Shifting metabolico e cancro: nuovi fattori molecolari coinvolti nell'insorgenza e progressione dell'epatocarcinoma

In recent years, it has emerged, with great resonance, the role of metabolism in cancer cells. The acquisition of genetic damage, inhibition of apoptosis in favor of shifting the metabolic and proliferative pathway are among the main mechanisms that define and promote the survival of the neoplastic clone. Recent studies have shown that the neoplastic cell is characterized by a metabolic profile dependent on glycolysis as the main source of energy, regardless of the levels of oxygen (Warburg effect). Malignant transformation alters the bioenergetic and biosynthetic requirements of the cell as well, including lipid metabolism that is altered resulting in an increase in de novo lipogenesis and decreased lipolysis. It 's well known the role of metabolic oncogene FASN (fatty acid synthase), a key enzyme for the synthesis of long chain fatty acids, whose expression is significantly increased in several human tumors compared to the corresponding healthy tissue. In our study we aimed to analyze the role of two other enzymes of lipid metabolism: CPT1A (carnitine palmitoyl transferase-I) and LOX-1 (Lectinlike oxidized LDL receptor-1) both are regulate or regulate the activity of FASN that appears to have a key role in the transition from normal to neoplastic phenotype. CPT1 is a protein belonging to the family of the carnitine / choline acetyltransferase, resides in the outer mitochondrial membrane and serves to convey the long chain fatty acids into the mitochondria for β-oxidation. The protein receptor LOX-1, however, is a transmembrane glycoprotein involved in internalization by endocytosis of ox-LD. In neoplastic cells, where FASN is overexpressed the β-oxidation of fatty acids is inhibited. The two processes are mutually regulated by malonyl-CoA, the substrate of FASN and physiological inhibitor of CPT1A. Previous studies in our laboratory showed a peculiar nuclear localization of CPT1A in several types of cancer tissues (breast, colon, liver and prostate). The nuclear localization was confirmed by in vitro studies on tumor cell lines (MCF-7, Caco-2, HepG2) compared to non-tumor lines. In tumor cells where the protein was found to be expressed at the nuclear level, we have highlighted the existence of a new transcript (CPT1A2) corresponding to a shorter isoform protein at the level of the C-terminal end. Transfection of HepG2 cells with vectors expressing the two isoforms of CPT1A, showed the ability of variant 2 to confer a proliferative advantage compared to classical isoform of CPT1A and control. Experiments of immunocytochemistry and co-immunoprecipitation have suggested a possible involvement of var2 of CPT1A in the regulation of histone acetylation, mediated by HDAC. To confirm this hypothesis, were performed experiments of RNA interference in HepG2 cells from which has resulted in a significant decrease in the activity of HDAC, as well as an increase of histone acetylation in cells silenced for var2, reinforcing the hypothesis that CPT1A could have a role linked to epigenetic regulation in tumors. We then analyzed the other protein factor that regulate the activity of FASN, LOX-1. Preliminary results have shown that the expression of LOX-1 is increased in several human cancers, colon, beast and HCC (hepatocellular carcinoma), compared to the corresponding normal tissue. In particular, by in vitro studies on a cell line of hepatocellular carcinoma, HepG2, was detected the overexpression of a particular splice variant of LOX-1, the variant 4, characterized in mouse embryonic cells. Transfection of HepG2 cells with vectors expressing the three isoforms of LOX-1 has highlighted the role of the pro-oncogenic isoform 4 of LOX-1. This isoform confers a distinct growth advantage when transfected as in neoplastic as in normal cells confirming its potential role as an oncogene. The results obtained by Western blot analysis also showed a potential role of this isoform in transcriptional modulation of proteins involved in apoptosis and cell cycle regulation.