Overexpression of E2F mRNAs associated with gastric cancer progression identified by the transcription factor and miRNA co-regulatory network analysis

E2F1 induces TINCR transcriptional activity and accelerates gastric cancer progression via activation of TINCR/STAU1/CDKN2B signaling axis

Recent evidence indicates that E2F1 transcription factor have pivotal roles in the regulation of cellular processes, and is found to be dysregulated in a variety of cancers. Long non-coding RNAs (lncRNAs) are also reported to exert important effect on tumorigenesis. E2F1 is aberrantly expressed in gastric cancer (GC), and biology functions of E2F1 in GC are controversial. The biological characteristics of E2F1 and correlation between E2F1 and lncRNAs in GC remain to be found. In this study, integrated analysis revealed that E2F1 expression was significantly increased in GC cases and its expression was positively correlated with the poor pathologic stage, large tumor size and poor prognosis. Forced E2F1 expression promotes proliferation, whereas loss of E2F1 function decreased cell proliferation by blocking of cell cycle in GC cells. Mechanistic analyses indicated that E2F1 accelerates GC growth partly through induces TINCR transcription. TINCR could bind to STAU1 (staufen1) protein, and influence CDKN2B mRNA stability and expression, thereby affecting the proliferation of GC cells. Together, our findings suggest that E2F1/TINCR/STAU1/CDKN2B signaling axis contributes to the oncogenic potential of GC and may constitute a potential therapeutic target in this disease.

IGF2BP3 functions as a potential oncogene and is a crucial target of miR-34a in gastric carcinogenesis

Background

Gastric cancer (GC) is one of the frequent causes of cancer-related death in eastern Asian population. IGF2BP2 lists in the top rank up-regulated genes in GC, but its functional role is unclear.

Method

The expression of IGF2BP3 in GC cell lines and primary samples was examined by qRT-PCR and Western blot. The biological role of IGF2BP3 was revealed by a series of functional in vitro studies. Its regulation by microRNAs (miRNAs) was predicted by TargetScan and confirmed by luciferase assays and rescue experiments.

Results

IGF2BP3 ranked the No.1 of the up-regulated genes by expression microarray analysis in GC cell lines. The expression level of IGF2BP3 was observed in GC tissues comparing with non-tumorous gastric epitheliums. The up-regulated IGF2BP3 expression was associated with poor disease specific survival. IGF2BP3 knockdown significantly inhibited cell proliferation and invasion. Apart from copy number gain, IGF2BP3 has been confirmed to be negatively regulated by tumor-suppressive miRNA, namely miR-34a. The expression of miR-34a showed negative correlation with IGF2BP3 mRNA expression in primary GC samples and more importantly, re-overexpression of IGF2BP3 rescued the inhibitory effect of miR-34a.

Conclusion

We compressively revealed the oncogenic role of IGF2BP3 in gastric tumorigenesis and confirmed its activation is partly due to the silence of miR-34a. Our findings identified useful prognostic biomarker and provided clinical translational potential.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0647-2) contains supplementary material, which is available to authorized users.

miR-564 is downregulated in gastric carcinoma and targets E2F3

Numerous aberrantly expressed microRNAs (miRNAs/miRs) have been identified in gastric cancer (GC); however, only a fraction of these have been functionally investigated and novel deregulated miRNAs in GC remain to be explored. Through examining two public miRNA expression profile datasets, the present study identified aberrantly expressed miRNAs in GC. One of these miRNA, miR-564, was identified to be downregulated in GC, which was validated in tissue samples from patients with GC by reverse transcription-quantitative polymerase chain reaction analysis. Targets of miR-564 were then predicted bioinformatically, including transcription factor E2F3 (E2F3), which was identified to be functionally enriched in several cancer signaling pathways. Furthermore, overexpression of miR-564 decreased the activity of a luciferase reporter carrying the 3'-untranslated region of E2F3, in addition to the mRNA and protein level of E2F3, indicating that miR-564 directly targets E2F3. These data suggest that by targeting E2F3, miR-564 may act as a tumor suppressor gene in gastric carcinogenesis.

Downregulated miR-31 level associates with poor prognosis of gastric cancer and its restoration suppresses tumor cell malignant phenotypes by inhibiting E2F2

The miRNA microarray analysis showed that miR-31 was reduced in gastric cancer. This study further assessed miR-31 expression and role of miR-31 in gastric cancer tissues and cell lines. The data showed that miR-31 expression was down-regulated in 40 cases of gastric cancer tissues compared to the adjacent normal tissues, and low expression of miR-31 was associated with poor tumor differentiation, lymph node metastasis, advanced T stage and worse overall survival of gastric cancer patients. Ectopic expression of miR-31 reduced tumor cell viability, enhanced apoptosis, arrested tumor cells at G1 transition, and reduced tumor cell migration and invasion in SGC-7901 and MGC-803 gastric cell lines in vitro. Enforced expression of miR-31 also inhibited growth of engrafted tumors in vivo. Luciferase reporter assays and western blot revealed that E2F2 is the direct target of miR-31. E2F2 expression was upregulated in gastric cancer tissues, and inversely associated with miR-31 levels, while knockdown of E2F2 expression mimicked miR-31 anti-tumor activity in gastric cancer cells, but the ectopic expression of E2F2 rescued the miR-31-mediated inhibition in gastric cell lines. Taken together, these results demonstrated that miR-31 acts as a crucial tumor suppressive activity by inhibiting E2F2s expression. Thus, miR-31 might be a candidate therapeutic target for gastric cancer patients.