Alteration in MARCKS phosphorylation and expression by methylmercury in SH-SY5Y cells and rat brain

Intracellular accumulation and DNA damage caused by methylmercury in glial cells

Mercury is widely used in industrial and extractive processes, and the improper disposal of waste or products containing this metal produces a significant impact on ecosystems, causing adverse effects on living organisms, including humans. Exposure to methylmercury, a highly toxic organic compound, causes important neurological and developmental impairments. Recently, the genotoxicity of mercurial compounds has gained prominence as one of the possible mechanisms associated with the neurological effects of mercury, mostly by disturbing the mitotic spindle and causing chromosome loss. In this sense, it is important to investigate if these compounds can also cause direct damage to DNA, such as single and double-strand breaks. Thus, the aim of this study was to investigate the cytotoxic and genotoxic potential of methylmercury in cell lines derived from neurons (B103) and glia (C6), exposed to methylmercury (MeHg) for 24 h, by analyzing cell viability, metabolic activity, and damage to DNA and chromosomes. We found that in comparison to the neuronal cell line, glial cells showed higher tolerance to MeHg, and therefore a higher LC₅₀ and consequent higher intracellular accumulation of Hg, which led to the occurrence of several genotoxic effects, as evidenced by the presence of micronuclei, bridges, sprouts, and chromosomal aberrations.

The MARCKS protein amount is differently regulated by calpain during toxic effects of methylmercury between SH-SY5Y and EA.hy926 cells

Methylmercury (MeHg) is an environmental pollutant that shows severe toxicity to humans and animals. However, the molecular mechanisms mediating MeHg toxicity are not completely understood. We have previously reported that the MARCKS protein is involved in the MeHg toxicity to SH-SY5Y neuroblastoma and EA.hy926 vascular endothelial cell lines. In addition, calpain, a Ca²⁺-dependent protease, is suggested to be associated with the MeHg toxicity. Because MARCKS is known as a substrate of calpain, we studied the relation between calpain activation and cleavage of MARCKS and its role in MeHg toxicity. In SH-SY5Y cells, MeHg decreased cell viability along with increased calcium mobilization, calpain activation and a decrease in MARCKS amounts. However, pretreatment with calpain inhibitors attenuated the decrease in cell viability and MARCKS amount induced only by 1 µM but not by 3 µM MeHg. In cells with a MARCKS knockdown, calpain inhibitors failed to attenuate the decrease in cell viability caused by MeHg. In EA.hy926 cells, although MeHg caused calcium mobilization and a decrease in MARCKS levels, calpain activation was not observed. These results indicate that the participation of calpain in the regulation of MARCKS amounts is dependent on the cell type and concentration of MeHg. In SH-SY5Y cells, calpain-mediated proteolysis of MARCKS is involved in cytotoxicity induced by a low concentration of MeHg.

MARCKS is involved in methylmercury-induced decrease in cell viability and nitric oxide production in EA.hy926 cells

Methylmercury (MeHg) is a persistent environmental contaminant that has been reported worldwide. MeHg exposure has been reported to lead to increased risk of cardiovascular diseases; however, the mechanisms underlying the toxic effects of MeHg on the cardiovascular system have not been well elucidated. We have previously reported that mice exposed to MeHg had increased blood pressure along with impaired endothelium-dependent vasodilation. In this study, we investigated the toxic effects of MeHg on a human endothelial cell line, EA.hy926. In addition, we have tried to elucidate the role of myristoylated alanine-rich C kinase substrate (MARCKS) in the MeHg toxicity mechanism in EA.hy926 cells. Cells exposed to MeHg (0.1-10 µM) for 24 hr showed decreased cell viability in a dose-dependent manner. Treatment with submaximal concentrations of MeHg decreased cell migration in the wound healing assay, tube formation on Matrigel and spontaneous nitric oxide (NO) production of EA.hy926 cells. MeHg exposure also elicited a decrease in MARCKS expression and an increase in MARCKS phosphorylation. MARCKS knockdown or MARCKS overexpression in EA.hy926 cells altered not only cell functions, such as migration, tube formation and NO production, but also MeHg-induced decrease in cell viability and NO production. These results suggest the broad role played by MARCKS in endothelial cell functions and the involvement of MARCKS in MeHg-induced toxicity.

X MARCKS the spot: myristoylated alanine-rich C kinase substrate in neuronal function and disease

Intracellular protein-protein interactions are dynamic events requiring tightly regulated spatial and temporal checkpoints. But how are these spatial and temporal cues integrated to produce highly specific molecular response patterns? A helpful analogy to this process is that of a cellular map, one based on the fleeting localization and activity of various coordinating proteins that direct a wide array of interactions between key molecules. One such protein, myristoylated alanine-rich C-kinase substrate (MARCKS) has recently emerged as an important component of this cellular map, governing a wide variety of protein interactions in every cell type within the brain. In addition to its well-documented interactions with the actin cytoskeleton, MARCKS has been found to interact with a number of other proteins involved in processes ranging from intracellular signaling to process outgrowth. Here, we will explore these diverse interactions and their role in an array of brain-specific functions that have important implications for many neurological conditions.