MCPIP1 contributes to the inflammatory response of UVB-treated keratinocytes

- MCPIP1 level is decreased during first hours after treatment of human primary keratinocytes with UVB light, then, 6 to 12 h after UVB exposure its level grows up above the level of the untreated cells.
- Regulation of MCPIP1 expression is driven by NF-κB, ERK1/2 and p38.
- Diminished level of MCPIP1 in UVB-treated keratinocytes correlates with increased metabolism, enhanced release of proinflammatory mediators and activation of antiapoptotic factors.

BackgroundMonocyte chemoattractant protein-1-induced protein-1 (MCPIP1), also known as regnase-1, negatively regulates many cellular processes including the cellular response to inflammatory agents, differentiation, viability, and proliferation. It possesses a PilT N-terminus (PIN) domain that is directly involved in regulating the stability of transcripts and miRNAs by recognizing stem loop structures and degrading them by endonucleolytic cleavage.ObjectiveWe investigated the role of MCPIP1 in the response of human primary keratinocytes to UVB stress.MethodsKeratinocytes were treated with UVB, siRNA against MCPIP1, pharmacological inhibitors of signaling pathways, or subjected to control treatments. The mRNA and protein levels of MCPIP1 and MCPIP1-dependent changes gene expression were analyzed by quantitative (Q)-RT-PCRs and Western blots. Secretion of TNFα and IL-8 was determined by ELISA.ResultsUVB treatment of keratinocytes induced upregulation of MCPIP1 at the mRNA level after 4-8 h and at the protein level after 8-16 h. MCPIP1 abundance depended on NF-κB activity. Using an siRNA strategy, we found that diminished MCPIP1 resulted in an up-regulation of transcripts coding for IL-8, TNFα, COX-2, and BCL-2, as well as an enhanced release of IL-8. Moreover, decreased phosphorylation of NF-κB and p38 signaling pathways were observed in addition to a slight up-regulation of ERK1/2 directly after UVB treatment. Twenty-four hours later, decreased phosphorylation was observed only for NF-κB and p38. Furthermore, in MCPIP1-suppressed cells, the levels of pro-apoptotic Puma, the phosphorylated form of p53 and the abundance of its target p21 as well as the activity of caspase 3 decreased, while the level of cyclin D1 increased.ConclusionMCPIP1 contributes to the UVB response of keratinocytes by altering metabolic and apoptotic processes and the release of inflammatory mediators.