SERCA Ca²+-ATPase IS ASSOCIATED WITH HPV INDUCED IMMNUNE SYSTEM REPROGRAMING IN OROPHARYNGEAL CANCER

Oropharyngeal Squamous Cell Carcinoma is a public health problem, responsible for more than 50,000 deaths each year worldwide. This pathology is associated with excessive consumption of alcohol, tobacco and persistent HPV infection. HPV-positive tumors show degradation of p53 by viral oncoprotein E6, and generally do not carry mutations in this gene, exhibiting a better overall survival. In the nucleus, p53 regulates transcription of genes involved in cell cycle arrest, DNA repair, and apoptosis. In the cytoplasm, p53 interacts with the endoplasmic reticulum Ca²+-ATPase (SERCA) to reduce its oxidation state of SERCA and triggering the translocation of Ca²+ from the cytoplasm to the endoplasmic reticulum and then to the mitochondria, culminating in programmed cell death (PCD). Approximately 50% of human tumors carry TP53 mutation, contributing to resistance to PCD in tumor cells. In this study, we compared the expression of SERCA genes in HPV-positive and HPV-negative oropharyngeal tumors to understand the relationship of SERCA in biological processes altered in cancer. Analyses of genomic and clinical data from the TCGA were used to compare the mRNA expression of the three SERCA genes (ATP2A1, ATP2A2 and ATP2A3) in tumors of the oropharynx, tonsil and tongue base. Gene Ontology was performed for enrichment analysis. Finally, confocal microscopy was performed to evaluate the SERCA (BODIPY-thapsigargin) localization in a thermo-sensitive cell line for TP53 mutation. TP53 and ATP2A3 showed significant correlation of expression (Spearman: 0.52; p = 1.008e-5), with both genes upregulated in HPV positive tumors (p = 1.981e-6). As observed for TP53, tumors with higher expression of ATP2A3 were correlated with a better prognosis, and tumors that carry mutation in TP53 showed less ATP2A3 expression when compared to tumors without mutation in TP53 (p<0.0001). Enrichment analysis of the differentially expressed genes between tumors with high (z-core>0.5) and low expression (z-score<-0.5) of ATP2A3 revealed a set of genes involved in the regulation of immune system, particularly proliferation, activation and differentiation of T lymphocytes. In addition, wild-type cells for TP53 showed a diffuse SERCA distribution while cells carrying a TP53 mutation exhibited higher SERCA intensity close to the nucleus. The data reveal an unanticipated interdependence between the SERCA ATP2A3 isoform and p53, suggesting functional interrelationships between these proteins with the disabling of lymphocyte immune responses by HPV infection, as part of the molecular mechanism of viral oncogenesis, highlighting these genes as possible prognosis biomarkers for oropharyngeal squamous cell carcinoma.