shRNA-induced silencing of Ras-related C3 botulinum toxin substrate 1 inhibits the proliferation of colon cancer cells through upregulation of BAD and downregulation of cyclin D1

Ras-related C3 botulinum toxin substrate 1 (RAC1) is a member of the Rho family of small GTPases. Recent studies have reported that RAC1 serves an important role in colon cancer cell proliferation. The present study aimed to investigate the effects of RAC1 knockdown on cell proliferation, cell cycle progression and apoptosis of colon cancer cells. Lentivirus-mediated short hairpin RNA (shRNA) was used to knockdown RAC1 expression in colon cancer cell lines, and cell proliferation, apoptosis, cell cycle progression were evaluated by MTT assays and flow cytometry. The differences in mRNAs expression were identified between RAC1-knockdown cells and control cells using a mRNA microarray, following which quantitative PCR (qPCR) and western blot were employed to confirm the results of the mRNA microarray. The proliferative ability of colon cancer cells was significantly decreased following RAC1 knockdown, and RAC1 knockdown increased the apoptotic rate and enhanced cell cycle arrest at G(1) phase in colon cancer cells. In addition, >1,200 known genes were demonstrated to be involved in RAC1-associated tumorigenic functions in SW620 colon cancer cells, as determined by gene chip analysis; these genes were associated with cell proliferation, cell cycle, apoptosis and metastasis. Furthermore, western blot analysis indicated that cyclin D1 was downregulated, whereas B-cell lymphoma 2-associated agonist of cell death (BAD) was upregulated following RAC1 knockdown in colon cancer cells. In conclusion, RAC1 silencing may suppress the proliferation of colon cancer cells by inducing apoptosis and cell cycle arrest. In addition, a large number of genes were revealed to be involved in the process, including BAD, which was upregulated and cyclin D1, which was downregulated. Further studies on these differentially expressed genes may provide a better understanding of the potential roles of RAC1 in colon carcinogenesis.