Interferon beta augments tuberous sclerosis complex 2 (TSC2)-dependent inhibition of TSC2-null ELT3 and human lymphangioleiomyomatosis-derived cell proliferation

Progress in Tuberous Sclerosis Complex Renal Disease

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder that affects both fetal development and postnatal tissue growth, resulting in altered brain structures and a tumor predisposition syndrome. Although every organ system is affected by the disease, kidney involvement is a leading cause of death in adults with TSC. Over the past decade, significant progress has been made in understanding the renal disease. This review focuses on the cystic and solid renal lesions in TSC, including their pathobiology and treatment.

Renal cystic disease in tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is associated with TSC1 or TSC2 gene mutations resulting in hyperactivation of the mTORC1 pathway. This mTORC1 activation is associated with abnormal tissue development and proliferation such that in the kidney there are both solid tumors and cystic lesions. This review summarizes recent advances in tuberous sclerosis complex nephrology and focuses on the genetics and cell biology of tuberous sclerosis complex renal disease, highlighting a role of extracellular vesicles and the innate immune system in disease pathogenesis.

Regulation of protein kinase Cδ Nuclear Import and Apoptosis by Mechanistic Target of Rapamycin Complex-1

Inactivation of the protein complex ‘mechanistic target of rapamycin complex 1’ (mTORC1) can increase the nuclear content of transcriptional regulators of metabolism and apoptosis. Previous studies established that nuclear import of signal transducer and activator of transcription-1 (STAT1) requires the mTORC1-associated adaptor karyopherin-α1 (KPNA1) when mTORC1 activity is reduced. However, the role of other mTORC1-interacting proteins in the complex, including ‘protein kinase C delta’ (PKCδ), have not been well characterized. In this study, we demonstrate that PKCδ, a STAT1 kinase, contains a functional ‘target of rapamycin signaling’ (TOS) motif that directs its interaction with mTORC1. Depletion of KPNA1 by RNAi prevented the nuclear import of PKCδ in cells exposed to the mTORC1 inhibitor rapamycin or amino acid restriction. Mutation of the TOS motif in PKCδ led to its loss of regulation by mTORC1 or karyopherin-α1, resulting in increased constitutive nuclear content. In cells expressing wild-type PKCδ, STAT1 activity and apoptosis were increased by rapamycin or interferon-β. Those expressing the PKCδ TOS mutant exhibited increased STAT1 activity and apoptosis; further enhancement by rapamycin or interferon-β, however, was lost. Therefore, the TOS motif in PKCδ is a novel structural mechanism by which mTORC1 prevents PKCδ and STAT1 nuclear import, and apoptosis.

Renal manifestation of tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a tumor predisposition syndrome with significant renal cystic and solid tumor disease. It commonly causes several types of cystic disease and benign tumors (angiomyolipomata) in the kidneys that can both lead to significant premature loss of glomerular filtration rate. The main risks of angiomyolipomata, severe bleeding, loss of renal function, and pulmonary lymphangioleiomyomatosis, can be ameliorated by active surveillance and preemptive therapy with mTOR inhibitors. The cystogenic mechanism may involve primary cilia, but also appears to also involve a majority of normal tubular cells and may be driven by a minority of cells with mutations inactivating both their TSC1 or TSC2 genes. Malignant tumors are rare.

Evidence Supporting a Lymphatic Endothelium Origin for Angiomyolipoma, a TSC2(-) Tumor Related to Lymphangioleiomyomatosis

Angiomyolipoma (AML) is a tumor closely related to lymphangioleiomyomatosis (LAM). Both entities are characterized by the proliferation of smooth muscle actin and melanocytic glycoprotein 100 (recognized by antibody HMB-45)-positive spindle-shaped and epithelioid cells. AML and LAM are etiologically linked to mutations in the tsc2 and tsc1 genes in the case of LAM. These genes encode the proteins tuberous sclerosis complex (TSC)-1 and TSC2, which are directly involved in suppressing the mechanistic target of rapamycin cell growth signaling pathway. Although significant progress has been made in characterizing and pharmacologically slowing the progression of AML and LAM with rapamycin, our understanding of their pathogenesis lacks an identified cell of origin. We used an AML-derived cell line to determine whether TSC2 restitution brings about the cell type from which AML arises. We found that AML cells express lymphatic endothelial cell markers consistent with lymphatic endothelial cell precursors in vivo and in vitro. Moreover, on TSC2 correction, AML cells mature into adult lymphatic endothelial cells and have functional attributes characteristic of this cell lineage, suggesting a lymphatic endothelial cell of origin for AML. These effects are dependent on TSC2-mediated mechanistic target of rapamycin inactivation. Finally, we demonstrate the in vitro effectiveness of norcantharidin, a lymphangiogenesis inhibitor, as a potential co-adjuvant therapy in the treatment of AML.

