REGULATION OF GENE-EXPRESSION OF A BINDING-PROTEIN FOR FIBROBLAST GROWTH-FACTORS BY RETINOIC ACID

Retinoids are potent regulators of growth and differentiation and have shown promise as chemotherapeutic agents against selected cancers in particular squamous cell carcinoma (SCC), Earlier studies from our lab oratory showed that a secreted binding protein for fibroblast growth f actors (BP) is expressed at high levels in SCC cell lines and tissue s amples. Here we investigate whether retinoids affect BP gene expressio n in SCC. In six different human SCC cell lines, we found that all-tra ns-retinoic acid (tRA) down-regulated BP mRNA by 39-89% within 24 h, F rom this group of cell lines, we selected the ME-180 cell line for mor e detailed studies of the mechanisms of this regulation, tRA down-regu lated BP mRNA in a time- and dose-dependent manner. The effect of tRA was reversible, and BP mRNA returned to control levels within 24 h aft er removal of tRA. We also measured BP mRNA half-life and performed nu clear run-on experiments to study if tRA down-regulates BP by destabil izing the mRNA and/or by decreasing the rate of transcription. BP mRNA in ME-180 cells is very stable with a half-life of >16 h, and tRA dec reased BP mRNA with a half-time of 5 h, Actinomycin D and cycloheximid e blocked the tRA effect, suggesting that transcriptional regulation a s well as de novo protein synthesis contribute to this post-transcript ional regulation of BP mRNA levels, In addition, tRA decreased the rat e of BP gene transcription by 2- to 3-fold within 1 h, We conclude tha t retinoids down-regulate BP gene expression by post-transcriptional a s well as by transcriptional mechanisms.