LACK OF CORRELATION BETWEEN GROWTH OF TF-1 CELLS AND TYROSINE PHOSPHORYLATION SIGNALS IN RESPONSE TO IL-3, IL-5 AND GM-CSF
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文摘
The human cell line, TF-1, was used to compare responses to interleukin 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 cytokines in early passages. However, the level of tyrosine phosphorylation was minimal in response to IL-5, and detection of a tyrosine phosphorylation signal required high concentration of IL-5. When grown for longer periods of time in the presence of one of the cytokines, there were dramatic differences in the cells' responses. IL-3 or GM-CSF-grown cells showed only half of the original bioassay response to IL-5. However, cells grown in IL-5 alone kept the same response, and all cells showed the same response to IL-3 and GM-CSF. IL-5 grown cells also had an increased tyrosine phosphorylation signal, along with increased sensitivity 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 phosphorylation signal. IL-5-grown cells had approximately 10-fold more IL-5 receptor α 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 tyrosine phosphorylation, but an increase in tyrosine phosphorylation can be correlated with an increase in the expression of IL-5 receptor α subunit.