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...

O-Linked N-acetylglucosamine (O-GlcNAc

The covalent attachment of different types of poly-ubiquitin chains signal different outcomes for the proteins so targeted. For example, a protein modified with Lys-48-linked poly-ubiquitin chains is targeted for proteasomal degradation, whereas Lys-63-linked chains encode non-degradative signals. The structural features that enable these different types of chains to encode different signals have not yet been fully elucidated. We report here the X-ray crystal structures of Lys-63-linked tri- and di-ubiquitin at resolutions of 2.3 and 1.9 Å, respectively. The tri- and di-ubiquitin species adopt essentially identical structures. In both instances the ubiquitin chain assumes a highly extended conformation with a left-handed helical twist; the helical chain contains four ubiquitin monomers per turn and has a repeat length of approximately 110 Å. Interestingly, Lys-48 ubiquitin chains also adopt a left-handed helical structure with a similar repeat length. However, the Lys-63 architecture is much more open than that of Lys-48 chains and exposes much more of the ubiquitin surface for potential recognition events. These new crystal structures are consistent with the results of solution studies of Lys-63 chain conformation, and reveal the structural basis for differential recognition of Lys-63 versus Lys-48 chains.

The Josephin domain is a conserved cysteine protease domain found in four human deubiquitinating enzymes: ataxin-3, the ataxin-3-like protein (ATXN3L), Josephin-1, and Josephin-2. Josephin domains from these four proteins were purified and assayed for their ability to cleave ubiquitin substrates. Reaction rates differed markedly both among the different proteins and for different substrates with a given protein. The ATXN3L Josephin domain is a significantly more efficient enzyme than the ataxin-3 domain despite their sharing 85% sequence identity. To understand the structural basis of this difference, the 2.6 Å x-ray crystal structure of the ATXN3L Josephin domain in complex with ubiquitin was determined. Although ataxin-3 and ATXN3L adopt similar folds, they bind ubiquitin in different, overlapping sites. Mutations were made in ataxin-3 at selected positions, introducing the corresponding ATXN3L residue. Only three such mutations are sufficient to increase the catalytic activity of the ataxin-3 domain to levels comparable with that of ATXN3L, suggesting that ataxin-3 has been subject to evolutionary restraints that keep its deubiquitinating activity in check.