The intersection of genotoxic stress and altered transcriptional programs impacts numerous disease and disease risk events, but surprisingly little is mechanistically known in this regard, particularly with respect to risk alleles for myocardial infarction. Based on our initial data, we can confirm that a single base alteration in a CTCF site in the SIRT1 promoter can increase the risk of MI. We will investigate the hypothesis that this is based on the functional importance of induced binding of CTCF to in response to hypoxia or genotoxic stress to the cognate site in the SIRT1 promoter, licensing a promoter pause release that results in an acute stimulation of SIRT1 transcription. The proposed research is directed at revealing a previously overlooked strategy for signal-dependent transcriptional regulation based on redistribution of the critical chromosomal architectural protein - CTCF- in activation of a large promoter pause release program with important biological consequences, including the gene encoding critical regulator - SIRT1. We will investigate the hypothesis that stress-induced increased transcription of SIRT1 and a global genomic program of response to oxidative stress in cardiomyocytes is mediated by CTCF promoter recruitment and, in part, by long distance interactions based on liquid-liquid phase separation of CTCF and lncRNAs in cardiomyocytes, which is lost in MI risk allele carriers. We will investigate the stress-induced transcriptional program in iPSC-derived, genome-sequenced cardiac myocytes and the test the hypothesis by assessing effects of introducing the risk allele in mice. With the availability of iPSCs harboring the causative SNP for the SIRT1 risk allele, we are now in a position to delve into the precise mechanism of these events, and assess the possibility that there is a large cardiomyocyte pause-release program important with respect to cardiac response to acute insults. The idea that a key arbiter of chromosome architecture is regulated by phosphorylation of a key architectural protein, binding to a set of promoters harboring weak sites for CTCF and licensing increased transcription based of promoter pause release events reveals an unappreciated signal-dependent mechanism for controlling important biological program.
We have taken leveraged identification of a risk allele for myocardial infarction (MI) to permit identification of a large promoter pause-release transcriptional program activated by genotoxic stress, uncovering an unexpected strategy by which CTCF and lncRNAs mediate cardio- protection based on actions in cardiac myocytes. In the case of the promoter of the Sirtuin1 gene (SIRT1), which encodes an evolutionarily conserved NAD+-dependent deacetylase involved in oxidative stress response, the stress-induced binding of CTCF permits interactions with an upstream CTCF and with an adjacent lncRNA harboring enhancer-like properties, which activates transcription of the SIRT1 promoter by a promoter pause release strategy, potentially mediated by CTCF-dependent liquid-liquid phase separation (LLPS) events. This proposal will provide new insights into stress-induced transcriptional regulation based on alterations in CTCF binding and altered chromosomal architecture.
