Transcriptional analyses of steroid-regulated gene networks

It has been proposed that cell-specific responses to steroid action are the result of coordinate expression of steroid gene networks. Using three different cell systems, we have performed transcriptional analyses to determine if the observed hormone-induced alterations in gene expression are consist-ent with a limited number of potential target genes in any one cell type. Our results indicate that greater than 95% of the transcripts in dexamethasonetreated rat hepatoma (HTC), or mouse lymphoma (WEHI7) cells, are similar to the mRNAs in untreated cells based on subtraction hybridization. In addition, we find that although the castration-induced expression of androgen-regulated transcripts in the rat ventral prostate (RVP) is significantly different between normal and castrated rats (19%), the majority of these mRNAs are accounted for by the over abundance of sulfated glycoprotein-2 sequences. Specifically, analysis of an RVP subtracted cDNA library revealed that sulfated glycoprotein-2 mRNA masked the presence of less abundant differentially expressed sequences, confirming that the actual size of the RVP androgen gene network is small. We conclude that steroid-mediated changes in transcription accurately reflect the expression of a few cell-specific target genes, and thus support the model of steroid gene networks. The potential to characterize key elements which determine both the time course and magnitude of cell-specific hormone responses is discussed.