肝臓星細胞(ビタミンA貯蔵細胞)の活性化とレチノイン酸受容体の機能

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Hepatic stellate cells (HSCs) store vitamin A and play an important role in liver fibrosis. During fibrogenesis, HSCs are activated and lose vitamin A-containing lipid droplets. However, relevance of retinoid receptor function in liver fibrogenesis is unknown. Here we demonstrate that expression of retinoic acid receptor α (RARα) is up-regulated in activated rat HSCs at a post-transcriptional level. RARα proteins showed a speckled distribution in the cytosol, in spite of their possession of a nuclear localization signal (NLS). Exogenously expressed RARα protein fragments containing an NLS were localized in the nuclei of activated rat HSCs and never colocalized with the endogenous RARα proteins in the cytosol, suggesting that the NLS of endogenous RARα proteins is masked. Biochemical analysis showed that 65% of RARα proteins in activated HSCs were insoluble in a mixture of detergents. This insoluble, speckled cytosolic distribution of RARα proteins may represent a new marker of HSC activation.
2009-10-25