Tle corepressors are differentially partitioned to instruct CD8+ T cell lineage choice and identity.

Tle/Groucho proteins are transcriptional corepressors interacting with Tcf/Lef and Runx transcription factors, but their physiological roles in T cell development remain unknown. Conditional targeting of Tle1, Tle3 and Tle4 revealed gene dose-dependent requirements for Tle proteins in CD8+ lineage cells. Upon ablating all three Tle proteins, generation of CD8+ T cells was greatly diminished, largely owing to redirection of MHC-I-selected thymocytes to CD4+ lineage; the remaining CD8-positive T cells showed aberrant up-regulation of CD4+ lineage-associated genes including Cd4, Thpok, St8sia6, and Foxp3 Mechanistically, Tle3 bound to Runx-occupied Thpok silencer, in post-selection double-positive thymocytes to prevent excessive ThPOK induction and in mature CD8+ T cells to silence Thpok expression. Tle3 also bound to Tcf1-occupied sites in a few CD4+ lineage-associated genes, including Cd4 silencer and St8sia6 introns, to repress their expression in mature CD8+ T cells. These findings indicate that Tle corepressors are differentially partitioned to Runx and Tcf/Lef complexes to instruct CD8+ lineage choice and cooperatively establish CD8+ T cell identity, respectively.

Tle1 tumor suppressor negatively regulates inflammation in vivo and modulates NF-κB inflammatory pathway.

Tle1 (transducin-like enhancer of split 1) is a corepressor that interacts with a variety of DNA-binding transcription factors and has been implicated in many cellular functions; however, physiological studies are limited. Tle1-deficient (Tle1(Δ/Δ)) mice, although grossly normal at birth, exhibit skin defects, lung hypoplasia, severe runting, poor body condition, and early mortality. Tle1(Δ/Δ) mice display a chronic inflammatory phenotype with increased expression of inflammatory cytokines and chemokines in the skin, lung, and intestine and increased circulatory IL-6 and G-CSF, along with a hematopoietic shift toward granulocyte macrophage progenitor and myeloid cells. Tle1(Δ/Δ) macrophages produce increased inflammatory cytokines in response to Toll-like receptor (TLR) agonists and lipopolysaccharides (LPS), and Tle1(Δ/Δ) mice display an enhanced inflammatory response to ear skin 12-O-tetradecanoylphorbol-13-acetate treatment. Loss of Tle1 not only results in increased phosphorylation and activation of proinflammatory NF-κB but also results in decreased Hes1 (hairy and enhancer of split-1), a negative regulator of inflammation in macrophages. Furthermore, Tle1(Δ/Δ) mice exhibit accelerated growth of B6-F10 melanoma xenografts. Our work provides the first in vivo evidence, to our knowledge, that TLE1 is a major counterregulator of inflammation with potential roles in a variety of inflammatory diseases and in cancer progression.

The MUC1 and galectin-3 oncoproteins function in a microRNA-dependent regulatory loop.

The MUC1 heterodimeric transmembrane glycoprotein is aberrantly overexpressed by diverse human carcinomas. Galectin-3 is a beta-galactoside binding protein that has also been associated with the development of human cancers. The present results demonstrate that MUC1 induces galectin-3 expression by a posttranscriptional mechanism. We show that the MUC1 C-terminal subunit is glycosylated on Asn-36 and that this modification is necessary for upregulation of galectin-3. N-glycosylated MUC1-C increases galectin-3 mRNA levels by suppressing expression of the microRNA miR-322 and thereby stabilizing galectin-3 transcripts. The results show that, in turn, galectin-3 binds to MUC1-C at the glycosylated Asn-36 site. The significance of the MUC1-C-galectin-3 interaction is supported by the demonstration that galectin-3 forms a bridge between MUC1 and the epidermal growth factor receptor (EGFR) and that galectin-3 is essential for EGF-mediated interactions between MUC1 and EGFR. These findings indicate that MUC1 and galectin-3 function as part of a miR-322-dependent regulatory loop.

Evolution of the human MUC1 oncoprotein.

The mucin (MUC) family consists of secreted and membrane-bound forms. The transmembrane mucin 1 (MUC1) is a heterodimer that is aberrantly overexpressed by diverse human carcinomas and certain hematologic malignancies. The MUC1 N-terminal (MUC1-N) and C-terminal (MUC1-C) subunits are generated by autocleavage within a SEA domain. The MUC1 cytoplasmic domain (MUC1-CD) located downstream of the SEA domain is sufficient for the induction of anchorage-independent growth and tumorigenicity; however, no information is available regarding the origin of these transforming sequences. Previous work demonstrated that, except for the SEA domain, MUC1 has no sequence homology with other membrane-bound mucins. The present results demonstrate that MUC1-CD evolved from repeat regions in the MUC5B secreted mucin. We also show that MUC1 sequences upstream to the SEA domain emerged from MUC5B. These findings indicate that both the MUC1-N and MUC1-C subunits evolved from secreted gel-forming mucins and that the MUC1-CD oncogenic function emerged by diversification after evolution from MUC5B.

Distinct evolution of the human carcinoma-associated transmembrane mucins, MUC1, MUC4 AND MUC16.

The MUC family of mucins consists of secreted and membrane-bound forms. Overexpression of the membrane-bound family members, MUC1 (CA15-3), MUC4 and MUC16 (CA125), is found in diverse human carcinomas. However, despite being classified in the same family, little is known about the genetic origins of the carcinoma-associated mucins. The present results show that MUC1 homologs are restricted to mammalian species. MUC1 has no sequence similarity with the other membrane-bound mucins, except for the presence of a sea urchin sperm protein-enterokinase-agrin (SEA) domain. The results indicate that the MUC1 SEA domain originated from heparin sulfate proteoglycan of basement membrane (HSPG2; perlecan), an inducer of tumor cell growth. MUC4 has no SEA domain, but does have (i) a NIDO domain that evolved from an ancestor common to nidogen, and (ii) AMOP and VWD domains that originated from an ancestor common to the Sushi-domain containing protein. MUC16 contains multiple SEA domains that are found in a chicken gene and were subsequently repeated through duplication events. The SEA domains in MUC16 appear to have evolved from agrin before the divergence of birds and mammals. These findings indicate that MUC1, MUC4 and MUC16 evolved from distinct ancestors and that the membrane-bound mucins consist of different subgroups based on their genetic backgrounds.