TGF-β cooperates with TGF-α to induce the self–renewal of normal erythrocytic progenitors: evidence for an autocrine mechanism

Abstract

Simultaneous addition of both TGF-alpha and TGF-beta induces the sustained, long-term outgrowth of chicken erythrocytic progenitor cells, referred to as T2ECs from both chick bone marrow and 2-day-old chicken embryos. By analysis for differentiation antigens and gene expression, these cells were shown to represent very immature haematopoietic progenitors committed to the erythrocytic lineage. T2ECs differentiate into almost pure populations of fully mature erythrocytes within 6 days, when TGF-alpha and TGF-beta are withdrawn and the cells exposed to anaemic chicken serum plus insulin. Outgrowth of these cells from various sources invariably required both TGF-alpha and TGF-beta, as well as glucocorticoids. Proliferating, established T2ECs still require TGF-alpha, but are independent of exogenous TGF-beta. Using a TGF-beta-neutralizing antibody or expressing a dominant-negative TGF-beta receptor II, we demonstrate that T2ECs generate an autocrine loop involving TGF-beta during their establishment, which is required for sustained proliferation. Using specific inhibitors, we also show that signalling via Mek-1 is specifically required for induction and maintenance of cell proliferation driven by cooperation between the TGF-alpha and -beta receptors. These results establish a novel mechanism by which self-renewal of erythrocytic progenitors is induced and establish avian T2ECs as a new, quasi-optimal model system to study erythrocytic progenitors.

Global transcription analysis of immature avian erythrocytic progenitors: from self-renewal to differentiation

“…Among them, the EpoR progenitors are very interesting because they can be obtained directly from T2EC cells by the expression of the murine Epo receptor and the growth in medium containing Epo, SCF, Dex, IGF1 (Bauer et al, 2001;Dazy et al, 2003). EpoR progenitors are more mature than T2EC cells as assessed by the expression level of stage-specific surface antigens (Gandrillon et al, 1999;Wessely et al, 1999). Furthermore, EpoR progenitors display a higher tendency to spontaneous differentiation (i.e.…”

“…In the hematopoietic system, self-renewal is generally considered to be a specific property of the HSC (Weissman, 2000), but neither the daily generation of 200 Â 10 9 red cells nor stress erythropoiesis can easily be explained by this idea. Thus, the hypothesis that other less immature progenitors can self-renew has been proposed (Gandrillon et al, 1999;Bauer et al, 2001), enabling the use of these progenitors to study the molecular basis of self-renewal.…”

“…We have devised a cellular model system in which selfrenewal can be investigated (Gandrillon et al, 1999). Normal immature erythroid progenitors (T2EC cells) can be maintained (>30 days) in proliferation without overt differentiation and can be induced to terminally differentiate into fully mature erythrocytes at any time.…”

“…Normal immature erythroid progenitors (T2EC cells) can be maintained (>30 days) in proliferation without overt differentiation and can be induced to terminally differentiate into fully mature erythrocytes at any time. Despite their self-renewal capacity, T2EC cells are restricted to the erythroid lineage (Gandrillon et al, 1999;Dazy et al, 2003). This monopotency is an advantage for the study of self-renewal, since the molecular changes governing the choice between selfrenewal versus differentiation will not be blurred by changes characteristic for lineage choices during commitment.…”

bFGF signaling and v-Myb cooperate in sustained growth of primitive erythroid progenitors

“…Furthermore, genetic mutations of SCF and SCF receptor in Steel (SI) and Dominant white spotting (WW) loci, respectively, were associated with severe anemia (Broudy, 1997). Other factors such as basic ®broblast growth factor (bFGF, FGF-2), transforming growth factor a (TGFa) and members of the TGFb family, including TGFb, bone morphogenic proteins (BMPs) and activin A, are also involved (Krystal et al, 1994;Dickson et al, 1995;Huber et al, 1998;Mead and Zon, 1998;Gandrillon et al, 1999;Koritschoner et al, 1999).…”