Interleukin-3 and p210 BCR/ABL activate both unique and overlapping pathways of signal transduction in a factor-dependent myeloid cell line

Chronic myelogenous leukemia (CML) is characterized by a specific chromosomal translocation occurring between the long arms of chromosomes 9 and 22 resulting in a fusion product, p210 BCR/ABL, which has elevated tyrosine kinase activity. Expression of p210 BCR/ABL in murine interleukin-3 (IL-3) dependent cell lines typically converts these cell lines to factor-independence by a non-autocrine mechanism. The IL-3 receptor is believed to function in part by activating a receptor-associated tyrosine kinase, leading to the hypothesis that p210 BCR/ABL may induce factor-independence of myeloid cells by constitutively phosphorylating some common signal-transducing proteins that normally would be phosphorylated on tyrosine residues in response to IL-3. p210 BCR/ABL subclones were constructed from an IL-3-dependent murine myeloid cell line, 32Dcl3, by transfection of a plasmid containing a full-length p210 BCR/ABL cDNA. Following transfection, the cells became completely factor-independent within 3 weeks. We examined the effects of p210 BCR/ABL and IL-3 on the pattern of tyrosine phosphorylation of cellular proteins in 32Dcl3 cells using one- and two-dimensional antiphosphotyrosine immunoblotting. WEHI-3B conditioned media (WEHI-CM) was used as a source of IL-3. The introduction of p210 BCR/ABL results in constitutively increased levels of tyrosine phosphorylation of more than 20 new proteins, while WEHI-CM induced transient tyrosine phosphorylation of 6 to 10 new proteins. Using two-dimensional immunoblots to examine phosphoproteins, four categories could be identified: (1) proteins that are inducibly tyrosine phosphorylated in response to WEHI-CM in 32Dcl3 cells only, (2) proteins inducibly tyrosine phosphorylated by WEHI-CM only in p210 BCR/ABL⁺ cells, (3) proteins that are inducibly tyrosine phosphorylated in response to WEHI-CM in both 32Dcl3 cells and p210 BCR/ABL⁺ cells, and (4) proteins inducibly tyrosine phosphorylated in response to WEHI-CM and constitutively phosphorylated in the presence of p210 BCR/ABL. We have identified one of the proteins in category 4 as p42 mitogen-activated protein (MAP) kinase (ERK2). Overall, however, we found that the signal transduction pathways of IL-3 and BCR/ABL are strikingly different, suggesting that most of the immediate substrates of the IL-3 receptor-activated tyrosine kinase and p210 BCR/ABL kinase are different. Convergence of signaling pathways at p42 MAP kinase is of interest since activation of this kinase has been linked to mitogenesis in many systems. Identification of the overlapping proteins of both IL-3 signal transduction in 32Dcl3 cells and p210 BCR/ABL⁺ cells may help explain the growth-promoting effects of this oncogene.