THE BCR-ABL ONCOGENE REQUIRES BOTH KINASE-ACTIVITY AND SRC-HOMOLOGY-2DOMAIN TO INDUCE CYTOKINE SECRETION

Expression of either the BCR-ABL or the v-abl oncogene in the factor-d ependent murine myeloid cell line FDCP-1 results in growth factor inde pendence. Studies with temperature-sensitive mutants of v-abl show tha t this growth factor independence is oncogene dependent. Likewise, cel ls expressing a kinase inactive mutant of BCR-ABL did not grow in the absence of interleukin-3 (IL-3). Conditioned media from cells expressi ng either v-abl or BCR-ABL contained growth factor(s) capable of stimu lating the proliferation of uninfected FDCP-1 cells. Based on enzyme-l inked immunosorbent assay studies and antibody neutralization studies, the major growth factor present in these conditioned media is IL-3. B ecause of the importance of SH2 domains in regulating substrate intera ctions, we examined the ability of SH2 deletion mutants in BCR-ABL to induce growth factor independence. Cells expressing a mutant of BCR-AB L lacking the SH2 domain were growth factor independent; however, they did not secrete growth factors, This finding suggests that while IL-3 produced by cells infected with BCR-ABL may contribute to autocrine o r paracrine growth factor independence, expression of an activated tyr osine kinase alone may be able to induce growth factor independence, F urthermore, the secretion of cytokines maybe correlated with a specifi c region of the BCR-ABL oncogene, suggesting that activation (phosphor ylation) of specific substrates may be critical for transcriptional ac tivation of cytokine genes. (C) 1996 by The American Society of Hemato logy.