The Pinx1 Gene Downregulates Telomerase and Inhibits Proliferation of CD133+ Cancer Stem Cells Isolated from a Nasopharyngeal Carcinoma Cell Line by Regulating Trfs and Mad1/C-Myc/p53 Pathways

Abstract

Background/Aims: Cancer stem cells (CSCs) are important factors for the continuous growth, recurrence, and metastasis of malignant tumors. They are responsible for the ineffectiveness of traditional radiotherapy and chemotherapy toward malignant tumors. Currently, stem cells or side-population cells have been isolated from many cancer cell lines and malignant tumor tissues, including nasopharyngeal carcinoma. Exploring the biological characteristics of CSCs for CSC-targeted therapy has gained importance. CSCs possess higher telomerase activity; thus, the use of the gene encoding telomerase inhibitor PinX1 gene to target telomerase in CSCs and inhibit proliferation, invasion, and metastasis of CSCs has become an important means for the treatment of malignant tumors. PinX1 may regulate complex pathways, including TRF1, Mad1/c-Myc, and p53. Methods: In this study, nasopharyngeal CD133+ CSCs were sorted using CD133 immunomagnetic beads by flow cytometry The successful isolation of CD133+ CSCs was confirmed by examining their surface markers, namely CD44, NaNOG, and SOX2 as well as their ability to undergo in vivo tumorigenesis and in vitro sphere formation, proliferation, migration, and invasion. In addition, CD133+ CSCs were transfected with the constructed PinX1 overexpression plasmid or siRNA and the resulting effects on their proliferation, migration, invasion, and apoptosis were detected using cell counting kit-8 (CCK-8), transwell assay, and scratch test, respectively. Furthermore, their effects on mRNA and protein levels of TRF1, TRF2, Mad1, c-Myc, and p53 were examined using quantitative real-time PCR and western blot, respectively. Results: The overexpression of PinX1 in CD133⁺ CSCs significantly decreased hTERT (P < 0.001), inhibited proliferation, migration, and invasion, induced apoptosis, and significantly decreased c-Myc mRNA levels (P < 0.001), while it increased TRF1, Mad1, and p53 mRNA levels (all P < 0.001). On the other hand, PinX1 silencing in CD133⁺ CSCs significantly decreased TRF1, Mad1, and p53 mRNA levels (all P < 0.01), while it increased hTERT and c-Myc mRNA levels (all P < 0.05). Conclusion: These results indicate that PinX1 downregulates telomerase activity in CD133⁺ CSCs, inhibits its proliferation, migration, and invasion, and induces apoptosis possibly through TRF1, Mad1/c-Myc, and p53–mediated pathways.