Syk(L)细胞核移位现象对乳腺癌细胞侵袭力的影响

Effects of Syk (L) nuclear translocation on breast cancer cell invasion

目的探讨2种Syk蛋白异构体在乳腺癌细胞中的表达、细胞亚细胞器中分布和对乳腺癌细胞侵袭力影响。方法采用Western blot方法检测6种乳腺癌细胞系中Syk的表达;采用胞核、胞浆分离试验及质粒定点突变技术检测2种Syk蛋白异构体在细胞亚细胞器中的分布并探讨Syk (L)的核移位机制;采用体外侵袭力实验研究2种Syk蛋白异构体和DEL域碱性氨基酸突变成非碱性氨基酸的Syk(L)对肿瘤细胞侵袭力的影响。结果2种Syk蛋白异构体在4种乳腺癌细胞系中同时表达;Syk(L)在乳腺癌细胞中的表达可明显抑制细胞的侵袭力,Syk(S)对侵袭力无影响;在同时表达2种Syk蛋白的乳腺癌细胞系MB468及分别表达Syk(L)、Syk(S)的稳定细胞株MB435中,只有分子量较大的Syk(L)可从胞浆移位到胞核内。DEL域内的碱性氨基酸被突变为非碱性氨基酸后, Syk(L)失去核移位功能,亦不能抑制乳腺癌细胞的侵袭力。结论Syk(L)-DEL域内的碱性氨基酸具有核定位信号功能,Syk(L)的核移位现象与其抑制乳腺癌细胞侵袭力功能密切相关,Syk(L)的抑癌功能是由它移位到细胞核内行使的核蛋白相关功能决定的。

Objective To explore Syk （L） and Syk （ S ） expression, subcellular localization in breast cancer cells and their effects on breast cancer cells invasion. Methods Western blot was used to examine 2 Syk isoform＇s expression in breast cancer cells. Cytosolic and nuclear fractionation and plasmids mutation techniques were used to examine the two Syk isoforms subcellular localization in the cells and the mechanisms of Syk（L） translocalization to the nuelears. The effects of the two Syk isoforms and Syk （L） mutants, whose basic amino acids on DEL domain were mutated into non basic amino acids, on breast cancer cells invasion were explored by chemoinvasion assay. Results Both Syk（L） and Syk （S） were expressed in 4 out of six breast cancer cell lines. The expression of Syk （ L ） in breast cancer cells inhibited cells invasion ability significantly. In breast cancer cell line MB468 expressing both Syk（L） and Syk（S） and in MB435 in which stable cells express either Syk （L） or Syk （S） , only Syk （L）, which is with large molecuar weight, was able to translocate into nuclears from cytoplasm. When the basic amino acids in the DEL domain of Syk（L） were mutated into non basic amino acids, Syk（L） was deprived of the ability to translocate into the nuclears and the ability to suppress cell invasion. Conclusions The basic amino acids on DEL domain of Syk（L） has nuclear localization signal function. Syk（L） invasion suppression activity in breast cancer cells is associated with its nuclear translocation. Syk （L） tumor suppression function is determined by its nuclear protein functions.