HPV16 E6/E7-mediated regulation of PiwiL1 expression induces tumorigenesis in cervical cancer cells

PURPOSE

PiwiL1 has been reported to be over-expressed in many cancers. However, the molecular mechanism by which these proteins contribute to tumorigenesis and their regulation in cancer cells is still unclear. We intend to understand the role of PiwiL1 in tumorigenesis and also its regulation in cervical cells.

METHODS

We studied the effect of loss of PiwiL1 function on tumor properties of cervical cancer cells in vitro and in vivo. Also we have looked into the effect of PiwiL1 overexpression in the malignant transformation of normal cells both in vitro and in vivo. Further RNA-seq and RIP-seq analyses were done to get insight of the direct and indirect targets of PiwiL1 in the cervical cancer cells.

RESULTS

Here, we report that PiwiL1 is not only over-expressed, but also play a major role in tumor induction and progression. Abolition of PiwiL1 in CaSki cells led to a decrease in the tumor-associated properties, whereas, its upregulation conferred malignant transformation of normal HaCaT cells. Our study delineates a new link between HPV oncogenes, E6 and E7 with PiwiL1. p53 and E2F1 directly bind and differentially regulate PiwiL1 promoter in a context-dependant manner. Further, RNA-seq together with RIP-RNA-seq suggested a strong and direct role for PiwiL1 in promoting metastasis in cervical cancer cells.

CONCLUSION

Our study demonstrates that PiwiL1 act as an oncogene in cervical cancer by inducing tumor-associated properties and EMT pathway. The finding that HPV oncogenes, E6/E7 can positively regulate PiwiL1 suggests a possible mechanism behind HPV-mediated tumorigenesis in cervical cancer.

RXR agonist, Bexarotene, effectively reduces drug resistance via regulation of RFX1 in embryonic carcinoma cells

Aberrant expression of multidrug resistance (MDR) proteins is one of the features of cancer stem cells (CSCs) that make them escape chemotherapy. A well-orchestrated regulation of multiple MDRs by different transcription factors in cancer cells confers this drug resistance. An in silico analysis of the major MDR genes revealed a possible regulation by RFX1 and Nrf2. Previous reports also noted that Nrf2 is a positive regulator of MDR genes in NT2 cells. But we, for the first time, report that Regulatory factor X1 (RFX1), a pleiotropic transcription factor, negatively regulates the major MDR genes, Abcg2, Abcb1, Abcc1, and Abcc2, in NT2 cells. The levels of RFX1 in undifferentiated NT2 cells were found to be very low, which significantly increased upon RA-induced differentiation. Ectopic expression of RFX1 reduced the levels of transcripts corresponding to MDRs and stemness-associated genes. Interestingly, Bexarotene, an RXR agonist that acts as an inhibitor of Nrf2-ARE signaling, could increase the transcription of RFX1. Further analysis revealed that the RFX1 promoter has binding sites for RXRα, and upon Bexarotene exposure RXRα could bind and activate the RFX1 promoter. Bexarotene, alone or in combination with Cisplatin, could inhibit many cancer/CSC-associated properties in NT2 cells. Also, it significantly reduced the expression of drug resistance proteins and made the cells sensitive towards Cisplatin. Our study proves that RFX1 could be a potent molecule to target MDRs, and Bexarotene can induce RXRα-mediated RFX1 expression, therefore, would be a better chemo-assisting drug during therapy.

PIWI proteins and piRNAs in cervical cancer: a propitious dart in cancer stem cell-targeted therapy

Any form of cancer is a result of uncontrolled cell growth caused by mutations and/or epigenetic alterations, implying that a balance of chromatin remodeling activities and epigenetic regulators is crucial to prevent the transformation of a normal cell to a cancer cell. Many of the chromatin remodelers do not recognize any specific sites on their targets and require guiding molecules to reach the respective targets. PIWI proteins and their interacting small non-coding RNAs (piRNAs) have proved to act as a guiding signal for such molecules. While epigenetic alterations lead to tumorigenesis, the stemness of cancer cells contributes to recurrence and metastasis of cancer. Various studies have propounded that the PIWI-piRNA complex also promotes stemness of cancer cells, providing new doors for target-mediated anti-cancer therapies. Despite the progress in diagnosis and development of vaccines, cervical cancer remains to be the second most prevalent cancer among women, due to the lack of cost-effective and accessible diagnostic and prevention methods. With the emergence of liquid biopsy, there is a significant demand for the ideal biomarker in the diagnosis of cancer. PIWI and piRNAs have been recommended to serve as prognostic and diagnostic markers, to differentiate early and later stages of cancer, including cervical cancer. This review discusses how PIWIs and piRNAs are involved in disease progression as well as their potential role in diagnostics and therapeutics in cervical cancer.