Isolation of cDNA for human epidermal type I transglutaminase

Keratinocytes of stratified epithelia, including the epidermis, express two distinct forms of transglutaminase, type I and type II. Type I transglutaminase activity is responsible for cell envelope formation in terminally differentiating cultured keratinocytes. Transglutaminase enzymatic activity has been associated with several proteins that are differentially expressed in vivo and in vitro. To elucidate the relationship between the epidermally expressed transglutaminases, cDNA for type I transglutaminase was cloned from a human high-calcium keratinocyte lambda gt11 library. cDNA fragments, generated by PCR primed with a mixture of oligonucleotides coding for five invariant amino acids in the active site, were used as a screening probe. Based on the sequence analysis of 1653 nt contained in the lambda 1-126a clone and on the pattern of expression of a complementary approximately 3-kb transcript, we report cloning of the epidermal type I transglutaminase gene. The expression of this gene is regulated by calcium ions and retinoic acid in cultured human keratinocytes. There are highly conserved regions near the active site cysteine residues that may be important for the enzyme's specialized functions.