Two candidate downstream target genes for E2A-HLF

The E2A-HLF fusion gene, formed by the t(17;19)(q22;p13) chromosomal transl ocation, is thought to drive the leukemic transformation of early B-cell pr ecursors by repressing an evolutionarily conserved apoptotic pathway. To te st this hypothesis, we sought to identify downstream targets of E2A-HLF in t(17;19)(+) pro-B leukemia cells (UOC-B1) that had been transfected with a zinc-inducible vector encoding a dominant-negative suppressor (E2A-HLF[dn]) of the oncoprotein, Representational difference analysis of mRNAs from E2A -HLF(dn)(+) UOC-B1 cells grown with (E2A-HLF inactive) or without (E2A-HLF active) the addition of zinc yielded several differentially expressed cDNA fragments that were individually subcloned. Two of the clones, designated F -5 and G-4, hybridized with mRNAs that were upregulated by E2A-HLF. Levels of both transcripts declined sharply within 8 to 12 hours after suppression of E2A-HLF DNA-binding activity, becoming undetectable after 96 hours. The F-5 cDNA was identified as a portion of ANNEXIN VIII,whose product was exp ressed in promyelocytic leukemia cells and UOC-B1 cells, but not in other l eukemic cell lines. A novel full-length cDNA cloned with the G-4 fragment e ncoded a protein that we have named SRPUL (sushi-repeat protein upregulated in leukemia). It is normally expressed in heart, ovary, and placenta, but could not be detected in leukemic cell lines other than UOC-B1. Neither pro tein prevented apoptosis in interleukin-3-dependent murine pro-B cells, sug gesting that they have paraneoplastic roles in leukemias that express E2A-H LF, perhaps in the disseminated intravascular coagulopathy and hypercalcemi a that characterize these cases. (C) 1999 by The American Society of Hemato logy.