Unravelling the Molecular Connection Between Pax9 and Autophagy To Regulate Oral Carcinogenesis

Abstract

PAired boX 9 (PAX9) gene belong to the PAX family, which encodes a family of metazoan transcription factors documented by a conserved DNA binding paired domain 128-amino- acids, critically essential for physiology and development. It has a significant role in maintaining squamous cell differentiation, and its deregulation is associated with tumor initiation and malignant transformation. Here, we have examined the mechanism of downregulation of PAX9 in oral carcinogenesis and its reactivation leading to lethal autophagy for potential cancer therapeutics in oral squamous cell carcinoma (OSCC). Our data showed that the expression of PAX9 was decreased in increasing grades of oral cancer and DMBA-induced hamster model of oral carcinogenesis. The downregulation of PAX9 is through promoter hypermethylation in exposure to alcohol and arecoline consumption was observed. Further, we showed that PAX9 inhibits proliferation and triggers apoptosis in OSCC. Interestingly, PAX9 activates lethal autophagy to degrade the EGFR signaling leading to cell death, establishing the tumor-suppressive potential of PAX9 in oral cancer. In another study, we have identified PAX9 for cellular differentiation by inhibiting EMT and stemness in cancer stem cells of OSCC. Notably, we revealed that protective autophagy in oral cancer stem cells maintains stemness through lysosomal degradation of PAX9 in oral cancer. In this setting, we have identified procaine, a local anesthetic, as DNA methyltransferase (DNMT) inhibitor to increase the expression of PAX9 in oral cancer. Interestingly, the reactivation of PAX9 by procaine found to inhibit cell growth and trigger apoptosis in OSCC in vitro and in vivo. Likely, the enhanced PAX9 expression after exposure to procaine controls stemness and differentiation through the autophagy-dependent pathway in OSCC cells. In SCC cells, procaine improved anticancer drug sensitivity through PAX9, and its deficiency significantly blunted the anticancer drug sensitivity mediated by procaine. Further, procaine promoted antitumor activity in FaDu xenografts in athymic nude mice, and immunohistochemistry data showed that PAX9 expression was significantly enhanced in the procaine group compared to the vehicle control. In conclusion, the reactivation of PAX9 by the discovery of small molecule anticancer drugs or increasing PAX9 copy number through gene therapy could offer a promising clinical outcome for the treatment of OSCC patients.