The discovery of NOTCH1 as a driver mutation in the majority of human T-ALL cases has raised hopes for targeted therapy in this cancer. NOTCH has also been implicated as an important oncogene in a diverse range of solid and hematologic cancers. However, complete blockade of the Notch pathway is impractical because of intolerable on-target side effects. There is also concern that this would cause cancer. Thus, clinical trials are forced to use lower doses of Notch inhibitors. However, these doses are poorly effective because collaborative networks amplify weak Notch signals and drive resistance. Our long-term goal is to identify and understand the networks that collaborate with Notch. Our preliminary data implicate the PIAS coactivator Zmiz1 as a new direct and selective regulator of Notch1. ZMIZ1 and activated NOTCH1 were co-expressed in a significant subset of primary human T-ALL specimens. Zmiz1 inhibition slowed proliferation and overcame resistance to Notch inhibitors. Here we show co-binding of Zmiz1 and Notch1 at a subset of Notch1 regulatory sites; regulation by Zmiz1 of a subset of Notch1 target genes; and a critical structural domain that attaches Zmiz1 directly to Notch1. Similar to Notch deficiency, Zmiz1 deficiency caused a cell autonomous loss of all T-cell subsets. In contrast to Notch deficiency, Zmiz1 deficiency did not cause myeloproliferative disease or severe GI toxicity. Importantly, deletion of Zmiz1 in established T-ALL led to tumor regression and prolonged survival. Our objective in this application is to elucidate the mechanism by which Zmiz1 enhances Notch1-activated T- ALL. Our central hypothesis is that Zmiz1 regulates an oncogenic subset of Notch1 signals by directly interacting with Notch1 in concert with other factors to drive T-ALL. In our first aim, we will determine the mechanisms by which Zmiz1 and Notch1 selectively co-bind and coregulate an oncogenic subset of Notch target genes. We will map the interactions at the amino acid level. We will identify the factors controlling the selectivity of Zmiz1 in gene regulation. In our second aim, we will use our newly generated Zmiz1 knockout mice to determine the effects of Zmiz1 on leukemia initiating cells. We will learn whether Zmiz1 inhibition could be effectively and safely combined with tolerable doses of Notch inhibitors. Our project is significant because it will elucidate a new direct and selective Notch regulator that is required for T-ALL maintenance and contributes to GSI resistance, but is dispensable for intestinal homeostasis and myeloid tumor suppression. Thus, it may lead to Notch-directed cancer therapy without the unacceptable consequences of pan-Notch inhibition. Our preliminary analysis suggests that Zmiz1 is expressed and functionally active in diverse cancers. Thus, our work may have broad implications. Our project is innovative because it is the first instance, to our knowledge, that a transcriptional regulator directly engages the core Notch complex to heterogeneously regulate Notch target genes. We employ new knockout mice and technologies that raise the standards of human sample validation in the T-ALL field to ensure that our project has the highest potential for clinical translation.
NIH ExPorter
NIH ExPorter