Expression of both TNF-α receptor subtypes is essential for optimal skin tumour development

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Abstract
Keratinocyte-derived TNF- acts as an endogenous tumour promoter and can also regulate AP-1 activity in mouse epidermis. To gain further insight into TNF- signalling during skin tumour formation, mice deficient in TNFR1 (TNFR1-/- mice) or TNFR2 (TNFR2-/- mice) were subjected to chemical carcinogenesis. Tumour multiplicity was significantly reduced in TNFR1-/- and TNFR2-/- mice compared to wild-type (wt) mice, suggesting that both receptors have protumour activity. However, TNFR1-/- mice were markedly more resistant to tumour development than TNFR2-/- mice indicating that TNFR1 is the major mediator of TNF--induced tumour formation. TNFR1 and TNFR2 were both expressed in wt epidermis during tumour promotion and by primary keratinocytes in vitro. TPA-induced c-Jun expression was transient in TNFR1-/- and TNFR2-/- compared to wt epidermis and this was reflected by reduced induction of the AP-1-responsive genes granulocyte/macrophage-colony stimulating factor, matrix metalloproteinase-9 and matrix metalloproteinase-3. These genes were differentially regulated in TNFR1-/- compared to TNFR2-/- epidermis, suggesting that the TNF- receptors act independently via different AP-1 complexes to transduce TNF- signals during tumour promotion. In addition, TNFR2 cooperated with TNFR1 to optimise TNFR1-mediated TNF- bioactivity on keratinocytes in vitro. Our data provide further insight into TNF- signalling in malignancy and provide some rationale for the use of TNF- antagonists in the treatment of cancer.