TBX3 functions as a tumor suppressor downstream of activated CTNNB1 mutants during hepatocarcinogenesis

J Hepatol. 2021 Jul;75(1):120-131. doi: 10.1016/j.jhep.2021.01.044. Epub 2021 Feb 10.

Abstract

Background & aims: Gain of function (GOF) mutations in the CTNNB1 gene are one of the most frequent genetic events in hepatocellular carcinoma (HCC). T-box transcription factor 3 (TBX3) is a liver-specific target of the Wnt/β-catenin pathway and thought to be an oncogene mediating activated β-catenin-driven HCC formation.

Methods: We evaluated the expression pattern of TBX3 in human HCC specimens. Tbx3 was conditionally knocked out in murine HCC models by hydrodynamic tail vein injection of Cre together with c-Met and ΔN90-β-catenin (c-Met/β-catenin) in Tbx3flox/flox mice. TBX3 was overexpressed in human HCC cell lines to investigate the functions of TBX3 in vitro.

Results: A bimodal expression pattern of TBX3 in human HCC samples was detected: high expression of TBX3 in GOF CTNNB1 HCC and downregulation of TBX3 in non-CTNNB1 mutant tumors. High expression of TBX3 was associated with increased differentiation and decreased expression signatures of tumor growth. Using Tbx3flox/flox mice, we found that ablation of Tbx3 significantly accelerates c-Met/β-catenin-driven HCC formation. Moreover, Tbx3(-) HCC demonstrated increased YAP/TAZ activity. The accelerated tumor growth induced by loss of TBX3 in c-Met/β-catenin mouse HCC was successfully prevented by overexpression of LATS2, which inhibited YAP/TAZ activity. In human HCC cell lines, overexpression of TBX3 inhibited HCC cell growth as well as YAP/TAZ activation. A negative correlation between TBX3 and YAP/TAZ target genes was observed in human HCC samples. Mechanistically, phospholipase D1 (PLD1), a known positive regulator of YAP/TAZ, was identified as a novel transcriptional target repressed by TBX3.

Conclusion: Our study suggests that TBX3 is induced by GOF CTNNB1 mutants and suppresses HCC growth by inactivating PLD1, thus leading to the inhibition of YAP/TAZ oncogenes.

Lay summary: TBX3 is a liver-specific target of the Wnt/β-catenin pathway and thought to be an oncogene in promoting liver cancer development. Herein, we demonstrate that TBX3 is in fact a tumor suppressor gene that restricts liver tumor growth. Strategies which increase TBX3 expression and/or activities may be effective for HCC treatment.

Keywords: HIPPO cascade; Hepatocellular carcinoma; T-box transcription factor 3; β-Catenin.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carcinogenesis / genetics*
  • Carcinoma, Hepatocellular* / genetics
  • Carcinoma, Hepatocellular* / metabolism
  • Drug Discovery
  • Gain of Function Mutation
  • Gene Expression Regulation, Neoplastic
  • Genes, Tumor Suppressor / physiology
  • Humans
  • Liver Neoplasms* / genetics
  • Liver Neoplasms* / metabolism
  • Mice
  • Mice, Knockout
  • Phospholipase D / metabolism
  • Proto-Oncogene Proteins c-met / metabolism
  • Wnt Signaling Pathway
  • beta Catenin* / genetics
  • beta Catenin* / metabolism

Substances

  • CTNNB1 protein, human
  • CTNNB1 protein, mouse
  • beta Catenin
  • Proto-Oncogene Proteins c-met
  • Phospholipase D
  • phospholipase D1