EXPRESSION OF HRAS-P21 AND KERATIN K13 IN UVR-INDUCED SKIN TUMORS IN SENCAR MICE

An ultraviolet radiation (UVR)-induced Sencar mouse skin carcinogenesi s model was established to investigate the expression of Hras-p21 and keratin K13 in different stages of carcinogenesis, including UV-expose d nontumor skin, papillomas, squamous-cell carcinomas (SCCs), and mali gnant spindle-cell tumors (SCTs). Expression of Hras-p21 and K13 was e xamined in paraffin-embedded tumor sections by using immunohistochemic al, immunofluorescent, and double staining techniques with specific an tibodies. Positive Hras-p21 staining was detected in 1/3 (33%) papillo mas, 24/36 (67%) of SCCs, but not in UVR-exposed nontumor skin or SCTs . Positive staining of the malignant progression marker K13 was found in 22/36 (61%) of SCCs only. Coexpression of Hras-p21 and K13 was foun d in 17/36(47%) SCCs. H-ras exons I and 2 were amplified from skin/tum or sections by using nested polymerase chain reaction (PCR). PCR-based single-strand conformation polymorphism (SSCP) analysis and gene sequ encing revealed three point mutations, one in UVR-exposed nontumor ski n (codon 56), and two in SCCs (codons 13 and 21). There were no clear relationships between point mutations of H-ras and the positive staini ng of Hras-p21 and K13. These results indicate that overexpression of ras-p21 in conjunction with aberrant expression of K13 is a frequent e vent in UVR-induced SCCs in Sencar mouse skin. Point mutation of the H -ras gene appeared to be a rare event in UVR skin carcinogenesis and n ot to be responsible for overexpression of Hras-p21.