The 5'-untranslated region of the IGF-I receptor gene modulates reporter gene expression by both pre- and post-transcriptional mechanisms.

The insulin-like growth factor I (IGF-I) receptor gene has a large, complex 5'-untranslated region (UTR). In order to examine the role that this region plays in regulating IGF-I receptor expression, we isolated fragments of the human IGF-I receptor 5'-UTR and interposed them between the SV40 early promoter and the chloramphenicol acetyl transferase reporter gene. Fragments of the IGF-I receptor gene 5'-UTR were found to enhance reporter gene expression by increasing gene transcription. In addition, the increased transcription and mRNA levels were in excess of the increase in enzyme activity, providing indirect evidence that these fragments inhibit translation, consistent with predictions.