Lymphangioleiomyomatosis: New Treatment Perspectives

Lymphangioleiomyomatosis (LAM) is a rare multisystem disease, occurs in women, usually premenopausal, caused by the proliferation of neoplastic smooth muscle-derived cells. Mutations in the tuberous sclerosis complex genes, lead to the activation of mammalian target of rapamycin kinase (mTOR), results in proliferation of LAM cells, its increasing motility, and survival. Polycystic lung destruction, extensive involvement of lymphatic channels, chylothorax, chyloperitoneum, and renal angiomyolipomas can develop in LAM patients. The new, promising treatment strategies have been recently introduced due to discovery of the genetic and molecular mechanisms of LAM. Comprehension of the disease pathogenesis has resulted in the implementation of other therapeutic agents such as mTOR inhibitors, VEGF-D inhibitors, statins, interferon, chloroquine analogs, cyclin-dependent kinase inhibitors, matrix metalloproteinase inhibitors, aromatase inhibitors, and their combinations. The mTOR inhibitors appear to be the most important, and the efficacy of sirolimus in LAM treatment has been proved. The article discussed the new control studies with mTOR inhibitors, doxycycline, simvastatin, and combination of them in LAM patients.

Analysis of gene expression array in TSC2-deficient AML cells reveals IRF7 as a pivotal factor in the Rheb/mTOR pathway

Mutations in tuberous sclerosis (TSC) genes cause the genetic disorder TSC, as well as other neoplasms, including lymphangioleiomyomatosis (LAM) and angiomyolipomas (AMLs). AMLs are benign renal tumors occur both in sporadic LAM and in TSC. As they carry the same mutations, AML cell lines serve as a model for TSC and LAM. Rheb/mammalian target of rapamycin complex 1 (mTORC1) pathway is chronically activated in TSC-deficient cells, and this activation can be diminished using the appropriate inhibitors. Rapamycin (sirolimus) is a known specific inhibitor of mTORC1, whereas S-trans,trans-farnesylthiosalicylic acid (FTS; salirasib) has been shown to inhibit Rheb. To examine the effect of the Rheb/mTOR inhibition pathway, we used human TSC2-deficient AML cells, derived from a LAM patient. FTS indeed inhibited Rheb in these cells and attenuated their proliferation. After comparative treatments with FTS or rapamycin or by re-expression of TSC2, we carried out a gene array analysis. This yielded a substantial number of commonly altered genes, many of which we identified as downstream targets of the interferon (IFN) regulatory factor 7 (IRF7) transcription factor, a central activator of the IFN type 1 immune response. Furthermore, nuclear localization of IRF7 was impaired by each of the three treatments. Interestingly, the phenomena seen on FTS or rapamycin treatment were selective for TSC2-deficient cells. Moreover, knockdown of IRF7 by siRNA mimicked the decrease in number of the abovementioned genes and also inhibited AML cell proliferation. Altogether, these findings support FTS as a potential treatment for TSC and its related pathologies and IRF7 as a novel target for treatment.

Targeted approaches toward understanding and treating pulmonary lymphangioleiomyomatosis (LAM)

Pulmonary lymphangioleiomyomatosis (LAM) is a rare disease found almost exclusively in women that is characterized by neoplastic growth of atypical smooth muscle-like cells in the lung, destruction of lung parenchyma, and obstruction of lymphatics. These processes lead to the formation of lung cysts, rupture of which results in spontaneous pneumothorax. Progression of LAM often results in loss of pulmonary function and death. LAM affects predominantly women of childbearing age and is exacerbated by pregnancy. The only proven treatment for LAM is lung transplantation, and even then LAM cells will often return to the transplanted lung. However, methodical and targeted approaches toward understanding LAM pathophysiology have led to the discovery of new potential therapeutic avenues. For example, the mutational inactivation of tumor suppressor complex genes tuberous sclerosis complex 1 or tuberous sclerosis complex 2 has been shown to be present in lung LAM cells. These mutations occur sporadically or in association with inherited hamartoma syndrome tuberous sclerosis (TSC). Since TSC genes function as negative regulators of the mammalian target of rapamycin, a major controller of cell growth, metabolism, and survival, rapamycin analogs have recently been used to treat LAM patients with promising results. Similarly, studies focusing on the importance of estrogen in LAM progression have suggested that anti-estrogen therapy might prove to be an alternative means of treating LAM. This minireview summarizes recent progress in understanding LAM pathophysiology, including the latest preclinical and clinical studies, and insights regarding the role of hormones in LAM.

