上海生化与细胞所连发Nature，Cell子刊文章揭示分子机制

　　

生物通报道：来自中科院上海生命科学研究院生化与细胞所宋保亮研究组，李伯良研究组，以及朱学良研究组的研究人员分别发表了题为“Ablation of gp78 in Liver Improves Hyperlipidemia and Insulin Resistance by Inhibiting SREBP to Decrease Lipid Biosynthesis”等两篇文章，解析了泛素连接酶gp78调控脂质代谢的机理，以及小RNA调控纤毛发生的机制，相关成果公布在Cell Metabolism和Nature Cell Biology杂志上。

胆固醇等脂质小分子具有重要的生物学功能，但过量的胆固醇会引起动脉粥样硬化，进而导致冠心病和脑中风等一系列严重的疾病。因此，体内脂质水平必须受到严密而精准的调控。

泛素连接酶是将泛素分子（一种小蛋白，它的主要功能是标记需要分解掉的蛋白质）连接到目的蛋白质，使其被降解的酶。gp78作为一个泛素连接酶，能调控胆固醇代谢过程中的一些重要蛋白质的降解。由于肝脏是脂质代谢的重要器官，为了探究gp78的生理功能，宋保亮与李伯良研究组在小鼠肝脏中特异性敲除了gp78基因。

博士研究生柳童斐等研究发现，gp78基因缺失的小鼠消瘦，脂肪含量减少，能够显著抵抗高脂饮食和年龄诱导的肥胖，并且表现为胰岛素敏感性增强。其分子机制在于一方面减少了胆固醇与脂肪酸等脂质合成，另一方面促进大量葡萄糖和脂肪酸等营养物质的消耗。这项研究发现了脂质合成与能量代谢之间的联系，并提示gp78可作为治疗肥胖、糖尿病等代谢疾病的靶标。

另外，朱学良研究组研究生曹景利、沈义栋和副研究员鄢秀敏等发现，一种叫做miR-129-3p的小RNA能够以不依赖于细胞周期的方式在体外培养的哺乳类细胞中诱导初级纤毛的发生，并阐明了其作用机理。

纤毛(cilium)是广泛分布于动物组织中的一种突出于细胞表面的细胞器，根据功能的不同可分为初级纤毛和动纤毛两类，前者负责多种重要信号通路的传递，后者则是细胞的一种运动器官。纤毛的发生首先需要将母中心粒（mother centriole）转变成基体（basal body），而这一过程需要将CP110蛋白从母中心粒上去除；另外，微丝的变化对纤毛发生也很重要，但是目前尚不清楚这两个过程是如何被调控的。小RNA（microRNA）则是近年来发现的能通过结合信使RNA尾部非翻译区来抑制其编码的蛋白质水平的一种非编码RNA。

研究人员发现miR-129-3p通过下调中心体蛋白质CP110和四个分枝状微丝的调节因子的蛋白质水平，从而促进母中心体向基体的转换和与纤毛形成相关的囊泡在基体周围的富集，最终促进纤毛的发生和延伸。小鼠中，miR-129-3p在富含初级纤毛的脑、视网膜、肾脏等组织中高表达。利用模式生物斑马鱼，研究证明miR-129-3p调节斑马鱼发育过程中的纤毛发生。抑制miR-129-3p会引起斑马鱼身体弯曲、心包囊水肿、内脏左右不对称性紊乱等典型的纤毛病征，纤毛的长度和数目也明显减少。

这些发现不仅揭示小RNA可以调控初级纤毛的发生，提示miR-129-3p的突变可能也是人类纤毛病的病因之一，而且还明确地把纤毛发生与分枝状微丝形成的抑制联系起来。此外，由于去掉培养基中的血清（血清饥饿）也能抑制分枝状微丝的产生，这些研究结果部分地解释了血清饥饿可高效诱导培养细胞产生纤毛的原因。

（生物通：万纹）

原文摘要：

Ablation of gp78 in Liver Improves Hyperlipidemia and Insulin Resistance by Inhibiting SREBP to Decrease Lipid Biosynthesis

gp78 is a membrane-anchored ubiquitin ligase mediating the degradation of HMG-CoA reductase (HMGCR) and Insig-1. As a rate-limiting enzyme in cholesterol biosynthesis, HMGCR undergoes rapid sterol-promoted degradation. In contrast, destruction of Insig-1 releases its inhibition on SREBP and stimulates the expression of lipogenic genes. Thus, gp78 has opposite effects on lipid biosynthesis. We here generated liver-specific gp78 knockout (L-gp78/) mice and showed that although the degradation of HMGCR was blunted, SREBP was suppressed due to the elevation of Insig-1/-2, and therefore the lipid biosynthesis was decreased. The L-gp78/ mice were protected from diet-/age-induced obesity and glucose intolerance. The livers of L-gp78/ mice produced more FGF21, which activated thermogenesis in brown adipocytes and enhanced energy expenditure. Together, the major function of gp78 in liver is regulating lipid biosynthesis through SREBP pathway. Ablation of gp78 decreases the lipid levels and increases FGF21, and is beneficial to patients with metabolic diseases.

miR-129-3p controls cilia assembly by regulating CP110 and actin dynamics

Ciliogenesis requires the removal of CP110 from the mother centriole; actin dynamics also influence ciliation, at least partly by affecting the centrosomal accumulation of ciliogenic membrane vesicles. How these distinct processes are properly regulated remains unknown. Here we show that miR-129-3p, a microRNA conserved in vertebrates, controlled cilia biogenesis in cultured cells by concomitantly downregulating CP110 and repressing branched F-actin formation. Blocking miR-129-3p inhibited serum-starvation-induced ciliogenesis, whereas its overexpression potently induced ciliation in proliferating cells and also promoted cilia elongation. Gene expression analysis further identified ARP2, TOCA1, ABLIM1 and ABLIM3 as its targets in ciliation-related actin dynamics. Moreover, miR-129-3p inhibition in zebrafish embryos suppressed ciliation in Kupffer’s vesicle and the pronephros, and induced developmental abnormalities including a curved body, pericardial oedema and defective left–right asymmetry. Therefore, our results reveal a mechanism that orchestrates both the centriole-to-basal body transition and subsequent cilia assembly through microRNA-mediated post-transcriptional regulation.