TGF-ß synergizes with defects in the Hippo pathway to stimulate human malignant mesothelioma growth.

Malignant mesothelioma (MM) is an incurable malignancy that is caused by exposure to asbestos and is accompanied by severe fibrosis. Because MM is usually diagnosed at an advanced stage and clinical identification of early lesions is difficult, its molecular pathogenesis has not been completely elucidated. Nearly 75% of MM cases have inactivating mutations in the NF2 (neurofibromatosis type 2; Merlin) gene or in downstream signaling molecules of the Hippo signaling cascade, which negatively regulates the transcription factor Yes-associated protein (YAP). In this study, we demonstrate a functional interaction between the Hippo and TGF-ß pathways in regulating connective tissue growth factor (CTGF). Expression of CTGF in MM cells was induced by the formation of a YAP-TEAD4-Smad3-p300 complex on the CTGF promoter. Knocking down CTGF expression in MM cells prolonged the survival of xenografted mice, and a significant association was seen between CTGF expression and extracellular matrix deposition in MM xenografts and in patient tissue specimens. We further suggest that CTGF may influence the malignancy of mesothelioma because of the different histological expression patterns observed in human MM tissues. These data suggest that CTGF is an important modulator of MM growth and pathology and represents a novel therapeutic target for this disease.

Characterization of murine CD160+ CD8+ T lymphocytes.

CD160 is an Ig-like glycoprotein expressed on NK, NKT and TCRgammadelta T cells, as well as intestinal intraepithelial T lymphocytes. In addition, a minor subset of CD8(+) but not CD4(+) T cells in the periphery is also known to express CD160, but the subset has not been fully characterized. In this study, we prepared anti-murine CD160 mAbs and investigated the expression profile of CD160 on various subsets of CD8(+) T cells. The amount of CD160 on almost all CD8(+) T cells was increased upon CD3-mediated stimulation in vitro, and soluble CD160 was found to be released. Flow cytometric analysis revealed most CD8(+) T cells expressing CD160 to show a CD44(high) phenotype in vivo. On further analysis, both CD44(high)CD62L(low) effector memory T cells (T(EM)) and CD44(high)CD62L(high) central memory T cells (T(CM)) expressed CD160 at an intermediate level. High levels were evident with recently activated CD8(+) T(EM). Naïve CD8(+) T cells presumably immediately after stimulation (CD44(low)CD62L(low)CD69(+)) also expressed CD160, but only at a low level. Purified CD160(+) CD8(+) T cells from OT-1 transgenic mice expressing TCR against OVA residues 257-264 presented by H-2K(b) produced IFN-gamma more rapidly than CD160(-) CD8(+) T cells upon antigen stimulation. These results together show that CD160 is expressed on the majority of CD8(+) memory T cells as well as recently activated CD8(+) T cells.

Immunity against mouse thymus-leukemia antigen (TL) protects against development of lymphomas induced by a chemical carcinogen, N-butyl-N-nitrosourea.

Mouse thymus-leukemia antigens (TL) are aberrantly expressed on T lymphomas in C57BL/6 (B6) and C3H/He (C3H) mice, while they are not expressed on normal T lymphocytes in these strains. When N-butyl-N-nitrosourea (NBU), a chemical carcinogen, was administered orally to B6 and C3H strains, lymphoma development was slower than in T3(b)-TL gene-transduced counterpart strains expressing TL ubiquitously as self-antigens, suggesting that anti-TL immunity may play a protective role. In addition, the development of lymphomas was slightly slower in C3H than in B6, which seems to be in accordance with the results of skin graft experiments indicating that both cellular and humoral immunities against TL were stronger in C3H than B6 mice. The interesting finding that B lymphomas derived from a T3(b)-TL transgenic strain (C3H background) expressing a very high level of TL were rejected in C3H, but not in H-2K(b) transgenic mice (C3H background), raises the possibility that TL-specific effector T cell populations are eliminated and/or energized to a certain extent by interacting with H-2K(b) molecules.

Thymus leukemia antigen (TL)-specific cytotoxic T lymphocytes recognize the alpha1/alpha2 domain of TL free from antigenic peptides.

The thymus leukemia antigens (TL) belong to the MHC class Ib family and can be recognized by CD8-dependent or -independent cytotoxic T lymphocytes (CTL) showing TL, but not H-2, restriction. We previously reported that the CTL epitope is TAP independent and in the present study we further characterize the recognition mechanism of CD8-dependent TL-specific TCRalphabeta CTL. We first prepared empty TL tetramers by way of peptide-independent folding with recombinant proteins produced in an Escherichia coli expression system, and showed that TL-specific CTL recognized TL without putative TL-associated peptide and/or post-translational modifications of TL by mammalian and insect cells. We next prepared transfectants expressing various chimeric TL molecules with mouse or human MHC class I as well as chimeric TL tetramers with recombinant proteins produced by insect cells, and demonstrated that chimeric TL whose alpha3 domain was replaced by that of H-2K(b), but not of HLA-A2, was sufficient for binding and activation of TL-specific CTL. These results indicate that TL-specific CTL recognize predominantly their alpha1/alpha2 domain as an epitope(s) and that the binding activity to the murine CD8 of the alpha3 domain of H-2K(b) is sufficient to induce their CTL activity, although it is known to be weaker than that of TL, but stronger than that of HLA. The results taken together indicate that CD8-dependent TL-specific TCRalphabeta CTL recognize an epitope(s) of the alpha1/alpha2 domain of TL free from antigenic molecules, and that CD8 plays an important role in stable interactions between TL and their corresponding TCR.