Brenda Cohen

Subversion of the T/B Lineage Decision in the Thymus by Lunatic Fringe-Mediated Inhibition of Notch-1

Notch-1 signaling is essential for lymphoid progenitors to undergo T cell commitment, but the mechanism has not been defined. Here we show that thymocytes ectopically expressing Lunatic Fringe, a modifier of Notch-1 signaling, induce lymphoid progenitors to develop into B cells in the thymus. This cell fate switch resulted from Lunatic Fringe-mediated inhibition of Notch-1 function, as revealed by experiments utilizing lymphoid progenitors in which Notch-1 activity was genetically manipulated. These data identify Lunatic Fringe as a potent regulator of Notch-1 during the T/B lineage decision and show that an important function of Notch-1 in T cell commitment is to suppress B cell development in the thymus.

Lunatic Fringe-mediated Notch signaling is required for lung alveogenesis

Distal lung development occurs through coordinated induction of myofibroblasts, epithelial cells, and capillaries. Lunatic Fringe (Lfng) is a beta(1-3) N-acetylglucosamine transferase that modifies Notch receptors to facilitate their activation by Delta-like (Dll1/4) ligands. Lfng is expressed in the distal lung during saccular development, and deletion of this gene impairs myofibroblast differentiation and alveogenesis in this context. A similar defect was observed in Notch2(beta-geo/+)Notch3(beta-geo/beta-geo) compound mutant mice but not in Notch2(beta-geo/+) or Notch3(beta-geo/beta-geo) single mutants. Finally, to directly test for the role of Notch signaling in myofibroblast differentiation in vivo, we used ROSA26-rtTA(/+);tetO-CRE(/+);RBPJkappa(flox/flox) inducible mutant mice to show that disruption of canonical Notch signaling during late embryonic development prevents induction of smooth muscle actin in mesenchymal cells of the distal lung. In sum, these results demonstrate that Lfng functions to enhance Notch signaling in myofibroblast precursor cells and thereby to coordinate differentiation and mobilization of myofibroblasts required for alveolar septation.

Plasminogen Activator uPA Is a Direct Transcriptional Target of the JAG1-Notch Receptor Signaling Pathway in Breast Cancer

Aberrant activation of the Notch receptor signaling pathway and overexpression of the Notch ligand JAG1 are associated with poor outcome in breast cancer. The plasminogen activator system, which includes urokinase-type plasminogen activator (uPA), has been validated as a marker of recurrence, high metastasis risk and death in breast malignancy. By using microarray profiling of breast cancer cell lines that had undergone siRNA-mediated abrogation of Notch signaling we uncovered a link between activated Notch signaling and uPA expression. An association between elevated expression of the Notch ligand JAG1, uPA, and the basal-like breast cancer subtype was confirmed in breast cancer cell lines. The association between JAG1 and uPA expression persisted in a survey of primary carcinomas of the breast. We found that Notch knockdown reduced transcription of uPA and phenocopied uPA knockdown in breast cancer cells. Through mutational analysis we identified a CBF-1 binding site in the uPA promoter that is required for direct transcriptional regulation by Notch. These data suggest that JAG1-induced Notch activation results in breast cancer progression through upregulation of the plasminogen activator system, directly linking these 2 important pathways of poor prognosis.

How do retinoblastoma tumours form

The causes of retinoblastoma (RB) can now be described with considerable accuracy, although many details are still unclear. Understanding the genetic changes leading to RB has provided an awareness of general mechanisms of cancer development and progression, previously only suspected. From the basic understanding have come new diagnostic technologies that are now ready to be applied directly to RB patients and their families, and a rational approach, based on this understanding, will help us to develop new therapies that avoid the severe complications of conventional treatment.

Molecular cloning and expression analysis of a mouse UDP-GlcNAc:Gal(β1-4)Glc(NAc)-R β1,3-N-acetylglucosaminyltransferase homologous to Drosophila melanogaster Brainiac and the β1,3-galactosyltransferase family

We have isolated a murine cDNA coding for a β1,3-N-acetylglucosaminyltransferase enzyme ( β3GnT). This enzyme is similar in sequence to Drosophila melanogaster Brainiac and to the murine and human β1,3-galactosyltransferase family of proteins. The mouse β 3GnT protein is 397 amino acids in length and contains 7 cysteine residues that are conserved in the human orthologue. β 3GnT is a type II membrane protein localized to the Golgi apparatus. Enzyme assays with recombinant mouse β 3GnT reveal that it has a preference for acceptors with Gal(β1-4)Glc(NAc) at the non-reducing termini. Proton NMR analysis of product showed incorporation of GlcNAc in β1,3 linkage to the terminal Gal of Gal(β1-4)Glc(β1-O-benzyl). Northern blot analysis revealed the presence of a single 3.0[emsp4 ]kb transcript in all adult mouse and human organs tested, with highest levels in the kidney, liver, heart and placenta. The β 3GnT gene is also expressed in a number of tumor cell lines. The human orthologue of β 3GnT is located on chromosome 2pl5.