Overexpression of metallothionein in CHO cells and its effect on cell killing by ionizing radiation and alkylating agents

Abstract

Metallothionein protein protects cells from the toxic effects of heavy metal ions. To establish its protective function against ionizing radiation and alkylating agents, a model system was created by transfecting two CHO cell lines (wild-type, K1-2 and X-ray sensitive, xrs-2 subclone Bc11) with the human metallothionein II-A (hMTII-A) gene integrated in a bovine papilloma derived autonomously replicating vector. The isolated transfectants are cadmium-resistant (Cdr), due to the overexpression of the hMTII-A gene. Their steady-state level of hMTII-A mRNA can be increased up to 40-fold after Cd treatment and 20-fold after induction with ionizing radiation. The transfected cell lines proved to be as sensitive as the recipient cell lines to ionizing radiation and bleomycin but the transfectants were significantly more resistant to N-methyl-N'-nitro-N'-nitrosoguanidine (MNNG) and mitomycin C (MMC). These results lead to the conclusion that the MT protein does provide a defence mechanism to protect cells from monofunctional alkylating and cross-linking agents but not from free radicals.

Expression of metallothionein I/II and Ki-67 antigen in various histological types of basal cell carcinoma

“…The protein plays a protective role, preventing against intoxication with heavy metals, such as Pb, Hg, Cu, Cd [8,9]. MT manifests also a strong anti-oxidative activity, protecting cells from the damaging effects of reactive oxygen species, ionizing radiation and chemotherapeutic agents [10][11][12]. Intensely dividing cells (including tumor cells) manifest an increased expression of MT, which supplies zinc (Zn) ions for enzymes involved in DNA replication and protects cells from apoptosis [13].…”

Significance of overexpression of metallothionein in mouse urinary bladder focal lesions induced by treatment with N‐butyl‐N‐(4‐hydroxybutyl)‐nitrosamine

“…3) In addition, MT appears to promote the resistance of cells to not only some alkylating agents and chemotherapeutic metal compounds, such as cisplatin, chlorambucil and melphalan, 4) but also electrophilic mutagens such as N-methyl-N′-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea. 5) Interestingly, MT has also been implicated in protection against the cytotoxic effects of oxidative stress, because it is a potent hydroxyl radical scavenger. 6) In vitro, MT protects cells against the cytotoxic and DNA-damaging effects of nitric oxide and the DNA-damaging effects of H 2 O 2 , 7) and also against radical-induced lipid peroxidation.…”

Metallothionein 1E mRNA is highly expressed in oestrogen receptor-negative human invasive ductal breast cancer

“…MTs are known to play putative roles in cancer cell proliferation and apoptosis (Abdel-Mageed and Agrawal, 1997;Jayasurya et al, 2000) as well as in resistance to radiation and chemotherapeutic agents (Lohrer and Robson, 1989;Yang et al, 1994, Kondo et al, 1995. In breast cancer, MT overexpression has been well documented by immunohistochemical analysis (Schmid et al, 1993;Fresno et al, 1993;Haerslev et al, 1995;Goulding et al, 1995;Jin et al, 1999), and shown to be predominantly associated with poor prognosis.…”