Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.
Department of Biology, Genetics Institute, University of Florida, Gainesville, FL, 32611, USA.
Mol Cell Biochem. 2018 Feb;439(1-2):151-161. doi: 10.1007/s11010-017-3144-4. Epub 2017 Aug 5.
Mammalian hibernation is a state of dormancy that is used by some animals to survive through the unfavorable conditions of winter, and is characterized by coordinated suppression of basal metabolism that is supported by global inhibition of energy/ATP-consuming processes. In this study, we examine the regulation of the anti-proliferatory TGF-β/Smad transcription factor signaling pathway in the liver tissue of the hibernating 13-lined ground squirrel Ictidomys tridecemlineatus. The TGF-β/Smad signaling pathway is known to mediate cell cycle arrest through induction of cell cycle dependent kinase inhibitors, and more recently, has been shown to regulate a wide range of cellular processes via its control of microRNA biosynthesis. We show that phosphorylation levels of the Smad3 protein at its activation residue is increased by ~1.5-fold during torpor, and this is associated with an increase in nuclear localization and DNA binding activity of Smad3. Expression levels of several TGF-β induced microRNAs previously described in human cells were also activated in ground squirrel during torpor. Among these were miR-21, miR-23a, and miR-107, which contain either the conserved R-SBE or R-SBE related motif found in microRNAs that are post-transcriptionally processed by Smad proteins. We show that levels of miR-21 were highly elevated at multiple stages of torpor, and predicted gene targets of miR-21 were enriched to multiple pro-growth cellular processes. Overall, we provide evidence that show the Smad3 transcription factor is activated in ground squirrels during torpor, and suggest a role for this signaling pathway in mediating anti-proliferatory signals via its transcriptional control of cell cycle inhibitors and downstream microRNAs.
哺乳动物冬眠是一种休眠状态，一些动物利用这种状态来度过冬季的不利环境，其特征是基础代谢协同抑制，同时支持能量/ATP 消耗过程的全局抑制。在这项研究中，我们研究了冬眠的十三线地松鼠（Ictidomys tridecemlineatus）肝脏组织中抗增殖 TGF-β/Smad 转录因子信号通路的调节。已知 TGF-β/Smad 信号通路通过诱导细胞周期依赖性激酶抑制剂来介导细胞周期停滞，最近还表明，它通过控制 microRNA 生物合成来调节广泛的细胞过程。我们发现，在蛰伏期间，Smad3 蛋白在其激活残基上的磷酸化水平增加了约 1.5 倍，这与 Smad3 的核定位和 DNA 结合活性增加有关。在蛰伏期间，几种在人类细胞中先前描述的 TGF-β 诱导的 microRNAs 的表达水平在地松鼠中也被激活。其中包括 miR-21、miR-23a 和 miR-107，它们都含有在由 Smad 蛋白转录后加工的 microRNAs 中发现的保守 R-SBE 或 R-SBE 相关基序。我们发现，miR-21 的水平在蛰伏的多个阶段高度升高，并且 miR-21 的预测基因靶标富集到多个促生长的细胞过程中。总体而言，我们提供的证据表明，Smad3 转录因子在蛰伏期间在地松鼠中被激活，并表明该信号通路通过其对细胞周期抑制剂和下游 microRNAs 的转录控制来介导抗增殖信号。