TSC2 modulates cell adhesion and migration via integrin-α1β1

Recent evidence suggests that the rare and progressive lung disease lymphangioleiomyomatosis (LAM) is metastatic in nature. Dysfunction of the tumor suppressor genes tuberous sclerosis complex (TSC), in particular mutational inactivation of TSC2, enhances both cell proliferation and migration. Although substantial progress has been made in understanding the role of TSC2 in abnormal LAM cell proliferation and its pharmacological targeting, the mechanisms underlying the enhanced migratory capacity in LAM are not well understood. In this study, we examined the role of TSC2 in cell attachment, spreading, and migration, processes that contribute to the metastatic phenotype. Here we show that loss of TSC2 increased both the attachment and spreading of mouse embryonic fibroblasts to the extracellular matrix proteins collagen type I and fibronectin and that reexpression of TSC2 reduced these effects. Integrin-α1β1 modulated cell migration with the β1-subunit involved in cell attachment and spreading as shown by using functional blocking antibodies. Loss of TSC2 increased integrin-α1 expression, and inhibition of this integrin subunit reduced cell migration. The enhanced attachment and spreading were independent of the intracellular signaling pathways mammalian target of rapamycin complex 1 and Rho-associated kinase, as pharmacological inhibition with rapamycin or Y27632, respectively, was without effect. Together, these data demonstrate that TSC2 controls cell migration, attachment, and spreading through the α1β1-integrin receptor and thus suggest a potential therapeutic target for the treatment of increased cell invasiveness in LAM.

Optimizing treatments for lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM), a multisystem disease predominantly affecting premenopausal women, is associated with cystic lung destruction and lymphatic and kidney tumors. LAM results from the proliferation of a neoplastic cell that has mutations in the tuberous sclerosis complex 1 or 2 genes, leading to activation of a critical regulatory protein, mammalian target of rapamycin. In this report, we discuss the molecular mechanisms regulating LAM cell growth and report the results of therapeutic trials employing new targeted agents. At present, inhibitors of mammalian target of rapamycin such as sirolimus appear to be the most promising therapeutic agents, although drug toxicity and development of resistance are potential problems. As the pathogenesis of LAM is being further recognized, other therapeutic agents such as matrix metalloproteinase inhibitors, statins, interferon, VEGF inhibitors, chloroquine analogs and cyclin-dependent kinase inhibitors, along with sirolimus or a combination of several of these agents, may offer the best hope for effective therapy.

mTORC2 is required for proliferation and survival of TSC2-null cells

Mutational inactivation of the tumor suppressor tuberous sclerosis complex 2 (TSC2) constitutively activates mTORC1, increases cell proliferation, and induces the pathological manifestations observed in tuberous sclerosis (TS) and in pulmonary lymphangioleiomyomatosis (LAM). While the role of mTORC1 in TSC2-dependent growth has been extensively characterized, little is known about the role of mTORC2. Our data demonstrate that mTORC2 modulates TSC2-null cell proliferation and survival through RhoA GTPase and Bcl2 proteins. TSC2-null cell proliferation was inhibited not only by reexpression of TSC2 or small interfering RNA (siRNA)-induced downregulation of Rheb, mTOR, or raptor, but also by siRNA for rictor. Increased RhoA GTPase activity and P-Ser473 Akt were inhibited by siRNA for rictor. Importantly, constitutively active V14RhoA reversed growth inhibition induced by siRNA for rictor, siRNA TSC1, reexpression of TSC2, or simvastatin. While siRNA for RhoA had a modest effect on growth inhibition, downregulation of RhoA markedly increased TSC2-null cell apoptosis. Inhibition of RhoA activity downregulated antiapoptotic Bcl2 and upregulated proapoptotic Bim, Bok, and Puma. In vitro and in vivo, simvastatin alone or in combination with rapamycin inhibited cell growth and induced TSC2-null cell apoptosis, abrogated TSC2-null tumor growth, improved animal survival, and prevented tumor recurrence by inhibiting cell growth and promoting apoptosis. Our data demonstrate that mTORC2-dependent activation of RhoA is required for TSC2-null cell growth and survival and suggest that targeting both mTORC2 and mTORC1 by a combination of proapoptotic simvastatin and cytostatic rapamycin shows promise for combinational therapeutic intervention in diseases with TSC2 dysfunction.

