Evidence that stratum corneum chymotryptic enzyme is transported to the stratum corneum extracellular space via lamellar bodies.

Stratum corneum chymotryptic enzyme (SCCE) is a recently discovered human serine proteinase that may be specific for keratinizing squamous epithelia. SCCE has properties compatible with a function in the degradation of intercellular cohesive structures during stratum corneum turnover and desquamation. SCCE is expressed in suprabasal keratinocytes. In this study, we demonstrate the subcellular localization of SCCE in the upper granular layer, in the stratum corneum of normal non-palmoplantar skin, and in cohesive parts of hypertrophic plantar stratum corneum, using immunoelectron microscopy of ultrathin cryosections labeled with SCCE-specific monoclonal antibodies detected with gold-labeled secondary antibodies. A narrow zone close to the transition between the granular and cornified layers showed positive SCCE staining after fixation. By means of immunoelectron microscopy, SCCE was found in association with structures resembling intracellular lamellar bodies in the uppermost granular cells and in similar structures undergoing extrusion to the extracellular space between the uppermost granular cells and the lowermost cornified cells. In the stratum corneum, the detected SCCE was confined to the extracellular space and was found in association with intact and partially degraded desmosomes, as well as in the parts of the extracellular space devoid of desmosomes. We conclude that SCCE may be stored in lamellar bodies in the stratum granulosum and transported via these structures to the stratum corneum extracellular space. The results further support the idea that the physiologic function of SCCE may be to catalyze the degradation of desmosomes in the stratum corneum during remodeling of the deeper layers of this tissue, and at a later stage serve as a prerequisite for desquamation.