title: Inhibitory role of Smad7 in hepatocarcinogenesis in mice and in vitro.
abstract: Smad7 is a principal inhibitor of the TGFβ-Smad signalling pathway. We have investigated the functional significance of Smad7 in hepatocellular carcinoma (HCC). Smad7 knockout (KO) and wild-type (WT) mice were injected with diethylnitrosamine (DEN) to induce HCC. The effects of Smad7 on cellular features were examined in HCC cells, using a Smad7 over-expression or deletion approach. Signalling pathway components modulated by Smad7 in HCC were evaluated using luciferase reporter assay and co-immunoprecipitation. Smad7 was down-regulated in human HCCs compared with the adjacent normal tissues (p < 0.001). Smad7 KO mice were more susceptible to DEN-induced HCC than WT mice (78% versus 22%, p < 0.05). HCCs from KO mice displayed a greater proliferation activity (p < 0.05) and a reduced apoptotic index compared with WT littermates (p < 0.05). Deletion of Smad7 promoted cell proliferation in primary cultured HCC cells. In addition, over-expression of Smad7 in HCC cell lines markedly suppressed cell growth (p < 0.0001) and colony formation (p < 0.01). Cell cycle analysis revealed an increase in the G1 phase and a reduction in the S-phase populations, accompanied by up-regulation of p27(Kip1) and down-regulation of cyclin D1. Smad7 increased cell apoptosis (p < 0.01) by mediating an intrinsic [caspase-9, caspase-3 and poly(ADP-ribose) polymerase] apoptotic pathway. Moreover, Smad7 inhibited NF-κB signalling by interacting with TAB2, an upstream activator of NF-κB, and inhibited TGFβ signalling by suppressing phosphorylation of Smad3. In conclusion, loss of Smad7 enhances susceptibility to HCC. Smad7 suppresses HCC cell growth by inhibiting proliferation and G1 -S phase transition and inducing apoptosis through attenuation of NF-κB and TGFβ signalling. Smad7 acts as a potential tumour suppressor in liver.
authors.affiliation: Institute of Digestive Disease and Department of Medicine and Therapeutics, Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong.
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.forename: Jingmin
authors.initials: J
authors.lastname: Zhao
authors.forename: Eagle S H
authors.initials: ES
authors.lastname: Chu
authors.forename: Myth T S
authors.initials: MT
authors.lastname: Mok
authors.forename: Minnie Y Y
authors.initials: MY
authors.lastname: Go
authors.forename: Kwan
authors.initials: K
authors.lastname: Man
authors.forename: Rainer
authors.initials: R
authors.lastname: Heuchel
authors.forename: Hui Yao
authors.initials: HY
authors.lastname: Lan
authors.forename: Zhijie
authors.initials: Z
authors.lastname: Chang
authors.forename: Joseph J Y
authors.initials: JJ
authors.lastname: Sung
authors.forename: Jun
authors.initials: J
authors.lastname: Yu
mesh_terms: D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D018797:Cell Cycle Proteins / Q000378:metabolism; D049109:Cell Proliferation; D004052:Diethylnitrosamine; D016193:G1 Phase; D017930:Genes, Reporter; D020022:Genetic Predisposition to Disease; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D047468:Immunoprecipitation; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016328:NF-kappa B / Q000378:metabolism; D010641:Phenotype; D061251:Primary Cell Culture; D016196:S Phase; D015398:Signal Transduction; D051906:Smad7 Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D018797:Cell Cycle Proteins; D016328:NF-kappa B; C497806:SMAD7 protein, human; D051906:Smad7 Protein; C497807:Smad7 protein, mouse; D016212:Transforming Growth Factor beta; D004052:Diethylnitrosamine
keywords: Smad7; animal model; hepatocellular carcinoma; tumour suppressor