Abstract. MicroRNAs (miRNAs) are important gene regulators that participate in tumorigenesis. Previous studies have implicated that miR-214 is a tumor suppressor that is capable of inhibiting human hepatocellular carcinoma (HCC) cell growth. However, the mechanism by which miR-214 suppresses tumor development remains unknown. In the present study, miR-214 was observed to suppress tumor proliferation by directly targeting E2F transcription factor 3 (E2F3) in HCC cells. Colony formation, cell cycle and proliferation assays were employed to study the tumor suppressor role of miR-214 in cell proliferation. In addition, western blotting and dual-luciferase reporter assays were used to evaluate whether E2F3 was a target of miR-214. The results of these analyses revealed that E2F3 was a novel target of miR-214. Furthermore, enhanced expression of miR-214 or silencing of E2F3 inhibited the proliferation of HCC SMMC-7721 cells. These findings suggest that miR-214 suppresses HCC growth by targeting E2F3, and may provide a novel approach for the treatment of human HCC.
IntroductionHepatocellular carcinoma (HCC) is one of the most common types of malignancy and the third leading cause of cancer-associated mortalities worldwide, due to its poor prognosis and frequent relapse and metastasis (1,2). Furthermore, HCC is difficult to treat, since it is usually diagnosed at advanced stages (3). Thus, studying the molecular mechanism of HCC in order to identify novel prognostic markers or therapeutic targets for the treatment of HCC is of value.MicroRNAs (miRNAs) are small noncoding RNAs of ~22 nucleotides (nt) in length that regulate gene expression at the post-transcriptional level (4). miRNAs are initially transcribed as long primary precursor molecules named pri-miRNAs, which are processed in a number of endonuclease reactions to produce the mature effector 22-nt miRNA molecule (5). Through the specific targeting of the 3'-untranslated regions (3'-UTRs) in the target genes of the miRNA, the translational repression and degradation of their target mRNA occurs (6). By targeting various transcripts, miRNAs are involved in a number of fundamental biological processes, including cell proliferation and differentiation, apoptosis, development and metabolism (7-9). Previous studies suggest that the expression of miRNAs is remarkably dysregulated in cancer, due to numerous epigenetic and genomic alterations (10,11). Several miRNAs have been demonstrated to act as tumor suppressor genes or oncogenes in tumors (12). As one miRNA may potentially regulate numerous mRNAs, it is clear that they are important regulatory molecules. Consistently, previous studies have considered miRNAs as important biomarkers and promising therapeutic targets for the treatment of various diseases (13). Recently, miR-214 was reported to be involved in certain types of cancer, including breast (14), adrenocortical (15), ovarian (16) and gastric cancer (17). Thus, the roles of miR-214 may be critical in the development of cancer.In the present study, bioinformatics...