E6A-P-dependent degradation of DLG4/PSD95 by high-risk human papillomavirus type 18 E6 protein
E6A-P-dependent degradation of DLG4/PSD95 by high-risk human papillomavirus type 18 E6 protein
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DOI：
10.1128/jvi.01712-06
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发表时间：
2007-02-01
影响因子：
5.4
通讯作者：
Kiyono, Tohru
中科院分区：
文献类型：
--
作者：
Handa, Keisuke;Yugawa, Takashi;Kiyono, Tohru
在大多数宫颈癌中，高危嗜粘性人乳头瘤病毒(HPV)的DNA，如16型和18型，保持不变，以表达两种病毒蛋白E6和E7，表明它们在肿瘤发生中发挥重要作用。事实上，E6蛋白的羧基末端PDZ结构域结合基序对于转化啮齿动物细胞和诱导E6转基因小鼠皮肤的增殖是必不可少的。到目前为止，包括DLG1/hDLG在内的7种含有PDZ结构域的蛋白已被确定为高危HPV E6蛋白的靶点。DLG1/hDLG是果蝇盘状大肿瘤抑制因子(DIG)的人类同源物。在这里，我们描述了DLG4/PSD95，另一个人类DIG同源物，作为一个新的E6靶点。研究发现，DLG4在包括宫颈角质形成细胞在内的正常人细胞中有表达，但在HPV阳性和HPV阴性的宫颈癌细胞株中仅有有限的表达。HPV18 E6在HCK1T中的表达比HPV16 E6更显著地降低DLG4的水平，而HPV16 E6是蛋白质的羧基末端，在体外对DLG4的结合和降解至关重要。E6AP特异性短发夹状RNA或牛乳头瘤病毒1型E2在HeLa细胞中的表达可恢复DLG4的水平，但不能在CaSki或SIHA细胞中表达，这反映了HPV16阳性癌细胞中DLG4 mRNA的下调，而不是蛋白质的下调。强制表达DLG4对CaSki细胞的致瘤性有明显的抑制作用，而对培养细胞的生长无明显影响。这些结果表明，DLG4可能在HPV相关肿瘤的发生发展中起到了肿瘤抑制的作用。
In most cervical cancers, DNAs of high-risk mucosotropic human papillomaviruses (HPVs), such as types 16 and 18, are maintained so as to express two viral proteins, E6 and E7, suggesting that they play important roles in carcinogenesis. The carboxy-terminal PDZ domain-binding motif of the E6 proteins is in fact essential for transformation of rodent cells and induction of hyperplasia in E6-transgenic mouse skin. To date, seven PDZ domain-containing proteins, including DLG1/hDLG, which is a human homologue of the Drosophila discs large tumor suppressor (Dig), have been identified as targets of high-risk HPV E6 proteins. Here, we describe DLG4/PSD95, another human homologue of Dig, as a novel E6 target. DLG4 was found to be expressed in normal human cells, including cervical keratinocytes, but only to a limited extent in both HPV-positive and HPV-negative cervical cancer cell lines. Expression of HPV18 E6 in HCK1T decreased DLG4 levels more strongly than did HPV16 E6, the carboxy-terminal motif of the proteins being critical for binding and degradation of DLG4 in vitro. DLG4 levels were restored by expression of either E6AP-specific short hairpin RNA or bovine papillomavirus type 1 E2 in HeLa but not CaSki or SiHa cells, reflecting downregulation of DLG4 mRNA as opposed to protein by an HPV-independent mechanism in HPV16-positive cancer lines. The tumorigenicity of CaSki cells was strongly inhibited by forced expression of DLG4, while growth in culture was not inhibited at all. These results suggest that DLG4 may function as a tumor suppressor in the development of HPV-associated cancers.