Telomere dysfunction and telomerase reactivation in the etiology and progression of liver cancer

PROJECT SUMMARY/ABSTRACT
Mutations in telomerase and telomere attrition are major risk factors for liver fibrosis and its progression
to hepatocellular carcinoma (HCC). However, due to a lack of adequate models and intrinsic difficulties in
studying human telomerase in physiologically relevant cells, the molecular mechanisms responsible for liver
fibrosis and cancer in settings of DNA damage arising from short telomeres remain elusive. While telomerase
knockout mice corroborate the importance of telomere maintenance and DNA repair for liver function, the
molecular mechanisms that govern liver abnormalities in patients with damaged telomeres are still unknown.
Likewise, the specific signaling pathways that trigger failure of hepatic cells following telomere shortening and
accumulation of DNA damage remain to be determined. In addition, mutations in the promoter region of the
telomerase reverse transcriptase component (TERT) have been described as the initial and most prevalent
mutation in HCC. While these mutations have been shown to reactivate telomerase, the functional relevance of
this process during failure and transformation of hepatic cells has yet to be interrogated.
The focus of this proposal is to use human pluripotent stem cells as a novel platform to understand the
detrimental effects of mutant telomerase, telomere shortening and accumulation of DNA damage in different
hepatic cell lineages. We have previously generated isogenic hPSC lines harboring several disease-specific
mutations in telomerase and have successfully derived telomerase-mutant human hepatocytes and hepatic
stellate cells in vitro, following established protocols that recapitulate the in vivo development of these lineages.
Here, two specific aims are proposed that utilize this platform to understand the molecular consequences
of telomere erosion, DNA damage, and telomerase impairment for the function of hepatic cells, and to determine
their role during early stages of transformation. In Aim 1 we will determine the role of telomere shortening and
DNA damage accumulation during fibrotic failure of different hepatic cell lineages with impaired telomerase. We
will determine the extent to which mitigation of DNA damage, reactivation of HNF4α, and modulation p53 prevent
fibrotic triggering in telomerase-mutant hepatocytes with variable telomere lengths. As liver fibrosis and its
progression to HCC are multicellular responses we will determine the role of progressive telomere shortening
during the direct and the paracrine fibrotic activation of hepatic stellate cells. In Aim 2, we will investigate the
molecular consequences of mutations in the TERT promoter region during progression of HCC, in settings of
exacerbated DNA damage due to eroded telomeres. Specifically, we will analyze the biochemical and functional
consequences of mutations in the TERT promoter region for hepatocyte function and immortalization.
These studies will determine the molecular mechanisms of liver fibrosis and its progression to HCC in
settings of mutant telomerase and DNA damage. Our unique tools, combined with our expertise in telomerase,
DNA repair, and stem cell biology puts us in an ideal position to make a significant impact in this field.

Grant Number: 5R01CA258386-04
NIH Institute/Center: NIH
Principal Investigator: Luis Batista