Altered expression of epidermal growth factor receptor ligands in tumor promoter–treated mouse epidermis and in primary mouse skin tumors induced by an initiation-promotion protocol

Abstract

Multiple epidermal growth factor receptor (EGFr) ligands have been identified, including transforming growth factor alpha (TGFalpha), heparin-binding epidermal growth factor (HB-EGF), amphiregulin (AR), and betacellulin (BTC). Previous work from our laboratory demonstrated that TGFalpha mRNA and protein are upregulated in epidermis during tumor-promoter treatment of mouse skin and in skin tumors produced by initiation-promotion regimens. The purpose of the study described here was to explore the role of other EGFr ligands in multistage skin carcinogenesis. A single topical treatment of either 12-O-tetradecanoylphorbol-13-acetate (TPA) or chrysarobin or a single full-thickness wound induced the expression of HB-EGF and AR in mRNA samples isolated from whole mouse skin. However, only full-thickness wounding significantly elevated expression of the BTC transcript. The levels of HB-EGF and AR transcripts were significantly elevated in skin tumors (both papillomas and squamous cell carcinomas) induced by initiation-promotion protocols. BTC transcript levels were low and barely detectable in all skin tumors examined. The level of keratinocyte growth factor (KGF) mRNA was also examined as a possible mechanism for upregulation of EGFr ligands. Only full-thickness wounding significantly elevated KGF transcript levels in whole-skin RNA samples. Furthermore, no evidence for upregulation of KGF mRNA in skin tumors was obtained. The results are discussed in terms of the role of EGFr activation in skin carcinogenesis and the mechanisms for altered regulation of EGFr ligands.