Arsenic-induced polyadenylation of canonical histone H3.1 mRNA displaces histone variant H3.3 from critical gene regulatory regions

The replication-dependent canonical histone genes are the only genes found in multicellular organisms whose messenger RNA (mRNA) does not terminate with a poly(A) tail at the 3' end. We previously demonstrated that arsenic exposure induces polyadenylation of canonical histone H3.1 mRNA in tissue culture system. We report that arsenic is capable of inducing high levels of H3.1 mRNA polyadenylation and marked loss of the Stem-loop binding protein (SLBP) in vivo, which is critical for canonical histone pre-mRNA processing. Ectopic expression of polyadenylated H3.1 mRNA enhances anchorage-independent cell growth and tumor formation in nude mice. Moreover, polyadenylation of H3.1 mRNA causes transcriptional deregulation, G2/M arrest, chromosome aneuploidy and aberration. Importantly, overexpression of H3.3 attenuates arsenic-induced cell transformation. Through ChIP-Seq and RNA-Seq, we try to decipher if polyadenylated H3.1 mRNA could result in depletion of histone variant H3.3 at critical gene regulatory regions. Our study uncovers polyadenylation of H3.1 and resulting displacement of variant H3.3 as a potential new mechanism for arsenic-induced carcinogenesis. Overall design: BEAS-2B cells were stably transfected with pcDNA3.1-NT-Empty or pcDNA3.1-NT-H3.1poly(A) plasmid. Through RNA-Seq, it will reveal the role of polyadenylated H3.1 mRNA in different cellular pathways. For ChIP-Seq, BEAS-2B cells were stably transfected with pcDNA3.1-FLAG-H3.3, and then pcDNA3.1-NT-H3.1poly(A), to obtain BEAS-2B FLAG-H3.3 and BEAS-2B FLAG-H3.3&NT-H3.1poly(A) stable cell lines. Then use FLAG-ChIP to pull down H3.3 specific binding DNA for ChIP-Seq.