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Two modes of ERK activation by TNF in keratinocytes: Different cellular outcomes and bi‐directional modulation by vitamin D
Author(s) -
Ziv Ester,
Rotem Carmela,
Miodovnik Mor,
Ravid Amiram,
Koren Ruth
Publication year - 2007
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.21650
Subject(s) - mapk/erk pathway , cancer research , calcitriol , keratinocyte , epidermal growth factor receptor , epidermal growth factor , tyrosine kinase , kinase , tumor necrosis factor alpha , cytokine , hacat , proto oncogene tyrosine protein kinase src , inflammation , chemistry , endocrinology , medicine , signal transduction , biology , microbiology and biotechnology , receptor , vitamin d and neurology , biochemistry , in vitro
Abstract Inflammation, elicited in the skin following tissue damage or pathogen invasion, may become chronic with deleterious consequences. Tumor necrosis factor (TNF) is a key mediator of cutaneous inflammation and the keratinocyte an important protagonist of skin immunity. Calcitriol, the hormonally active vitamin D metabolite, and its analogs attenuate epidermal inflammation and inhibit the hyperproliferation of keratinocytes associated with the inflammatory disorder, psoriasis. Since activation of extracellular signal‐regulated kinase (ERK) promotes keratinocyte proliferation and mediates epidermal inflammation, we studied the effect of calcitriol on ERK activation in HaCaT keratinocytes exposed to the ubiquitous inflammatory cytokine TNF. By using the EGF receptor (EGFR) tyrosine kinase inhibitor, AG1487 and the Src family inhibitor, PP‐1, we established that TNF activated ERK in an EGFR and Src dependent and an EGFR and Src independent modes. EGFR dependent activation resulted in the upregulation of the transcription factor, c‐Fos, while the EGFR independent activation mode was of a shorter duration, did not affect c‐Fos expression but induced IL‐8 mRNA expression. Pretreatment with calcitriol, enhanced TNF‐induced EGFR‐Src dependent ERK activation and tyrosine phosphorylation of the EGFR, but abolished the EGFR‐Src independent ERK activation. These effects were mirrored by enhancement of c‐Fos and inhibition of IL‐8 induction by TNF. Treatment with calcitriol increased the rate of the de‐phosphorylation of activated ERK, accounting for the inhibition of EGFR‐Src independent ERK activation by TNF. It is possible that effects on the ERK cascade contribute to the effects of calcitriol and its synthetic analogs on cutaneous inflammation and keratinocyte proliferation. J. Cell. Biochem. 104: 606–619, 2008. © 2007 Wiley‐Liss, Inc.