TM2D3, a mammalian homologue of Drosophila neurogenic gene product Almondex, regulates surface presentation of Notch receptors.

Notch signaling is an evolutionarily conserved mechanism required for numerous types of cell fate decisions in metazoans. It mediates short-range communication between cells with receptors and ligands, both of which are expressed on the cell surfaces. In response to the ligand-receptor interaction, the ligand and the extracellular domain of the Notch receptor (NECD) in the complex are internalized into ligand-expressing cells by endocytosis, a prerequisite process for the conformational change of the membrane proximal region of Notch to induce critical proteolytic cleavages for its activation. Here we report that overexpression of transmembrane 2 (TM2) domain containing 3 (TM2D3), a mammalian homologue of Drosophila melanogaster Almondex (Amx), activates Notch1. This activation requires the ligand-binding domain in Notch1 and the C-terminal region containing TM2 domain in TM2D3. TM2D3 physically associates with Notch1 at the region distinct from the ligand-binding domain and enhances expression of Notch1 on the cell surface. Furthermore, cell surface expression of Notch1 and Notch2 is reduced in Tm2d3-deficient cells. Finally, amx-deficient Drosophila early embryos exhibit impaired endocytosis of NECD and Delta ligand, for which surface presentation of Notch is required. These results indicate that TM2D3 is an element involved in Notch signaling through the surface presentation.

Expression and localization of membrane-type-1 matrix metalloproteinase, CD 44, and laminin-5gamma2 chain during colorectal carcinoma tumor progression.

Membrane-type-1 matrix metalloproteinase (MT1-MMP) is overexpressed in many malignant tumor tissues and would be involved in tumor-cell migration. Using dual immunofluorescence of frozen sections, this study examined the expression and localization of MT1-MMP and its interacting molecules, CD44 and laminin-5gamma2 chain (LN-5gamma2) monomer, in 48 cases of colorectal tumors. Recent studies have shown that MT1-MMP, CD44 and LN-5gamma2 are direct downstream targets in the adenomatosis polyposis coli (APC)/beta-catenin (Wnt)-signaling pathway, which is upregulated in most colorectal epithelial tumors. MT1-MMP overexpression was observed in adenocarcinoma cases with moderate and/or less differentiation coinciding with CD44 downmodulation. Recent observations indicate that MT1-MMP overexpression disrupts tubulogenesis of MDCK cells in type-I collagen-rich tissues. Therefore, MT1-MMP overexpression might involve disturbances of neoplastic glandular structures during colorectal adenocarcinoma tumor progression. Intensity distribution analyses of images with dual immunofluorescence indicated that overexpressed MT1-MMP is closely associated with the enhanced expression of the LN-5gamma2 monomers at the invasive front of dedifferentiated tumor cells. Additionally, the graded expression of nuclear active beta-catenin was found in moderately differentiated and dedifferentiated areas of adenocarcinomas, where MT1-MMP overexpression was observed. Therefore, this study reveals that MT1-MMP might be a major effector of Wnt signaling in the late stage of colorectal carcinoma tumor progression.