Forschungsgruppe - J.-F. Dufour

Hepatocarcinogenesis

Dufour Jean-François, Principal Investigator,
Maurhofer Olivier
Rajasekaran Raviprasadh
Kellmann Philipp
Bélet David


Primary liver cancer

Hepatocellular carcinoma (HCC), a problem of increasing magnitude

Hepatocellular carcinoma is the fifth most common neoplasm worldwide and the third cause of cancer-related death, responsible for over 500,000 deaths per year.
The aetiology of HCC is linked to cirrhosis due to chronic viral hepatitis (C, B and/or D), fatty liver, alcohol and iron overload. An increase in the incidence of HCC was documented in several epidemiological studies. The incidence has doubled during the last 20 years and is expected to peak between 2015 and 2020. As the incidence increases, the age at onset of diagnosis shows an alarming trend towards younger individuals.

There are two reasons for the increase in HCC incidence: the frequency of chronic hepatitis C and factors relating to lifestyle.  The peak in the epidemic of chronic hepatitis C probably has passed. But, the lifestyle factors have given rise to a surge in metabolic diseases such as obesity and diabetes.

Multifocal HCC and local therapies

There are several reasons explaining why HCC is a tumor particularly challenging to treat:

  1. Patients are frequently diagnosed at an advanced stage, since it develops without symptoms
  2. Patients have most of the time an underlying cirrhosis
  3. Conventional chemotherapy has marginal effect against HCC, since hepatocytes are professional detoxifiers,
  4. HCC is frequently a multifocal tumor in the liver.

This last feature is a peculiar characteristic of HCC. It can form metastases outside the liver but this is a late, infrequent event. In contrary, HCC forms already early on multiple foci in the hepatic parenchyma. This behaviour has important therapeutic and prognostic consequences.
Among the three different therapeutic options, which are surgery, local treatments and systemic targeted therapy, most of the patients are diagnosed at a stage where a local modality is the treatment of choice. Two local treatment modalities are possible: transarterial chemoembolization (TACE) or radiofrequency thermal ablation (RFTA). They both permit the treatment of multiple hepatic lesions. The third option, systemic targeted therapies, is designed to block key signalling pathways that are suspected to be dysfunctional. Several molecules are undergoing clinical trials and this approach inspires hope for an otherwise mortal disease.

Effective use of targeted therapy implies an intimate understanding of signalling pathways involved in HCC and the consequences of their manipulation.Among the affected pathways is the PI(3)K/AKT/mTOR pathway. It is activated in more than 50% of hepatocellular carcinoma and and an mTOR-targeted therapy of HCC with rapamycin derivatives is designed to inhibit some of its components (Figure). It is now recognized that mTOR functions in two complexes, one defined by its association with raptor and another one defined by its association with rictor. The rictor/mTOR complex, also called mTORC2, phosphorylates AKT and therefore promotes cell proliferation. The raptor/mTOR complex, also called mTORC1, phosphorylates S6K and controls protein synthesis. Rapamycin inhibits mTOR but although we know that rapamycin derivatives act upon mTORC1, it is still debated whether they also affect the rmTORC2 complex.

HIT family

The histidine triad (HIT) family of proteins forms a ubiquitous superfamily of small cytosolic, nucleotide binding proteins. The distinguishing feature of these enzymes is an active site motif composed of the sequence His-X-His-X-His-XX, where X is a hydrophobic amino acid.  HIT proteins are phosphoramidases, dinucleotide hydrolyases and nucleotidylyl transferases. These proteins have been highly conserved throughout evolution and are present in all kingdoms of life. The human genome encodes for 7 HIT proteins, which can be classified into 5 groups:

PDB_4RHN
Figure - Hint2 -Structural characterization PDB_4INC
- HIT motif - dimeric binding domain -reference
Helices in pink, Beta- sheets in yellow

1. Hint proteins (HIstidine triad NucleoTide-binding proteins)

Hint proteins constitute the most ancient and conserved HIT proteins, with at least one representative found in all fully sequenced genomes. The human genome contains three different HINT genes that code for HINT1, HINT2 and HINT3.

Publications :
Disruption of tumor suppressor gene Hint1 leads to remodeling of the lipid metabolic phenotype of mouse liver - Beyo─člu D1, Krausz KW2, Martin J1, Maurhofer O1, Dorow J3, Ceglarek U3, Gonzalez FJ2, Dufour JF, Idle JR, 2014 - J. Lipid Res.

Characterization of the effect of the mitochondrial protein Hint2 on intracellular Ca(2+) dynamics - Ndiaye D1, Collado-Hilly M, Martin J, Prigent S, Dufour JF, Combettes L, Dupont G, 2013 - Biophys J.

