Expression of L-type amino acid transporter 1 in various skin lesions.

L-type amino acid transporter 1 (LAT1) is a Na(+)-independent neutral amino acid transporter that has an essential role in cell proliferation. Although the involvement of LAT1 in human carcinogenesis has been investigated by immunohistochemistry in various organs, LAT1 expression in skin has not been reported yet. Therefore, in the present study, immunohistochemistry for LAT1 was performed in 15 keratoacanthoma (KA), 10 seborrheic keratosis, 16 Bowen's disease, 11 basal cell carcinoma (BCC), and 9 squamous cell carcinoma (SCC) cases as well as 61 normal epidermis as control. It was demonstrated that LAT1 expression limited to the basal layer was occasionally observed in normal epidermis while its expression was significantly decreased in the epithelium of seborrheic keratosis and Bowen's disease (P<0.05). By contrast, a significantly higher rate of LAT1 expression was observed in the epithelium of KA, BCC, and SCC than in normal epidermis (P<0.05). Although LAT1 expression was limited to the basal layer or rim of the nests in KA, LAT1 expression was also observed in the center of the nests in BCC and SCC (P<0.001). Thus, LAT1 is differentially expressed in various skin lesions and may be an especially useful marker to distinguish KA from SCC.