UC San Diego

Of the 25% of T-cell acute lymphoblastic leukemia (T-ALL) patients who relapse or do not respond to chemotherapy, only 10-50% are ultimately curable. Genetic lesions involving the T cell receptor for antigen (TCR) have been correlated with poor prognosis, suggesting the events triggered by TCR signaling are involved in the disease. We have recently reported extensive transcript splicing of the lipid phosphatase SHIP1 in primary T-ALL which we believe may influence aberrant TCR signaling in the Ras/ Erk and PI3K/Akt pathways. To determine the significance of such splicing, extensively spliced SHIP1 isoforms from primary T-ALL samples were cloned and expressed in a PMA- dependent Jurkat cell line model to study SHIP1 protein stability as well as phosphatase activity. We report that the removal of exon 8 of SHIP1 prevented the formation of stable protein while removal of exons 25 and 26 conferred protein stability. Further, removal of exon 26 was sufficient to increasing SHIP1 phosphatase activity two fold compared to full length protein, a phenomenon we ascribe to catalytic autoinhibition. We also made PMA- independent SHIP1 expressing stable Jurkat clones to study SHIP1 involvement in the Ras/Erk pathway and report for the first time that full length SHIP1 downregulated Ras activity in T cells. Finally, in a search for novel therapeutic targets in T-ALL, we inhibited both Ras and PI3K in Jurkat cells using S-trans,trans- farnesylthiosalicylic acid and LY294002 and found synergistic effects on cell growth, confirming the efficacy of dual Ras and PI3K targeting in T-ALL