RESTORING THE APOPTOSIS SUPPRESSION RESPONSE TO IL-5 CONFERS ON ERYTHROLEUKEMIC CELLS A PHENOTYPE OF IL-5-DEPENDENT GROWTH

We have established a human IL-5 (hIL-5) dependent cell line, JYTF-1, derived from TF-1 parental human erythroleukemic cells by long-term cu ltivation in the presence of hIL-5. The ED(50) values of hIL-5 for bot h TF-1 and JYTF-1 cell lines remained similar. However, when cells wer e grown in an optimal concentration of IL-5, some TF-1 cells but not J YTF-1 cells died via apoptosis. Although the rates of DNA synthesis we re similar for TF-1 and JYTF-1 cells grown in IL-5, [H-3]thymidine rel easing of pulse-labeled DNA analysis indicated that the viable TF-1 ce lls in IL-5 were more apoptosis-prone than were JYTF-1 cells. Therefor e, in the JYTF-1 variant, the ability to suppress apoptosis has appare ntly been restored. The following findings suggest that overexpression of the hIL-5 receptor alpha-chain may be responsible for restoring th e apoptosis suppression ability of IL-5: 1) the growth of JYTF-1 cells remained cytokine-dependent; 2) the proliferation of JYTF-1 cells in IL-5 was not mediated by autocrine secretion; 3) JYTF-1 and TF-1 cells responded similarly to other cytokines such as human erythropoietin; 4) Northern blot analysis revealed that JYTF-1 cells expressed approxi mately eightfold more IL-5 receptor alpha-chain mRNA than did TF-1. To our knowledge, JYTF-1 represents the first example in which coupling of mitogenesis stimulation and apoptosis suppression from otherwise un coupled parental cells confers a phenotype of IL-5 dependent growth.