Exposure of Human Proximal Tubule Cells to Cd 2+ ,Zn 2+ , and Cu 2+ Induces Metallothionein Protein Accumulation but not Metallothionein Isoform 2 mRNA

Abstract

The oranization of the human meallothionein (MT) gene family is more complex than the commonly used mouse and rat models. The human MTs are encoded by a family of genes consisting of 10 functional and 7 nonfunctional MT isoforms. One objective of this study was to determine if the accumulation of MT protein in culue of human proximal tubule (HPI) cells exosed to metals is similar to that expected from the knowledge base obtained from rodent models. To accomplish this objective, HIT cells were exposed to both lethal and sublethal concentrations of Cd2, Zn2*, Cu2+ Ag2t Hg2, and Pb2+ and MT ptein l were determinedThe results were in general ment th animal modal suiehre were some : exceptions, mainly in areas w the model database was l Inlr aeement with animal models, Cd2, 7.2, a C2 were demonstted t b pot idcs of MT protein accumulation. In contrast to aity in MT protein expression, w eo evidence that the human renal MT-2 gene.hs a unique pattern of rlation cmred to both animal models and human-derived ceil cultures.. In the present study, we determined that MT-2A mRNA was not induced by exposure of HPT cells to Cd2 or the other metals, a finding in contrat to studies in both animal models and other human cel culture systems in which a high level ofMT-2 mRNA induction occurs upon eposure to Ct or Zn2+. While MT protein pression may be similar betwee humans and animal modals, this finding provides initial evidence that regulation of the genes underlying MT protein expression may be dierent beteen species.

Alterations in metal toxicity and metal-induced metallothionein gene expression elicited by growth medium calcium concentration

“…Posttranscriptional regulation of MT may be more widespread than originally thought, as evidenced in the bladder where MT immunostaining is absent despite significant mRNA levels (Somji et al 2001). The ability to increase the levels of MT protein in response to metal loading with cadmium does appear cell-type-specific with bladder cells accumulating only up to 12 ng/μg protein in response to cadmium , whereas human proximal tubule cells attain levels over 100 ng/μg protein (Garrett et al 1998). While it is known through in vitro studies with purified MT protein that zinc and cadmium can protect the 20 Fig.…”

“…MT protein determination The immunoblot protocol used for the determination of the coexpressed levels of the MT-1 and MT-2 protein in cell lysates has been described previously by this laboratory (Garrett et al 1998). The MT-1 and MT-2 proteins were detected by immunoblotting using a mouse antihorse antibody (DAKO-MT, E9, Dako, Carpinteria, CA, USA) as the primary antibody.…”

Metallothionein isoform 1 and 2 gene expression in the human prostate: Downregulation of MT-1X in advanced prostate cancer

“…Protein concentration was determined by the BCA protein assay (Pierce Chemical Co., Rockford, IL). MT protein was detected by immunoblotting using a mouse anti-horse antibody (DAKO-MT, E9, Dako, Carpinteria, CA) as the primary antibody [13,14]. This antibody detects both the MT-1 and MT-2 isoforms, and the product detected is referred to as MT-1/2 in this report.…”

Ecological Risk Assessment of Alfalfa Medicago Varia L.) Genetically Engineered to Express a Human Metallothionein (hMT) Gene

“…Unlike metallothionein expression encoded by the hMT gene, the ß-glucuronidase encoded by GUS would not be expected to affect Cu accumulation. In vertebrate and invertebrate species, differences in accumulation and toxicity of Cd, Zn and Cu and in the induction of specific metallothioneins by those metals have been reported (Garret et al, 1998;Goyer, Haust and Cherian 1992;Kondo et al, 1999;Pedersen et al, 1998;Syring, Hoexium-Brouwer and Brouwer, 2000). It is possible that accumulations of Cd and Zn in plants expressing the MT gene would be greater than those observed for Cu in this study.…”