Postnatal Notch1 activation induces T-cell malignancy in conditional and inducible mouse models

Abstract

Abstract. the notch1 signaling pathway is essential for hematopoietic development. However, the effects of postnatal activation of notch1 signaling on hematopoietic system is not yet fully understood. We previously generated ZEG-IC-Notch1 transgenic mice that have a floxed β-geo/stop signal between a cMV promoter and intracellular domain of notch1 (ic-notch1). constitutively active ic-notch1 is silent until the introduction of cre recombinase. in this study, endothelial/hematopoietic specific expression of IC-Notch1 in double transgenic Zeg-ic-notch1/tie2-cre embryos induced embryonic lethality at e9.5 with defects in vascular system but not in hematopoietic system. Inducible IC-Notch1 expression in adult mice was achieved by using tetracycline regulated cre system. the Zeg-ic-notch1/tie2-tta/tet-o-cre triple transgenic mice survived embryonic development when maintained on tetracycline. Post-natal withdrawal of tetracycline induced expression of IC-Notch1 transgene in hematopoietic cells of adult mice. The triple transgenic mice displayed extensive T-cell infiltration in multiple organs and T-cell malignancy of lymph nodes. in addition, the protein levels of p53 and alternative reading frame (arf) were decreased in lymphoma-like neoplasms from the triple transgenic mice while their mrna expression remained unchanged, suggesting that IC-Notch1 might repress arf-p53 pathway by a post-transcriptional mechanism. this study demonstrated that activation of constitutive notch1 signaling after embryonic development alters adult hematopoiesis and induces t-cell malignancy. Introductionnotch is a family of highly conserved cell-surface receptors that are required in many mammalian developmental processes (1). the interaction of notch receptors and its ligands initiates a cascade of proteolytic cleavages. tnf-α converting enzyme, a metalloprotease, cleaves the extracellular subunit to leave membrane-bound form of the transmembrane subunit of notch receptors. Then a presenilin-associated multiprotein complex with γ-secretase activity recognizes and cleaves a site within the transmembrane domain to release the intracellular domain of notch (ic-notch). ic-notch translocates to the nucleus and converts the transcription factor cBf1/Su(H)/lag1 (cSl) from a repressor to a transcriptional activator (2). the downstream targets of notch/cSl include Hairy-enhancer of split (HeS) and Hes-related protein (HerP/Hey) families, which function as transcriptional repressors suppressing the expression of cell type specific target genes (3).to date, four notch receptors (notch 1-4) and five ligands (δ-like 1, 2 and 4; jagged 1 and 2) have been described in mammals (2). Notch1 is expressed in most embryonic and adult tissues. Notch1 protein has an extracellular domain consisting of multiple egf-like repeats and three cysteine-rich lin12 repeats with heterodimerization (HD) domain, a transmembrane domain and intracellular domain containing a CSL associating motif domain, six ankyrin repeats, nuclear localization signals (nlS), a glutamine-ric...