A RETINOIC ACID-INDUCIBLE SKIN-SPECIFIC GENE (RIS-1 PSORIASIN) - MOLECULAR-CLONING AND ANALYSIS OF GENE-EXPRESSION IN HUMAN SKIN IN-VIVO AND CULTURED SKIN CELLS IN-VITRO

A retinoic acid (RA) inducible skin-specific gene transcript (RIS-1) was isolated by differential hybridization screening of a RA-treated human skin cDNA library. The library was constructed from pooled RNA derived from normal adult human skin treated with all trans-RA for 4 h (n = 6) and 12 h (n = 6) in vivo. RIS-1 cDNA corresponded to a 0.6 kb transcript that was barely detectable in normal adult human skin but was significantly induced by 8 h in RA-treated compared to vehicle-treated skin (range 1.1-3.6 fold). Prolonged RA treatment for up to 24 h further increased relative RIS-1 mRNA levels by 1.3-5.5 fold. HPLC analysis of the RA content of 0.1% RA-treated skin in vivo revealed significant levels at 6 h (18.8-120.6 ng RA/g wet weight tissue; approximately 240 nM), immediately preceding the time point at which the increased RIS-1 mRNA level was first seen. This concentration of RA also induced the mRNA levels for cellular RA binding protein II (1.6-19 fold), a marker of RA activity in human skin. RIS-1 mRNA was detected by Northern and dot blotting only in normal skin but not in any other normal human tissues examined, indicating a tissue-specific pattern of gene expression. RIS-1 transcripts were detected at very low levels in untreated cultured human epidermal keratinocytes, while no expression was seen in dermal fibroblasts and melanocytes, the other major cell types in skin. Southern analysis of human and mouse DNA indicated the existence of evolutionarily conserved sequences for RIS-1 between these two species. The polypeptide sequence derived from the partial RIS-1 cDNA was found to be identical to the calcium binding domain found in 'psoriasin', a gene whose expression appears to be increased in the skin of psoriasis patients.