An open reading frame element mediates posttranscriptional regulation of tropoelastin and responsiveness to transforming growth factor beta1

Identification and cDNA cloning of a novel RNA-binding protein that interacts with the cyclic nucleotide-responsive sequence in the Type-1 plasminogen activator inhibitor mRNA

Incubation of HTC rat hepatoma cells with 8-bromo-cAMP results in a 3-fold increase in the rate of degradation of type-1 plasminogen activator inhibitor (PAI-1) mRNA. We have reported previously that the 3'-most 134 nt of the PAI-1 mRNA is able to confer cyclic nucleotide regulation of message stability onto a heterologous transcript. R-EMSA and UV cross-linking experiments have shown that this 134 nt cyclic nucleotide-responsive sequence (CRS) binds HTC cell cytoplasmic proteins ranging in size from 38 to 76 kDa. Mutations in the A-rich region of the CRS both eliminate cyclic nucleotide regulation of mRNA decay and abolish RN-protein complex formation, suggesting that these RNA-binding proteins may be important regulators of mRNA stability. By sequential R-EMSA and SDS-PAGE we have purified a protein from HTC cell polysomes that binds to the PAI-1 CRS. N-terminal sequence analysis and a search of protein data bases revealed identity with two human sequences of unknown function. We have expressed one of these sequences in E. coli and confirmed that the recombinant protein interacts specifically with the PAI-1 CRS. Mutation of the A-rich portion of the PAI-1 CRS reduces binding by the recombinant PAI-1 RNA-binding protein. The amino acid sequence of this protein includes an RGG box and two arginine-rich regions, but does not include other recognizable RNA binding motifs. Detailed analyses of nucleic acid and protein data bases demonstrate that blocks of this sequence are highly conserved in a number of metazoans, including Arabidopsis, Drosophila, birds, and mammals. Thus, we have described a novel RNA-binding protein that identifies a family of proteins with a previously undefined sequence motif. Our results suggest that this protein, PAI-RBP1, may play a role in regulation of mRNA stability.

Identification of a GA-rich sequence as a protein-binding site in the 3'-untranslated region of chicken elastin mRNA with a potential role in the developmental regulation of elastin mRNA stability

Synthesis of aortic elastin peaks in the perinatal period and then is strongly down-regulated with postnatal development and growth. Decreased stability of elastin mRNA contributes to this developmental decrease in chick aortic elastin production. We have previously shown that destabilization of elastin mRNA is correlated with decreased binding of cytosolic protein(s) to a large, GC-rich region of secondary structure in the 3'-untranslated region (3'-UTR) of elastin mRNA. In this study, using gel migration shift assays, deletion constructs, and antisense competition assays, we identify a major protein-binding site in the 3'-UTR of elastin as a GA-rich sequence (UGGGGGGAGGGAGGGAGGGA), which we have designated the G3A motif. This motif is present in the 3'-UTR of elastin from several species. Binding proteins are present in both nuclear and cytoplasmic extracts, and their abundance is associated with tissues producing elastin and correlated with circumstances in which elastin mRNA is stable. These results suggest that the conserved GA-rich sequence of the elastin 3'-UTR is an important element in the regulation of stability of the elastin mRNA.