Let-7a suppresses cell proliferation via the TGF-β/SMAD signaling pathway in cervical cancer

Cervical cancer is the second most commonly diagnosed type of cancer among women after breast cancer. Recent research has addressed the role of microRNAs in cervical cancer. In the present study, we aimed to determine the effect of let-7a on the regulation of the cell proliferation of cervical cancer and the related signaling pathway. Real-time RT-PCR was used to detect the expression of let-7a in the blood of cervical cancer patients and normal controls. The expression of let-7a was also assessed in cervical cancer cell lines: HeLa, SiHa and normal human immortalized keratinocyes HaCaT. Cell proliferation was tested by MTT assay, and cell apoptosis and cell cycle were examined by flow cytometric analysis in HeLa cells. Moreover, bioinformatic analysis, dual-luciferase reporter assay and western blotting were used to confirm the target gene for let-7a. In addition, the expression of TGF-beta 1, SMAD4 and p53 were assessed by western blotting and real-time PCR. Our studies showed that the expression of let-7a in cervical cancer was significantly reduced in cervical cancer patients compared with the expression in the normal control group. Cell proliferation of HeLa cells was inhibited by overexpression of let-7a. The cell cycle analysis showed that an increased population was arrested in the G2 phase in the let-7a mimic group when compared with that in the mimic control and untreated groups. In addition, the cell cycle-related factor p53 was increased in the let-7a overexpression group compared with that in the control and untreated groups. Furthermore, TGFBR1 was confirmed to be a target of let-7a. Moreover, the expression of TGF-beta 1 and SMAD4 proteins was elevated in cervical squamous carcinoma and cervical adenocarcinoma tissues. However, the expression of TGF-beta 1 and SMAD4 was decreased in the let-7a-overexpressing cervical cancer cell lines (HeLa, SiHa and CaSki). Our data suggest that let-7a may play a role in the cell proliferation of cervical cancer by regulating the TGF-beta/SMAD pathway, and may participate in the regulation of the occurrence and development of cervical cancer.