Cell biology of osteoclasts: GTPases, exchange factors and actin dynamics during bone degradation

破骨细胞是一种多核细胞，专门从事骨降解。为了消化骨，它们需要粘附在骨表面，通过将富含肌动蛋白的足体重组成紧密的带来建立密封区，并修改膜运输的关键步骤。我们的建议集中在FGD 6，Rho鸟嘌呤交换因子强烈上调成骨过程中。我们的初步研究结果表明，FGD 6调节足体的形成和潜在的本地化的内体周围的足体带。为了理解FGD 6的功能，有必要1）在真实的时间内研究其动态行为，2）仔细说明内源性FGD 6耗尽的破骨细胞的表型，3）说明FGD 6的PH和FYVE磷酸肌醇结合结构域如何有助于其功能，4）鉴定FGD 6结合配偶体，特别是活化的RhoGT 3，和5）理解FGD 6活化和/或定位如何受到Src和PI-3激酶信号传导的影响。我们想要检验的假设是FGD 6通过其PH结构域与质膜的PI（3，4，5）P3之间的相互作用控制足体动力学，以及通过其FYVE结构域与早期内体的PI 3-P之间的相互作用控制足体带周围的早期内体的定位，这些过程可能受Src依赖性磷酸化调节。这些研究应该为其他RhoGEFs的功能探索铺平道路，这些RhoGEFs像FGD 6一样在破骨细胞生成过程中强烈上调。

Osteoclasts are multinucleated cells specialized in bone degradation. To digest bone, they need to adhere onto its surface, to build a sealing zone by reorganizing their actin-rich podosomes into tight belts and to modify key steps of membrane traffic. Our proposal focuses on FGD6, a Rho guanine exchange factor strongly upregulated during osteolastogenesis. Our preliminary results indicate that FGD6 regulates podosome formation and potentially the localization of endosomes around podosomal belts. To understand FGD6 function, it will be necessary 1) to study its dynamic behavior in real time, 2) to carefully illustrate the phenotype of osteoclasts depleted in endogenous FGD6, 3) to illustrate how the PH and FYVE phosphoinositide binding domains of FGD6 contribute to its function 4) to identify the FGD6 binding partners, in particular the activated RhoGTPase, and 5) to understand how FGD6 activation and/or localization can be affected by Src and PI-3 kinase signaling. The hypothesis that we want to test is that FGD6 controls podosome dynamics via interactions between its PH domains and PI(3,4,5)P3 of the plasma membrane as well as the localization of early endosomes around podosomal belts via interactions between its FYVE domain and PI3-P of early endosomes, processes that might be regulated by Src-dependent phosphorylation. These studies should pave the way for the functional exploration of other RhoGEFs, which like FGD6 are strongly upregulated during osteoclastogenesis.