In situ epithelial cell invasion in organ culture

Organ cultures were established from 2-mm punch biopsies of human skin and maintained for 12 days in either serum-free, growth-factor-free basal medium or in medium supplemented with a number of epithelial cell growth factors including epidermal growth factor, insulin, hydrocortisone and pituitary extract. Normal histological architecture was preserved in growth-factor-free basal medium. However, in the presence of exogenous growth factors, the epidermis was thickened and hypertrophied. There was focal loss of the usual maturation progression, accompanied by abnormal keratinization patterns. In some areas, basement membrane disruption occurred and epithelial cells penetrated into the dermis in these areas. Isolated squamous epithelial cells and nests of cells could be clearly seen within the dermal stroma. In additional studies, an enzyme-linked immunosorbent assay was used to assess fibronectin and laminin production. Increased levels of both matrix components were seen in the culture fluids from tissues maintained under conditions which promote invasion. Taken together these findings indicate that growth-factor-stimulated normal squamous epithelial cells have the capacity to carry out functions that lead to concomitant synthesis and break-down of the underlying basement membrane and to invasion of mesenchymal tissue. This organ culture system may help to elucidate mechanisms of in situ invasion by squamous epithelial cells.