New Insights into the Regulatory Functions and Mechanisms of Action of MicroRNA-197 Duo in the Pathophysiology of Human Fibrosarcoma

Abstract

MicroRNAs (miRNAs) are vital regulators of biological pathways by reinforcing transcriptional programs and moderating transcripts. The abnormal expression of miRNAs is involved in the pathophysiology of many human diseases, including cancer. Among miRNAs, miR-197 plays a dynamic role either as an oncogene or tumor suppressor in different types of carcinomas by modulating apoptosis, angiogenesis, migration, and drug resistance pathways. However, its role in fibrosarcoma, a highly aggressive and malignant soft tissue sarcoma that originates from the mesenchymal tissues, has not yet been elucidated. Therefore, in the current thesis, we studied two mature miRNAs, miR-197-5p and miR 197-3p, which originated from two arms of miR-197 precursor in fibrosarcoma to decode mechanistic insights into their functions by executing several molecular biology assays in vitro. We found from the qRT-PCR study that both the miRNAs are significantly underexpressed in HT1080 fibrosarcoma cells compared to IMR90-tert cells, overexpression of which inhibited viability and proliferation of the cells in both concentration and time-dependent manner. Functional studies of miR-197-5p revealed that miRNA inhibits metastatic properties like migration, invasion, and anchorage independent growth and induce cellular senescence in fibrosarcoma instead of apoptosis via repression of its target KIAA0101, which is a proliferating cell nuclear antigen-associated factor overexpressed in this malignancy. While investigating miR-197-3p, we observed miRNA significantly inhibits viability, colonyforming, and migratory ability of fibrosarcoma cells similar to that of miR-197-5p but triggers G2/M cell cycle phase arrest and autophagy, unlike cellular senescence in the earlier case. We discovered RAN (ras-related nuclear protein) as a target through which miR-197-3p represses tumorigenesis by binding to its 3´ UTR, validated by luciferase reporter assay. Seeing tumorsuppressive functions played by these two miRNAs, we intended to study whether they modulate chemosensitivity of Doxorubicin in fibrosarcoma. Doxorubicin resistance is an obstinate issue in chemotherapy, mainly responsible for tumor recurrence and metastasis and, finally, treatment failure. Intriguingly, we found miR-197 5p increases the sensitivity of fibrosarcoma cells for Doxorubicin through an additive mechanism. However, miR-197 3p did not sensitize the effect of the drug. Overall, we found that both miRNAs inhibit tumor growth in fibrosarcoma but by different mechanisms and targets. Hence, these findings raise the possibility of miR-197 as a novel RNA based therapeutic intervention to treat this malignancy.