LACK OF CORRELATION BETWEEN GROWTH OF TF-1 CELLS AND TYROSINE PHOSPHORYLATION SIGNALS IN RESPONSE TO IL-3, IL-5 AND GM-CSF

The human cell line, TF-1, was used to compare responses to interleuki n 3 (IL-3), IL-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF), TF-1 cells grew well in the presence of any one of the cytok ines in early passages, However, the level of tyrosine phosphorylation was minimal in response to IL-5, and detection of a tyrosine phosphor ylation signal required high concentrations of IL-5, When grown for lo nger periods of time in the presence of one of the cytokines, there we re dramatic differences in the cells' responses, IL-3 or GM-CSF-grown cells showed only half of the original bioassay response to IL-5. Howe ver, cells grown in IL-5 alone kept the same response, and all cells s howed the same response to IL-3 and GM-CSF, IL-5-grown cells also had an increased tyrosine phosphorylation signal, along with increased sen sitivity to IL-5, yet there was no difference in an IL-5 bioassay, The relative level of detection of tyrosine phosphorylated JAK-2, STAT-5, SHC, and other substrates corresponded to the overall tyrosine phosph orylation signal. IL-5-grown cells had approximately 10-fold more IL-5 receptor alpha subunit message compared to IL-3-grown. These results suggest that response of TF-1 cells to IL-5 may be deceiving in that a good response in a bioassay can be observed with relatively little ty rosine phosphorylation, but an increase in tyrosine phosphorylation ca n be correlated with an increase in the expression of IL-5 receptor al pha subunit. (C) 1997 Academic Press Limited.