Thyrotropin can increase the steady state level of a messenger ribonucleic acid species (glyceraldehyde-3-phosphate dehydrogenase) in thyroid cells by decreasing its rate of disappearance.

A cDNA clone (G18) was selected from an FRTL5 rat thyroid cell cDNA library by a differential screening procedure designed to identify TSH-responsive genes in thyroid cells. Nucleotide sequence analysis indicated that G18 was rat alpha-glyceraldehyde-3-phosphate dehydrogenase (GAPD). On Northern blot analysis, TSH increased GAPD mRNA levels in FRTL5 cells, reaching a maximum (4- to 10-fold above basal in different experiments) after approximately 24 h of TSH stimulation. Run-on transcription assays with nuclei prepared from quiescent and TSH-stimulated FRTL5 cells indicated that the action of TSH to increase GAPD mRNA levels was not associated with an increase in the transcriptional activity of this gene. Examination of the rate of disappearance of GAPD mRNA levels after inhibition of mRNA transcription by actinomycin-D revealed that TSH stimulation of FRTL5 cells stabilized the GAPD mRNA (t 1/2 extended from 9 to 56 h). In summary, the present data provide the first demonstration that TSH can increase the level of a mRNA transcript in thyroid cells by reducing its rate of degradation. GAPD is a useful model for future studies on the mechanism by which TSH alters gene expression at a posttranscriptional level.