The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway is hyperactivated in a variety of cancers and disorders, including lymphangioleiomyomatosis (LAM) and tuberous sclerosis complex (TSC), which are characterized by mutations in tumor suppressors TSC1 or TSC2.
LAM is typically caused by tuberous sclerosis complex 2 (TSC2) mutations resulting in mTORC1 activation in proliferative smooth muscle-like cells in the lung.
Using a LAM patient-derived cell line (bearing biallelic Tuberin inactivation), we demonstrate that E2 stimulates a robust and biphasic activation of ERK2 and transcription of the late response-gene Fra1 associated with epithelial-to-mesenchymal transition.
Simvastatin, but not atorvastatin, showed a concentration-dependent (0.5-10 μM) inhibitory effect on mouse TSC2-null and human LAM-derived cell growth.
We hypothesized that these cellular mechanisms of OPG may be involved in the growth and proliferation of lymphangioleiomyomatosis (LAM) cells, abnormal smooth muscle-like cells with mutations in one of the tuberous sclerosis complex tumor-suppressor genes (TSC1/TSC2) that cause LAM, a multisystem disease characterized by cystic lung destruction, lymphatic infiltration, and abdominal tumors.
The mTOR inhibitor, Rapamycin, stabilizes lung function in LAM and decreases the volume of renal angiomyolipomas, but lung function declines and angiomyolipomas regrow when treatment is discontinued, suggesting that factors induced by mTORC1 inhibition may promote the survival of TSC2-deficient cells.
Our findings demonstrate a mechanistic link between loss of TSC2 and alveolar destruction and suggest that treatment with rapamycin and simvastatin together could benefit patients with LAM by targeting cells with TSC2 dysfunction and preventing airspace enlargement.
Loss of heterozygosity analysis demonstrated that not only lymphangioleiomyomatosis and renal angiomyolipoma but also the uterine angiosarcoma had loss of heterozygosity on TSC2.
In HBV-D treated patients the dominant resistance mutation was rtL80V (31.4%) and rtM204I (60%) in LAM+ADV group while LAM-treated patients showed a preference of rtM204V (51.9%).
Surprisingly, TSC2-deficient cells administered intratracheally resulted in rapid dissemination to lymph node basins throughout the body, and histopathological changes in the lung consistent with LAM.
We studied immortalized cells that lack TSC2 derived from an angiomyolipoma of a patient with LAM, a TSC2 addback derivative, and murine embryonic fibroblast cells that lack Tsc1 or -2 and respective controls.
Examination of LAM tissues shows the expression of cleaved β-catenin products and MMP7 consistent with a model that tuberin-deficient cells acquire invasive properties through a β-catenin-dependent mechanism, which may underlie the development of LAM.
The TSC1/TSC2 protein-related signaling pathways are involved in the pathogenesis and may provide novel therapeutic targets for lymphangioleiomyomatosis and diseases associated with TSC1 / TSC2 dysfunction.
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.
Failure in the regulation of mTOR (mammalian target of rapamycin) appears to be critical to the pathogenesis of the inherited disorder tuberous sclerosis and the related lung disease LAM (lymphangioleiomyomatosis).
In vitro, CCL2 or MCP-1 induced selective migration of cells, showing loss of heterozygosity of TSC2 from a heterogeneous population of cells grown from explanted LAM lungs.
These findings suggest a higher rate of LAM in TSC1 than previously recognised, as well as a fundamental difference in CT presentation between TSC1 and TSC2.
Our study demonstrates that IFNbeta-dependent activation of STATs and p38 MAPK is not sufficient to fully inhibit proliferation of cells with TSC2 dysfunction and that TSC2-dependent inhibition of mTOR/S6K1 cooperates with IFNbeta in inhibiting human LAM and TSC2-null ELT3 cell proliferation.
A TSC2 loss or mutation leads to disruption of the tuberin-hamartin heteromer and dysregulation of S6K1 activation leading to aberrant cell proliferation seen in LAM disease.