The research in this proposal continues our studies of the role of glycoproteins in epidermal desquamation, with emphasis on three related serine proteinases that we have isolated from human epidermis (and also find in the more differentiated cells of the oral cavity). Predesquamin (600 kD), immunolocalized to the upper viable layers and the lower stratum corneum, has both thrombin and tryptase activities. It is the precursor of a 400 kD molecule with thrombin activity and of a 40 kD glycoprotein (desquamin) with tryptase activity. Desquamin, immunolocalized to the stratum corneum only, is also a lectin. We showed in cell aggregation experiments that desquamin affects cohesion and desquamation, and we believe that all three molecules are crucial to the degradative events of terminal differentiation. They are not ordinarily expressed in vitro, but we have developed a culture system in which interferon-gamma induces their expression. We will determine to what extent our three enzymes can degrade various structural components of the stratum corneum and whether they act in successive stages. We will elucidate the processing of predesquamin to the other two (and any intermediates) from structural and functional correlations. In particular, we will completely sequence desquamin biochemically, partially sequence the other two, and seek homology with known serine proteinases. Polyclonal antibodies to selected peptides will be used to immunoprecipitate intermediates and for immunolocalization in different cell populations. Given the amino acid sequences of degraded peptides, we will develop oligonucleotide probes to clone for the gene. We will study gene expression, in normal and diseased tissue, and its modulation by agents known to affect proliferation and differentiation, in vitro (with our interferon-gamma system) and in vivo.
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