IQGAP1通过C末端促进肿瘤细胞增殖的初步研究

IQGAP1 promotes proliferation of tumor cells through C-terminal fragment

目的探讨含IQ模序的GTP酶活化蛋白1(IQGAP1)对肺癌、乳腺癌和结肠癌细胞增殖的影响。方法转染编码IQGAP1和IQGAP1-C末端的腺病毒载体并检测细胞中IQGAP1和IQGAP1-C的表达水平;转染靶向IQGAP1的小干扰RNA(siRNA),检测内源性IQGAP1的表达水平;用MTT和BrdU掺入法检测IQGAP1对肿瘤细胞增殖的影响;用western blot检测增殖细胞核抗原(PCNA)和细胞周期素E的表达。结果转染腺病毒Ad-IQGAP1或Ad-IQGAP1-C使A549、MCF7和SW480细胞高表达IQGAP1或IQGAP1-C,其增殖能力较Ad-LacZ组均提高(t分别为19.418和25.643、29.283和16.261、23.138和56.739,P均<0.05);A549细胞转染Ad-IQGAP1-C组的促增殖效果明显优于Ad-IQGAP1组(t=25.643,P<0.05);用siRNA沉默内源性IQGAP1的表达后,与对照siRNA组相比,A549、MCF-7和SW480细胞增殖活性受到显著抑制(t分别为18.324、18.931、19.609,P均<0.05)。BrdU掺入法结果显示,增加IQGAP1和IQGAP1-C表达均可明显提高A549、MCF7和SW480的细胞DNA合成率(t分别为14.224和12.079、13.035和15.677、11.291和16.675,P均<0.05),在MCF7和SW480细胞中IQGAP1-C组促DNA合成效果明显优于IQGAP1组(t分别为15.677、16.675,P均<0.05);抑制IQGAP1的表达可显著降低DNA的合成(t分别为8.043、11.381、5.966,P均<0.05);western blot结果显示,在高表达IQGAP1或IQGAP1-C的A549、MCF7和SW480细胞中,PCNA和细胞周期素E表达明显增加(t PCNA分别为6.541和7.460、17.769和13.048、10.261和6.544,P均<0.05;t细胞周期素E分别为17.243和12.258、10.109和14.216、12.011和12.058,P均<0.05);而干扰IQGAP1表达的细胞,与对照siRNA组比较,两者的表达明显降低(t分别为4.475和6.058,7.476和8.404,12.559和14.792,P均<0.05)。结论IQGAP1和IQGAP1-C促进肺癌、乳腺癌和结肠癌细胞增殖,且IQGAP1可能主要通过C末端影响细胞增殖。

Objective To detect the effects of IQ domain-containing GTPase activating protein 1 （ IQGAP1 ） on the cellular prolifera- tion of lung cancer, breast cancer and colon cancer. Methods The adenoviral vector encoding IQGAP1 or its C-terminal fragment was transfected into tumor cells and the expression of proteins of IQGAP1 and its C-terminal fragment was determined. The siRNA-targeting IQGAP1 was also transfected into the tumor cells to suppress the expression of target proteins and the level of endogenous IQGAP1 was determined. MTT method and BrdU incorporation assay were used to analyze the effects of IQGAP1 on the proliferation of tumor cells. Western blot method was used to detect the expression of proliferating cell nuclear antigen （PCNA） and cyclin E. Results Compared to Ad-LacZ-infected group, the results of MTT showed that the expression of IQGAP1 or IQGAP1-C after the adenovirus vector infection was significantly increased and the cell proliferation was accelerated in A549, MCF-7 and SW480 cell lines （t = 19. 418 and 25. 643, 29. 283 and 16. 261,23. 138 and 56. 739 respectively, P 〈 0.05 ）. In A549 cells , the effect of IQGAP1-C on proliferation was stronger than that of IQGAP1 （ t = 25. 643, P 〈 0.05）. After the expression of endogenous IQGAP1 was silenced by siRNA, the cell prolifera-tions in the above 3 cell lines were obviously attenuated （t = 18. 324, 18. 931, 19. 609, P 〈 0.05 ）. BrdU incorporation assay showed that high expression of IQGAP1 and IQGAP1-C markedly promoted DNA synthesis in A549, MCF-7 and SW480 cell lines （t = 14. 224 and 12. 079, 13. 035 and 15. 677, 11. 291 and 16. 675, P 〈 0.05）. In MCF-7 and SW480 cells, the beneficial effect of IQGAP1-C on DNA synthesis was stronger than that of IQGAP1 （ t = 15. 677, 16. 675, P 〈 0.05 ）, and DNA synthesis markedly decreased following reduction of IQGAP1 expression by siRNA （t = 8. 043, 11. 381, 5. 966, P 〈 0.05）. Western blot showed that the increase of IQGAP1 and IQGAP1-C in A549, MCF-7 and SW480 cell lines stimulated the expression of PCNA and cyclin E （ tPCNA = 6. 541 and 7. 460, 17. 769 and 13. 048, 10. 261 and 6. 544, P 〈0.05, tCyclin E = 17. 243 and 12. 258, 10. 109 and 14. 216, 12. 011 and 12. 058, P 〈 0.05） , and the silence of IQGAP1 by siRNA inhibited the expressions of PCNA and cyclin E （ t = 4. 475 and 6. 058, 7. 476 and 8. 404, 12. 559 and 14. 792, P 〈 0.05 ）. Conclusion Both IQGAP1 and IQGAP1-C could promote the cell proliferation of lung canc-er, breast cancer cell and colon cancer and IQGAP1 may affect the cell proliferation through its C-terminal fragment.