PLCε cooperates with the NF-κB pathway to augment TNFα-stimulated CCL2/MCP1 expression in human keratinocyte

Phospholipase C epsilon (PLC epsilon) is a unique class of PLC regulated by both Ras family small GTPases and heterotrimeric G proteins. We previously showed by using mice bearing its null or transgenic allele that PLC epsilon plays a crucial role in various forms of skin inflammation through upregulation of proinflammatory cytokine production from keratinocytes. However, molecular mechanisms how PLC epsilon augments cytokine production were largely unknown. We show here using cultured human keratinocyte PHK16-0b cells that induction of the expression of chemokine (C-C motif) ligand 2 (CCL2) following stimulation with tumor necrosis factor (TNF)alpha, which primarily depends on the activation of the NF-kappa B pathway, is abrogated by small interfering RNA-mediated knockdown of PLC epsilon. Enforced expression of PLC epsilon causes substantial CCL2 expression and cooperates with low level TNF alpha stimulation to induce marked overexpression of CCL2, both of which are only partially blocked by pharmacological inhibition of the NF-kappa B signaling. However, PLC epsilon knockdown exhibits no effect on both the NF-kappa B-cis-element-mediated transcription per se and the post-translational modifications of NF-kappa B implicated in transcriptional regulation, suggesting that PLC epsilon constitutes a yet unknown signaling pathway distinct from the NF-kappa B pathway. This pathway can cooperate with the NF-kappa B pathway to achieve a synergistic TNF alpha-stimulated CCL2 induction in keratinocytes. (C) 2011 Elsevier Inc. All rights reserved.