MECHANISMS OF STEM-CELL FACTOR AND ERYTHROPOIETIN PROLIFERATIVE COSIGNALING IN FDC2-ER CELLS

Studies of hematopoietic progenitor cell development in vivo, ex vivo, and in factor-dependent cell lines have shown that c-kit promotes pro liferation through synergistic effects with at least certain type 1 cy tokine receptors, including the erythropoietin (Epo) receptor. Present ly, c-kit is shown to efficiently support both mitogenesis and surviva l in the FDCP1 cell subline, FDC2, In this system, mitogenic synergy w ith c-kit was observed for ectopically expressed wild-type Epo recepto rs (wt-ER), an epidermal growth factor (EGF) receptor/Epo receptor chi mera, and a highly truncated Epo receptor construct ER-Bx1. Thus, the Epo receptor cytoplasmic box 1 subdomain appears, at least in part, to mediate mitogenic synergy with c-kit. In studies of potential effecte rs of this response, Jak2 tyrosine phosphorylation was shown to be ind uced by Epo, but not by stem cell factor (SCF). In addition and in con trast to signaling in Mo7e and BM6 cell lines, in FDC2-ER cells SCF an d Epo each were shown to rapidly activate Pim 1 gene expression, Recen tly, roles also have been suggested for the nuclear trans-factor GATA- 1 in regulating progenitor cell proliferation. In FDC2-ER cells, the e ctopic expression of GATA-1 had no detectable effect on Epo inhibition of apoptosis. However, GATA-1 expression did result in a selective an d marked inhibition in mitogenic responsiveness to SCF and to a decrea se in c-kit transcript expression. These studies of SCF and Epo signal ing in FDC2-wt-ER cells serve to functionally map the ERB1 region as a c-kit-interactive domain, suggest that Pim1 might contribute to SCF a nd Epo mitogenic synergy and support the notion that SCF and Epo may a ct in opposing ways during red cell differentiation. (C) 1997 by The A merican Society of Hematology.