Electronic Thesis and Dissertation Repository


Master of Science


Microbiology and Immunology


Dr. Sung O. Kim


Cellular adaptation to microbial stresses has been demonstrated in several cell types. Macrophages (MФ) are sentinel immune cells fending off invading microbes. Anthrax lethal toxin (LeTx) is a key virulence factor released by Bacillus anthracis that causes rapid cell death, pyroptosis. A small number of RAW246.7 macrophages (~4%) exposed to a non-lethal dose of LeTx become resistant to LeTx-induced pyroptosis for ~ 4 weeks, termed “toxin-induced resistance (TIR)”. Here, I showed that high levels of DNA methyl transferase1 (DNMT1) expression were maintained although global genomic methylation levels were not high in TIR. TIR cells treated with the DNMT inhibitor 5-azacitidine or (si)RNA targeting DNMT1 became susceptible to LeTx-induced pyroptosis. Knocking down DNMT1 also increased expression of the mitochondrial cell death proteins Bnip3 and Bnip3L involved in pyroptosis. However, DNA methylation of CpG islands in Bnip3 and Bnip3L were not different between wild type and TIR cells. Among histone modification genes examined, histone deacetylase (HDAC) 8 was up-regulated in TIR cells. The HDAC inhibitor panobinostat or siRNAs against HDAC8 rendered TIR cells sensitive to LeTx-induced pyroptosis and induced Bnip3 and Bnip3L expression. Acetylation of histone H3 lysine 27 (H3K27Ac) leads to binding of BNIP3 to H3, but this association was decreased in TIR cells. Also treatments of panobinostat or 5-azacitidine enhanced the levels of H3K27Ac in TIR cells. Collectively, these results suggest that TIR was maintained by multiple epigenetic mechanisms through up-regulating expression of DNMT1 and HDAC8. This resulted in decrease of H3K27Ac and subsequently suppressed the expression of BNIP3.