salicylates and Lymphangioleiomyomatosis

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.

Topics: Angiomyolipoma; Cell Proliferation; Farnesol; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Humans; Interferon Regulatory Factor-7; Kidney; Lymphangioleiomyomatosis; Microarray Analysis; Monomeric GTP-Binding Proteins; Neuropeptides; Ras Homolog Enriched in Brain Protein; RNA, Small Interfering; Salicylates; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 2 Protein; Tumor Cells, Cultured; Tumor Suppressor Proteins

The small GTPase proteins, Ras and Rheb, serve as molecular switches regulating cell proliferation, differentiation and apoptosis. Ras also regulates Rheb by inactivating the tuberous sclerosis complex (TSC), which includes products of the TSC1 and TSC2 genes encoding hamartin (TSC1) and tuberin (TSC2), respectively, and acts as a Rheb-specific GTPase-activating protein. Loss of function of TSC1 or TSC2 results in an increase in active Rheb.GTP with the consequent translational abnormalities and excessive cell proliferation characteristic of the genetic disorders, tuberous sclerosis and lymphangioleiomyomatosis (LAM). To determine whether inactivation of Rheb, Ras or both might be a potential treatment for LAM, we used TSC2-null ELT3 cells as a LAM model. The cells were treated with the Ras inhibitor S-trans,trans-farnesylthiosalicylic acid (FTS; salirasib), which mimics the C-terminal S-farnesyl cysteine common to Ras and Rheb. This C-terminus is critical for their attachment to cellular membranes and for their biological activities. Untreated, the ELT3 cells expressed significant amounts of Rheb but little Ras.GTP, and this phenotype was reversed by TSC2 reexpression. Treatment with FTS decreased Ras.GTP only slightly in the TSC2-null cells, but reduced their overactive Rheb as well as their proliferation, migration and tumor growth. Notably, TSC2 reexpression in these ELT3 cells rescued them from the inhibitory effect of FTS. Evidently, therefore, FTS blocks active Rheb in TSC2-null ELT3 cells and may have therapeutic potential for LAM.

Topics: Animals; Cell Line, Tumor; Cell Movement; Cell Proliferation; Cysteine; Farnesol; Lymphangioleiomyomatosis; Lymphocytes, Null; Mice; Mice, Nude; Monomeric GTP-Binding Proteins; Mutation; Neuropeptides; Phosphorylation; Ras Homolog Enriched in Brain Protein; ras Proteins; Rats; Ribosomal Protein S6 Kinases; Salicylates; Tuberous Sclerosis Complex 2 Protein; Tumor Suppressor Proteins