The Loss of Tuberin Promotes Cell Invasion through the β-Catenin Pathway

Abstract

Mutations in the tumor suppressor tuberin (TSC2) are a common factor in the development of lymphangioleiomyomatosis (LAM). LAM is a cystic lung disease that is characterized by the infiltration of smooth muscle-like cells into the pulmonary parenchyma. The mechanism by which the loss of tuberin promotes the development of LAM has yet to be elucidated, although several lines of evidence suggest it is due to the metastasis of tuberin-deficient cells. Here we show that tuberin-null cells become nonadherent and invasive. These nonadherent cells express cleaved forms of b-catenin. In reporter assays, the b-catenin products are transcriptionally active and promote MMP7 expression. Invasion by the tuberin-null cells is mediated by MMP7. Examination of LAM tissues shows the expression of cleaved b-catenin products and MMP7 consistent with a model that tuberin-deficient cells acquire invasive properties through a b-catenin-dependent mechanism, which may underlie the development of LAM.Keywords: caspase 3; MMP7; LAM; tuberous sclerosis complex Lymphangioleiomyomatosis (LAM) is a potentially fatal cystic lung disease that occurs almost exclusively in women. There are no proven medical therapies for the treatment of LAM, and the health of patients with LAM deteriorates over an average span of 10 years due to the progressive destruction of the lungs (1). LAM is predominantly caused by tuberin loss-of-function mutations, forming a genetic link with tuberous sclerosis complex (TSC) (2-4). Recent analyses estimate that 30 to 40% of women with TSC may also be affected with LAM (5).TSC is a multisystem disease that results in the growth of benign tumors in the brain, kidneys, heart, and skin. It commonly affects the central nervous system, resulting in any combination of disorders including seizures, mental retardation, and behavioral problems (6). One of the most common phenotypic factors for TSC is the development of renal angiomyolipomas (AMLs), which occur in approximately 70 to 80% of patients with TSC (7,8). AMLs are characterized by the abnormal proliferation of dysplastic vessels and adipose and smooth muscle-like cells. Up to 60% of patients with sporadic LAM are diagnosed with AMLs (9). Genetic analyses have demonstrated that LAM cells and AML cells isolated from patients with LAM contain identical TSC2 mutations, suggesting that tuberin-deficient AML smooth muscle-like cells may have the potential to migrate and infiltrate the lung (3).The benign metastasis hypothesis of LAM is further supported by two independent clinical observations. First, after lung transplantation, there have been several case reports in which LAM develops anew in the transplanted donor lung, with LAM cells expressing the same TSC2 mutation identified in the native lung (10-13). Second, LAM cells have recently been isolated from the circulatory system and other bodily fluids of patients with LAM, indicating that these migratory cells have the potential to invade a variety of host tissues (14). These lines of evidence strongly suggest that the dev...

A signaling loop of REST, TSC2 and β-catenin governs proliferation and function of PC12 neural cells

“…Furthermore, previous studies in PC12 cells reported the ability of Wnt to increase b-catenin levels and cell proliferation only upon application of the ligand or overexpression of Wnt, its frizzled receptors or the intracellular effector dishevelled (Chou et al, 2000;Kaliwara et al, 2008;Chacòn et al, 2008;Spinsanti et al, 2008), which is not the case in our study. Thus, our data suggest that, as previously reported in other cell systems (Mak et al, 2003;Jozwiak and Wlodarski, 2006;Barnes et al, 2010), a decrease of TSC2 hinders the stability of the GSK3b complex and hence favors the decreased degradation and nuclear translocation of b-catenin, with ensuing strengthening of its transcriptional activity.…”

“…Although the complex, by its binding to the small GTPase Rheb, inhibits mTORC1, it promotes mTORC2 signaling (Huang et al, 2008;Huang and Manning, 2009;Laplante and Sabatini, 2009). In addition, the TSC1-TSC2 complex can have an impact on cell proliferation through its positive control of the turnover of b-catenin (Mak et al, 2003;Jozwiak and Wlodarski, 2006;Barnes et al, 2010). We thus investigated the expression of the TSC complex and b-catenin in wtPC12 and PC12-27 cells.…”

Tuberin Regulates E-Cadherin Localization

“…For example, an ϳ70-kDa truncated ␤-catenin expressed by the Tsc2-null cells was shown to be a strong coactivator of MMP7 transcription, and the secreted MMP7 promoted their invasive behavior. 34 These observations fit nicely with the role of TSC2 in EMT. Because mTORC1 is frequently activated in human cancers, the relevance of our finding deserves further investigation in the context of tumor invasion and metastasis in general.…”

“…Indeed, we recently reported that the nonadherent Tsc2-null cells acquire an invasive phenotype that is mediated via ␤-catenin-dependent, matrix metalloproteinase (MMP) 7 activity. 34 As the Tsc2(Ϫ/Ϫ) cells detach, ␤-catenin undergoes caspase-dependent cleavage, resulting in transcriptionally active products. For example, an ϳ70-kDa truncated ␤-catenin expressed by the Tsc2-null cells was shown to be a strong coactivator of MMP7 transcription, and the secreted MMP7 promoted their invasive behavior.…”

Cystic Lung Disease in Genetic Syndromes with Deficient Tumor Suppressor Gene Function

“…Epithelioid cells also express the melanocytic marker gp100, which reacts with the human melanin black antibody HMB-45, and spindle cells express the proliferation cell nuclear antigen [30]. LAM cells also express estrogen and progesterone receptors [30], matrix metalloproteinases (MMP) [31], vascular endothelial growth factor receptor 3 [32-35], β-catenin and E-cadherin [36, 37], CD44v6, an adhesion molecule associated with metastatic behavior [38], and chemokines and chemokine receptors involved in homing of LAM cells to specific organs [39, 40]. LAM nodules contain cleft-like spaces lined by lymphatic endothelial cells, which express lymphangiogenic factors and their receptors [41].…”