Enhanced Apoptosis in Metallothionein Null Cells

Abstract

Metallothioneins (MTs) are major intracellular, zinc-binding proteins with antioxidant properties. Mouse embryonic cells null for MT due to loss of functional MT I and II genes (MT-/-) were more susceptible to apoptotic death after exposure to tert-butyl hydroperoxide or the anti-cancer agents cytosine arabinoside, bleomycin, melphalan, and cis-dichlorodiammineplatinum(II) compared with wild-type mouse embryonic cells (MT+/+). We measured basal levels of the tumor suppressor protein p53 and the death effector protein Bax and found the basal levels of both proteins were higher in MT null cells compared with MT+/+ cells. After treatment with the DNA-damaging agent cis-dichlorodiammineplatinum(II), p53 protein levels were induced in both MT+/+ and MT-/- cells with MT null cells always maintaining the highest p53 levels. The elevated sensitivity to apoptosis was not restricted to embryonic cells. Primary pulmonary fibroblasts were isolated from distinct litters of MT null, heterozygous, and wild-type mice, and all had undetectable basal MT levels. Zinc exposure increased MT levels in the wild-type and heterozygous fibroblasts but not in the MT null fibroblasts. Consistent with the induced MT levels, we found MT+/+ and MT+/- embryonic cells were less sensitive to cis-dichlorodiammineplatinum(II)-induced apoptosis compared with MT-/- cells. Our results implicate MT as a stress-responsive factor that can regulate apoptotic engagement.

Role of Ca2+ influx in the tert-butyl hydroperoxide-induced apoptosis of HepG2 human hepatoblastoma cellse

“…The results showed that TBHP produced oxidative stress (Figure 1) and induced apoptotic cell death in the HepG2 cells (Figure 3). These results are consistent with previous other reports that in non-hepatocytes TBHP induced apoptosis through the induction of oxidative stress (Langley et al, 1993;Kondo et al, 1997).…”

Metallothioneins Are Upregulated in Symptomatic Mice with Astrocyte-Targeted Expression of Tumor Necrosis Factor-α

“…MTs bind zinc and copper and presumably function in metal ion regulation and detoxification in peripheral tissues as well as in the CNS (4,33). Early studies suggested that MT-I ϩ II could have significant antioxidant capacity and functions (32,55,63), and recent reports with transgenic mice overexpressing these MT isoforms and with MT-I ϩ II KO mice fully support such roles (22,28,37,39,40,42,43). We have recently shown that the inflammatory response to glial cell death and the wound healing capacity of the CNS is severely impaired in MT-I ϩ II KO mice (49,50), suggesting a major role of these MT isoforms during CNS injury.…”

Metallothionein expression in ovarian cancer in relation to histopathological parameters and molecular markers of prognosis

“…6 In addition, mouse embryonic cells null for MT due to loss of functional MT-1 and MT-2 genes were more susceptible to apoptotic death after exposure to cisplatin. 7 Nevertheless, results from 2 independent groups led to the conclusion that unexposed MT-1/2 knockout mice are viable and reproduce normally. 8,9 Although the role of MT in cisplatin susceptibility of normal kidney cells appears to be clear, the situation remains inconclusive for tumor cells.…”

“…10 Furthermore, induction of MT synthesis by incubation of cell lines with dexamethasone also induced resistance against cisplatin. 7,11 MT content and MT mRNA levels correlated with level of resistance to cisplatin in several human small-cell lung-cancer cell lines. 12 Although a large number of studies have shown MT involvement in resistance to platinum compounds, its precise influence on susceptibility of tumor cells remains elusive since transfection of cell lines with MT-expression constructs also generated clones that are not more resistant 10,13 or that are even more susceptible.…”