Levels of transforming growth factor β and transforming growth factor β receptors in rat liver during growth, regression by apoptosis and neoplasia

Abstract

Transforming growth factor β 1 (TGF-β 1 ) has been implicated as inhibitor of cell proliferation and a potent inducer of apoptosis in vitro and in vivo after the administration of high doses. To assess the role of endogenous TGF-β 1 , we quantitated the cytokine and its receptors in rat liver during regenerative and hyperplastic growth, regression by apoptosis, and in hepatocellular carcinoma (HCC). This was accomplished by Northern blot analysis and by RNase protection assay of the messenger RNA (mRNA) of TGF-β 1 and TGF-β receptors (TβR) types I to III and by an activity bioassay of the TGF-β proteins. Untreated rat livers were found to contain 15.6 ؎ 4.8 ng TGF-β 1 protein/g tissue; TGF-β 2 protein was not detected. To induce toxic cell death and subsequent regenerative DNA synthesis in the liver, rats were treated with a necrogenic dose of carbon tetrachloride (CCl 4 ). After 24 and 48 hours, there was an upregulation of TGF-β 1 (mRNA, up to tenfold; protein, about twofold) and of TβRs (mRNA: two-to fourfold); that indicates an overall enhanced production of and sensitivity to TGF-β 1 , which may serve to confine the regenerative response. Hyperplastic liver growth and regression of the hyperplasia were induced by treatment with cyproterone acetate (CPA) or nafenopin (NAF) followed by withdrawal; neither mRNAs of TGF-β 1 and TβR types I to III nor TGF-β 1 protein exhibited significant changes during the growth phase or during regression by apoptosis. We also studied neoplastic growth. HCC, obtained after long-term treatment with NAF, exhibited high rates of cell replication and apoptosis. The majority of lesions contained mRNA and protein of TGF-β 1 and mRNA of TβR types I to III at concentrations similar to those of the surrounding tissue. In conclusion, during liver regeneration there is a pronounced upregulation of expression of both TGF-β 1 and TβRs I to III, but not during mitogen-induced liver growth or regression. It appears that apoptosis is induced via altered local concentration of TGF-β 1 in a paracrine and/or autocrine way. By this mechanism the lethal effects of TGF-β 1 may be locally confined, and overshoots of apoptosis in the liver may be prevented. (HEPATOLOGY 1998;28:717-726.)

Implication of Bcl-2 family genes in basal and d-amphetamine–induced apoptosis in preneoplastic and neoplastic rat liver lesions

“…This is in keeping with the absence of any change in Tgf-␤1 expression in nafenopin-induced nodules and HCCs. 6 AMPH treatment strongly stimulates c-myc expression but it does not significantly modify the expression of Tgf-␣ and Tgf-␤1/Tgf-␤1-Rs system, although, in these conditions, relatively high apoptosis rates could be found in nodules and HCCs. Cooperation between c-myc and wild type p53, in generation of apoptosis 57,58 cannot be excluded, at least in late lesions, in our experimental conditions.…”

“…[2][3][4][5][6] The molecular mechanisms underlying this phenomenon during the regression of liver hyperplasia induced by promoters have not yet been completely clarified, although a role of TGF-␤1 has been postulated. 5,6 Moreover, recent evidence indicates that the inhibition of apoptosis by nongenotoxic hepatocarcinogens is associated with overexpression of Bcl-2 and Bcl-X L . 7 The growth of initiated hepatocytes leads to the development of persistent liver nodules and hepatocellular carcinomas (HCCs).…”

Interferon α-induced apoptosis on rat preneoplastic liver is mediated by hepatocytic transforming growth factor β1

“…35 These data indicate that loss of TGF-␤ 1 responsiveness is not an initiating or strongly predisposing event, but rather a late event in carcinogenesis. 36,39 Therefore, it is of interest to study if liver preneoplasia at an early stage is still sensitive toward TGF-␤ 1 actions.…”

“…39 In view of the fact that TGF-␤ 1 hepatic content may not reflect the induction of apoptosis by this cytokine, we determined the nuclear content of p-Smads-2/3. We observed high levels of p-Smads-2/3 proteins in the nuclear extracts of IFN-␣2b-treated groups 2 to 4.…”

Hepatocytic precursor (stem-like) WB-F344 cells reduce tumorigenicity of hepatoma CBRH-7919 cells via TGF-β/Smad pathway

“…The intracellular effectors of TGF-ß signaling, Smad proteins, are activated by receptors and translocated to the nucleus, where they regulate transcription of target genes (17). TGF-ß can be produced by hepatic non-parenchymal cells and acts as an inhibitory cytokine on hepatocytes (18) and as a negative regulator of hepatocyte proliferation after viral infection-induced chronic injury (19). In addition, TGF-ß induces apoptosis in several established human liver cancer cell lines, including HepG2 and HepG3 cells (20).…”