Retinoic acid mediates post-transcriptional regulation of keratin 19 mRNA levels.

Stratified squamous epithelia have been shown to preferentially express a site-specific pattern of keratin intermediate filaments. Retinoic acid (RA) is known to modulate expression of the basal cell keratins K19 and K5. Expression of these genes is dependent on extracellular RA concentration. We have found that K19 mRNA levels increase over time in cultured keratinocytes exposed to elevated concentrations of RA. K5 mRNA levels decrease in response to RA in a similar fashion. The observed changes in K5 message are primarily the result of RA-induced alterations in gene transcription. However, the RA-mediated induction of K19 mRNA is not the result of increased transcription but is primarily due to enhanced mRNA stability. These results suggest that an RA-dependent post-transcriptional mechanism modulates K19 intermediate filament expression in stratified squamous epithelia.