Epigenetic regulation of chromatin structure by dKeap1 and CncC in Drosophila melanogaster

Abstract

The Nrf2-Keap1 pathway regulates transcriptional response to xenobiotic and oxidative stress, thereby reducing the adverse effects of these compounds on the health of an organism. According to the classic model, Keap1 interacts with Nrf2 in the cytoplasm and targets Nrf2 for ubiquitination and degradation. When xenobiotic compounds or reactive oxygen species are present, they disrupt the interaction between Keap1 and Nrf2, releasing Nrf2 to enter the nucleus and activate transcription of response genes. Although the short-term responses to xenobiotic factors are well understood, the mechanisms that mediate the effects of long-term exposure to xenobiotics on development remain unknown. It has been found that the Nrf2-Keap1 pathway can regulate normal development in Drosophila and mice. For example, Drosophila Nrf2 and Keap1 (CncC and dKeap1) regulate the synthesis of and response to ecdysone (an important hormone in metamorphosis). Elucidating other mechanisms by which Nrf2 and Keap1 can regulate development could help us understand how xenobiotics affect development and the complicated roles of Nrf2 and Keap1 in disease. Given the importance of epigenetic regulation in development, we investigated the role of CncC and dKeap1 in regulating chromatin package. A position effect variegation (PEV) assay uses a transcriptional reporter gene to assess heterochromatin formation. PEV assays revealed that knockdown of CncC and/or dKeap1 resulted in a reduction of gene silencing caused by pericentric heterochromatin. Knockdown of CncC or dKeap1 in embryos reduced the level of heterochromatin marker histone H3K9 dimethylation. However, knockdown of CncC or dKeap1 did not affect the expression of genes that encode heterochromatin components Su(var)3-9 and HP1 . These results indicate that CncC and Keap1 promote or maintain pericentric heterochromatin formation, likely at the post-transcriptional level. Thus, epigenetic regulation of chromatin may represent a novel mechanism by which the Kea[p1-Nrf2 xenobiotic response signaling controls development. Future studies will aim to determine the interacting partners of Nrf2 and Keap1 and establish whether Nrf2 and Keap1 also regulate euchromatin structure. Elucidating the roles of Nrf2 and Keap1 will help us understand how environmental toxins may impact epigenetics, development, and human health.