Regulation of the interleukin-3 (IL-3) receptor by IL-3 in the fetal liver-derived FL5.12 cell line

To determine the effects of a cytokine on cognate receptor expression in normal and neoplastic cells, the interleukin-3 receptor (IL-3R) complex was examined in the parental IL-3-dependent line FL5.12, which was isolated from fetal liver, and in autocrine- and v-abl-transformed derivative lines. IL-3 decreased the amount of the IL-3R alpha and beta chains detected on the cell surface of the parental IL-3-dependent cells. In contrast, high levels of IL-3R beta were constitutively detected on the autocrine-transformed lines in the absence and presence of exogenous IL-3. Only low levels of IL-3R beta were observed in the two v-abl-transformed derivative cell lines examined, which no longer required IL-3 for growth. The levels of the IL-3R alpha chain detected were similar in these transformed cells and were not regulated by IL-3. These results were substantiated further by RNA analysis, because IL-3 decreased the levels of IL-3R transcripts in the parental factor- dependent FL5.12 line. The pattern of IL-3R gene expression was opposite to that of other receptors or proto-oncogenes, because RNA transcripts for all other genes examined were induced by IL-3. We conclude that IL-3 tightly controls IL-3R expression in the IL-3- dependent FL5.12 cells, whereas steady-state mRNA levels were not altered in the two v-abl-transformed derivative cell lines examined in this study.