Notch-1 inhibits apoptosis in murine erythroleukemia cells and is necessary for differentiation induced by hybrid polar compounds

Abstract

Strikingly increased expression of notch-1 has been demonstrated in several human malignancies and pre-neoplastic lesions. However, the functional consequences of notch-1 overexpression in transformed cells remain unclear. We investigated whether endogenously expressed notch-1 controls cell fate determination in mouse erythroleukemia (MEL) cells during pharmacologically induced differentiation. We found that notch-1 expression is modulated during MEL cell differentiation. Premature downregulation of notch-1 during differentiation, by antisense S-oligonucleotides or by enforced expression of antisense notch-1 mRNA, causes MEL cells to abort the differentiation program and undergo apoptosis. Downregulation of notch-1 expression in the absence of differentiation inducer increases the likelihood of spontaneous apoptosis. We conclude that in MEL cells, endogenous notch-1 expression controls the apoptotic threshold during differentiation and growth. In these cells, notch-1 allows differentiation by preventing apoptosis of pre-committed cells. This novel function of notch-1 may play a role in regulating apoptosis susceptibility in notch-1 expressing tumor cells.

The notch pathway positively regulates programmed cell death during erythroid differentiation

“…15,18,19,24 For this reason, we aimed to characterize the physiological role of the Notch pathway in erythropoiesis by comparing WT and RBPjk À/À embryos. Despite the absence of intraembryonic hematopoiesis in the RBPjk À/À embryos and the presence of different angiogenic abnormalities in the yolk sac, we found that primitive hematopoiesis does occur in the yolk sac of the RBPjk À/À embryos (Figure 1a), similar to the Notch1 À/À mutants.…”

“…Although previous reports have attempted to decipher which is the Notch function in apoptosis of erythroid cells, 15,19 this is the first time that this question is addressed in primary cells. The use of cell lines in the previous published reports may explain the controversial data.…”

“…[15][16][17] However, the overall data linking Notch and erythroid apoptosis is controversial. 18,19 In this work, we demonstrate that the Notch signaling pathway is a positive regulator of apoptosis in primitive erythropoiesis in the yolk sac but also in erythroid cells from adult bone marrow (BM). Complementary studies using the murine erythroleukemia (MEL) cell line indicate that Notch induces erythroid-specific apoptosis.…”

Hexamethylene bisacetamide as a treatment for T-cell leukemia (T-ALL)

“…In general, hybrid polar compounds have been used to induce differentiation in many different tissues of all embryonic lineages [2]. HMBA is a prototype compound from this class, and has been shown specifically to differentiate the MEL murine erythroleukemia cell line [2,3], with concomitant downregulation of Notch1 [4].Notch1 is a transmembrane receptor important in stem cell renewal and T versus B lineage differentiation, which has a unique mechanism of activation, releasing an intracellular subunit upon ligand binding, which translocates into the nucleus to induce the expression of target genes such as Deltx, Hes1 and pTalpha [5]. Mutations in its HD and PEST domains have recently been strongly implicated in the pathogenesis of T-ALL, being found in more than half of these patients [6].…”

“…In general, hybrid polar compounds have been used to induce differentiation in many different tissues of all embryonic lineages [2]. HMBA is a prototype compound from this class, and has been shown specifically to differentiate the MEL murine erythroleukemia cell line [2,3], with concomitant downregulation of Notch1 [4].…”