THE PU.1/SPI-1 PROTOONCOGENE IS A TRANSCRIPTIONAL REGULATOR OF A LENTIVIRUS PROMOTER

The enhancer unit present in the retrovirus equine infectious anemia virus (EIAV) was previously shown to contain binding sites for proteins belonging to MDBP, PEA2, AP-1, and ets families. The EIAV ets motif matches the consensus sequence for both PEA3- and PU.1-binding sites. Here, we show by gel shift analysis that PU.1, present in nuclear extracts from monocyte and B-lymphocyte cell lines, binds to oligonucleotides containing the EIAV ets element. HeLa cells transiently transfected with a PU. 1 expression plasmid expressed nuclear factors that formed complexes indistinguishable from those seen with monocyte extracts. Antibodies to PU.1 protein either supershifted or abolished formation of these complexes, depending on the PU.1 epitopes recognized. The binding of PU.1 to the EIAV ets motif in vitro correlated with transcriptional activity of the EIAV promoter in transfected monocyte cell lines. In HeLa cells, the product of PU.1 cDNA bound to the EIAV ets motif and activated transcription from the EIAV promoter. The PU.1-binding site was the primary determinant of EIAV promoter activity in cell lines that express PU.1. Nucleotide determinants of PU.1 binding and a consensus PU.1 binding sequence were defined in gel shift assays using a panel of mutated oligonucleotides. To our knowledge, this is the first report of a retroviral promoter controlled by PU.1.