IGF Binding Protein-5 Synthesis is Regulated by Testosterone through Transcriptional Mechanisms in Androgen Responsive Cells

We found that androgen and IGF-I up-regulated IGFBP-5 mRNA in androgen-responsive normal human fibroblast, which was blocked by co-treatment with 5,6-dichloro-1-β-D-ribofuranosyl-benzimidazole, but not cycloheximide. IGFBP-5 promoter activity was stimulated by androgen. Nuclear run-on assay revealed that IGFBP-5 transcripts were increased in response to androgen, which was not enhanced by co-addition of IGF-I. These results collectively indicate that IGFBP-5 synthesis is regulated by androgen through transcriptional mechanisms in androgen responsive cells.