Metabolic reprogramming identifies the most aggressive lesions at early phases of hepatic carcinogenesis

Abstract

Metabolic changes are associated with cancer, but whether they are just bystander effects of deregulated oncogenic signaling pathways or characterize early phases of tumorigenesis remains unclear. Here we show in a rat model of hepatocarcinogenesis that early preneoplastic foci and nodules that progress towards hepatocellular carcinoma (HCC) are characterized both by inhibition of oxidative phosphorylation (OXPHOS) and by enhanced glucose utilization to fuel the pentose phosphate pathway (PPP). These changes respectively require increased expression of the mitochondrial chaperone TRAP1 and of the transcription factor NRF2 that induces the expression of the rate-limiting PPP enzyme glucose-6-phosphate dehydrogenase (G6PD), following miR-1 inhibition. Such metabolic rewiring exclusively identifies a subset of aggressive cytokeratin-19 positive preneoplastic hepatocytes and not slowly growing lesions. No such metabolic changes were observed during non-neoplastic liver regeneration occurring after two/third partial hepatectomy. TRAP1 silencing inhibited the colony forming ability of HCC cells while NRF2 silencing decreased G6PD expression and concomitantly increased miR-1; conversely, transfection with miR-1 mimic abolished G6PD expression. Finally, in human HCC patients increased G6PD expression levels correlates with grading, metastasis and poor prognosis. Our results demonstrate that the metabolic deregulation orchestrated by TRAP1 and NRF2 is an early event restricted to the more aggressive preneoplastic lesions.

MicroRNAs in Animal Models of HCC

“…High G6PD expression levels were detected in CK19-positive lesions and early preneoplastic foci, but not in CK-19-negative lesions, and, in line, increased G6PD mRNA levels were observed in two HCC patient cohorts where it positively correlated with CK19 expression, higher tumor grade, and increased metastasis formation. In agreement, a negative correlation between miR-1 and G6PD was identified in CK19-positive lesions, and lower miR-1 levels were quantified in human HCCs with respect to surrounding livers, confirming the high concordance in terms of dysregulated pathways between aggressive preneoplastic rat lesions and human HCCs [176]. Interestingly, a global proteomic analysis from glutathione S-transferase-P (GST-P) positive laser micro-dissected nodules identified G6PD among protein markers discriminating R-H model-derived focal lesion from normal liver with or without progenitor cell activation, demonstrating LCM coupled with mass-spectrometry-based proteomics as an effective approach to characterize preneoplastic lesions and to identify early diagnostic markers for effective clinical intervention.…”

The Chaperone TRAP1 As a Modulator of the Mitochondrial Adaptations in Cancer Cells

“…Indeed, PH is a stress factor that boosts proliferation and profound metabolic changes in hepatocytes, which is somehow reminiscent of neoplastic growth, but expression levels of TRAP1 do not change after PH in wild-type animals (57). Therefore, the importance of TRAP1 in responding to stress conditions and its modes of regulation are probably context dependent, a concept that could be crucial for understanding TRAP1 functions in tumorigenesis.…”

“…Elevation of TRAP1 protein levels correlates with malignant progression and metastasis in several neoplastic models, including prostate and breast cancer, hepatocellular carcinoma (HCC), and colorectal carcinoma (57–61), and with disease recurrence in non-small cell lung cancer (62). Hence, in these malignancies, TRAP1 is a candidate biomarker for cancer progression and for prognosis outcome.…”

“…In accord with the importance of TRAP1 induction along tumor progression, we have recently observed that its protein levels are markedly increased in very early, pre-neoplastic foci in a model of liver carcinogenesis. In this setting, the enhancement of TRAP1 expression is restricted to lesions that progress to malignancy, where it associates with a marked SDH inhibition that can be reverted by HSP90-family inhibitors (57). …”

“…Handling of oxidative stress might be extremely important at the beginning of tumorigenesis, to avoid that a deregulated ROS increase becomes detrimental for viability of cells in which adequate antioxidant defenses are not yet fully established. Accordingly, in the hepatocarcinogenesis model in which TRAP1 levels are induced from the very early stages, malignant cells build up an anti-oxidant program mastered by the transcription factor Nrf2, which also affects TRAP1 expression (57). Hence, in this tumor type a strong correlation exists among early TRAP1 induction, Warburg-like metabolic rewiring and protection from oxidative insults, and these adaptations are required for neoplastic progression to malignancy.…”