A new class of soluble basic protein precursors of the cornified envelope of mammalian epidermis

The cornified envelope hs been shown to be formed beneath the plasma membrane as a result of the cross-linking of soluble and membrane-associated precursor proteins by transglutaminase. We have obtained a monoclonal antibody which reacts with the periphery of cells in the upper layers of human epidermis by indirect immunofluorescence (IIF) following immunization of mice with cornified envelopes of cultured human keratinocytes. The antibody also stained the cell peripheries of bovine, rat and mouse epidermis as well as stratified epithelium. Neutral buffer extracts of human cultured keratinocytes and epidermis examined under denaturing conditions contained polypeptides of molecular weight 14 900 and 16 800 which reacted with the antibody, and an additional component of molecular weight 24 800 was found in cultured cells. The polypeptides were shown to have a pI of about 9.0. Under non-denaturing conditions the two lower-molecular-weight polypeptides had an apparent molecular weight of 30 000, while the 24 800 protein had one of 60 000. Incubation of the polypeptides under conditions that activate transglutaminase resulted in a disappearance of the polypeptides or the formation of cross-linked products. Basic polypeptides with somewhat different pI values and molecular weights were identified in neutral buffer extracts of bovine and rat epidermis. The HCE-2 antibody appears to identify a new class of basic protein precursors of mammalian cornified envelope.