RhoA controls retinoid signaling by ROCK dependent regulation of retinol metabolism

The ubiquitously expressed small GTPase RhoA is essential for embryonic development and mutated in different cancers. Functionally, it is well described as a regulator of the actin cytoskeleton, but its role in gene regulation is less understood. Using primary mouse keratinocytes with a deletion of the RhoA gene, we have now been exploring how the loss of RhoA affects gene expression. Performing transcription factor reporter assays, we found a significantly decreased activity of a RAR luciferase reporter in RhoA-null keratinocytes. Inhibition of the RhoA effector ROCK in control cells reproduced this phenotype. ATRA and retinal, but not retinol increased RAR reporter activity of keratinocytes with impaired RhoA/ROCK signaling, suggesting that retinol metabolism is regulated by RhoA/ROCK signaling. Furthermore a significant percentage of known ATRA target genes displayed altered expression in RhoA-null keratinocytes. These data reveal an unexpected link between the cytoskeletal regulator RhoA and retinoid signaling and uncover a novel pathway by which RhoA regulates gene expression.

普遍表达的小GTP酶RhoA对胚胎发育至关重要，且在多种癌症中存在突变。从功能上来看，RhoA作为肌动蛋白细胞骨架的调控因子已被广泛研究，但它在基因调控中的作用仍未被充分阐明。本研究利用RhoA基因敲除的原代小鼠角质形成细胞，探究了RhoA缺失对基因表达的影响。通过转录因子报告基因实验，我们发现RhoA敲除的角质形成细胞中，视黄酸受体（retinoic acid receptor, RAR）荧光素酶报告基因的活性显著降低。在对照细胞中抑制RhoA的效应蛋白ROCK（Rho相关蛋白激酶），可重现该表型。全反式维甲酸（all-trans retinoic acid, ATRA）与视黄醛能够增强RhoA/ROCK信号受损的角质形成细胞的RAR报告基因活性，而视黄醇无此作用，这表明视黄醇代谢受RhoA/ROCK信号通路调控。此外，在已知的ATRA靶基因中，有显著比例的基因在RhoA敲除的角质形成细胞中出现表达异常。本研究结果揭示了细胞骨架调控因子RhoA与类视黄醇信号通路之间此前未被发现的联系，并阐明了RhoA调控基因表达的全新通路。