Abstract Hexavalent chromium [Cr(VI)] is a well-established carcinogen linked to respiratory cancer and has been found at half of US toxic waste sites. In spite of considerable research efforts, the mechanism of Cr(VI)-induced carcinogenesis remains largely unknown. A growing body of evidence suggests that Cr is capable of inducing epigenetic changes, such as DNA methylation, histone modification, and microRNA. Acetylation of histone lysine residues neutralizes the positive charge from their side chains and decreases the affinity between histone tails and DNA, which subsequently leads to increased DNA accessibility and transcriptional activation in the gene promoter region. However, the effect of Cr(VI) on histone acetylation is still not clear. Here, we report that BEAS-2B cells exposed to 5 or 10 uM of Cr(VI) for 24 hours resulted in a striking and dose dependent decrease in H4K16ac. Co-treatment with Cr(VI) and Benzo(a)pyrene diolepoxide (BPDE) induced further decrease in H4K16ac. Cr (VI) transformed cells showed considerable decrease in H4K16ac compared to the control cells, which further indicates the correlation between Cr(VI) exposure and hypoacetylation of H4K16. H4K16 acetylation is known as an important determinant in higher-order chromatin structure and active gene expression. Male Absent on the First gene (MOF) is a H4K16 specific acetyltransferase. Our results indicate that Cr(VI) exposure significantly reduced MOF activity while its expression levels remained the same, thus suggesting that Cr(VI) may affect MOF activity rather than its expression. Moreover, Nuclear protein 1 (NUPR1), a MOF inhibitor, was increased in Cr(VI)-exposed cells. Depletion of NUPR1 in cells by small RNA interference rescued Cr(VI)- reduced H4K16ac. Together, our results indicate that Cr(VI) inhibits MOF activity through inducing NUPR1 expression which subsequently leads to H4K16 hypoacetylation. Since hypoacetylation of H4K16 is a known hallmark of human cancer, the results from our study presents strong evidence supporting the role of H4K16 hypoacetylation in chromium carcinogenesis. . Citation Format: Qiao Yi Chen, Xiaoru Zhang, Thomas Kluz, Max Costa, Hong Sun. Hexavalent chromium induces H4K16 hypoacetylation by NUPR1-mediated inactivation of histone acetyltransferase hMOF. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4537.