Isolation of a GC-rich cDNA identifying mRNA present in human epidermis and modulated by calcium and retinoic acid in cultured keratinocytes. Homology with murine loricrin mRNA.

Differential screening of a human epidermal cDNA library led to the isolation of cDNA clones homologous to mRNAs specifically expressed in epidermis but weakly or not expressed in the undifferentiated squamous carcinoma cell line TR146. One of these 'differentiation-specific' cDNA clones, A8, hybridized with a 1.7 kb transcript among RNAs isolated from normal human epidermis, but with several transcripts ranging from 1.4 to 2.1 kb when mRNAs were isolated from cultured keratinocytes. We examined the effects of modulators of epidermal differentiation such as calcium and retinoic acid on the production of these transcripts. Their amount was found to increase in the presence of high calcium concentration, but to decrease in the presence of retinoic acid. These results strongly suggest that A8 messages are up-regulated during epidermal differentiation. The sequence of the 1371 bp of A8 cDNA shows a very high GC content. Because of its homology with the murine loricrin mRNA, A8 is likely to correspond either to the human loricrin or to a related protein.