Superfund Research Program
Critical Events in the Transformation of Human Bladder Cells by Low-Level Arsenic Exposure
Project Leader: A. Jay Gandolfi
Grant Number: P42ES004940
Funding Period: 2000-2015
Final Progress Reports
The vascular system is a major target for arsenic toxicity. Dr. Vaillancourt has shown that the serine/threonine protein kinase, MEKK4, is involved in arsenic signal transduction. His group found that annexin II interacts with MEKK4 and since annexin II is a calcium-binding protein, the interaction between MEKK4 and annexin II suggests that MEKK4 is regulated by calcium. Angiotensin II is a hormone that increases blood pressure and is frequently used to study these types of proteins in aortic smooth muscle cells. A recent discovery in Vaillancourt’s laboratory has demonstrated that arsenic regulates the interaction between annexin II and MEKK4 in a similar manner as angiotensin II. These results suggest that arsenic behaves like an endogenous hormone (i.e., angiotensin II). Since arsenic is known to cause peripheral vascular disease in humans and may result in the loss of limbs through amputation, Dr. Vaillancourt will continue testing the hypothesis that arsenic produces its toxic effects by mimicking the biological activity of a natural hormone.
Since the arsenic drinking water standard is based on the incidence of human bladder cancer, recent studies in Dr. Gandolfi’s laboratory have focused on the effects of ppb exposure levels of arsenic on human bladder cells (UROtsa cell line) where the bladder cancer occurs. These cells were capable of converting arsenite to arsenate and various methylated metabolites, including monomethyl arsonous acid [MMA(III)]. MMA(III) was shown to be 20-times more toxic than arsenite to the UROtsa cells, and if the cells are stressed the toxicity of MMA(III) is increased another 5-fold. Low-level As(III) exposure elicits alterations in gene expression in UROtsa cells characterized by increases in stress genes and metallothionein genes. Interestingly, MMA(III) induces a similar stress response that does not induce metallothionein genes but enhances the expression of numerous zinc-finger associated genes. As(III) has previously been shown to transform UROtsa cells and Dr. Gandolfi’s laboratory has now demonstrated that MMA(III) can also transform these cells by long-term, low exposures. At 4 ppb exposure level, MMA(III) was found to inhibit the processing of damaged proteins. Enhanced expression of genes demonstrating oxidative stress and protein damage support that ppb exposure levels of arsenic can affect this critical target cell population. These results bring into question the safety of the new drinking water standard for arsenic.