Impact of overexpression of metallothionein-1 on cell cycle progression and zinc toxicity

Abstract

Metallothioneins (MTs) have an important role in zinc homeostasis and may counteract the impact of oversupply. Both intracellular zinc and MT expression have been implicated in proliferation control and resistance to cellular stress, although the interdependency is unclear. The study addresses the consequences of a steady-state overexpression of MT-1 for intracellular zinc levels, cell cycle progression, and protection from zinc toxicity using a panel of cell lines with differential expression of MT-1. The panel comprised parental Chinese hamster ovary-K1 cells with low endogenous expression of MT and transfectants with enhanced expression of mouse MT-1 on an autonomously replicating expression vector with a noninducible promoter. Cell cycle progression, determined by flow cytometry and time-lapse microscopy, revealed that enhanced cytoplasmic expression of MT-1 does not impact on normal cell cycle operation, suggesting that basal levels of MT-1 expression are not limiting for background levels of oxidative stress. MT-1 overexpression correlated with a steady-state increase in cytoplasmic free Zn(2+), assessed using the fluorescent zinc-sensor Zinquin, particularly at high levels of overexpression, further suggesting that zinc availability is normally not limiting for cell cycle progression. Enhanced MT-1 expression, over a 10-fold range, had a clear impact on resistance to Cd(2+) and Zn(2+) toxicity. In the case of Zn(2+), the degree of protection afforded was less, indicating that MT-1 has a limited range and saturable capacity for effecting resistance. The results have implications for the use of cellular stress responses to exogenously supplied zinc and zinc-based systemic therapies.

Effect of resveratrol and zinc on intracellular zinc status in normal human prostate epithelial cells

“…Zinquin ethyl ester, instead of zinquin, was chosen because of an ethyl ester in place of the 6-methoxy group of toluenesulfonamidoquinoline in the molecular structure of zinquin ethyl ester, which facilitates its retention in living cells and enhances its fluorescence. Using zinquin ethyl ester, we were able the identify the subcellular localization of free labile Zn(II) in the extranu- clear secretory granule, which is consistent with the findings of two previous reports (33,37). Results from both methods indicate that free labile zinc increases along with the extracellular zinc concentration, whereas resveratrol tends to increase the free labile zinc level in ZA and ZS cells but to decrease the free labile zinc level in ZN and ZD cells (not statistically significant; Figs.…”

The Protective Role of Zinc against Acute Toxicity of Depleted Uranium in Rats

“…Many studies have shown that zinc induces MT synthesis and subsequently plays a role in antioxidation. MT binds to heavy metal ions and expels them from the cytoplasm, thereby protecting cells from oxidative damage .…”

Zinc: The Metal of Life

“…An examination of the 2nd shell amino acids surrounding the catalytic zinc ion of these enzymes indicated that the active site of TACE is more polar than that of MMP‐2 and of other MMPs (Solomon ). The consequences of a steady‐state overexpression of metallothioneins (MT‐1) for intracellular zinc levels, cell cycle progression, and protection from zinc toxicity was addressed using a panel of cell lines with differential expression of MT‐1, suggesting that zinc availability is normally not limiting for cell cycle progression (Smith ).…”