Antioxidants protect against dopamine-induced metallothionein-III (GIF) mRNA expression in mouse glial cell line (VR-2g)

Metallothionein-3 as a multifunctional player in the control of cellular processes and diseases

Transition metals, such as iron, copper, and zinc, play a very important role in life as the regulators of various physiochemical reactions in cells. Abnormal distribution and concentration of these metals in the body are closely associated with various diseases including ischemic seizure, Alzheimer's disease, diabetes, and cancer. Iron and copper are known to be mainly involved in in vivo redox reaction. Zinc controls a variety of intracellular metabolism via binding to lots of proteins in cells and altering their structure and function. Metallothionein-3 (MT3) is a representative zinc binding protein predominant in the brain. Although the role of MT3 in other organs still needs to be elucidated, many reports have suggested critical roles for the protein in the control of a variety of cellular homeostasis. Here, we review various biological functions of MT3, focusing on different cellular molecules and diseases involving MT3 in the body.

Expression of metallothionein-III and cell death in differentiated catecholaminergic neuronal cells

Metallothionein (MT)-III, an isomer of metallothionein, is also known to be a growth inhibitory factor. MT-III has been reported to decrease the number of surviving neuronal cells in culture medium containing brain extract. Using differentiated catecholaminergic neuronal CATH.a cells treated with dibutyryl cyclic AMP, we examined MT-III expression and the effect of mouse forebrain extract on cell viability. Increase in MT-III expression was revealed in the differentiated cells. Moreover, treatment with mouse forebrain extract induced apoptotic cell death in differentiated CATH.a cells, accompanied by decreases in both MT-III and a neuronal differentiation marker, growth-associated protein-43, expression in surviving cells. These results imply that MT-III expression during the developmental period may be associated with the regulation of normal neural differentiation.

Metallothionein-III prevents gamma-ray-induced 8-oxoguanine accumulation in normal and hOGG1-depleted cells

Metallothioneins (MT) play an important biological role in preventing oxidative damage to cells. We have previously demonstrated that the efficiency of the protective effect of MT-III against the DNA degradation from oxidative damage was much higher than that of MT-I/II. As an extension of the latter investigation, this study aimed to assess the ability of MT-III to suppress 8-oxoguanine (8-oxoG), which is one of the major base lesions formed after an oxidative attack to DNA and the mutant frequency of the HPRT gene in human fibroblast GM00637 cells upon exposure to gamma-rays. We found that human MT-III expression decreased the level of 8-oxoG and mutation frequency in the gamma-irradiated cells. Using an 8-oxoguanine DNA glycosylase (OGG1)-specific siRNAs, we also found that MT-III expression resulted in the suppression of the gamma-radiation-induced 8-oxoG accumulation and mutation in the OGG1-depleted cells. Moreover, the down-regulation of MT in human neuroblastoma SKNSH cells induced by MT-specific siRNA led to a significant increase in the 8-oxoG level, after exposure to gamma-irradiation. These results suggest that under the conditions of gamma-ray oxidative stress, MT-III prevents the gamma-radiation-induced 8-oxoG accumulation and mutation in normal and hOGG1-depleted cells, and this suppression might, at least in part, contribute to the anticarcinogenic and neuroprotective role of MT-III.

Age-related changes in expression of metallothionein-III in rat brain

Metallothionein (MT)-III is a metal binding protein, called growth inhibitory factor, and is mainly expressed in the central nervous system. Since MT-III decreases in the brain of Alzheimer's disease (AD), a growing interest has been focused on its relationship to neurodegenerative diseases. To clarify age-related changes in the MT-III expression and its inducibility against oxidative stress, we analyzed the expression of MT-III and its mRNA in the brain of lipopolysaccharide (LPS)-treated aged rats. In the frontal cortex, basal expression of MT-III mRNA was significantly increased with aging, while it was observed no induction of MT-III mRNA against LPS administration in the aged rat brain. MT-III immunopositive cells were increased in the frontal, parietal and piriform cortices, hypothalamus and amygdaloid nucleus with aging. The LPS treatment induced MT-III expression in the brain of young-adult rats, but not in the aged rat brain. Furthermore, the MT-III induction with LPS treatment was mainly observed in oligodendrocyte and microglia. In the present study, we showed that inducibility of brain MT-III against oxidative stress may be reduced with aging. Since it has been reported that MT-III has neuroprotective roles as an antioxidant, present results suggest that MT-III is closely related to the neurodegeneration in the aged animals.

Localization of metallothionein (MT) and expression of MT isoforms induced by cadmium in rat dental pulp

We investigated the induction of metallothionein (MT) by cadmium (Cd) in the dental pulp of rat incisors. Time-course studies of MT mRNA expression after single Cd injection were observed by Northern-blot analysis. The isoform-specific expressions of MT mRNAs (MT-I, MT-II and MT-III) were observed using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Both MT-I and MT-II mRNA levels increased within 3 h, peaked at 3 h and then decreased. These findings demonstrated that MT-I and MT-II mRNA were rapidly induced by Cd in dental pulp. MT-III mRNA was constitutively expressed in rat dental pulp, but the expression level did not change by Cd treatment. The localization of MT protein in Cd-treated rat dental pulp was determined by immunohistochemical staining using anti-MT antibody against MT-I and MT-II. MT protein was localized in the specific cell type of odontoblasts (secretory odontoblasts and resting odontoblasts). In conclusion, it is likely that stained MT in the immunohistochemical study should be MT-I and/or MT-II. Furthermore, MT-I and/or MT-II in Cd-treated rat dental pulp was localized in odontoblasts, in which accumulation of Cd were reported. The cell-specific synthesis of MT may be associated with its metal storage and detoxification role in dental tissues.

Metallothionein III is reduced in Alzheimer's disease

Metallothionein III (MT-III) is a functionally distinct member of the metallothionein family that displays neuroinhibitory activity and is involved in the repair of neuronal damage. Altered expression levels of MT-III have been observed in Alzheimer's disease (AD) which has led to suggestions that it could be a mitigating factor in AD-related neuronal dysfunction. However, conflicting results have been reported on this issue which may be due to methodological differences and/or sampling size. In the current study, we have assessed MT-III expression in a large number of AD cases through the quantification of mRNA as well as by immunohistochemistry and Western blotting using an MT-III specific antibody. The results of this comprehensive study indicate that the mononucleosome DNA encoding MT-III is occluded preventing transcription and that message levels are reduced by approximately 30%. In addition, protein levels were specifically decreased by approximately 55% in temporal cortex. These data support the conclusion that MT-III is significantly downregulated in AD and may contribute to the loss of its protective effects and/or repair functions that lead to an exacerbation of the pathogenic processes.