Lymphangioleiomyomatosis LAM is a female predominant and devastating pulmonary disease, characterized by diffusely infiltrated smooth muscle like cells that carry mutations in the tuberous sclerosis complex (TSC) genes. TSC1, TSC2 and TBC1D7 interact and inhibit the mammalian target of rapamycin complex 1 (mTORC1). The reasons that LAM exclusively affects women and how TSC1 or TSC2 deficiency contributes to the pathogenesis of LAM are not yet fully understood. We previously discovered that estrogen promotes the survival and lung metastases of tuberin-deficient rat uterine leiomyoma-derived ELT3 cells in a xenograft tumor model (PNAS 2009). Recently, we reported that estrogen and mTORC2 coordinate to enhance prostaglandin biosynthesis and tumorigenesis in LAM (J. Expt. Med. 2013). Prostaglandins are lipid mediators that participate in tumor survival, growth, invasion, and inflammation. Phospholipase A2 (PLA2), Cyclooxygenase-2 (COX-2) and prostacyclin synthase (PTGIS) are critical enzymes responsible for the production of prostaglandins. Prostaglandin receptors (EPs) mediate the biological function of prostaglandins. This study is to determine whether suppression of prostaglandin biosynthesis pathway potentially leads to tumor regression LAM in both cell culture and preclinical models of LAM.

To identify additional pathways activated by TSC loss, we performed bioinformatics analysis of public expression arrays and found a rapamycin-insensitive upregulation of prostaglandin biosynthesis genes including (PLA2), cyclooxygenase-2 (COX-2), prostacyclin synthase (PTGIS), and prostaglandin E2 (PGE2) receptor 3 (EP3), in TSC2-deficient LAM patient-derived cells compared to TSC2-addback cells. Real-time RT-PCR assays validated the enhanced expression of PLA2, COX-2, PTGIS and EP3 in TSC2-deficient cells. Immunoblotting analysis showed the increased levels of PLA2, COX-2, PTGIS and EP3 in TSC2-deficient cells compared to TSC2-addback cells. Immunohistochemistry demonstrated abundant accumulation of PLA2, COX-2 and EP3 in LAM lung lesions compared to adjacent normal tissues. Interestingly, PGE2 specifically stimulated the growth of TSC2-deficient LAM patient-derived cells compared to TSC2-addback cells. Importantly, treatment of TSC2-deficient LAM patient-derived cells with PLA2 inhibitor or EP3 inhibitor more potently reduced cell proliferation in dose-dependent manner compared to TSC2-addback cells.

Our data documents that loss of TSC2 leads to the aberrant expression and accumulation of prostaglandin biosynthesis regulators PLA2, COX-2, PTGIS and EP3, thereby enhancing prostaglandin production and promoting TSC-related cell growth and tumor development. Our data supports the potential application of prostaglandin metabolites as biomarkers of disease severity and the development of prostaglandin biosynthesis inhibitors as alternative therapeutic options for lesions occurring in LAM patients and in other gender-specific neoplasm.

Citation Format: Chenggang Li, Po-Shun Lee, Yang Sun, Erik Zhang, Xiaoxiao Gu, Jing Li, Kai-Feng Xu, Alfredo Csibi, John Blenis, Elizabeth Petri Henske, Bruce Levy, David Kwiatkowski, Jane J. Yu. Estradiol and mTORC2 cooperate to enhance prostaglandin biosynthesis and tumorigenesis in tuberous sclerosis complex. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B10.