Lymphangioleiomyomatosis (LAM) is an often fatal disease primarily affecting young women in which tuberin (TSC2)-null cells metastasize to the lungs. The mechanisms underlying the striking female predominance of LAM are unknown. We report here that 17-␤-estradiol (E2) causes a 3-to 5-fold increase in pulmonary metastases in male and female mice, respectively, and a striking increase in circulating tumor cells in mice bearing tuberin-null xenograft tumors. E 2-induced metastasis is associated with activation of p42/44 MAPK and is completely inhibited by treatment with the MEK1/2 inhibitor, CI-1040. In vitro, E 2 inhibits anoikis of tuberin-null cells. Finally, using a bioluminescence approach, we found that E 2 enhances the survival and lung colonization of intravenously injected tuberin-null cells by 3-fold, which is blocked by treatment with CI-1040. Taken together these results reveal a new model for LAM pathogenesis in which activation of MEKdependent pathways by E 2 leads to pulmonary metastasis via enhanced survival of detached tuberin-null cells.L AM, the pulmonary manifestation of tuberous sclerosis complex (TSC), affects women almost exclusively (1). LAM affects 30Ϫ40% of women with TSC (2, 3). In a Mayo Clinic series, LAM was the third most frequent cause of TSC-related death, after renal disease and brain tumors (4). LAM can also occur in women who do not have germline mutations in TSC1 or TSC2 (sporadic LAM). LAM cells from both TSC-LAM and sporadic LAM carry inactivating mutations in both alleles of the TSC1 or TSC2 genes (5). The protein products of TSC1 and TSC2, hamartin and tuberin, respectively, form heterodimers (6, 7) that inhibit the small GTPase Ras homologue enriched in brain (Rheb), via tuberin's highly conserved GTPase activating domain. In its active form, Rheb activates the mammalian target of rapamycin (mTOR) complex 1 (TORC1), which is a key regulator of protein translation, cell size, and cell proliferation (8). Evidence of TORC1 activation, including hyperphosphorylation of ribosomal protein S6, has been observed in tumor specimens from TSC patients and LAM patients (9-11). Independent of its activation of mTOR, Rheb inhibits the activity of B-Raf and C-Raf/Raf-1 kinase, resulting in reduced phosphorylation of p42/44 MAPK (12-14), but the impact of the Raf/MEK/ MAPK pathway on disease pathogenesis is undefined.LAM is characterized pathologically by widespread proliferation of abnormal smooth muscle cells and by cystic changes within the lung parenchyma (1). About 60% of women with the sporadic form of LAM also have renal angiomyolipomas. The presence of TSC2 mutations in LAM cells and renal angiomyolipoma cells from women with sporadic LAM, but not in normal tissues, has led to the hypothesis that LAM cells spread to the lungs via a metastatic mechanism, despite the fact that LAM cells have a histologically benign appearance (15,16). Genetic and fluorescent in situ hybridization analyses of recurrent LAM after lung transplantation support this benign metastatic model (16).The female...

Members of the Protein 4.1 superfamily have highly conserved FERM domains that link cell surface glycoproteins to the actin cytoskeleton. Within this large and constantly expanding superfamily, at least five subgroups have been proposed. Two of these subgroups, the ERM and prototypic Protein 4.1 molecules, include proteins that function as tumor suppressors. The ERM subgroup member merlin/schwannomin is inactivated in the tumor-predisposition syndrome neurofibromatosis 2 (NF2), and the prototypic 4.1 subgroup member,Protein 4.1B, has been implicated in the molecular pathogenesis of breast,lung and brain cancers. This review focuses on what is known of mechanisms of action and critical protein interactions that may mediate the unique growth inhibitory signals of these two Protein 4.1 tumor suppressors. On the basis of insights derived from studying the NF2 tumor suppressor, we propose a model for merlin growth regulation in which CD44 links growth signals from plasma membrane to the nucleus by interacting with ERM proteins and merlin.

Tuberous sclerosis complex (TSC) is a tumor suppressor gene syndrome in which severe renal cystic disease can occur. Many renal cystic diseases, including autosomal dominant polycystic kidney disease (ADPKD), are associated with absence or dysfunction of the primary cilium. We report here that hamartin (TSC1) localizes to the basal body of the primary cilium, and that Tsc1−/− and Tsc2−/− mouse embryonic fibroblasts (MEFs) are significantly more likely to contain a primary cilium than wild-type controls. In addition, the cilia of Tsc1−/− and Tsc2−/− MEFs are 17–27% longer than cilia from wild-type MEFs. These data suggest a novel type of ciliary disruption in TSC, associated with enhanced cilia development. The TSC1 and TSC2 proteins function as a heterodimer to inhibit the activity of the mammalian target of rapamycin complex 1 (TORC1). The enhanced ciliary formation in the Tsc1−/− and Tsc2−/− MEFs was not abrogated by rapamycin, which indicates a TORC1-independent mechanism. Polycystin 1 (PC1), the product of the PKD1 gene, has been found to interact with TSC2, but Pkd1−/− MEFs did not have enhanced ciliary formation. Furthermore, while activation of mTOR has been observed in renal cysts from ADPKD patients, Pkd1−/− MEFs did not have evidence of constitutive mTOR activation, thereby underscoring the independent functions of the TSC proteins and PC1 in regulation of primary cilia and mTOR. Our data link the TSC proteins with the primary cilium and reveal a novel phenotype of enhanced ciliary formation in a cyst-associated disease.

The mTOR/p70S6 kinase signaling pathway is activated in most clear cell renal cell carcinomas. Moreover, the growth of renal clear cell carcinoma derived cell lines is inhibited by rapamycin. This is especially significant in light of new agents such as CCI-779, an ester of rapamycin and inhibitor of mTOR, which has shown promise in the treatment of renal carcinoma.

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