Disruption of the histidine triad nucleotide-binding hint2 gene in mice affects glycemic control and mitochondrial function- Martin J1, Maurhofer O, Bellance N, Benard G, Graber F, Hahn D, Galinier A, Hora C, Gupta A, Ferrand G, Hoppeler H, Rossignol R, Dufour JF, St-Pierre MV, 2013 - Hepatology
 

  • Hint1. Hint1 forms homodimers, with each subunit binding a nucleotide. Hint1 catalyses the hydrolysis of nucleosides phosphoraminidate and acyl-adenylates but has a preference for purine phosphoramidates over pyrimidine phosphoramidates. Endogenous substrates for Hint1 might be aminoacyl-AMP intermediates. Aminoacyl-tRNA synthetases charge aminoacids with their corresponding cognate tRNAs to form aminoacyl-tRNAs. The reaction proceeds by the formation of an aminoacyl-AMP intermediate. Hint1 knockout mice (Hint1-/)- mice develop normally, but present an enhanced susceptibility to carcinogens. We found that Hint1-/- mice are resistant to hepatic ischemia/reperfusion injury. 
  • Hint2. We have reported that Hint2 is located in mitochondria and that HINT2 mRNA is significantly downregulated in several human carcinomas. The characterization of our Hint2 knockout mice (Hint2-/-) mice revealed a striking metabolic phenotype.  Major changes in Hint2-/- mice were the accumulation of hepatic triglycerides, associated with a decrease in the activity of the β-oxidation enzyme short chain 3-hydroxyacyl-CoA dehydrogenase, and an impaired glucose tolerance.
  • Hint3. A third HINT gene can be found in the human genome at 6q22.33. This HINT3 gene is predicted to encode a 182 amino acid protein with a 31 and 25 amino acid extension at the N- and C-terminus, respectively. The group of Rick Wagner (University of Minnesota) reported that Hint3 can assemble into multimeric oligomers and prefers acyl-adenylates to nucleoside phosphoramidates. Hint3 seems to form aggregates both in the cytosol and in the nucleus.

2. Aprataxin

In 2001, linkage analysis showed that aprataxin was mutated in patients with ataxia-ocular apraxia. The aprataxin gene (APTX) encodes a member of the histidine triad (HIT) superfamily and plays a role in DNA single-strand-break repair. Aprataxin catalyses the nucleophilic release of adenylate groups covalently linked to 5'-phosphate termini at single-strand nicks and gaps, resulting in the production of 5'-phosphate termini that can be efficiently rejoined. Aprataxin has also been localized to mitochondria where it protects mtDNA. DNA repair functions of aprataxin have pharmacological implications in oncology: aprataxin gene expression levels were found to negatively correlate with irinotecan sensitivity in tumour samples.

3. Scavenger decapping enyzme, DCPS

The 3’-5’ mRNA degradation pathway generates small capped m7G-containing oligonucleotides (m7GpppN) that are hydrolyzed into m7GMP by the scavenger mRNA decapping enzyme DcpS, a member of the histidine triad (HIT) family of proteins.

PDB_4RHN

4. FHIT (Fragile Hit protein)

The FHIT gene is localized within the most fragile region of the human genome. FHIT is inactivated in many types of human tumours like lung, oesophagus, stomach, kidney, cervical and hepatocellular carcinomas, indicating that Fhit is a pro-apoptotic tumour suppressor. More recently Fhit was found to have not only a cytosolic but also mitochondrial localization where it stabilizes ferredoxin reductase. Fhit-negative cells produce lower levels of apoptosis-inducing reactive oxygen species.

5. Galactose-1-phosphate uridylyltransferase

Galactose-1-phosphate uridylyltransferase, which contains tandem HIT domains, is the second enzyme in the metabolism of galactose in the liver. It catalyzes the transfer of UMP from UDP-glucose to galactose-1-phosphate producing UDP-galactose and glucose-1-phosphate. Mutations in the galactose-1-phosphate uridylyltransferase gene result in galactosemia, a disease characterized by a failure to thrive, cataracts and mental retardation.


 

Research Focus

Hepatocellular carcinoma
Hint proteins
Aprataxin
DcpS
FHIT
Galactose-1-phosphate uridylyltransferase

Research ratios

Humans : Animals

119 : 46

Top Major MeSH Headings

Carcinoma, Hepatocellular
Liver Neoplasms
Hepatitis C, Chronic
Treatment Outcome
Liver Cirrhosis
Liver Transplantation
Fatty Liver
Hepacivirus
 

Histology


Normal liver
 

NASH
 

HCC