The human TSH beta gene is expressed only in the thyrotrophs of the anterior pituitary where it is regulated by hypothalamic hormones, cyclic AMP as well as thyroid hormone. Recent studies have indicated that TRH and cyclic AMP mediate their transcriptional action in large part through changes in phosphorylation of the specific pituitary factor pit-1 which binds to a region upstream of the start of transcription. In contrast, thyroid hormone mediates its inhibition through binding to a regulatory element downstream of the start of transcription in the first untranslated exon. We have also characterized in detail a TGGGTCA motif at -1/+6 of the hTSH-beta gene that mediates, in conjunction with the upstream pit-1 site, protein kinase C and A as well as TRH stimulation of hTSH-beta gene expression. We have also shown that c-fos and c-jun which interact with this downstream site modulate T3 inhibition of hTSH-beta gene expression. We have recently recognized other important regulatory sequences for hTSH-beta gene expression. One such area is a pituitary-specific TATAAA sequence at -25 which is vital for both basal and regulated expression. Other regions include unique silencer regions at two locations upstream in the promoter. These regions include Oct-1 binding sites and appear to act as nuclear matrix attachment regions.
