Molecular and biochemical basis of Lymphangioleiomyomatosis

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Abstract Pulmonary Lymphangioleiomyomatosis (LAM) is a slowly progressing disease characterized by cystic destruction of the lungs and eventual respiratory failure, and affects 3.4-7.8 per million women. Biochemically, LAM is caused by loss of function of the Tuberous Sclerosis Complex (TSC) and appears to require activation of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. Despite encouraging clinical trial results from the use of mTORC1 inhibitors to treat LAM, these drugs are limited for two reasons: first, rapamycin-based treatments are not curative as tumors regrow following cessation of treatment; and second, long-term rapamycin usage has tremendous side effects including immune disorders and diabetes. To resolve this currently, unmet clinical need, this proposal will investigate three unresolved mechanistic questions, with the long-term goal of developing long-lasting therapies for LAM. The first aim will determine the contribution of glutamine (Gln) metabolism in AML and LAM cells and its importance in cellular survival as inability of mTORC1-targeted therapies to induce toxicity remains an unaddressed hurdle. This aim will investigate the mechanism of Gln metabolism in these cells as well as new approaches to target the growth and survival of AML and LAM cells via pharmacologic and shRNA methods, both in vitro and in vivo. The second aim will garner a greater understanding of how the mTORC1 pathway regulates the alternative splicing of key genes involved in the "benign metastasis" phenotype seen in LAM. While mRNA splicing is highly regulated and pervasive (occurring in ~95% of human genes and frequently deregulated in cancer), the mechanisms causing deregulation are unknown. Using novel hits from a phospho-proteomic screen we recently completed, this aim will investigate how the mTORC1 pathway regulates the splicing of key genes involved in the "benign metastasis" phenotype of LAM. Finally, the third aim will identify key mechanistic insights into how estrogen contributes to the pathogenesis of LAM, which occurs almost exclusively in females during childbearing years. The aim will investigate the role of estrogen receptor signaling via the ERK-Fra1-ZEB pathway, in the context of mTORC1 hyperactivation, in regulating LAM cell survival, migration and invasion. In addition to addressing basic questions of LAM biology, each of these aims has clinical implications, and in two of the aims animal studies have been proposed to translate the cell biology discoveries into relevant in vivo models. In conclusion, there's a great need for greater understanding of the biology of LAM, and the expectations are that successful completion of the proposed work will impact LAM treatment through identification of new biomarkers as well as novel drugs that can specifically eliminate abnormal cell growth, migration and tumor formation in TSC and LAM patients.