Functional analysis of intracellular factors involved in the growth, differentiation, and transformation of lymphocytes

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IRF-1 is a transcription factor that functions in the interferon system. We observed that expression of an activated Ha-ras gene in embryo fibroblasts from IRF-1-deficient mice resulted in their oncogenic transformation, indicating that IRF-1 can function as an anti-oncogene. We also observed that Ha-ras-induced apoptosis did not occur in embryo fibroblasts lacking IRF-1. These results strongly suggest that IRF-1 can determine oncogene-induced cell transformation and death. IRF-1 maps to the chromosomal 5q regon, a region frequently deleted in patients afflicted with leukemia or preleukemic myelodysplastic syndrome (MDS). We have shown previously that IRF-1 is a critically-deleted gene in these "5q syndrome" patients. Recently we discovered the existence of an alternatively-spliced form of the IRF-1 mRNA that encodes a protein lacking DNA-binding and anti-oncogenic activities. We found this abnormally-spliced product, but not the normal IRF-1 mRNA,in approximately 20% of patients affli … More cted with leukemia or MDS.Abnormal splicing may thus represent a new mechanism by which IRF-1 is inactivated, thereby promoting the development of leukemia.We have also found that Syk, a non-receptor-type protein kinase (PTK), associates with the intracellular "serine-rich" region of the interleukin-2 receptor beta chain (IL-2Rbeta) and is activated upon IL-2 stimulation. This "serine-rich" region is essential for induction of the c-myc gene and cell proliferation following IL-2 stimulation. Furthermore, we have found that two recently-identified members of the Jak PTK family, Jak-1 and Jak-3, specifically associate with regions of the IL-2Rbeta and -g chains, respoctively, which are critical for transmission of the IL-2 signal, and are rapidly activated upon IL-2 stimulation. Ectopic expression of Jak-3 in NIH 3T3 fibroblasts, which express functional endogenous IL-2R and Jak-1, conferred upon these cells the ability to respond to IL-2 and thereby progress from the G1 to S phase of the cell cycle. Less