Silencing the Transcription Factor FOSL1 in Hyperproliferative HaCaT Cells Makes Them Susceptible to IFN-γ

Abstract

Background: The immortalized human epidermal keratinocytes HaCaT often serve as an experimental model of psoriasis. Previously, we reported that Th1 cytokines TNF, IFN-γ and IL17 suppressed proliferation in cultured HaCaT cells. Our results also suggested that at certain conditions, HaCaT cells could become susceptible to the named cytokines. Objective: The aim of this study was to analyze the consequences of FOSL1 silencing in HaCaT cells and explore the role of the transcription factor FOSL1 in the above mentioned antiproliferative effect. Methods: Lentiviral transduction was used to knock FOSL1 down in HaCaT cells. Changes in cell proliferation were assessed by analyzing the growth of transduced cells. Changes in gene expression were examined by qPCR. Results: We found that the treatment of FOSL1-deficient HaCaT cells with a combination of TNF, IFN-γ and IL17 led to growth arrest and apoptosis. In turn, exposure of these cells to the individual cytokines suggested that the presence of IFN-γ in the culture medium was the primary cause of cell death. FOSL1-deficient cells exposed to IFN-γ exhibited a dramatic shape change and intensive blebbing. Moreover, TNF and IL17 accelerated IFN-γ- induced apoptosis. A comparative analysis of gene expression in control and FOSL1- deficient HaCaT cells discovered that only TNF induced ten FOSL1 target genes previously implicated in the pathogenesis of psoriasis, namely CCL2, FOSL1, HMOX1, IL8, IL6, IVL, MGP, MMP1, MMP9, and PLAUR. In contrast, neither IFN-γ nor IL17 produced similar changes in the expression profiles of the mentioned genes. Conclusion: The obtained results suggest that the transcription factor FOSL1 protects HaCaT cells from apoptosis triggered by IFN-γ. This study also reveals distinct roles of Th1 cytokines in the regulation of FOSL1 target genes. Keywords: Apoptosis, FOSL1, HaCaT, IFN-γ, IL17, psoriasis, TNF.