Klinger Maren, Wang Wenbo, Kuhns Stefanie, Bärenz Felix, Dräger-Meurer Stefanie, Pereira Gislene, Gruss Oliver J
Zentrum für Molekulare Biologie der Universität Heidelberg, 69120 Heidelberg, Germany Molecular Biology of Centrosomes and Cilia Group, Deutsches Krebsforschungszentrum-Zentrum für Molekulare Biologie der Universität Heidelberg Alliance, 69120 Heidelberg, Germany.
Mol Biol Cell. 2014 Feb;25(4):495-507. doi: 10.1091/mbc.E13-09-0526. Epub 2013 Dec 19.
In differentiated human cells, primary cilia fulfill essential functions in converting mechanical or chemical stimuli into intracellular signals. Formation and maintenance of cilia require multiple functions associated with the centriole-derived basal body, from which axonemal microtubules grow and which assembles a gate to maintain the specific ciliary proteome. Here we characterize the function of a novel centriolar satellite protein, synovial sarcoma X breakpoint-interacting protein 2 (SSX2IP), in the assembly of primary cilia. We show that SSX2IP localizes to the basal body of primary cilia in human and murine ciliated cells. Using small interfering RNA knockdown in human cells, we demonstrate the importance of SSX2IP for efficient recruitment of the ciliopathy-associated satellite protein Cep290 to both satellites and the basal body. Cep290 takes a central role in gating proteins to the ciliary compartment. Consistent with that, loss of SSX2IP drastically reduces entry of the BBSome, which functions to target membrane proteins to primary cilia, and interferes with efficient accumulation of the key regulator of ciliary membrane protein targeting, Rab8. Finally, we show that SSX2IP knockdown limits targeting of the ciliary membrane protein and BBSome cargo, somatostatin receptor 3, and significantly reduces axoneme length. Our data establish SSX2IP as a novel targeting factor for ciliary membrane proteins cooperating with Cep290, the BBSome, and Rab8.
在分化的人类细胞中，初级纤毛在将机械或化学刺激转化为细胞内信号方面发挥着重要作用。纤毛的形成和维持需要与中心粒衍生的基体相关的多种功能，轴丝微管从基体生长出来，基体还组装了一个门来维持特定的纤毛蛋白质组。在这里，我们描述了一种新型中心粒卫星蛋白——滑膜肉瘤X断点相互作用蛋白2（SSX2IP）在初级纤毛组装中的功能。我们发现SSX2IP定位于人类和小鼠纤毛细胞中初级纤毛的基体。通过在人类细胞中使用小干扰RNA敲低，我们证明了SSX2IP对于将纤毛病相关卫星蛋白Cep290有效募集到卫星和基体上的重要性。Cep290在将蛋白质转运到纤毛区室中起核心作用。与此一致的是，SSX2IP的缺失极大地减少了BBSome（其功能是将膜蛋白靶向到初级纤毛）的进入，并干扰了纤毛膜蛋白靶向的关键调节因子Rab8的有效积累。最后，我们表明SSX2IP敲低限制了纤毛膜蛋白和BBSome货物生长抑素受体3的靶向，并显著缩短了轴丝长度。我们的数据确定SSX2IP是一种与Cep290、BBSome和Rab8协同作用的新型纤毛膜蛋白靶向因子。
