Overexpressed human metallothionein IIA gene protects Chinese hamster ovary cells from killing by alkylating agents.

Abstract

Experiments were designed to detect survival advantages that cells gain by overexpressing metallothionein (MT). Chinese hamster ovary K1-2 cells and an x-ray-sensitive derivative were transfected with a bovine papillomavirus (BPV)-linked construct carrying the human metallothionein HA (hMT-HA) gene. Transfectants survived 40-fold higher levels of cadmium chloride, harbored at least 30 copies of hMT-HA, and contained 25-to 166-fold more MT than the parent cells. Even under conditions of reduced glutathione synthesis, the transfectants were not more resistant to the lethal effects of ionizing radiation and bleomycin than the parent cells. Thus free radicals generated by these agents cannot be scavenged efficiently by MT in vivo. The hMT-HA transfectants, however, but not control transfectants harboring a BPV-MT promoter-neo construct, tolerated significantly higher doses of the alkylating agents N-methyl-N-nitrosourea and N-methyl-N'-nitro-N-nitrosognanidine. Resistance and MT overexpression occurred irrespective of selection and cultivation in cadmium and zinc. There was no increase in resistance to methyl methanesulfonate and N-hydroxyethyl-N-chiroethylntrosourea. MT did not affect the degree of overall DNA methylation after N-methyl-N-nitrosourea treatment nor the level of 06-methylgnanlne-DNA methyltransferase. The results suggest that MT participates as a cofactor or regulatory element in repair or tolerance of toxic alkylation lesions.

The Escherichia coli AlkB protein protects human cells against alkylation-induced toxicity

“…The overexpression of metallothionein in mammalian cells confers resistance to the SN1 but not the SN2 alkylating agents, but this occurs via an unknown mechanism that appears not to involve either the prevention or the repair of DNA alkylation damage (13). The …”

Metallothionein expression in human breast cancer

“…Recently, metallothionein has been found to be elevated in neoplastic cells (Murphy et al, 1991) and overexpression has been found to confer resistance to radiotherapy (Thornally and Vasak 1985;Renan and Dowman, 1989) and chemotherapeutic agent toxicity (Andrews et al,1987;Kelley et al, 1988;Webber et al, 1988;Kaina et al, 1990), although this has been disputed (Schilder et al, 1990;Murphy et al, 1991). Metallothionein overexpression has been described in human breast carcinoma and appears to be associated with a poorer prognosis (Fresno et al, 1993;Schmid et al, 1993 (Page and Anderson, 1987;Ellis et al, 1992) Sections 3 ,um thick were also cut and used for immunohistochemical staining of metallothionein according to a standard ABC method.…”

Metallothionein levels in ovarian tumours before and after chemotherapy

“…Platinum has been shown to be bound to the metallothionein fraction isolated from cells treated with cisplatin (Endresen et al, 1984). Metallothionein levels have also been associated with resistance to some alkylating agents, although the proposed mechanism advances a role for these proteins as cofactors or regulatory elements in the repair process, rather than as direct chemical scavengers (Kaina et al, 1990).There remains uncertainty as to whether data describing mechanisms of resistance in vitro is relevant to human tumours. This work describes the investigation of metallothionein levels in tumour samples obtained either before chemotherapy (initial debulking) or following combination chemotherapy (second look laparotomy).…”