CLONAL VARIABILITY IN BETA-GLOBIN MESSENGER-RNA CONTENT IN AN INTERLEUKIN-3-DEPENDENT BONE-MARROW CELL-LINE TRANSFECTED WITH THE ERYTHROPOIETIN RECEPTOR BEFORE AND AFTER STIMULATION WITH ERYTHROPOIETIN

Unexpected clonal variability was observed in the content of beta-glob in mRNA in erythropoietin receptor (EpoR)-transfected Ba/F3 cells befo re and after exposure to erythropoietin (Epo). Of 11 clones selected b y virtue of G418 resistance and positive EpoR expression, 5 clones sho wed high levels of beta(major)-globin mRNA before Epo exposure, with s ubsequent Epo treatment causing little or no increase in globin mRNA. Five clones had undetectable levels of globin mRNA before Epo stimulat ion, and they did not accumulate globin mRNA when exposed to Epo, exhi biting resistance to the differentiation inducing action of Epo. Only one clone exhibited the expected phenotype, a low level of globin mRMA before exposure to Epo, and a significant Epo-dependent accumulation of globin mRNA. Phosphorylation of tyrosyl residues of the EpoR, Stat5 , and JAK2 occurred upon Epo stimulation in clones representing each c ategory. Furthermore, electrophoretic mobility shift assays using a St at5 consensus sequence showed a difference in the nuclear binding comp onent among these clones, These findings indicate that (1) the attainm ent of EpoR(+) Ba/F3 clones with the anticipated sensitivity to both t he growth and differentiation inducing actions of Epo is a rare event and (2) STATS transcription factors were differently activated by Epo in clones that differed in sensitivity to Epo. (C) 1997 by The America n Society of Hematology.