Identification of a Network of Inflammatory Genes Associated with Differences in Skin Tumor Promotion Susceptibility.

Genetic susceptibility to two-stage skin carcinogenesis is known to vary significantly among different stocks and strains of mice. In an effort to identify specific protein changes or altered signaling pathways associated with skin tumor promotion susceptibility, a proteomic approach of two-dimensional (2-D) gel electrophoresis and mass spectrometry was used to examine and identify proteins that were differentially expressed in epidermis between promotion-sensitive DBA/2 and promotion-resistant C57BL/6 mice following treatment with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate. We identified 19 differentially expressed proteins of which 5 were the calcium-binding proteins including annexin A1, parvalbumin a, S100A8, S100A9, and S100A11. The differential expression of two of these calcium-binding proteins, S100A8 and S100A9, was further examined and validated by the following methods: i) one-dimensional (1-D) Western blot analysis; ii) 2-D Western blot analysis; iii) immunohistochemical analysis; and iv) quantitative real-time PCR. Further analyses revealed that S100A8 and S100A9 protein levels were also similarly differentially up-regulated in epidermis of DBA/2 vs C57BL/6 mice following topical treatment with two other skin tumor promoters, okadaic acid and chrysarobin. Pathway analysis of all 19 identified proteins from the present study suggested that these proteins were components of several networks that included inflammation associated proteins known to be involved in skin tumor promotion (e.g. TNF-a, NFkB). Follow-up studies revealed that Tnf, Nfkb1, Il22, and Il1a mRNAs were highly expressed in epidermis of TPA-treated DBA/2 (>2-fold, P <0.001) compared with TPA-treated C57BL/6 mice. Taken together, the present data suggest that differential expression of genes involved in inflammatory pathways in epidermis may play a key role in genetic differences in susceptibility to skin tumor promotion in DBA/2 and C57BL/6 mice.