The cellular protein La functions in enhancement of virus release through lipid rafts facilitated by murine leukemia virus glycosylated Gag.
The cellular protein La functions in enhancement of virus release through lipid rafts facilitated by murine leukemia virus glycosylated Gag.
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作者：
Nitta T;Tam R;Kim JW;Fan H
小鼠白血病病毒（MuLV）编码两种形式的Gag多蛋白：病毒核心蛋白的前体（Moloney MuLV [M-MuLV]的Pr 65 gag）和更长的糖基化形式（glyco-gag或gPr 80 gag）。gPr 80 gag由与Pr 65 gag相同的未剪接病毒RNA翻译而来，来自上游符合读框的CUG起始密码子。因此，gPr 80 gag含有88个独特的N-末端氨基酸，其包括将gPr 80 gag引导到粗面内质网中的信号肽，在粗面内质网中，其被糖基化，输出到细胞表面，并切割成55和40 kDa的两种蛋白质。氨基末端55-kDa蛋白保持与暴露于胞质溶胶的88个独特氨基酸相关的细胞。我们先前表明，gPr 80 gag通过脂筏促进有效的M-MuLV释放。在本报告中，我们发现gPr 80 gag的独特N-末端结构域足以促进转染的293 T细胞释放增强的M-MuLV颗粒。对参与gPr 80 gag功能的细胞蛋白的搜索导致细胞La蛋白。过表达的小鼠或人的La增强M-MuLV颗粒释放的情况下，glyco-gag，和释放的病毒有一个降低的浮力密度增加的胆固醇含量的特点。此外，小干扰RNA（siRNA）敲低人La废除glyco-gag增强M-MuLV释放。这些结果暗示La作为参与M-MuLV glyco-gag功能的细胞蛋白。我们还发现，小鼠或人La的过表达可以增强HIV-1的释放，在gPr 80 gag的情况下。因此，M-MuLV和HIV-1可能共享通过涉及La的脂筏释放的途径。逆转录病毒会引起白血病和艾滋病等疾病。病毒复制的一个重要方面是病毒如何从受感染的细胞中释放出来。我们以前发现，由小鼠白血病病毒（MuLVs）编码的一种独特的蛋白质，glyco-gag（或gPr 80 gag），通过称为脂筏的富含胆固醇的膜亚结构域增强了病毒的有效释放。在这项研究中，我们发现gPr 80 gag的N-末端结构域足以增强病毒释放。对参与gPr 80 gag功能的细胞蛋白的搜索导致了细胞La蛋白。La的过表达模拟了glyco-gag增强M-MuLV释放的作用，而La的敲低则消除了glyco-gag的功能。M-MuLV glyco-gag也增强了HIV-1的释放，在glyco-gag不存在的情况下过表达La也是如此。因此，M-MuLV和HIV-1可能共享通过涉及La的脂筏释放的细胞途径。这些结果也可能与通过脂筏释放的其他病毒相关。
Murine leukemia viruses (MuLVs) encode two forms of Gag polyprotein: the precursor for the viral core proteins (Pr65gag for Moloney MuLV [M-MuLV]) and a longer glycosylated form (glyco-gag, or gPr80gag). gPr80gag is translated from the same unspliced viral RNA as Pr65gag, from an upstream in-frame CUG initiation codon. As a result, gPr80gag contains 88 unique N-terminal amino acids that include a signal peptide that conducts gPr80gag into the rough endoplasmic reticulum, where it is glycosylated, exported to the cell surface, and cleaved into two proteins of 55 and 40 kDa. The amino-terminal 55-kDa protein remains cell associated with the 88 unique amino acids exposed to the cytosol. We previously showed that gPr80gag facilitates efficient M-MuLV release through lipid rafts. In this report, we found that the unique N-terminal domain of gPr80gag is sufficient to facilitate enhanced M-MuLV particle release from transfected 293T cells. A search for cellular proteins involved in gPr80gag function led to cellular La protein. Overexpression of mouse or human La enhanced M-MuLV particle release in the absence of glyco-gag, and the released virus had a reduced buoyant density characteristic of increased cholesterol content. Moreover, small interfering RNA (siRNA) knockdown of human La abolished glyco-gag enhancement of M-MuLV release. These results implicate La as a cellular protein involved in M-MuLV glyco-gag function. We also found that overexpression of mouse or human La could enhance HIV-1 release in the absence of gPr80gag. Therefore, M-MuLV and HIV-1 may share a pathway for release through lipid rafts involving La. Retroviruses cause diseases such as leukemia and AIDS. An important aspect of viral replication is how viruses are released from infected cells. We previously found that a unique protein encoded by murine leukemia viruses (MuLVs), glyco-gag (or gPr80gag), enhances efficient virus release through cholesterol-rich membrane subdomains called lipid rafts. In this study, we found that the N-terminal domain of gPr80gag is sufficient to enhance viral release. A search for cellular proteins that participate in gPr80gag function led to cellular La protein. Overexpression of La phenocopied glyco-gag in enhancing M-MuLV release, and knockdown of La abolished glyco-gag function. M-MuLV glyco-gag also enhanced release of HIV-1, as did overexpression La in the absence of glyco-gag. Thus, M-MuLV and HIV-1 may share a cellular pathway for release through lipid rafts involving La. These results may also be relevant for other viruses that are released through lipid rafts.