Molecular cloning and tissue expression of the murine analog to human stratum corneum chymotryptic enzyme

Human stratum corneum chymotryptic enzyme (SCCE) may play a central part in epidermal homeostasis. Its proposed function is to catalyze the degradation of intercellular structures, including desmosomes, in the stratum corneum as part of the desquamation process. In order to facilitate physiologic and pathophysiologic studies on SCCE we have looked for the corresponding murine enzyme. A cDNA obtained by reverse transcription-polymerase chain reaction with total RNA prepared from mouse tails as starting material was cloned, and the expression of the corresponding mRNA studied. The murine cDNA showed 77% homology to human SCCE cDNA. It had an open-reading frame encoding a protein comprising 249 amino acids with 82% amino acid sequence homology to human SCCE including the conserved sequences of the catalytic traid of mammalian serine proteases. The murine protein was deduced to have a 21 amino acid signal peptide and a four amino acid propeptide ending with a tryptic cleavage site, followed by a sequence motif identical to the N-terminal amino acid sequence of native active human SCCE. As in human SCCE the P2 position of the propeptide was occupied by an acidic amino acid residue, and the position corresponding to the suggested bottom of the primary substrate specificity pouch occupied by an asparagine residue. Analyses of mouse tissues by reverse transcriptase-polymerase chain reaction showed high expression in the skin, low expression in lung, kidney, brain, heart, and spleen, and no expression in liver or skeletal muscle. In situ hybridization of mouse skin showed expression in high suprabasal keratinocytes and in the luminal parts of hair follicles. Our results strongly suggest that we have cloned the murine analog of human SCCE cDNA.