that RARalpha partners with many RNA-binding proteins and translation factors conveyed in dendritic RNA transport granules, including the purine-rich element-binding protein, Pur alpha. The interaction of RARalpha with Pur alpha, an RNA-binding protein required for dendritic RNA transport, and other RNA-binding proteins was confirmed by tandem affinity purification. Confocal microscopy confirmed localization of neuronal RARalpha in dendritic RNA granules with Pur alpha and FMRP (the fragile x mental retardation protein). Hippocampal RARalpha also associates with mRNA, e.g. encoding GluR1 and calcium calmodulin-dependent protein kinase II alpha. Consistent with a granule function of conveying translationally silenced mRNA, RARalpha inhibits translation initiation, independent of 7-methylguanylate cap or poly(A) tail, and prompts mRNA redistribution to silencing ribonucleoprotein particles. These data afford a mechanism for rapid stimulation of dendritic growth by all-trans-retinoic acid and reveal that the ligand-dependent transcription factor RARalpha also regulates translation.