Lymphangioleiomyomatosis and TSC2-/- cells

The cells comprising pulmonary lymphangioleiomyomatosis (LAM) and renal angiomyolipomas (AMLs) are heterogeneous, with variable mixtures of cells exhibiting differentiation towards smooth muscle, fat, and vessels. Cells grown from LAM and AMLs have likewise tended to be heterogeneous. The discovery that LAM and AMLs contain cells with mutations in the TSC1 or TSC2 genes is allowing investigators to discriminate between "two-hit" cells and neighboring cells, providing insights into disease pathogenesis. In rare cases, it has been possible to derive cells from human tumors, including AMLs and TSC skin tumors that are highly enriched for TSC2(-/-) cells. Cells derived from an Eker rat uterine leiomyoma (ELT3 cells) are Tsc2-null and these have been used in a rodent cell models for LAM. Further improvements in the ability to reliably grow well-characterized TSC2(-/-) cells from human tumors are critical to developing in vitro and in vivo model systems for studies of LAM pathogenesis and treatment.

mTOR signaling in lymphangioleiomyomatosis

The protein mammalian target of rapamycin (mTOR) plays a central role in cell growth and proliferation. Excessive mTOR activity is a prominent feature of many neoplasms and hamartoma syndromes, including lymphangioleiomyomatosis (LAM), a destructive lung disease that causes progressive respiratory failure in women. Although pharmacological inhibitors of mTOR should directly target the pathogenesis of these disorders, their clinical efficacy has been suboptimal. Recent scientific findings reviewed here have greatly improved our understanding of mTOR signaling mechanisms, provided new insights into the control of cell growth and proliferation, and facilitated the development of new therapeutic approaches in LAM, as well as other neoplastic disorders that exhibit excessive mTOR activity.

Therapeutic options for lymphangioleiomyomatosis (LAM): where we are and where we are going

Lymphangioleiomyomatosis (LAM), a multisystem disease affecting predominantly premenopausal and middle-aged women, causes progressive respiratory failure due to cystic lung destruction and is associated with lymphatic and kidney tumors. In the past, the treatment of LAM comprised exclusively anti-estrogen and related hormonal therapies. These treatments, however, have not been proven effective. In this article, we discuss new findings regarding the molecular mechanisms involved in the regulation of LAM cell growth, which may offer opportunities to develop effective and targeted therapeutic agents.

Signal transducer and activator of transcription 3 is required for abnormal proliferation and survival of TSC2-deficient cells: relevance to pulmonary lymphangioleiomyomatosis

Tumor suppressor complex TSC1/TSC2 represents a key negative regulator of mammalian target of rapamycin (mTOR)-S6 kinase 1 signaling. Mutational inactivation of TSC1 or TSC2, linked to a rare lung disease, lymphangioleiomyomatosis (LAM), manifests as neoplastic growth of smooth-muscle (SM)-like cells and cystic destruction of the lungs that induces loss of pulmonary function. However, the precise mechanisms of abnormal cell growth in LAM remain uncertain. Here, we demonstrate increased signal transducer and activator of transcription (STAT) 3 expression, phosphorylation, and nuclear localization in SM-like cells in LAM lungs and in TSC2-null xenographic tumors. Treatment of TSC2-null tumors with mTOR inhibitor rapamycin attenuated STAT3 expression and phosphorylation. Increased STAT3 level and activation were also observed in LAM-dissociated (LAMD) cell cultures compared with normal human bronchus fibroblasts (HBFs) from LAM patients. Although interferon (IFN)-gamma inhibited proliferation of HBFs, IFN-gamma treatment had little effect on proliferation of LAMD and TSC2-null cells. Re-expression of TSC2 or treatment with rapamycin inhibited IFN-gamma-induced STAT3 phosphorylation and synergized with IFN-gamma in inhibiting TSC2-null and LAMD cell proliferation. Reduction of STAT3 protein levels or activity using specific small interfering RNA or inhibitory peptide, respectively, decreased proliferation and induced apoptosis in TSC2-null and LAMD cells and sensitized cells to growth-inhibitory and proapoptotic effects of IFN-gamma. Collectively, our data demonstrate that STAT3 activation is required for proliferation and survival of cells with TSC2 dysfunction, that STAT3 impedes growth-inhibitory and proapoptotic effects of IFN-gamma, and that TSC2- and rapamycin-dependent inhibition of STAT3 restores antiproliferative effects of IFN-gamma. Thus, STAT3 may provide a novel therapeutic target for diseases associated with TSC1/TSC2 dysfunction.