Nongenomic estrogen action regulates tyrosine phosphatase activity and tuberin stability

Lymphangioleiomyomatosis: what do we know and what are we looking for?

Lymphangioleiomyomatosis (LAM) is a rare disease characterised by proliferation of abnormal smooth muscle-like cells (LAM cells) leading to progressive cystic destruction of the lung, lymphatic abnormalities and abdominal tumours. It affects predominantly females and can occur sporadically or in patients with tuberous sclerosis complex. This review describes the recent progress in our understanding of the molecular pathogenesis of the disease and LAM cell biology. It also summarises current therapeutic approaches and the most promising areas of research for future therapeutic strategies.

Lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is a rare disease that mainly affects women, particularly at fertile age. It is sporadic or associated with tuberous sclerosis complex. It is characterised by an abnormal proliferation of immature smooth muscle cells (SMC), which grow aberrantly in the airway, parenchyma, lymphatics and pulmonary blood vessels and which can gradually lead to respiratory failure. It affects several systems, affecting the lymphatic ganglia and causing abdominal tumours. Given its very low prevalence, a difficult to establish early diagnosis, absence of curative treatment and the difficulty in obtaining information, places LAM under the heading of the so-called Rare Diseases. There is a growing interest in the study of this disease which has led to the setting up of patient registers and an exponential growth in LAM research, both at a clinical level and cellular level.

Estrogen-induced activation of mammalian target of rapamycin is mediated via tuberin and the small GTPase Ras homologue enriched in brain

Inhibitors of the mammalian target of rapamycin (mTOR) are currently in clinical trials for the treatment of breast cancer. The mechanisms through which mTOR are activated in breast cancer and the relationship of mTOR activation to steroid hormones, such as estrogen, that are known to influence breast cancer pathogenesis, are not yet understood. Using MCF-7 cells as a model, we found that 17-beta estradiol (E(2)) rapidly increased the phosphorylation of downstream targets of mTOR: p70 ribosomal protein S6 kinase, ribosomal protein S6, and eukaryotic initiation factor 4E-binding protein 1. The phosphoinositide-3-kinase inhibitor, wortmannin, and the mTOR inhibitor, rapamycin, blocked E(2)-induced activation of p70 ribosomal protein S6 kinase. We hypothesized that tuberin and the small GTPase Ras homologue enriched in brain (Rheb), regulators of the mTOR pathway, mediate E(2)-induced activation of mTOR. Consistent with this hypothesis, E(2) rapidly (within 5 minutes) stimulated tuberin phosphorylation at T1462, a site at which Akt phosphorylates and inactivates tuberin. E(2) also rapidly decreased the inactive, GDP-bound form of Rheb. Finally, we found that small interfering RNA down-regulation of endogenous Rheb blocked the E(2)-stimulated proliferation of MCF-7 cells, demonstrating that Rheb is a key determinant of E(2)-dependent cell growth. Taken together, these data reveal that the TSC/Rheb/mTOR pathway plays a critical role in the regulation of E(2)-induced proliferation, and highlight Rheb as a novel molecular target for breast cancer therapy.

Synthesis and biological evaluation of SERMs with potent nongenomic estrogenic activity

We have synthesized novel SERMs that activate a rapid response in CNS neurons, but which lack the ability to bind to the nuclear estrogen receptors (ERalpha and ERbeta). These compounds are analogues of 4-hydroxytamoxifen, but unlike 4-hydroxytamoxifen, they do not exist as a mixture of E/Z isomers. They contain a carboxamide insertion between the olefin and basic phenyl side chain, which results in more stable geometric isomers. The amide insertion also eliminates their ability to bind to the nuclear estrogen receptors, and hence, they are unable to modulate ER-mediated gene transcription as do classical estrogens and SERMs. We show that one of these analogues, ST-X, elicits a potent nongenomic estrogen response in the CNS by rapidly inhibiting GIRK activation in hypothalamic gamma-aminobutyric acid (GABA) and proopiomelanocortin (POMC) neurons. To our knowledge, ST-X is the only SERM that modulates rapid estrogen responses, but which lacks nuclear ER activity.

Molecular pathogenesis of lymphangioleiomyomatosis: lessons learned from orphans

Lymphangioleiomyomatosis (LAM) is a rare progressive cystic lung disease affecting young women. The pivotal observation that LAM occurs both spontaneously and as part of the tuberous sclerosis complex (TSC) led to the hypothesis that these disorders share common genetic and pathogenetic mechanisms. In this review we describe the evolution of our understanding of the molecular and cellular basis of LAM and TSC, beginning with the discovery of the TSC1 and TSC2 genes and the demonstration of their involvement in sporadic (non-TSC) LAM. This was followed by rapid delineation of the signaling pathways in Drosophila melanogaster with confirmation in mice and humans. This knowledge served as the foundation for novel therapeutic approaches that are currently being used in human clinical trials.

Cross-talk between tuberin, calmodulin, and estrogen signaling pathways

Lymphangioleiomyomatosis (LAM) is a rare disease that occurs primarily in women and has been linked to both estrogen-mediated signaling events and mutations associated with the tuberous sclerosis complex 2 gene product tuberin. These two observations fostered the hypothesis that tuberin's impact on estrogen-mediated signaling might be through a direct interaction with the intracellular receptor for estrogen, estrogen receptor alpha (ERalpha). In the study presented here, tuberin was shown to co-immunoprecipitate and directly bind ERalpha through a domain localized within the carboxyl 73 amino acids of tuberin. This domain had previously been shown to serve as a binding domain for the intracellular calcium signaling molecule calmodulin (CaM). Competition binding studies identified a potential competitive relationship for binding of tuberin by ERalpha and CaM. Additionally, tuberin-ERalpha interactions were found to be modulated by the presence of tuberin's predominant intracellular binding partner hamartin, suggesting that tuberin-hamartin interactions negatively impact the ability of tuberin to modulate ERalpha-mediated gene transcription events. Cumulatively, data presented here support the hypothesis that interactions between tuberin, ERalpha, and CaM may play a critical role in the pathology of LAM disease.

Abdominal lymphangioleiomyomatosis in a man with Klinefelter syndrome: the first reported case

Lymphangioleiomyomatosis (LAM) is an uncommon progressive disease characterized by a hamartomatous tumor-like proliferation of smooth muscle cells that occurs most often in women. This disease commonly involves the lymph nodes, lungs, and mediastinum, and rarely the abdominal sites. We report a case of mesenteric LAM occurring in a 37-year-old man affected by Klinefelter syndrome with a 17-year history of androgen replacement therapy. Histology revealed a hamartomatous proliferation of spindle cells surrounding multiple ectatic lymphatic spaces intermixed with lymphatic follicles. When subjected to immunohistochemical studies, the tumor cells stained positive for muscular markers and negative for estrogen, progesterone, and androgen receptors. The occurrence of LAM in association with Klinefelter syndrome has never been reported in the literature and could represent a further clue in the still unclear pathogenesis of this disease.