Paolo Comoglio

The c-met protooncogene encodes a 190-kd transmembrane
tyrosine kinase. This molecule is the receptor for
the hepatocyte growth factor (HGF), which is an important
mitogen for hepatocytes both in vitro and in
uivo. In experimental models, the c-met transcripts appeared
strongly expressed by actively proliferating oval
cells (OCs). We evaluated the phenotypic modulation of
the c-met protooncogene product (c-met pp), in 10 hepatocellular
carcinomas (HCCs), 5 focal nodular hyperplasias
(FNHs), 4 cases of fulminant hepatitis (FH), and 1
regenerated liver, selected to include the different biological
states of hepatocyte (mature normal hepatocytes,
transformed ones, and OCs). The supposed mitogenic effect
of HGF was analyzed by comparing c-met pp overexpression
with the Ki67 index, whereas anti-OV-6 antibody
was used for comparison with the presence of OCs.
The anti-c-met pp showed a typical plasma membranespecific
staining in all cases. The signal was much
stronger in the HCCs than in the benign conditions. The
anti-OV-6 monoclonal antibody showed positive immunostaining
in many of the cells expressing c-met pp. The
percentage of Ki67+ nuclei in high-grade HCCs paralleled
c-met protooncogene overexpression. The c-met pp
in OV-6+ cells suggests that the paracrine mechanism
postulated in experimental models could also apply

Ischaemic heart disease is the main cause of death in western countries. Cardiac tissue is primarily damaged by cardiomyocyte cell death triggered by low oxygen supply to the heart (hypoxia). The current therapeutic approach is coronary angioplastic intervention or thrombolytic treatments to resume blood flow in the ischaemic heart. Unfortunately, reperfusion itself causes a burst of ROS production responsible for cardiomyocyte death and myocardial dysfunction. Indeed, the majority of patients surviving to acute myocardial infarction undergoes progressive heart failure, with 50% mortality at five years from diagnosis. Apoptosis of cardiomyocytes is dangerous both during ischaemia and reperfusion. In line with this concept, we have shown that treatment of H9c2 cardiomyoblasts with cobalt chloride (CoCl2), a chemical mimetic of hypoxia, induces caspase-dependent apoptosis. Unexpectedly, we found that 3-methyladenine, an inhibitor of autophagy initiation, partially prevents CoCl2-mediated cell death, indicating that also autophagy contributes to cardiomyoblast death. Consistently, we found an increase in the autophagic flux in dying cells. Mechanistically, we have shown that CoCl2 upregulates Redd1, Bnip3 and phospho-AMPK proteins and causes inhibition of mTOR, the main negative regulator of autophagy. In light of these observations, it is important to discover new therapeutic tools displaying a dual prosurvival mechanism. To this aim, we have analyzed the cardioprotective action of HGF/Met axis in hypoxic injury. To activate Met signaling we have used either the HGF ligand or two different monoclonal antibodies (mAbs) directed against the extracellular moiety of Met receptor. Owing a divalent structure, the two mAbs can dimerize and activate Met receptor, thus displaying agonist activity. Hypoxic injury was fully prevented by either HGF or Met agonist mAbs through both anti-apoptotic and anti-autophagic functions. By pharmacological inhibition we showed that activation of mTOR is the protective signaling downstream to Met, being involved in the anti-autophagic effect. In conclusion, HGF or Met agonist mAbs promote cell survival by negative dual regulation of apoptotic and autophagic cell death and represent promising new therapeutic tools to manage cardiac diseases.