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Two candidate downstream target genes for E2A-HLF
1Department of Experimental Oncology and the Center for Biotechnology, St Jude Children's Research Hospital, Memphis, TN 38105-2794, USA.
Abstract:
The E2A-HLF fusion gene, formed by the t(17;19)(q22;p13) chromosomal translocation, is thought to drive the leukemic transformation of early B-cell precursors by repressing an evolutionarily conserved apoptotic pathway. To test 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 expressed in promyelocytic leukemia cells and UOC-B1 cells, but not in other leukemic cell lines. A novel full-length cDNA cloned with the G-4 fragment encoded 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 protein prevented apoptosis in interleukin-3-dependent murine pro-B cells, suggesting that they have paraneoplastic roles in leukemias that express E2A-HLF, perhaps in the disseminated intravascular coagulopathy and hypercalcemia that characterize these cases.
Insights
The E2A-HLF fusion gene drives leukemia by inhibiting apoptosis. Researchers identified two upregulated genes, ANNEXIN VIII and SRPUL, which may play paraneoplastic roles in leukemia.
Area of Science:
- Molecular Biology
- Oncology
- Genetics
Background:
- The E2A-HLF fusion gene, resulting from t(17;19) translocation, is implicated in B-cell precursor leukemic transformation.
- This transformation is hypothesized to occur via repression of a conserved apoptotic pathway.
Purpose of the Study:
- To identify downstream targets of the E2A-HLF oncoprotein in t(17;19)+ pro-B leukemia cells.
- To investigate the role of these targets in the leukemic process.
Main Methods:
- Utilized a zinc-inducible dominant-negative E2A-HLF suppressor in UOC-B1 leukemia cells.
- Employed representational difference analysis to identify differentially expressed mRNAs.
- Subcloned and characterized upregulated cDNA fragments (F-5 and G-4).
Main Results:
- Identified two E2A-HLF-upregulated transcripts: ANNEXIN VIII (F-5) and a novel protein SRPUL (G-4).
- Transcript levels decreased significantly upon suppression of E2A-HLF DNA-binding activity.
- ANNEXIN VIII and SRPUL were specifically expressed in UOC-B1 cells and not other leukemia lines, with SRPUL also found in normal heart, ovary, and placenta.
Conclusions:
- ANNEXIN VIII and SRPUL do not directly prevent apoptosis in pro-B cells.
- These proteins may have paraneoplastic roles in E2A-HLF-expressing leukemias, potentially contributing to symptoms like DIC and hypercalcemia.