MicroRNA and energy metabolism in gastrointestinal tumors

Abstract

MicroRNAs (miRNAs) contribute to cancer development and drug resistance via cellular biological processes, including metabolic pathways. Energy metabolism plays a significant role to maintain tumor proliferation in gastrointestinal (GI) cancers. However, the roles of miRNAs and energy metabolism in GI cancers are not fully understood. The studies presented in this thesis aim to provide further insights into the biological role of miRNAs, energy metabolism, and the interplay between miRNAs and energy metabolism in GI cancers, using gastrointestinal stromal tumor (GIST) and colon cancer as the models.

In Paper I, we explored the downstream target of miR-125a-5p-PTPN18 axis that contributes to imatinib resistance in GIST. We found that over-expression of miR-125a-5p and silencing of PTPN18 increased phosphorylated focal adhesion kinase (pFAK). FAK inhibitor 14, which blocks phosphorylation of Y397-FAK, enhances imatinib response in imatinib-resistant GIST cells. Furthermore, FAK inhibitor 14 could rescue the imatinib resistance mediated by overexpression of miR-125a-5p, suggesting that pFAK is the downstream target of the miR-125a-5p-PTPN18 axis.

In Paper II, we profiled the bioenergetic phenotype of imatinib-resistant GIST cells. We identified two major types of bioenergetics in imatinib-resistant GIST cell lines and clinical samples, i.e. highly metabolically active phenotype with higher glycolysis and oxidative phosphorylation (OXPHOS) and low OXPHOS types. Metabolic inhibitor assays revealed that imatinib-resistant GIST 882R cells (with highly metabolically active phenotype) were more sensitive to glycolysis inhibition than the parental GIST 882 cells, while imatinib-resistant GIST T1R cells (with low OXPHOS) were more resistant to OXPHOS inhibition than GIST T1. Our study demonstrates metabolic heterogeneity and diverse vulnerability of GIST cells to metabolic inhibitors, suggesting the potential of targeting energy metabolism for overcoming imatinib resistance in GIST.

In Paper III, we further explored the relationship between miRNA and imatinib treatment in GIST and the effect on OXPHOS. Using microarray and RT-qPCR, we identified miR-483-3p as one of the most downregulated miRNAs in imatinib-treated GISTs. Imatinib treatment resulted in downregulation of miR-483-3p and upregulation of OXPHOS in imatinib sensitive GIST cells. Modulation of miR-483-3p altered protein expression of mitochondrial respiratory Complex II, suggesting its involvement in OXPHOS regulation. This study reveals a potential role of miR-483-3p in imatinib-induced OXPHOS expression.

In Paper IV, we investigated the association of metformin treatment, an inhibitor of OXPHOS, with patient survival in colorectal cancer. We showed that metformin users were associated with 44% lower risk of mortality compared with nonusers. These findings suggest that metformin could be an adjunct to standard treatment of colorectal cancer. Overall, this thesis work provides new insights into the role of miRNAs and energy metabolism in drug response and potential clinical use in GI cancers.