Highlights
- •Downregulation of TLR3 in HCC is associated with poor prognosis and with resistance to TLR3-triggered apoptosis.
- •Downregulation of TLR3 is an escape mechanism for HCC cells which prevents their apoptosis and enhances tumor progression.
- •The effect of TLR3 on apoptosis, which limits tumor progression, is independent of the immune response.
- •TLR3 ligands may represent an effective treatment option for HCC expressing TLR3.
Background & Aims
Low levels of toll-like receptor 3 (TLR3) in patients with hepatocellular carcinoma
(HCC) are associated with poor prognosis, primarily owing to the loss of inflammatory
signaling and subsequent lack of immune cell recruitment to the liver. Herein, we
explore the role of TLR3-triggered apoptosis in HCC cells.
Methods
Quantitative reverse transcription PCR, western blotting, immunohistochemistry and
comparative genomic hybridization were used to analyze human and mouse HCC cell lines,
as well as surgically resected primary human HCCs, and to study the impact of TLR3
expression on patient outcomes. Functional analyses were performed in HCC cells, following
the restoration of TLR3 by lentiviral transduction. The role of TLR3-triggered apoptosis
in HCC was analyzed in vivo in a transgenic mouse model of HCC.
Results
Lower expression of TLR3 in tumor compared to non-tumor matched tissue was observed
at both mRNA and protein levels in primary HCC, and was predictive of shorter recurrence-free
survival after surgical resection in both univariate (hazard ratio [HR] 1.79; 95%
CI 1.04–3.06; p = 0.03) and multivariate analyses (HR 1.73; CI 1.01–2.97; p = 0.04). Immunohistochemistry confirmed frequent downregulation of TLR3 in human
and mouse primary HCC cells. None of the 6 human HCC cell lines analyzed expressed
TLR3, and ectopic expression of TLR3 following lentiviral transduction not only restored
the inflammatory response but also sensitized cells to TLR3-triggered apoptosis. Lastly,
in the transgenic mouse model of HCC, absence of TLR3 expression was accompanied by
a lower rate of preneoplastic hepatocyte apoptosis and accelerated hepatocarcinogenesis
without altering the tumor immune infiltrate.
Conclusion
Downregulation of TLR3 protects transforming hepatocytes from direct TLR3-triggered
apoptosis, thereby contributing to hepatocarcinogenesis and poor patient outcome.
Lay summary
Hepatocellular carcinoma (HCC) is a heterogeneous disease associated with a poor prognosis.
In patients with HCC, TLR3 downregulation is associated with reduced survival. Herein,
we show that the absence of TLR3 is associated with a lower rate of apoptosis, and
subsequently more rapid hepatocarcinogenesis, without any change to the immune infiltrate
in the liver. Therefore, the poor prognosis associated with low TLR3 expression in
HCC is likely linked to tumors ability to escape apoptosis. TLR3 may become a promising
therapeutic target in TLR3-positive HCC.
Graphical abstract
Graphical Abstract
Keywords
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Article info
Publication history
Published online: June 17, 2019
Accepted:
May 21,
2019
Received in revised form:
May 17,
2019
Received:
January 29,
2019
Identification
Copyright
© 2019 Published by Elsevier B.V. on behalf of European Association for the Study of the Liver.
