Immunohistochemical localization of syndecan in mouse skin tumors induced by UV irradiation. Loss of expression associated with malignant transformation.

Immunoreactivity for syndecan, a cell surface proteoglycan, which binds extracellular matrix molecules and growth factors, was studied in hairless (hr/hr) mice exposed to UV-A and UV-B irradiation. Positive staining was observed at the surface of normal epidermal cells as well as in the dermal abortive hair follicle cysts characteristic to this mouse strain. Early reaction to UV-irradiation showing hyperplastic epidermis with slight cellular atypia showed also positive, although reduced, staining of epidermal cell surfaces. Specimens with severe dysplasia showed weak staining in the granular cell layer, whereas the basal cell layer was negative. In papillomas and keratoacanthomas, immunoreactivity for syndecan was observed in the benign hyperplastic epidermal cells as well as in the proliferating epidermal cells of the horn cysts. Malignant transformation of epithelium, expressed as the formation of early invasive and anaplastic squamous cell carcinomas, was uniformly associated with loss of syndecan staining. These results are consistent with the previous findings of reduced expression of syndecan associated with malignant transformation of cultured epithelial cells, but also suggest an important role for syndecan in the maintenance of normal tissue architecture and differentiation pattern of the skin.