Tef, An Antiapoptotic Bzip Transcription Factor Related To The Oncogenic E2a-Hlf Chimera, Inhibits Cell Growth By Down-Regulating Expression Of The Common Beta Chain Of Cytokine Receptors

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;1 9)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 (TIEF), 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, TIEF protected the cells from apoptosis due to IL-3 deprivation. Unexpectedly, TIEF also almost completely down-regulated expression of the common beta (beta c) chain of cytokine receptors. Consequently, TEF-expressing cells accumulated in G(0)/G(1), phase without undergoing apoptosis. These findings suggest that TIEF is one of the apoptotic regulators in hematopoietic progenitors and controls hematopoietic-cell proliferation by regulating the expression of the Pc chain. In contrast, E2A-HLF promoted cell survival more efficiently than TIEF but did not down-regulate Pc chain expression, suggesting that E2A-HLF retains ideal properties for driving leukemic transformation.