CHANGES IN PROTEIN EXPRESSION DURING MULTISTAGE MOUSE SKIN CARCINOGENESIS

To directly compare the expression patterns of different proteins know n to be altered during mouse skin carcinogenesis, serial sections of n ormal and hyperplastic skin and tumors from various stages of 7,12-dim ethylbenz[a]anthracene-initiated, 12-O-tetradecanoylphorbol-13-acetate -promoted female SENCAR mice were examined by immunohistochemistry. In untreated, normal mouse skin, keratin 1 (K1) and transforming growth factor-beta 1 (TGF beta 1) were strongly expressed in the suprabasal l ayers, whereas integrin alpha 6 beta 4 was expressed only in basal cel ls and only moderate staining for transforming growth factor-alpha (TG F alpha) was seen. In hyperplastic skin, TGF alpha expression became s tronger, whereas expression of another epidermal growth factor (EGF) r eceptor ligand, heparin-binding EGF-like growth factor (HB-EGF), was s trongly induced in all epidermal layers from no expression in normal s kin. Likewise, the gap-junctional protein connexin 26 (Cx26) became hi ghly expressed in the differentiated granular layers of hyperplastic s kin relative to undetectable expression in normal skin. Expression of cyclin D1 in the proliferative cell compartment was seen in all benign and malignant tumors but not in hyperplastic skin. Beginning with ver y early papillomas (after 10 wk of promotion), expression of alpha 6 b eta 4 in suprabasal cells and small, focal staining for keratin 13 (K1 3) were seen in some tumors. Later (after 20-30 wk), focal areas of ga mma-glutamyl transpeptidase (GGT) activity appeared in a few papilloma s, whereas TGF beta 1 expression began to decrease. Cx26 and TGF alpha staining became patchier in some late-stage papillomas (30-40 wk), wh ereas suprabasal alpha 6 beta 4, K13, and GGT expression progressively increased and K1 expression decreased. Finally, in squamous cell carc inomas (SCCs), there was an almost complete loss of K1 and a further d ecline in TGF alpha, HB-EGF, TGF beta 1, and Cx26 expression. On the o ther hand, almost all SCCs showed suprabasal staining for alpha 6 beta 4 and widespread cyclin D1 and K13 expression, whereas only about hal f showed positive focal staining for CCT activity. (C) 1997 Wiley-Liss , Inc.