Rap1 GAP inhibits tumor growth in oropharyngeal squamous cell carcinoma
Rap1 GAP inhibits tumor growth in oropharyngeal squamous cell carcinoma
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DOI：
10.2353/ajpath.2006.050132
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发表时间：
2006-02-01
影响因子：
6
通讯作者：
D'Silva, NJ
中科院分区：
文献类型：
--
作者：
Zhang, ZC;Mitra, RS;D'Silva, NJ
Rap 1是一种在人鳞状细胞癌（SCC）中强表达的生长调节蛋白，rap 1GAP可使其失活。最近在正常大鼠细胞中的证据表明，rap 1GAP调节增殖。本研究的目的是探讨rap 1GAP是否在SCC中作为肿瘤抑制因子发挥作用。使用下拉分析，活性GTP结合rap 1在SCC中上调相比，正常或永生化的角质形成细胞。因为rap 1的rap 1A和rap 1B亚型都在SCC中表达，所以使用用EGFP-rap 1A或EGFP-rap 1B转染的细胞或用FLAG标记的rap 1GAP共转染的细胞验证了两种rap 1亚型的rap 1GAP失活。结果表明，rap 1GAP在口咽SCC中的表达下调了活性rap 1、ERK活化和增殖。与载体对照相比，用有丝分裂抑制剂诺考达唑孵育稳定转染的SCC细胞，导致rap 1GAP转染的细胞在G1期的积累较慢，这表明rap 1GAP转染的SCC细胞在G1期的积累较慢。细胞在细胞周期中的进展较慢。在rap 1GAP转染的SCC细胞中，细胞周期蛋白D1、cdk 4和cdk 6的下调支持了这一点。转染rap 1GAP的SCC细胞在裸鼠体内的成瘤率明显低于对照组（P < 0.01）。这些新的发现表明rap 1GAP在SCC中起肿瘤抑制蛋白的作用。
Rap1, a growth regulatory protein that is strongly expressed in human squamous cell carcinoma (SCC), is inactivated by rap1GAP. Recent evidence in normal rat cells suggests, that rap1GAP regulates proliferation. The objective of the current study was to investigate whether rap1GAP functions as a tumor suppressor in SCC. Using a pull-down assay, active GTP-bound rap1 was up-regulated in SCC compared to normal or immortalized keratinocytes. Because both rap1A and rap1B isoforms of rap1 are expressed in SCC, the rap1GAP inactivation of both rapl isoforms was verified using cells transfected with EGFP-rap1A or EGFP-rap1B or co-transfected with FLAG-tagged rap1GAP. The results demonstrate that expression of rap1GAP in oropharyngeal SCC down-regulated active rapl, ERK activation, and proliferation. incubation of stably transfected SCC cells with nocodazole, an inhibitor of mitosis, caused a slower accumulation of rap1GAP-transfected cells in the G, phase, in comparison to the vector control, indicating that rap1GAP-transfected. cells have slower progression through the cell cycle. This was supported by down-regulation of cyclin D1, cdk4, and cdk6 in rap1GAP-transfected SCC cells. Furthermore, SCC cells transfected with rap1GAP produced significantly smaller tumors in nude mice as compared to controls (P < 0.01). These novel findings suggest that rap1GAP acts as a tumor suppressor protein in SCC.