2009年10月9日,，北京生命科學(xué)研究所王曉晨實(shí)驗(yàn)室在PLoS Genetics雜志在線發(fā)表題為“Caenorhabditis elegans Myotubularin MTM-1 Negatively Regulates the Engulfment of Apoptotic Cells”的文章,。該文章報(bào)道了秀麗線蟲肌管素磷酸酶MTM-1負(fù)調(diào)控凋亡細(xì)胞吞噬過(guò)程,。
細(xì)胞凋亡是動(dòng)物發(fā)育中的重要環(huán)節(jié)之一,。其中凋亡細(xì)胞的清除能防止凋亡細(xì)胞中的有害物質(zhì)外泄而傷害正常細(xì)胞,，凋亡細(xì)胞清除缺陷會(huì)導(dǎo)致炎癥和免疫紊亂,。在秀麗線蟲中,，凋亡細(xì)胞會(huì)迅速被相鄰的吞噬細(xì)胞識(shí)別,、吞噬并降解,。已知兩條部分冗余的信號(hào)通路ced-1/6/7/；psr-1/ced-2/5/12/10正調(diào)控該過(guò)程,，但其如何被負(fù)調(diào)控尚不清楚,。
該文章以秀麗線蟲為模式生物，通過(guò)RNA干擾篩選獲得候選基因mtm-1.該基因編碼一個(gè)具有雙特異性的磷酸酶,，可特異地水解PI3P和PI(3,5)P2生成PI和PI5P,。該基因在進(jìn)化上較為保守，人類mtm1基因與線蟲有很高的同源性,。人mtm1基因突變會(huì)導(dǎo)致X染色體連鎖的肌管性疾病,，但其致病機(jī)制尚不清楚。RNA干擾mtm-1可部分減輕ced-1/6/7/2突變體的凋亡細(xì)胞吞噬缺陷,，但ced-5/12/10突變體無(wú)顯著改變,。表明遺傳學(xué)上mtm-1作用于psr-1/ced-2/5/12/10信號(hào)通路并通過(guò)CED-5/12/10復(fù)合體起作用。
該文章利用顯微成像技術(shù),，跟蹤細(xì)胞凋亡的發(fā)生以及凋亡細(xì)胞的持續(xù)時(shí)間,，證明mtm-1調(diào)控凋亡細(xì)胞吞噬而不影響細(xì)胞凋亡的總數(shù)。進(jìn)一步,，利用CED-1:GFP,、ACT-5:GFP、LMP-1:GFP和GFP:RAB-7等熒光蛋白標(biāo)記,，證明mtm-1 RNA干擾可加快ced-1/6/7/2突變體凋亡細(xì)胞吞噬過(guò)程,。
為了研究mtm-1是否通過(guò)調(diào)控PI3P而調(diào)控凋亡細(xì)胞吞噬，該文章檢測(cè)了負(fù)責(zé)生成PI3P的激酶piki-1與vps-34的突變體及雙突變體,，發(fā)現(xiàn)單個(gè)突變體表現(xiàn)出較弱的凋亡細(xì)胞吞噬缺陷表型,，而在雙突變體中表型明顯增強(qiáng)。在兩個(gè)激酶都缺失的遺傳背景下,，mtm-1 RNA干擾不能減輕ced-1/6/7突變體的凋亡細(xì)胞吞噬缺陷表型,，說(shuō)明mtm-1調(diào)控該過(guò)程是依賴于其水解PI3P的磷酸酶功能,。
MTM-1在數(shù)種已知的吞噬細(xì)胞中表達(dá)，并特異的定位在細(xì)胞膜上,。跟蹤熒光蛋白發(fā)現(xiàn)GFP:MTM-1可結(jié)合到凋亡細(xì)胞的吞噬體膜上并在數(shù)十分鐘后與膜分離,。該文章利用特異識(shí)別PI3P的熒光蛋白標(biāo)記YFP:2xFYVE, 發(fā)現(xiàn)在mtm-1突變體的表皮細(xì)胞內(nèi)的膜泡結(jié)構(gòu)上PI3P水平顯著增加。以上結(jié)果表明mtm-1很有可能是通過(guò)調(diào)控細(xì)胞膜上的PI3P水平而影響Rac GTPase CED-10的活性從而實(shí)現(xiàn)對(duì)凋亡細(xì)胞吞噬的調(diào)控,。（生物谷Bioon.com）
相關(guān)鏈接：NIBS王曉晨實(shí)驗(yàn)室招聘博士后
生物谷推薦原始出處：
PLoS Genet 5(10): e1000679. doi:10.1371/journal.pgen.1000679
Caenorhabditis elegans Myotubularin MTM-1 Negatively Regulates the Engulfment of Apoptotic Cells
Wei Zou1,2#, Qun Lu1,2#, Dongfeng Zhao2, Weida Li2, James Mapes3, Yuting Xie2, Xiaochen Wang2*
1 College of Biological Sciences, China Agricultural University, Beijing, China, 2 National Institute of Biological Sciences, Zhongguancun Life Sciences Park, Beijing, China, 3 Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado, United States of America
During programmed cell death, apoptotic cells are recognized and rapidly engulfed by phagocytes. Although a number of genes have been identified that promote cell corpse engulfment, it is not well understood how phagocytosis of apoptotic cells is negatively regulated. Here we have identified Caenorhabditis elegans myotubularin MTM-1 as a negative regulator of cell corpse engulfment. Myotubularins (MTMs) constitute a large, highly conserved family of lipid phosphatases. MTM gene mutations are associated with various human diseases, but the cellular functions of MTM proteins are not clearly defined. We found that inactivation of MTM-1 caused significant reduction in cell corpses in strong loss-of-function mutants of ced-1, ced-6, ced-7, and ced-2, but not in animals deficient in the ced-5, ced-12, or ced-10 genes. In contrast, overexpression of MTM-1 resulted in accumulation of cell corpses. This effect is dependent on the lipid phosphatase activity of MTM-1. We show that loss of mtm-1 function accelerates the clearance of cell corpses by promoting their internalization. Importantly, the reduction of cell corpses caused by mtm-1 RNAi not only requires the activities of CED-5, CED-12, and CED-10, but also needs the functions of the phosphatidylinositol 3-kinases (PI3Ks) VPS-34 and PIKI-1. We found that MTM-1 localizes to the plasma membrane in several known engulfing cell types and may modulate the level of phosphatidylinositol 3-phosphate (PtdIns(3)P) in vivo. We propose that MTM-1 negatively regulates cell corpse engulfment through the CED-5/CED-12/CED-10 module by dephosphorylating PtdIns(3)P on the plasma membrane.
