Investigation of Potential piRNA-mediated Regulation of Oncogenicity and Chemoresistance Imparted by FDFT1 in the pathophysiology of Tongue Squamous Cell Carcinoma

Abstract

Piwi-interacting RNAs (piRNAs) are key regulators of biological processes that mediate gene regulations at various levels. The abnormal expression of piRNAs is involved in pathophysiological diseases, such as cancer. However, its role in tongue squamous cell carcinoma (TSCC), a highly malignant carcinoma originating from tongue squamous epithelium, has not yet been elucidated. Therefore, in the current thesis, we first investigated the presence of PIWILs and piRNAs in TSCC cell lines and found that 407 piRNAs are dysregulated. Among these, we found only 46 piRNAs target 158 differentially expressed genes, of which only 5 genes are enriched in TSCC significantly. Then, we validated the reciprocal expression pattern among the target–piRNA pairs through qRT-PCR, from which we selected FDFT1, the only upregulated target that could be a potential oncogene. To decode mechanistic insights into the functions of FDFT1, we executed several molecular biology assays in SCC-9 and H357 TSCC cell lines in vitro. We overexpressed FDFT1 in TSCC cells and found an increase in viability, proliferation, migration, and ROS generation, indicating its oncogenic nature. We found overexpression of piR-39980, a key regulator in various cancers, and downregulated in TSCC inhibit FDFT1 as its target, which was confirmed from the luciferase reporter assay. To explore the effect of piR-39980 in TSCC, we overexpressed and silenced it in TSCC. We found that its overexpression could attenuate the oncogenicity of FDFT1 and inhibit cell viability, proliferation, migration, and ROS generation by suppressing the EIF3H/HIF1α axis, inducing hypoxia and causing p53-induced apoptosis and its silencing, showing the reverse. This tumor-suppressive nature of piR-39980 and the oncogenic nature of FDFT1 encouraged us to study whether these modulate the chemosensitivity of Doxorubicin in TSCC, an obstinate issue in chemotherapy. Interestingly, we found piR-39980 increases the sensitivity of Doxorubicin in TSCC cells by increasing its accumulation synergistically by deregulation of FDFT1, CYPOR, and EIF3H/HIF1α axis. In summary, these findings build the possibility of piR-39980 as a novel RNA-based therapeutic agent and FDFT1 as a therapeutic target to treat TSCC and overcome chemoresistance, which needs further investigation.