Modulation of Translation by the 5' Leader Sequence of the MRNA Encoding Murine Tissue Inhibitor of Metalloproteinases

Murine tissue inhibitor of metalloproteinases (TIMP) is a Mr 28,000 secreted glycoprotein. The nucleotide sequence has been determined previously, and evidence for a multiplicity of TIMP transcripts presented. The longest TIMP transcript contains a small open reading frame (ORF) which is upstream of and overlaps the TIMP ORF, whereas the shorter inducible transcripts lack the AUG start codon of the upstream putative ORF. Serum stimulation of quiescent fibroblasts selectively enhances the abundance of the shorter transcripts (Edwards, D. R., Waterhouse, P., Holman, M. L., and Denhardt, D. T. (1986) Nucleic Acids Res. 14, 8863-8878). Here we have used an in vitro transcription/translation system to determine the effect of the upstream region on the efficiency of TIMP translation. TIMP transcripts either containing or lacking a segment including the AUG of the 5' ORF were generated by SP6 polymerase, and equal amounts of these transcripts were translated in reticulocyte lysates. TIMP synthesized in vitro was immunoprecipitable by an antiserum raised against a recombinant TIMP protein. TIMP was translated 3-fold more efficiently from the 5'-truncated transcript, consistent with the possibility that induction of shorter, more efficiently translated, TIMP transcripts are an important means of amplifying TIMP expression in response to serum.