RESUMO
The major effects of the epidermal growth factor receptor (EGFR) signalling pathway on keratinocytes are cell proliferation, cell differentiation, and wound healing. In addition to these effects, an immunosuppressive effect of EGFR signalling has been reported. However, the precise mechanism of immunosuppression by EGFR signalling is not well understood. In this study, we clarified the involvement of increased local cortisol activation in EGFR signalling-induced immunosuppression in keratinocytes. EGF treatment up-regulated the expression of 11ß-hydroxysteroid dehydrogenase 1 (11ß-HSD1) and supernatant cortisol levels in a dose-dependent manner in keratinocytes. 11ß-HSD1 is an enzyme that catalyses the conversion of cellular hormonally inactive cortisone into active cortisol. qRT-PCR and ELISA assays indicated that EGF significantly decreased tumour necrosis factor α (TNF- α)-induced interleukin-6 (IL-6) expression in keratinocytes. Similarly, 11ß-HSD1 overexpression significantly decreased TNF-α-induced IL-6 expression. We evaluated the role of 11ß-HSD1 in immunosuppression through EGFR signalling. Blockade of 11ß-HSD1 via 11ß-HSD1 inhibitor reversed both the expression and production of TNF-α-induced IL-6, which was decreased by EGF in keratinocytes. Therefore, increased local cortisol activation by 11ß-HSD1 is involved in EGFR signalling-induced immunosuppression in keratinocytes. Finally, we evaluated whether EGFR inhibition by cetuximab affects the expression of 11ß-HSD1. We found that 0.1 µg cetuximab decreased 11ß-HSD1 transcript levels in keratinocytes. The changes in 11ß-HSD1 were more apparent in TNF-α-treated cells. As 11ß-HSD1 expression in keratinocytes is associated with inflammation and cell proliferation, this mechanism may be associated with adverse skin reactions observed in patients treated with EGFR inhibitors.
RESUMO
BACKGROUND: Nerve growth factor (NGF), a neurotrophin that plays a critical role in developmental neurobiology, is released by proliferating keratinocytes and induces proliferation. OBJECTIVE: The aim of this study was to investigate the role of tyrosine kinase receptor A (TrkA), a high-affinity receptor of NGF, in human keratinocytes. METHODS: Expression of TrkA and NGF in skin diseases was investigated by immunohistochemistry. Expression of TrkA in cells was examined by Western blotting and RT-PCR. Cell proliferation was assessed by BrdU assay. RESULTS: We first determined the expression of TrkA and NGF in skin samples from patients with atopic dermatitis, prurigo nodularis, psoriasis vulgaris, and seborrheic keratosis. TrkA was only expressed in proliferating basal cells, and its expression was enhanced in atopic dermatitis samples. NGF expression was enhanced in atopic dermatitis and prurigo nodularis samples and in some samples from seborrheic keratosis patients. Investigation of the role of TrkA in vitro using normal human epidermal keratinocytes (NHEK) revealed that TrkA was significantly enhanced by the T helper type 2 (Th2) cytokines interleukin (IL)-4 and IL-13 but not by other inflammatory cytokines, such as IL-1ß, tumor necrosis factor α, interferon γ, or epidermal growth factor. On the other hand, expression of NGF was not altered by Th2 cytokines. Notably, inhibition of TrkA significantly reversed the effects of IL-4 on proliferation and differentiation. Furthermore, overexpression of TrkA enhanced proliferation of NHEK. These results indicate that IL-4-induced TrkA expression in keratinocytes modulates proliferation and differentiation of these cells. CONCLUSION: Increased TrkA expression in keratinocytes in atopic dermatitis may contribute to the observed epidermal hyperproliferation in these patients.