The regulated production of hematopoietic growth factors (HGF) such as GM-CSF (granulocyte-macrophage colony stimulating factor), EL-3 (interleukin 3) and IFNgamma (interferon gamma) in response to environmental stimuli are preceded by an accumulation of HGF mRNAs. This is partially due to increased transcription but primarily due to increased degradation of HGF messages. Normally HGF mRNAs are extremely unstable due to the presence of multiple reiterations of the pentanucleotide sequence adenosine-uridine-uridine-uridine-adenosine (B) in their 3' untranslated region. Several investigators have hypothesized that HGF mRNAs interact with cytoplasmic protein factors through their B elements. The binding of B specific, HGF mRNA binding proteins could mediate HGF mRNA stabilization and hence accumulation after environmental stimuli. We have recently identified a novel, cytoplasmic protein (denoted the adenosine-uridine binding factor or AUBF) which specifically binds to the B elements of HGF mRNAs. We hypothesize that the regulated binding of AUBF to the B elements of HGF mRNAs alters their turnover. Thus, our specific aims are to: 1). Purify AUBF from bovine brain by affinity chromatography or classical biochemical methods, 2). Determine the amino acid sequence of AUBF and produce polyclonal and monoclonal anti-AUBF antibodies in rodents, 3). Use antibodies or oligonucleotide probes to clone bovine and human AUBF, 4). Employ a cell-free RNA degradation system to assess the functional significance of AUBF. Active or inactive AUBF will be added into the cell-free degradation system and the turnover rate of HGF mRNAs measured. We will prepare the cell-free degradation extract from quiescent or activated cell or tissue sources with low, moderate or high endogenous AUBF activity and 5). Determine the effects of nucleotide changes within the B elements of GM-CSF, IL-3 and IFNgammamRNA on a). binding to AUBF in vitro and b). turnover rates in the cell-free degradation system. Cumulatively, these studies will help elucidate the function of AUBF in HGF mRNA turnover and provide biochemical insights into molecular events leading to HGF mRNA accumulation in response to cell activation.
