Background and Aim: MicroRNA-21 (miR-21) is an established onco-miR which is over expressed in a variety of human cancers and its elevated expression has been demonstrated to suppress key tumour suppressor genes. This study aimed to investigate the regulation of miR-21 and its contributions in Stat3-dependent gastric cancers.
Methods: Expression of miR-21 in Stat3 driven gastric tumours were measured in polyps of gp130F/F mice, which spontaneously and reproducibly develops polyps at approximately 6-7 weeks. The role of Stat3 signalling to miR-21 regulation was assessed using human gastric cancer cell lines and a shStat3 mouse model. miR-21’s contribution in gastric tumour progression was determined in vitro and in vivo via treatment of 6-7 week old gp130F/F mice with either a control or a miR-21 antisense oligonucleotide (ASO). The oncogenic properties of miR-21 in gastric cancer were assessed via IHC analysis of PTEN and PDCD4 in the stomach/polyps of the mice treated with the control or miR-21 ASO. Finally, the tumour suppressive effects of PTEN in gastric cancer were confirmed using an A33CreERT2;FF;PTENfl/fl mouse model.
Results: miR-21 expression was significantly higher in adenomas/stomachs extracted from gp130F/F mice (P<0.01) and its expression was determined to be dependent on Stat3. miR-21 is a direct Stat3 target gene and the activation of Stat3 signalling via IL-6 and IL-11 directly induced miR-21. Furthermore, knockout of Stat3 attenuated miR-21 expression by IL-11 stimulation. Treatment of gp130F/F mice with the miR-21 ASO inhibited tumour growth at an early phase; however, had no effect the number of adenomas which developed. gp130F/F mice treated with the miR-21 ASO demonstrated a significantly higher re-expression of PTEN and PDCD4 compared to control mice. Finally, PTEN’s tumour suppressive activity in gastric cancer was re-confirmed with gp130F/F: PTENfl/fl mice developing larger gastric tumours.
Conclusion: miR-21 is a Stat3 driven onco-miR in gastric cancer which mechanistically inhibits the tumour suppressor genes PTEN and PDCD4 to facilitate tumour development.