Contente Sara, Yeh Tze-Jou Annie, Friedman Robert M
Department of Pathology, F. Edward Hébert School of Medicine, and United States Military Cancer Institute, Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
Genes Cancer. 2011 Feb;2(2):166-72. doi: 10.1177/1947601911405042.
H-Ras functions as a signal switch molecule in numerous signaling pathways in the cytoplasm, requiring H-Ras localization to the inner surface of the cytoplasmic membrane, and H-Ras is considered to be a cytoplasmic protein. Immunoblot studies of cells transformed by overexpression of c-H-ras indicated that H-Ras protein was present in both cytoplasmic and nuclear extracts, suggesting a possible correlation of nuclear H-Ras and cellular transformation. Unexpectedly, additional studies revealed that H-Ras protein was also present in the nuclei of nontransformed and primary mouse cells, which do not overexpress H-Ras. Mouse fibroblast NIH 3T3 cells, L cells, and a primary fibroblast line all had H-Ras present in both cytoplasmic and nuclear extracts. Nuclear extracts of cells synchronized by growth without serum displayed an increasing amount of H-Ras and cyclin D1 as cells grew after serum addition. Treatment with farnesyltransferase inhibitor caused loss of H-Ras from the nucleus. Immunofluorescence in situ studies of nuclei from synchronized cultures showed that H-Ras protein appeared in and disappeared from the nuclei as the cells moved through the growth cycle. This cycling occurred in both nontransformed and ras-transformed cells. Flow cytometry measurements on parallel cultures revealed that the time point at which the greatest percentage of cells were in S phase, for each line, corresponded to appearance of a noticeably stronger in situ signal for H-Ras. H-Ras may participate in nuclear signaling pathways associated with replication in addition to its cytoplasmic signaling functions.
H-Ras在细胞质中的众多信号通路中充当信号开关分子，这需要H-Ras定位于细胞质膜的内表面，并且H-Ras被认为是一种细胞质蛋白。对通过c-H-ras过表达转化的细胞进行的免疫印迹研究表明，H-Ras蛋白存在于细胞质和细胞核提取物中，这表明核H-Ras与细胞转化之间可能存在关联。出乎意料的是，进一步的研究发现，H-Ras蛋白也存在于未转化的原代小鼠细胞的细胞核中，这些细胞并未过表达H-Ras。小鼠成纤维细胞NIH 3T3细胞、L细胞和原代成纤维细胞系的细胞质和细胞核提取物中均存在H-Ras。通过无血清培养同步化的细胞的细胞核提取物显示，随着血清添加后细胞生长，H-Ras和细胞周期蛋白D1的量增加。用法尼基转移酶抑制剂处理导致H-Ras从细胞核中丢失。对同步化培养物的细胞核进行的免疫荧光原位研究表明，随着细胞在生长周期中移动，H-Ras蛋白在细胞核中出现和消失。这种循环在未转化和ras转化的细胞中均发生。对平行培养物进行的流式细胞术测量显示，对于每条细胞系，处于S期的细胞百分比最高的时间点与H-Ras原位信号明显增强的出现相对应。除了其细胞质信号功能外，H-Ras可能还参与与复制相关的核信号通路。
