Thrombospondin-1 (TSP-1) is a matricellular protein that participates in 
numerous normal and pathological tissue processes and is rapidly modulated by 
different stimuli. The presence of 8 highly-conserved AU rich elements (AREs) 
within the 3'-untranslated region (3'UTR) of the TSP-1 mRNA suggests that 
post-transcriptional regulation is likely to represent one mechanism by which 
TSP-1 gene expression is regulated. We investigated the roles of these AREs, and 
proteins which bind to them, in the control of TSP-1 mRNA stability. The 
endogenous TSP-1 mRNA half-life is approximately 2.0 hours in HEK293 cells. 
Luciferase reporter mRNAs containing the TSP-1 3'UTR show a similar rate of 
decay, suggesting that the 3'UTR influences the decay rate. Site-directed 
mutagenesis of individual and adjacent AREs prolonged reporter mRNA halflife to 
between 2.2 and 4.4 hours. Mutation of all AREs increased mRNA half life to 8.8 
hours, suggesting that all AREs have some effect, but that specific AREs may 
have key roles in stability regulation. A labeled RNA oligonucleotide derived 
from the most influential ARE was utilized to purify TSP-1 ARE-binding proteins. 
The AU-binding protein AUF1 was shown to associate with this motif. These 
studies reveal that AREs in the 3'UTR control TSP-1 mRNA stability and that the 
RNA binding protein AUF1 participates in this control. These studies suggest 
that ARE-dependent control of TSP-1 mRNA stability may represent an important 
component in the control of TSP-1 gene expression.