Role of PPM1D and PPM1D mutations in hematopoiesis and response to stress

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Project Summary PPM1D encodes for a serine/threonine phosphatase that is recurrently amplified and mutated in a wide range of cancers. We have shown that recurrent C-terminal truncations impair PPM1D degradation by the proteasome, leading to increased protein levels and activity, and are common in clonal hematopoiesis and myeloid malignancies after the receipt of chemotherapy. However, the role that PPM1D plays in hematopoiesis during steady state and under conditions of stress, and the molecular mechanism by with PPM1D is degraded via the C-terminus remains unclear. We developed two novel mouse models to study PPM1D and now propose in Aim 1 to use these models to investigate how PPM1D loss and PPM1D activation via C-terminal truncation affect normal hematopoiesis and hematopoiesis in the setting of radiation and inflammation. I have also performed a genetic screen and found that UBE3C, an E3 ubiquitin ligase, regulates the levels of PPM1D and propose in Aim 2 to determine how UBE3C degrades PPM1D via interactions with the C-terminus and to define the broader ubiquitin ligase complex regulating PPM1D ubiquitination and degradation by the proteasome. Collectively, this work will help explain the prevalence of PPM1D mutations in clonal hematopoiesis and therapy-related myeloid malignancies, define the molecular machinery that regulates PPM1D levels, and shed light on PPM1D as a potential therapeutic target. The applicant, Dr. Peter Miller, is an oncologist at the Dana-Farber Cancer Institute (DFCI). He spends 80% of his time in translational research and 20% in clinical practice caring for patients with cancer. He has outlined a five-year career development plan to meet his goal of becoming an independent investigator in translational research. Dr. Miller has assembled an Advisory Committee of internationally recognized experts to provide scientific and career mentorship. He has established collaborations with expertise in hematopoiesis, mouse models, the ubiquitin proteasome system, mass spectrometry, and applied biostatistics to provide experimental advice and specific training in the field. Dr. Miller will conduct this research at the DFCI and leverage the exceptional research and teaching environment at the DFCI, Harvard, and the Broad Institute. The DFCI, which harbors an outstanding research community and has a long track record for successful mentorship of independent physician scientists, is an ideal environment for completion of these experiments and the realization of Dr. Miller's long-term career goal of being an independent physician-scientist.