Evi3, a common retroviral integration site in murine B-cell lymphoma, encodes an EBFAZ-related Krüppel-like zinc finger protein

Abstract

Retroviral insertional mutagenesis in inbred mouse strains provides a powerful method for cancer gene discovery. Here, we show that a common retroviral integration site (RIS) in AKXD B-cell lymphomas, termed Evi3, encodes a novel zinc finger protein with 30 Krüppel-like zinc finger repeats. Most integrations at Evi3 are located upstream of the first translated exon and result in 3' long-terminal repeat (LTR)-driven overexpression of Evi3. Evi3 is highly related to the early B-cell factor-associated zinc finger gene (Ebfaz), and all 30 zinc fingers found in EVI3 are conserved in EBFAZ. EBFAZ binds to and negatively regulates early B-cell factor (EBF) (also known as olfactory-1, OLF1), a basic helix-loop-helix (bHLH) transcription factor required for B-lineage commitment and the development of the olfactory epithelium. EBFAZ also binds to SMA- and MAD-related protein-1 (SMAD1) and SMAD4 in response to bone morphogenetic protein-2 (BMP2) signaling, which in turn activates the homeobox regulator of Xenopus mesoderm and neural development Xvent-2. Surprisingly, while Ebfaz and Evi3 are coexpressed in many tissues, and both proteins are nuclear, we could not detect Ebfaz expression in B cells by reverse transcriptase-polymerase chain reaction (RT-PCR), whereas Evi3 expression could be detected at all stages of B-cell development. Our results suggest that EVI3, like EBFAZ, is a multifunctional protein that participates in many signaling pathways via its multiple zinc fingers. Furthermore, our results suggest that EVI3, not EBFAZ, is the member of this protein family that interacts with and regulates EBF in B cells.