Transcriptional regulation of glyceraldehyde-3-phosphate dehydrogenase by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The action of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) on transcription and steady-state mRNA levels, protein expression, and enzymatic activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in cultured human keratinocytes was examined. GAPDH transcription increased as a function of time of exposure to TCDD, reaching a maximum of 23-fold after 8 days. Northern blot analysis showed a 4-fold increase in mRNA after 8 days exposure. Protein levels were increased 4-fold, and dehydrogenase activity by 5-fold, under the same exposure conditions. GAPDH is commonly thought of as a constitutive housekeeping gene and is often used as a loading control for northern blot analysis. Our data suggest that caution should be used when using GAPDH as an RNA control, especially in studies examining cell proliferation and carcinogenesis.