Soluble Jagged-1 is able to inhibit the function of its multivalent form to induce hematopoietic stem cell self-renewal in a surrogate in vitro assay

Abstract

Stem cells reside in customized microenvironments (niches) that contribute to their unique ability to divide asymmetrically to give rise to self and to a daughter cell with distinct properties. Notch receptors and their ligands are highly conserved and have been shown to regulate cell-fate decisions in multiple developmental systems through local cell interactions. To assess whether Notch signaling may regulate hematopoiesis to maintain cells in an immature state, we examined the functional role of the recombinant, secreted form of the Notch ligand Jagged-1 during mouse hematopoietic stem cell (HSC) and progenitor cell proliferation and maturation. We found that ligand immobilization on stromal layer or on Sepharose-4B beads is required for the induction of self-renewing divisions of days 28-35 cobblestone area-forming cell. The free, soluble Jagged-1, however, has a dominant-negative effect on self-renewal in the stem-cell compartment. In contrast, free as well as immobilized Jagged-1 promotes growth factor-induced colony formation of committed hematopoietic progenitor cells. Therefore, we propose that differences in Jagged-1 presentation and developmental stage of the Notch receptor-bearing cells influence Notch ligand-binding results toward activation or inhibition of downstream signaling. Moreover, these results suggest potential clinical use of recombinant Notch ligands for expanding human HSC populations in vitro.

Novel Cross-Talk between Three Cardiovascular Regulators: Thrombin Cleavage Fragment of Jagged1 Induces Fibroblast Growth Factor 1 Expression and Release

“…The biological roles of soluble Notch ligands are insufficiently understood, although we know that naturally occurring soluble forms of Notch ligands arise due to proteolytic cleavage (Qi et al, 1999), including the cleavage stimulated by their interaction with Notch receptors (Ikeuchi and Sisodia, 2003;LaVoie and Selkoe, 2003) or differential mRNA processing (Zimrin et al, 1996;Li et al, 1997;Aho, 2004). Several reports indicate that soluble forms of Jagged1 may play crucial roles in hematopoietic and nerve stem cell self-renewal, cell proliferation, angiogenesis, and vascular repair (Masuya et al, 2002;Vas et al, 2004;Nikopoulos et al, 2007;Scehnet et al, 2007). Our in vitro studies demonstrated that fibroblastoid cells expressing sJ1 117-kDa form chord-like structures, similar to those formed by endothelial cells during angiogenesis (Wang et al, 2000;Small et al, 2001;Trifonova et al, 2004).…”

Rbm15 Modulates Notch-Induced Transcriptional Activation and Affects Myeloid Differentiation

“…Several studies show that Notch facilitates bone marrow stem cell expansion and plays a role in the stem cell niche in vivo (11). In vitro activation of Notch in hematopoietic stem cells leads to increased proliferation and survival (13,49). Notch signaling facilitates T-cell development and plays a role in biphenotypic fate decisions (24).…”

The roles of receptor and ligand endocytosis in regulating Notch signaling

“…Soluble, non-membrane bound ligands have been shown to retain signaling activity in some, but not all, cultured cell assays (Hicks et al, 2002;Li et al, 1998;Ohishi et al, 2002;Shimizu et al, 2000;Shimizu et al, 2002;Vas et al, 2004;Wang et al, 1998). The antibody-induced oligomerization of soluble ligands, which were produced as fusions with human IgG Fc, has been reported to increase the signaling activity of these ligands, suggesting that ligand clustering promotes signaling (Hicks et al, 2002;Shimizu et al, 2002).…”