Oncogene database

6929

TCF3

transcription factor 3;TCF3;transcription factor 3

VDR interacting repressor|class B basic helix-loop-helix protein 21|helix-loop-helix protein HE47|immunoglobulin transcription factor 1|kappa-E2-binding factor|negative vitamin D response element-binding protein|transcription factor 3 (E2A immunoglobulin

19p13.3

protein-coding

The E2A-HLF fusion gene transforms human pro-B lymphocytes by interfering with an early step in apoptotic signaling. In a search for E2A-HLF-responsive genes, we identified a zinc finger transcription factor, SLUG, whose product belongs to the Snail family of developmental regulatory proteins. Importantly, SLUG bears close homology to the CES-1 protein of C. elegans, which acts downstream of CES-2 in a neuron-specific cell death pathway. Consistent with the postulated role of CES-1 as an antiapoptotic transcription factor, SLUG was nearly as active as Bcl-2 or Bcl-xL in promoting the survival of IL-3-dependent murine pro-B cells deprived of the cytokine. We conclude that SLUG is an evolutionarily conserved transcriptional repressor whose activation by E2A-HLF promotes the aberrant survival and eventual malignant transformation of mammalian pro-B cells otherwise slated for apoptotic death.

In pro-B cell acute lymphoblastic leukemia (ALL), expression of the E2A-HLF fusion gene as a result of t(17;19)(q22;p13) is associated with poor prognosis, hypercalcemia, and hemorrhagic complications. We previously reported that the E2A-HLF fusion protein protects interleukin-3 (IL-3)-dependent lymphoid cells from apoptosis caused by cytokine starvation. Here, we report that annexin II, a surface phospholipid-binding protein and one of the proposed causes of the hemorrhagic complications of acute promyelocytic leukemia (APL), is also implicated in t(17;19)+ ALL. Annexin II was expressed at high levels in APL cells and in each of 4 t(17;19)+ leukemia cell lines, and annexin II expression was induced by enforced expression of E2A-HLF in leukemia cells. In IL-3-dependent cells, we found that annexin II expression was regulated by IL-3 mainly by Ras pathways, including Ras/phosphatidylinositol 3-kinase pathways. Moreover, E2A-HLF increased annexin II expression in IL-3-dependent cells in the absence of the cytokine. These findings indicate that E2A-HLF induces annexin II by substituting for cytokines that activate downstream pathways of Ras.

Gain and/or loss of function mediated by chimeric transcription factors generated by nonrandom translocations in leukemia is a key to understanding oncogenesis. E2A-hepatic leukemia factor (HLF), a chimeric basic region/leucine zipper (bZIP) transcription factor expressed in t(17;19)-positive leukemia cells, contributes to leukemogenesis through its potential to inhibit apoptosis. To identify physiologic counterparts of this chimera, we investigated the function of other bZIP factors that bind to the same DNA sequence recognized by E2A-HLF. Here, we show that thyrotroph embryonic factor (TEF), which shares a high level of sequence identity with HLF and recognizes the same DNA sequence, is expressed in a small fraction of each subset of hematolymphoid progenitors. When TEF was introduced into FL5.12 interleukin 3 (IL-3)-dependent cells, TEF protected the cells from apoptosis due to IL-3 deprivation. Unexpectedly, TEF also almost completely down-regulated expression of the common beta (betac) chain of cytokine receptors. Consequently, TEF-expressing cells accumulated in G(0)/G(1) phase without undergoing apoptosis. These findings suggest that TEF is one of the apoptotic regulators in hematopoietic progenitors and controls hematopoietic-cell proliferation by regulating the expression of the betac chain. In contrast, E2A-HLF promoted cell survival more efficiently than TEF but did not down-regulate betac chain expression, suggesting that E2A-HLF retains ideal properties for driving leukemic transformation.

The chimeric oncoprotein E2A-HLF, generated by the t(17;19) chromosomal translocation in pro-B-cell acute lymphoblastic leukemia, incorporates the transactivation domains of E2A and the basic leucine zipper (bZIP) DNA-binding and protein dimerization domain of HLF (hepatic leukemic factor). The ability of E2A-HLF to prolong the survival of interleukin-3 (IL-3)-dependent murine pro-B cells after IL-3 withdrawal suggests that it disrupts signaling pathways normally responsible for cell suicide, allowing the cells to accumulate as transformed lymphoblasts. To determine the structural motifs that contribute to this antiapoptotic effect, we constructed a panel of E2A-HLF mutants and programmed their expression in IL-3-dependent murine pro-B cells (FL5.12 line), using a zinc-inducible vector. Neither the E12 nor the E47 product of the E2A gene nor the wild-type HLF protein was able to protect the cells from apoptosis induced by IL-3 deprivation. Surprisingly, different combinations of disabling mutations within the HLF bZIP domain had little effect on the antiapoptotic property of the chimeric protein, so long as the amino-terminal portion of E2A remained intact. In the context of a bZIP domain defective in DNA binding, mutants retaining either of the two transactivation domains of E2A were able to extend cell survival after growth factor deprivation. Thus, the block of apoptosis imposed by E2A-HLF in pro-B lymphocytes depends critically on the transactivating regions of E2A. Since neither DNA binding nor protein dimerization through the bZIP domain of HLF is required for this effect, we propose mechanisms whereby protein-protein interactions with the amino-terminal region of E2A allow the chimera to act as a transcriptional cofactor to alter the expression of genes regulating the apoptotic machinery in pro-B cells.