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.
Subject(s)
Carcinoma, Hepatocellular/metabolism , Cell Transformation, Neoplastic/metabolism , Cellular Reprogramming , Energy Metabolism , Hepatocytes/metabolism , Liver Neoplasms/metabolism , Precancerous Conditions/metabolism , Aged , Aged, 80 and over , Animals , Carcinoma, Hepatocellular/genetics , Carcinoma, Hepatocellular/secondary , Cell Transformation, Neoplastic/genetics , Cell Transformation, Neoplastic/pathology , Cellular Reprogramming/drug effects , Energy Metabolism/genetics , Female , Gene Expression Regulation, Enzymologic , Gene Expression Regulation, Neoplastic , Glucosephosphate Dehydrogenase/genetics , Glucosephosphate Dehydrogenase/metabolism , Glycolysis , HSP90 Heat-Shock Proteins/genetics , HSP90 Heat-Shock Proteins/metabolism , Hepatocytes/pathology , Humans , Keratin-19/metabolism , Liver Neoplasms/genetics , Liver Neoplasms/pathology , Male , Middle Aged , NF-E2-Related Factor 2/genetics , NF-E2-Related Factor 2/metabolism , Neoplasm Grading , Oxidative Phosphorylation , Pentose Phosphate Pathway , Precancerous Conditions/genetics , Precancerous Conditions/pathology , RNA Interference , Rats, Inbred F344 , Time Factors , Transfection , Tumor Cells, CulturedABSTRACT
Mitochondria of Drosophila melanogaster undergo Ca(2+)-induced Ca(2+) release through a putative channel (mCrC) that has several regulatory features of the permeability transition pore (PTP). The PTP is an inner membrane channel that forms from F-ATPase, possessing a conductance of 500 picosiemens (pS) in mammals and of 300 pS in yeast. In contrast to the PTP, the mCrC of Drosophila is not permeable to sucrose and appears to be selective for Ca(2+) and H(+). We show (i) that like the PTP, the mCrC is affected by the sense of rotation of F-ATPase, by Bz-423, and by Mg(2+)/ADP; (ii) that expression of human cyclophilin D in mitochondria of Drosophila S2R(+) cells sensitizes the mCrC to Ca(2+) but does not increase its apparent size; and (iii) that purified dimers of D. melanogaster F-ATPase reconstituted into lipid bilayers form 53-pS channels activated by Ca(2+) and thiol oxidants and inhibited by Mg(2+)/γ-imino ATP. These findings indicate that the mCrC is the PTP of D. melanogaster and that the signature conductance of F-ATPase channels depends on unique structural features that may underscore specific roles in different species.
