E2F1-mediated FOS induction in arsenic trioxide–induced cellular transformation: Effects of global H3K9 hypoacetylation and promoter-specific hyperacetylation in vitro

Abstract

Background: Aberrant histone acetylation has been observed in carcinogenesis and cellulartransformation associated with arsenic exposure; however, the molecular mechanisms and cellularoutcomes of such changes are poorly understood.Objective: We investigated the impact of tolerated and toxic arsenic trioxide (As 2 O 3) exposure inhuman embryonic kidney (HEK293T) and urothelial (UROtsa) cells to characterize the alterationsin histone acetylation and gene expression as well as the implications for cellular transformation.Methods: Tolerated and toxic exposures of As 2 O 3 were identified by measurement of cell death,mitochondrial function, cellular proliferation, and anchorage-independent growth. Histoneextraction, the MNase sensitivity assay, and immunoblotting were used to assess global histone acetylation levels, and gene promoter-specific interactions were measured by chromatin immunoprecipitationfollowed by reverse-transcriptase polymerase chain reaction.Results: Tolerated and toxic dosages, respectively, were defined as 0.5 μM and 2.5 μM As 2 O 3 in HEK293T cells and 1 μM and 5 μM As 2 O 3 in UROtsa cells. Global hypoacetylationof H3K9 at 72 hr was observed in UROtsa cells following tolerated and toxic exposure. In both cell lines, toleratedexposure alone led to H3K9 hyperacetylationand E2F1 binding at the FOS promoter, whichremained elevated after 72 hr, contrary to global H3K9 hypoacetylation.Thus, promoter-specificH3K9 acetylation is a better predictor of cellular transformation than are global histone acetylationpatterns. Tolerated exposure resulted in an increased expression of the proto-oncogenes FOS andJUN in both cell lines at 72 hr.Conclusion: Global H3K9 hypoacetylationand promoter-specific hyperacetylationfacilitateE2F1-mediated FOS induction in As 2 O 3 -induced cellular transformation.