Cloning and Regulation of Cornifin β, a New Member of the Cornifin/spr Family

In this study, we describe the isolation and characterization of a cDNA clone C12 that encodes a new member of the cornifin/small proline-rich protein (spr) family, which we have named cornifin β. C12 encodes a 1.1-kilobase pair mRNA and a 24.3-kDa cytosolic protein with a high proline content (19%). Its total amino acid sequence exhibits a 37-66% identity while the first 30 amino acids at the amino terminus are 87% identical to that of members of the cornifin family. At its carboxyl terminus, cornifin β contains 21 tandem repeats of an octapeptide. Cornifin β expression is restricted to several squamous epithelia. It is highly expressed in esophagus, tongue, and oral mucosa but, in contrast to cornifin α, is not detectable in the epidermis. Both retinoic acid and a retinoid selective for the nuclear retinoic acid receptors were very potent suppressors of cornifin β expression while an analog selective for the nuclear retinoid X receptors was much less effective, suggesting that a specific retinoid signaling pathway is involved in this suppression. Cornifin β can function through some of its Gln residues as an amine acceptor in transglutaminase-catalyzed cross-linking reactions. These results indicate that cornifin β functions as a cross-linked envelope precursor.