Expression of the bcl-2 homologue bax in normal human skin, psoriasis vulgaris and non-melanoma skin cancers.

Bax (bcl-2-associated X protein) is a recently identified member of the bcl-2 family and one of the principal inducers of apoptosis. We examined the distribution of bax protein in normal human skin and several skin diseases by immunohistochemistry. Bax immunoreactivity was present in normal epidermis and its appendages, with the suprabasal compartment being stained more strongly than basal keratinocytes. Bax immunostaining was also detected in the epidermis of psoriasis vulgaris and 5 keratoacanthomas examined. We could observe only weak bax immunoreactivity in 15 squamous cell carcinomas examined, with the exception of well-differentiated tumour islands in two tumours, which expressed immunostaining for bax comparable to that of normal suprabasal epidermis. Immunostaining for bax was negative in 12 out of 17 basal cell carcinomas and the remaining five tumours showed weak bax reactivity in tumour cells scattered within tumour masses and in palisading layers of some tumour formations. Western blot analysis confirmed the expression of bax protein in normal skin, psoriasis vulgaris and squamous cell carcinoma as well as the absence of bax in basal cell carcinoma. Our findings suggest that the loss of pro-apoptotic bax protein in basal cell carcinoma and its reduced expression in squamous cell carcinoma might be an important step in the development of these two skin cancers.