Induction of metallothionein gene expression by epidermal growth factor and its inhibition by transforming growth factor-β and dexamethasone in rat hepatocytes

Abstract

Metallothionein (MT) is a small cysteine-rich protein thought to be mainly involved in metal regulation and detoxification. The implication of MT in cell growth and differentiation has also been suggested. This latter hypothesis was further investigated in adult rat hepatocytes induced to proliferate by epidermal growth factor (EGF). Exposure of hepatocytes to EGF resulted in significant increases (approximately twofold) in MT protein and MT-1 messenger RNA (mRNA) levels, which were maximal after 48 hours. As revealed by nuclear run-on analysis, these changes were the result of transcriptional activation. Increases of MT occurred concomitantly with stimulation of DNA synthesis (48 hours). Addition of ZnSO4 or dexamethasone (Dex) was also effective at inducing MT protein (approximately 3.6 to 3.3 times) and mRNA. Combined addition of Zn and EGF produced an additive increase in MT protein and MT-1 mRNA levels. When both Dex and EGF were present together, the EGF-induced MT protein and mRNA expression was lost, whereas it had only minor inhibitory effects on DNA synthesis. Transforming growth factor beta (TGF-beta), a known antagonist of EGF on hepatocytes, blocked the EGF-induced MT accumulation and stimulation of DNA synthesis. In addition, under the same conditions, the EGF-induced c-fos mRNA accumulation was blocked by Dex whereas TGF-beta had no effect. These results show that growth factors believed to play a role in liver regeneration can also modulate MT gene expression in vitro. This modulation does not strictly parallel that of DNA synthesis. The possibility that c-fos stimulation may play a role in MT induction by EGF cannot be ruled out.

Coordinated regulation of ceruloplasmin and metallothionein mRNA by interleukin‐1 and copper in HepG2 cells

“…The HepG2 cells that were used here are adherent cells which were seeded from confluent flasks and are so likely to have been at least partially synchronized in the cell cycle and could so produce a simultaneous rise in the MT just prior to cell division as seen for other cells [26]. MT is an important housekeeping gene and induction of growth in rat hepatocytes has been shown to induce high levels of mRNA which were maximal at 48 h. It was also shown that the effects of growth and metals were additive which would support the observations that we have made here [27].…”

Transcriptional profiling of ErbB signalling in mammary luminal epithelial cells - interplay of ErbB and IGF1 signalling through IGFBP3 regulation

“…Members of the MT family were also potently induced by EGF. Whilst induction of MT1 expression by EGF has been shown in rat hepatocytes [41], this is the first report of MT1 (and MT3) induction by EGF in human epithelial cells. Since the altered expression of MT family members has been implicated in neoplasia and drug resistance [42,43], it will be interesting to investigate whether MT expression is linked to deregulated GF signalling in cancer.…”

Metallothioneins: potential therapeutic aids for wound healing in the skin

“…The implications are based on research using isolated rat hepatocytes that were induced to proliferate with epidermal growth factor. 27 The proliferative activity in this system was accompanied by appreciable increases in MT-1 mRNA and MT-protein within 48 hours. This was augmented by addition of zinc sulfate.…”

“…Earlier work suggests that cytokines and growth factors are implicated in the activation of the MT‐gene in wounded tissue. The implications are based on research using isolated rat hepatocytes that were induced to proliferate with epidermal growth factor 27 . The proliferative activity in this system was accompanied by appreciable increases in MT‐1 mRNA and MT‐protein within 48 hours.…”