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42 43 > Research Report // AR 2006
doses for patients. This is an important issue since the rate at
which drugs are cleared from the body can vary substantially
between individuals and have a major influence on the
effectiveness and toxicity of treatment.
In a collaborative project with the Family Cancer group and
the Kathleen Cuningham Consortium for Research into
Familial Breast Cancer (kConFab), Translational Oncology
also reported a study in 2006 that described the pathology
features of breast cancer in carriers of variants in a gene that
has been implicated in increased breast cancer risk; ataxia
telangiectasia mutated (ATM). This was of interest because
certain types of familial breast cancer are associated with
particular pathologic features although these were not seen in
carriers of ATM variants.
Another major project that Translational Oncology is
involved with is establishment of a Breast Cancer Tissue
Bank in centres across New South Wales that will make
breast cancer tissue specimens available for research Australiawide.
Supported by funding from the National Health
and Medical Research Council, National Breast Cancer
Foundation and Cancer Institute NSW this initiative will
form important infrastructure for future translational breast
cancer research.
Genomics and genetic epidemiology
The Genomics and Genetic Epidemiology Group focuses
on identifying the genes that strongly affect cancer risk
and discovering how that genetic risk interacts with the
environment to cause cancer. Hundreds of families of people
with a strong family history of melanoma have supported the
groups projects over the last twenty years and their samples
continue to be used intensively to identify new melanoma
genes. Over 2006 they were used in three searches involving
22 research groups of the international melanoma genetics
consortium (GenoMEL) and several million dollars’ funding
from the European Union and the US National Institutes of
Health. They cover each of the main high-throughput ways
of identifying new disease genes: genetic linkage, genetic
association and candidate gene analysis.
The group also completed the Australian Melanoma Family
Study (AMFS), with the University of Melbourne’s MEGA
Centre and the Queensland Cancer Fund Epidemiology
Research Unit. This is one of the world’s largest populationbased
studies of melanoma, enrolling over 1100 people who
developed melanoma before age 40 in Melbourne, Sydney
and Brisbane, or unaffected controls, plus thousands of their
family members. Early-onset melanoma can be indicative of
increased susceptibility, but little is known about what genes
contribute to risk in this setting. The AMFS has shown that
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in at least some cases (2%) a gene that is commonly mutated
in familial melanoma is responsible: the CDKN2A (p16)
tumour suppressor gene. The group has also showed that
the risk caused by these mutated genes in the population is
not as high as it is in people with a strong family history of
melanoma.
As part of her successful PhD Nadine Kasparian reported
some of the first research anywhere in the world that has
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studied perception of melanoma risk and the psychological
consequences of high melanoma risk in melanoma families.
These are collaborations with Prince of Wales Hospital and
the University of Sydney.
Both the NHMRC and Cancer Institute NSW Program
Grants have enabled the group to start wide-ranging studies
with collaborators at the Sydney Melanoma Unit, directed
at understanding the genetic abnormalities in melanomas
themselves. The goals of these high-throughput studies
of gene and protein expression are to understand how
apparently similar melanomas can have such different clinical
behaviour, whether a greater propensity to relapse after
surgery, or differing responsiveness to drug and biological
treatment, for example. Since the SMU is the largest
melanoma treatment and clinical research centre in the
world, these are intended to be benchmark studies of these
issues and will be the main focus of the group in 2007-8.
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Liver and Metabolic
Storr Liver Unit
The role of leptin in the pathogenesis of hepatic fibrosis
The mechanisms by which the hormone leptin, which
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circulates in increased concentrations in obese individuals,
exerts its pro-fibrogenic (scarring) effects on the liver are
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currently unclear. In this project we examined the expression
of pro-fibrogenic genes and proteins in cultured rat hepatic
7`-hydroxylase
stellate cells (HSCs; the main cellular source of scar tissue
in the liver) following exposure to leptin. We were able
to demonstrate that leptin did not directly enhance HSC
activation. In contrast, there were remarkable increases in
pro-fibrogenic gene and protein expression in HSCs after
these cells were cultured in the medium of Kupffer cells that
had been previously exposed to leptin. Furthermore, we
found that the effect of leptin on Kupffer cells was mediated
by increasing the production of connective tissue growth
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factor (CTGF) and transforming growth factor beta. 2 Both
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these cytokines are potent stimulators of fibrosis in hepatic
stellate cells. We have taken these data further and have now
characterized the intracellular molecular basis by which leptin
exerts its affects. This project has demonstrated that Kupffer
cells play an important role in leptin-mediated liver fibrosis
and provide a novel molecular mechanism by which obesity
causes scarring of the liver and cirrhosis.
Molecular mechanisms for the development of fatty liver
disease in humans
Non-alcoholic fatty liver disease (NAFLD) is the commonest
cause of progressive liver damage in Australia leading to
cirrhosis and liver cancer in some individuals. To date,
altered lipid (fat) homeostasis has been shown to contribute
to the accumulation of liver fat, but the mechanisms by
which a fatty liver is converted to one with liver damage
(steatohepatitis) has not been fully elucidated. In this project,
researchers from the Storr Liver Unit sought to identify
the molecular determinants leading to the progression to
steatohepatitis. We therefore examined the expression of
a number of critical nuclear receptors (NXRs) and key
genes regulating carbohydrate, cholesterol and bile acid
metabolism, synthesis and transport within the liver. In
addition, we examined the expression of key inflammatory
cytokines and pro- and anti-apoptotic cell death genes.
This study was unique in that it was conducted on minute
quantities of human liver tissue removed at the time of liver
biopsy. Our results indicated that several nuclear receptors
NADP +
(LXR, PXR, FXR and CAR) which regulate key genes for
bile acid synthesis and export were up-regulated in patients
with steatohepatitis compared with healthy controls.
Likewise, the expression of key cell death genes (BAD, BID,
BAX) and those which mediate liver inflammation, were
increased in livers from patients with steatohepatitis. These
data are consistent with our novel proposal that alterations
in nuclear receptor expression are a critical mediator of liver
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damage in patients with non-alcoholic steatohepatitis.
The role of bile acids as a mediator of liver injury in an
animal model of fatty liver disease
In this study, we attempted to further characterise the
several steps
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molecular and cellular basis for the development of nonalcoholic
steatohepatitis (NASH) by studies using an animal
model that was developed at the Storr Liver Unit. NASH
is characterized by the presence of hepatic steatosis (fat),
liver injury, inflammation and variable fibrosis (scarring).
The mechanisms which initiate hepatitis in a fatty liver
are important, and at present unknown. In this research,
analogous to our human studies, we sought to examine the
role of nuclear receptors and key genes regulating bile acid and
cholesterol metabolism, synthesis and transport within the
liver of animals with NASH. Our results demonstrated that
bile acids were significantly increased early in the development
of NASH in mice. By day 5, we noted major changes in
nuclear receptors and their downstream targets and of genes
which regulate bile acid synthesis and export. Taken together
these data strongly suggest that nuclear receptors and their
ligands (bile acids and oxysterols) may be important mediators
of liver injury in our nutritional model of NASH. It is hoped
that linking these molecular studies in animals with a fatty
liver, to that in humans with NASH will permit a better
understanding of NAFLD and suggest novel treatments.
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