Increased Granulocyte-Macrophage Colony-Stimulating Factor mRNA Instability in Cord Versus Adult Mononuclear Cells Is Translation- Dependent and Associated With Increased Levels

The level of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA is fourfold lower in phorbol myristate acetate (PMA) + phytohemagglutinin (PHA)-activated mononuclear cells (MNC) from newborns compared with adults. The GM-CSF transcription rate is similar in umbilical cord and adult MNC, but transcript half-life is threefold lower in cord activated MNC. Interaction of RNA binding proteins, such as the cloned adenosine + uridine-rich element, binding factor, AUF1, with eight AUUUA motifs in the human GM-CSF mRNA 3‘-untranslated region (GM3‘-UTR) has been implicated in regulating transcript stability. Translational inhibition by cycloheximide (CHX) significantly increased GM-CSF mRNA accumulation and half-life by threefold in activated cord MNC, but had a minimal effect in activated adult MNC as compared with PMA + PHA alone. Electrophoretic mobility-shift assays with a 32P-labeled, 305nucleotide RNA comprising the GM-3’-UTR revealed two RNaseT1-resistant, bound complexes that were almost