Mutant p53-dependent alterations of cancer metabolism and tumor microenvironment in pancreatic adenocarcinoma cells

Pancreatic adenocarcinoma (PDAC) is one of the most aggressive and devastating human malignancies. Late diagnosis is due to an absence of specific symptoms at initial stages. In about 70% of PDACs, the tumor suppressor gene TP53 is mutated generally resulting in conformational changes of mutant p53 (mutp53) proteins, making an important key in the carcinogenesis process not only through loss of wild type activity, but also through gain of specific mutant functions. In contrast to the tumor suppressive roles of wild-type p53, mutant p53 proteins support cancer progression by enhancing the ability of cancer cells to invade and metastasize, to confer chemoresistance, and to stimulate genomic instability. We focused our attention on novel molecular mechanisms by which gain of function (GOF) mutant p53 proteins play their oncogenic roles promoting cancer cell proliferation and chemoresistance. The main project is based on intracellular alterations induced by mutant p53 in cancer metabolism and reactive oxygen species (ROS) production, contributing to cancer development and aggressiveness. ROS are highly reactive byproducts of mitochondrial oxidative phosphorylation and are implicated in a plethora of biological events addressed to sustain each aspect of human cancer being able to act as second messengers in cellular signaling. In particular, we unveiled that mutp53 is able to inhibit SESN1 expression and consequently the amount of SESN1/AMPK complex, resulting in the downregulation of the AMPK/PGC-1α/UCP2 axis and ROS production. In this way GOF mutant p53 proteins, contrarily to its wild-type p53 counterpart, lead i) antiapoptotic effects, ii) proliferation and iii) chemoresistance in PDAC cells. These oncogenic roles given by GOF mutp53 are also detected through another mechanism that supports glycolytic metabolism in PDAC cells. Indeed, we demonstrated that mutant p53 prevents the nuclear translocation of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) stabilizing its cytoplasmic localization, thus supporting glycolysis of cancer cells and inhibiting cell death mechanisms mediated by nuclear GAPDH. We further show that the prevention of nuclear localization of GAPDH is mediated by both stimulation of AKT and repression of AMPK signaling, and is also associated with the formation of SIRT1:GAPDH complex. The blockage of GAPDH mutp53-dependent cytoplasmic stabilization is able to restore the sensitivity of PDAC cells to the treatment with gemcitabine, permitting cancer cells to acquire sensitivity to anti-glycolytic drugs and suggesting a potential personalized therapeutic approach in human cancers carrying mutant TP53 gene. In addition, we addressed our research on the extracellular roles of mutant p53 in the tumor microenvironment of PDAC cells. The cancer secretome is a rich repository to find useful information for both cancer biology and clinical oncology. A better understanding of biological features that are common or peculiar to different tumors could allow the identification of specific prognostic/predictive biomarkers for early diagnosis and tumor progression monitoring. This is particularly relevant for PDAC, which has extremely high mortality rate and is mainly due to lack of recognizable symptoms and exact assays for early detection. The objective of this study was to recognize a specific signature of biomarkers secreted by PDAC cells carrying GOF mutant p53. Comparing the secretome of p53-null PDAC cells before and after ectopic overexpression of R273H-mutp53 and R175H-mutp53, we found 23 differentially secreted proteins by both mutant p53 isoforms that might constitute a secreted signature driven by the hot-spot p53 mutants in PDAC. Furthermore, we also studied the functional effect of mutp53-driven secretome on cancer cells showing its influence on proliferation, chemoresistance, apoptosis, autophagy, and cell migration. These data constitute a prerequisite for the identification of a secreted biomarker signature for the early identification of mutant p53 PDAC patients. In conclusion, the discovery of novel mechanisms by which hot-spot mutant p53 isoforms induce pancreas cancer growth is crucial to identify specific and personalized therapies for PDAC patients bearing mutant TP53 gene, representing a major therapeutic challenge for modern molecular oncology.