PROJECT SUMMARY/ABSTRACT Melanoma is the deadliest type of skin cancer and one of the most difficult-to-treat cancers. Oncogenic NRAS mutations are frequently observed in 20-30% of melanoma and drive the most aggressive malignancy. However, current therapies for NRAS-mutant melanoma remain limited due to the “undruggability” of NRAS protein. The long-term goal of the application is to develop effective pharmacological intervention strategies blocking NRAS mutant-driven melanoma initiation and development. To achieve the goal, a better understanding of NRAS activation by upstream regulators is urgent and critical. Recent findings showed that the kinase STK19 phosphorylates NRAS at S89 to promote NRAS activation and NRAS mutant-driven melanocyte transformation. Preliminary studies further identified a new phosphorylation site of NRAS at T158 and revealed that the protein phosphatase 1D (PPM1D), an oncogene in multiple different cancers, mediates its dephosphorylation. The proposed study focuses on elucidating the role of posttranslational modifications in NRAS functions and NRAS mutant-dependent melanocyte transformation and will test the hypothesis that modulating posttranslational modifications of NRAS is a potential pharmacological option to suppress NRAS-mutant melanoma. Specifically, the study aims to investigate in-depth the molecular mechanism underlying regulation of NRAS functions by PPM1D-mediated dephosphorylation, and characterize the biological functions of PPM1D in NRAS-mutant driven melanomagenesis in vivo. To translate the basic science to clinical application, the study will further evaluate the treatment effects of pharmacologically targeting STK19/PPM1D on NRAS mutant-melanoma suppression. Together the proposed studies will provide critical new knowledge into the regulation of NRAS signaling pathways and the development of therapeutic strategies for oncogenic NRAS-driven melanoma. The K99/R00 award will provide great opportunities for the applicant to expand the research trainings in melanoma pathogenesis and treatment in preclinical mouse models, and the professional trainings in grant writing, lab management and career development, which will contribute to fulfilling the applicant's career goal of achieving independence as a researcher in the field of melanoma research.