Background: Phosphorylated Smad3 isoforms are reversible and antagonistic, and the tumour-suppressive pSmad3C can shift to an oncogenic pSmad3L signal. In addition, Nrf2 has a two-way regulatory effect on tumours, protecting normal cells from carcinogens and promoting tumour cell survival in chemotherapeutics. Accordingly, we hypothesised that the transformation of pSmad3C/3L is the basis for Nrf2 to produce both pro- and/or anti-tumourigenic effects in hepatocarcinogenesis. Astragaloside IV (AS-IV), the major component of Astragalus membranaceus, exerts anti-fibrogenic and carcinogenic actions. Lately, AS-IV administration could delay the occurrence of primary liver cancer by persistently inhibiting the fibrogenesis and regulating pSmad3C/3 L and Nrf2/HO-1 pathways synchronously. However, effect of AS-IV on hepatocarcinogenesis implicated in the bidirectional cross-talking of pSmad3C/3 L and Nrf2/HO-1 signalling, especially which one contributes palpably than the other still remains unclear.
Purpose: This study aims to settle the above questions by using in vivo (pSmad3C+/- and Nrf2-/- mice) and in vitro (plasmid- or lentivirus- transfected HepG2 cells) models of HCC.
Study design and methods: The correlation of Nrf2 to pSmad3C/pSmad3L in HepG2 cells was analysed by Co-immunoprecipitation and dual-luciferase reporter assay. Pathological changes of Nrf2, pSmad3C, and pSmad3L in human HCC patients, pSmad3C+/- mice, and Nrf2-/- mice were gauged by immunohistochemical, haematoxylin and eosin staining, Masson, and immunofluorescence assays. Finally, western blot and qPCR were used to verify the bidirectional cross-talking of pSmad3C/3L and Nrf2/HO-1 signalling protein and mRNA in vivo and in vitro models of HCC.
Results: Histopathological manifestations and biochemical indicators revealed that pSmad3C+/- could abate the ameliorative effects of AS-IV on fibrogenic/carcinogenic mice with Nrf2/HO-1 deactivation and pSmad3C/p21 transform to pSmad3L/PAI-1//c-Myc. As expected, cell experiments confirmed that upregulating pSmad3C boosts the inhibitory activity of AS-IV on phenotypes (cell proliferation, migration and invasion), followed by a shift of pSmad3L to pSmad3C and activation of Nrf2/HO-1. Synchronously, experiments in Nrf2-/- mice and lentivirus-carried Nrf2shRNA cell echoed the results of pSmad3C knockdown. Complementarily, Nrf2 overexpression resulted in the opposite result. Furthermore, Nrf2/HO-1 contributes to AS-IV's anti-HCC effect palpably compared with pSmad3C/3L.
Conclusion: These studies highlight that harnessing the bidirectional crosstalk pSmad3C/3 L and Nrf2/HO-1, especially Nrf2/HO-1 signalling, acts more effectively in AS-IV's anti-hepatocarcinogenesis, which may provide an important theoretical foundation for the use of AS-IV against HCC.
Keywords: AS-IV; Hepatocarcinogenesis; Nrf2; Oxidative stress; pSmad3C.
Copyright © 2023. Published by Elsevier GmbH.