Project description:The mammalian circadian clock is a molecular oscillator composed of a feedback loop that involves transcriptional activators CLOCK and BMAL1, and repressors Cryptochrome (CRY) and Period (PER). Here we show that a direct CLOCK-BMAL1 target gene, Gm129, is a novel regulator of the feedback loop. ChIP analysis revealed that the CLOCK:BMAL1:CRY1 complex strongly occupies the promoter region of Gm129. Both mRNA and protein levels of GM129 exhibit high amplitude circadian oscillations in mouse liver, and Gm129 gene encodes a nuclear-localized protein that directly interacts with BMAL1 and represses CLOCK:BMAL1 activity. In vitro and in vivo protein-DNA interaction results demonstrate that, like CRY1, GM129 functions as a repressor by binding to the CLOCK:BMAL1 complex on DNA. Although Gm129-/- or Cry1-/- Gm129-/- mice retain a robust circadian rhythm, the peaks of Nr1d1 and Dbp mRNAs in liver exhibit significant phase delay compared to control. Our results suggest that, in addition to CRYs and PERs, GM129 protein contributes to the transcriptional feedback loop by modulating CLOCK:BMAL1 activity as a transcriptional repressor. Examination of 3 transcriptional regulators in mouse liver
Project description:Oncogene induced senescence (OIS) is a tumor suppressive mechanism typified by stable proliferative arrest, a persistent DNA damage response and the senescent-associated secretory phenotype (SASP). MacroH2A1, a tumor suppressive histone variant, is upregulated during OIS. Using ChIP-seq, we found that macroH2A1 undergoes dramatic relocalization during OIS. SASP genes are enriched in macroH2A1-containing chromatin and macroH2A1 is a critical component of the positive feedback loop that maintains SASP expression. Endoplasmic reticulum (ER) stress, a feature of OIS that requires macroH2A1, leads to ATM activation. ER stress triggers a negative feedback loop reducing SASP expression by causing the ATM-dependent removal of macroH2A1 from SASP genes. MacroH2A1 represents a critical control point in the regulation of SASP expression during OIS by We demonstrate that SASP gene expression is regulated by the combined actions of a positive feedback loop that requires macroH2A1 and a negative feedback loop where ER stress leads to ATM activation critical for the removal of macroH2A1 from SASP genes and consequently their repression.