TGF-beta cooperates with TGF-alpha to induce the self-renewal of normal erythrocytic progenitors: evidence for an autocrine mechanism

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 anal ysis for differentiation antigens and gene expression, these cells were sho wn to represent very immature haematopoietic progenitors committed to the e rythrocytic lineage. T2ECs differentiate into almost pure populations of fu lly mature erythrocytes within 6 days, when TGF-alpha and TGF-beta are with drawn and the cells exposed to anaemic chicken serum plus insulin. Outgrowt h of these cells from various sources invariably required both TGF-alpha an d TGF-beta, as well as glucocorticoids, Proliferating, established T2ECs st ill require TGF-alpha, but are independent of exogenous TGF-beta, Using a T GF-beta-neutralizing antibody or expressing a dominant-negative TGF-beta re ceptor II, we demonstrate that T2ECs generate an autocrine loop involving T GF-beta during their establishment, which is required for sustained prolife ration. Using specific inhibitors, we also show that signalling via Mek-1 i s specifically required for induction and maintenance of cell proliferation driven by cooperation between the TGF-alpha and -beta receptors, These res ults establish a novel mechanism by which self-renewal of erythrocytic prog enitors is induced and establish avian T2ECs as a new quasi-optimal model s ystem to study erythrocytic progenitors.