c-MYC-dependent transcriptional inhibition of autophagy is implicated in Cisplatin sensitivity in HPV-positive Head and Neck Cancer
Autophagy is important for removal, degradation and recycling of damaged organelles, proteins, and lipids through the degradative action of lysosomes. In addition to its catabolic function, autophagy is important in cancer and viral-mediated tumorigenesis, including Human Papillomavirus (HPV) positive cancers. HPV infection is a major risk factor in a subset of Head and Neck Cancer (HNC), for which no targeted therapies are currently available. Herein, we assessed autophagy function in HPV-positive HNC. We showed that HPV-positive HNC cells presented a transcriptional and functional impairment of autophagic process compared to HPV-negative cells, which was reactivated by knocking-down HPV E6/E7 oncoproteins, the drivers of cellular transformation. We found that the oncoprotein c-MYC was stabilized and triggered in HPV-positive cell lines. This resulted in the reduced binding of the MiT/TFE transcription factors to their autophagy targets due to c-MYC competition. Thus, knock-down of c-MYC induced the upregulation of autophagic and lysosomal genes in HPV-positive HNC cells, as well as the increase of autophagic markers at the protein level. Moreover, HPV oncoprotein E7 upregulated the expression of the phosphatase inhibitor CIP2A, accounting for c-MYC upregulation and stability in HPV+ HNC cells. CIP2A mRNA expression negatively correlated with autophagy gene expression in tumor tissues from HNC patients, showing, for the first time, its implication in a transcriptional autophagic context. Both CIP2A and c-MYC knock-down, as well as pharmacological downregulation of c-MYC, resulted in increased resistance to Cisplatin treatment. Our results not only show a novel way by which HPV oncoproteins manipulate the host machinery, but also provide more insights on the role of autophagy in chemoresistance, with possible implications for targeted HPV-positive HNC therapy. Overall design: 4 biological replicates of Primary human keratinocytes were transduced with the retroviral vector pLXN Empt, HPV16 E6, HPV16 E7, or HPV16 E6/E7. After 5 days of selection with G-418 at the appropriate concentration cells were harvested and RNA extracted.RNA was used to generate the library using Truseq kit from Illumina.