DEMONSTRATION OF SKIN-DERIVED ANTILEUKOPROTEINASE (SKALP) AND ITS TARGET ENZYME HUMAN-LEUKOCYTE ELASTASE IN SQUAMOUS-CELL CARCINOMA

Skin-derived antileukoproteinase (SKALP), also known as elafin, is a s trong and specific inhibitor of elastase and proteinase 3. SKALP is no t present in normal epidermis, but is expressed by epidermal keratinoc ytes under hyperproliferative conditions such as psoriasis, wound heal ing, and in cell culture. In human epidermal tumours, SKALP is differe ntially expressed and restricted to tumours with distinct squamous dif ferentiation. We have studied the presence of both SKALP and one of it s known target enzymes, leukocyte elastase, in 41 squamous cell carcin omas of the skin. SKALP expression correlated with the degree of diffe rentiation: strong expression was seen in well-differentiated cells an d expression was absent in poorly differentiated tumour cells. Most of the squamous cell carcinomas showed elastase-positive cells in the tu mour stroma and also within the tumour cell nests. SKALP may interfere with the proteolytic activity of infiltrating inflammatory cells or w ith hitherto unknown proteinases from the tumour cells. We hypothesize that in squamous cell carcinoma progressive loss of SKALP expression could facilitate tumour spread.