Mechanisms and targeting of aberrant Gas activation in myeloid neoplasms

点击翻译按钮获取中文摘要

PROJECT SUMMARY/ABSTRACT Myelodysplastic syndromes (MDS) are myeloid neoplasms with dismal prognosis, frequent progression to acute myeloid leukemia (AML) and no effective treatment. A decade ago, a development with transformative potential for this disease was the discovery that more than half of MDS patients have somatic mutations in genes encoding splicing factors (SFs, i.e. RNA binding proteins that regulate pre-mRNA splicing). While the high frequency and early occurrence during the disease course of SF mutations rendered them promising targets, efforts to therapeutically leverage this through splicing modulator drugs did not show promise in clinical testing and the drug development pipeline for these targets, and for MDS in general, is currently nearly empty. We developed genetically faithful human induced pluripotent stem cell (iPSC) models of SF-mutated MDS using CRISPR gene editing and performed integrative analyses of splicing (RNA-Seq) and RNA binding (eCLIP) to search for mis-spliced transcripts that are direct common targets of two of the main SF mutations (SRSF2 P95L and the U2AF1 S34F). We found that both mutant SRSF2 and mutant U2AF1 cause altered splicing of the gene GNAS, promoting the production of a longer isoform (GNAS-L), which in turn produces a longer form of the alpha subunit of the stimulatory G protein, G⍺s (G⍺s-L). G proteins are key signaling molecules involved in many important signaling pathways and cell functions, including oncogenic processes. Our preliminary data using functional, biochemical and population genetics approaches support a critical role for the long form of G⍺s (G⍺s-L) as an MDS driver and reveal a new mechanism by which SF mutations drive MDS that opens a completely novel and unexplored therapeutic avenue for MDS, AML and other cancers with SF gene mutations. The goal of this proposal is to investigate G⍺s as a therapeutic target for MDS and identify opportunities for therapeutic interventions that inhibit signaling by G⍺s-L. Specifically, we propose to: (1) Evaluate the effects of direct degradation (through a dTAG) or inhibition (by novel cyclic peptides) of G⍺s in splicing factor (SF)-mutated MDS and AML hematopoietic cells (primary and iPSC-derived) using recently developed iPSC-based models of MDS-to-sAML progression and longitudinal bone marrow samples from MDS patients who progressed to AML; (2) Characterize and target cell signaling downstream of Gs-L through candidate and unbiased approaches (Reverse Phase Protein Array, CyTOF, transcriptomics); and (3) Identify the G-protein coupled receptors (GPCRs) involved in Gs-L activation in SF-mutated MDS and AML through focused CRISPR KO screens. This study can establish a novel therapeutic target that may transform the treatment of MDS, AML and possibly other cancers.