Arsenic Trioxide Reduces Global Histone H4 Acetylation at Lysine 16 through Direct Binding to Histone Acetyltransferase hMOF in Human Cells

Abstract

Histone post-translational modification heritably regulates gene expression involved in most cellular biological processes. Experimental studies suggest that alteration of histone modifications affects gene expression by changing chromatin structure, causing various cellular responses to environmental influences. Arsenic (As), a naturally occurring element and environmental pollutant, is an established human carcinogen. Recently, increasing evidence suggests that As-mediated epigenetic mechanisms may be involved in its toxicity and carcinogenicity, but how this occurs is still unclear. Here we present evidence that suggests As-induced global histone H4K16 acetylation (H4K16ac) partly due to the direct physical interaction between As and histone acetyltransferase (HAT) hMOF (human male absent on first) protein, leading to the loss of hMOF HAT activity. Our data show that decreased global H4K16ac and increased deacetyltransferase HDAC4 expression occurred in arsenic trioxide (As2O3)-exposed HeLa or HEK293T cells. However, depletion of HDAC4 did not affect global H4K16ac, and it could not raise H4K16ac in cells exposed to As2O3, suggesting that HDAC4 might not directly be involved in histone H4K16 de-acetylation. Using As-immobilized agarose, we confirmed that As binds directly to hMOF, and that this interaction was competitively inhibited by free As2O3. Also, the direct interaction of As and C2CH zinc finger peptide was verified by MAIDI-TOF mass and UV absorption. In an in vitro HAT assay, As2O3 directly inhibited hMOF activity. hMOF over-expression not only increased resistance to As and caused less toxicity, but also effectively reversed reduced H4K16ac caused by As exposure. These data suggest a theoretical basis for elucidating the mechanism of As toxicity.

Influence of Arsenic on Global Levels of Histone Posttranslational Modifications: a Review of the Literature and Challenges in the Field

“…The majority of studies on arsenic and histone PTMs have been conducted in vitro [28–47]. However, there are a few supporting studies in rodents [48, 49] and human populations [50–54].…”

“…Arsenic has not been shown to alter H4K5ac [44, 47] or H4K8ac [36, 44]. Furthermore, As III did not alter H3K14ac in APL cell lines [30].…”

“…In addition to its role in regulating nucleosome-level interactions, which are essential for the formation of 30 nm chromatin fibers, H4K16ac influences interactions between chromatin fibers, which determine the higher order tertiary structure of the chromatin [68]. Four studies, three of which utilized UROTsa cells, measured this PTM by either Western blot or mass spectrometry, and observed that As III and MMA III , across a range of doses (0.2–10 µM) induced a global loss of H4K16ac [34, 40, 44, 47], which is a hallmark of most human cancers [68]. However, two studies, both of which measured H4K16ac by Western blot, have been less consistent.…”

“…Although three studies have examined MMA III or DMA III in addition to As III and observed consistent effects [34, 40, 42], the majority have solely evaluated As III [28–33, 35–39, 41, 43, 45–47]. Additional studies will therefore be needed to evaluate whether arsenic metabolites differentially influence histone PTMs.…”

“…While some studies have examined the effects of arsenic on multiple cell lines or in different tissue types and observed similar effects [32, 37, 45, 47, 48, 53], the majority have evaluated a single cell line or tissue [28–31, 33–35, 38–44, 46, 50, 51]. Furthermore, one study observed that arsenic influenced H3K4me3 and H3K9ac in a region-dependent manner in the mouse brain [49], and another observed that arsenic was associated with lower levels of H3K9me3 in CD4+, but not CD8+, lymphocytes [54].…”