Specificity of the Metallothionein-1 Response by Cadmium-Exposed Normal Human Urothelial Cells

Abstract

Occupational and environmental exposure to cadmium is associated with the development of urothelial cancer. The metallothionein (MT) family of genes encodes proteins that sequester metal ions and modulate physiological processes, including zinc homeostasis. Little is known about the selectivity of expression of the different MT isoforms. Here, we examined the effect of cadmium exposure on MT gene and isoform expression by normal human urothelial (NHU) cell cultures. Baseline and cadmium-induced MT gene expression was characterized by next-generation sequencing and RT-PCR; protein expression was assessed by Western blotting using isoform-specific antibodies. Expression of the zinc transporter-1 (SLC30A1) gene was also assessed. NHU cells displayed transcription of MT-2A, but neither MT-3 nor MT-4 genes. Most striking was a highly inducer-specific expression of MT-1 genes, with cadmium inducing transcription of MT-1A, MT-1G, MT-1H, and MT-1M. Whereas MT-1G was also induced by zinc and nickel ions and MT-1H by iron, both MT-1A and MT-1M were highly cadmium-specific, which was confirmed for protein using isoform-specific antibodies. Protein but not transcript endured post-exposure, probably reflecting sequestration. SLC30A1 transcription was also affected by cadmium ion exposure, potentially reflecting perturbation of intracellular zinc homeostasis. We conclude that human urothelium displays a highly inductive profile of MT-1 gene expression, with two isoforms identified as highly specific to cadmium, providing candidate transcript and long-lived protein biomarkers of cadmium exposure.

Human placental cell line HTR-8/SVneo accumulates cadmium by divalent metal transporters DMT1 and ZIP14

“…3A). This finding is in very good agreement with a previous report 64 in which MT1X, MT1A and MT1E levels were identified at 8.5%, 0.001% and 0.01% of MT2A levels (we found 2.5%, 0.015% and 0.021% respectively) and other studies in HeLa cells, 64 human urothelial cells 65 and various endothelial cells 66 showing that MT2A is the constitutively most strongly expressed MT form.…”

The Evolving Role for Zinc and Zinc Transporters in Cadmium Tolerance and Urothelial Cancer

“…It is likely that the inconsistent responses to Zn supplementation or depletion, reflected by changes in the variable expression levels of ZIP1 and ZnT1, could be related to differences in Cd exposure among study subjects, given that Cd is a potent inducer of MT [48,49]. Furthermore, Cd and Zn are both found to be inducers of ZnT1 [22,50,51]. Overexpression of ZnT1 decreased intracellular zinc concentrations [25].…”

Metallothionein isoforms as double agents – Their roles in carcinogenesis, cancer progression and chemoresistance

“…The antioxidant function of MTs protects the cells from free radicals and oxidative stress arising from mutagens, anticancer drugs, and radiation. The ability of MTs to bind Cd ++ , Hg ++ , Pt and other similar heavy metals protects cells from the toxicity of these metals (Krizkova et al, 2012;McNeill et al, 2019;Rahman et al, 2017;Wong and Stillman, 2018). On the other hand, it has been demonstrated that changes in MT expression could be associated with the process of carcinogenesis and 10 cancer progression (Krizkova et al, 2018;Si and Lang, 2018).…”