Loss of serum response factor in keratinocytes results in hyperproliferative skin disease in mice
Heidi Koegel, … , Alfred Nordheim, Sabine Werner
Heidi Koegel, … , Alfred Nordheim, Sabine Werner
Published March 23, 2009
Citation Information: J Clin Invest. 2009;119(4):899-910. https://doi.org/10.1172/JCI37771.
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Loss of serum response factor in keratinocytes results in hyperproliferative skin disease in mice

Abstract

The transcription factor serum response factor (SRF) plays a crucial role in the development of several organs. However, its role in the skin has not been explored. Here, we show that keratinocytes in normal human and mouse skin expressed high levels of SRF but that SRF expression was strongly downregulated in the hyperproliferative epidermis of wounded and psoriatic skin. Keratinocyte-specific deletion within the mouse SRF locus during embryonic development caused edema and skin blistering, and all animals died in utero. Postnatal loss of mouse SRF in keratinocytes resulted in the development of psoriasis-like skin lesions. These lesions were characterized by inflammation, hyperproliferation, and abnormal differentiation of keratinocytes as well as by disruption of the actin cytoskeleton. Ultrastructural analysis revealed markedly reduced cell-cell and cell-matrix contacts and loss of cell compaction in all epidermal layers. siRNA-mediated knockdown of SRF in primary human keratinocytes revealed that the cytoskeletal abnormalities and adhesion defects were a direct consequence of the loss of SRF. In contrast, the hyperproliferation observed in vivo was an indirect effect that was most likely a consequence of the inflammation. These results reveal that loss of SRF disrupts epidermal homeostasis and strongly suggest its involvement in the pathogenesis of hyperproliferative skin diseases, including psoriasis.

Authors

Heidi Koegel, Lukas von Tobel, Matthias Schäfer, Siegfried Alberti, Elisabeth Kremmer, Cornelia Mauch, Daniel Hohl, Xiao-Jing Wang, Hans-Dietmar Beer, Wilhelm Bloch, Alfred Nordheim, Sabine Werner

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Figure 7

siRNA-mediated downregulation of SRF in primary human keratinocytes disrupts the actin cytoskeleton and affects cell adhesion but not proliferation.

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siRNA-mediated downregulation of SRF in primary human keratinocytes disr...
(A) SRF protein is efficiently downregulated in primary human keratinocytes as shown by Western blot analysis. Scrambled siRNA and siRNA against Bid served as controls. GAPDH was used as a loading control. (B) Schematic representation of SRF mRNA. Black bars indicate siRNA-binding sites. (C) Immunofluorescence analysis of SRF (red) shows reduced nuclear staining in SRF siRNA–treated keratinocytes. Costaining with phalloidin-FITC (green) revealed reduced cell size (see upper panels) and less filopodia (see lower panels) in SRF1 and SRF2 siRNA–treated keratinocytes. Scale bars: 20 μm (upper panels); 5 μm (lower panels). (D) Western blot analysis showing expression of SRF, E-cadherin, γ-catenin (plakoglobin), and β-actin in keratinocytes treated with scrambled or SRF siRNAs. siRNA against an unrelated protein (caspase-5) was used as an additional control. (E) Adhesion efficiency of SRF siRNA–treated keratinocytes is significantly reduced (n = 3). Error bars show mean ± SEM, *P = 0.021 (Bid/SRF1); †P = 0.038 (scrambled/SRF1); **P = 0.005 (Bid/SRF2); ‡P = 0.009 (scrambled/SRF2), ANOVA with Bonferroni’s post hoc test. (F) BrdU incorporation was analyzed in keratinocytes that had been treated for 3 days with SRF siRNAs or with control siRNAs (n = 3 wells per treatment group; 10 microscopic fields per dish were counted). Error bars show mean ± SEM. No significant difference was detected using ANOVA with Bonferroni post hoc test.