Activating Notch mutations are found in 60% of human T cell acute lymphoblastic leukemia cases (T-ALL). A direct transcriptional target of Notch is the cell cycle regulator Myc, which is the most frequently amplified oncogene across a wide range of malignancies. In the proposed work, I will characterize Myc transcriptional regulation in T-ALL. We have previously identified an enhancer region termed the Notch-Dependent Myc Enhancer (NDME) that is active in a reporter assay and loops to the Myc promoter in mouse and human T- ALL cells. Four T cell transcription factors bind in this region, but their role in activating the NDME is unknown. Previous work from our lab showed that T-ALL cells created to be resistant to Notch inhibition maintain Myc expression through a switch in enhancer usage to another region, termed the Brd4-Dependent Myc Enhancer (BDME). A potential treatment for T-ALL is the BET family inhibitor JQ1, which has already proved efficacious in AML. I have generated JQ1-resistant human T-ALL cells that maintain MYC expression.
In Aim 1, I will determine the roles of four T cell transcription factors, Notch1, E2A, Gata3, and Runx1 in activating the NDME in T-ALL. I will specifically target the Notch1 binding site in the NDME using CRISPR/Cas9 technology in T-ALL cell lines. I will assay the activity of the NDME using growth curve analysis and local ChIP for histone marks of activation. In addition, I will perform chromatin looping studies to determine the effects of loss of factor binding on looping of the NDME to the Myc promoter. This will determine the importance of T cell-specific factors in regulating Myc expression through the NDME.
In Aim 2, I will determine the mechanism of MYC expression in JQ1-resistant human T-ALL cells. In nave T- ALL cells, both the NDME and the BDME loop to the Myc promoter. I hypothesize that in contrast to the GSI- resistant cells previously characterized, these cells will use only the NDME and not the BDME to drive Myc expression. BET family members are also crucial for the activation of a class of enhancers termed super or stretch enhancers. These super enhancers often regulate key oncogenic targets. I will also determine the activation status of T cell-specific supe enhancers in JQ1-resistant T-all cells. This work will provide important knowledge into mechanisms of JQ1 resistance in T-ALL. This work will provide critical insights into the mechanisms of regulation of the gene Myc and may identify novel targets for treatment of both neoplastic de novo and refractory T-ALL.
Myc is an oncogene in a diverse group of cancers, including leukemia, due to its central role in regulating transcription, metabolism, proliferation, and survival. My research will provide key insights into how oncogenic Notch signaling dysregulates Myc in T-cell leukemia and identify novel therapeutic targets in this disease.
