Inactivation of mitogen-activated protein kinase signaling pathway reduces caspase-14 expression in impaired keratinocytes


1 Department of Dermatology, Jinan Central Hospital affiliated to Shandong University, Jinan, Shandong Province, 250013, China

2 College of Life Science, Shandong Normal University, Jinan Shandong Province, 250014, China

3 Department of Endocrinology, Jinan Central Hospital affiliated to Shandong University, Jinan, Shandong Province, 250013, China

4 Central Laboratory, Jinan Central Hospital affiliated to Shandong University, Jinan, Shandong Province, 250013, China


Objective(s):Several investigations have revealed that caspase-14 is responsible for the epidermal differentiation and cornification, as well as the regulation of moisturizing effect. However, the precise regulation mechanism is still not clear. This study was aimed to investigate the expression of caspase-14 in filaggrin-deficient normal human epidermal keratinocytes (NHEKs) and to explore the possible mechanism that contributes to the regulation of caspase-14.
Materials and Methods:The filaggrin-deficient NHEKs were induced by transfection with lentivirus (LV) vector encoding small hairpin RNAs (shRNA). The inhibitors SB203580, PD98059 and SP600125 were used for suppressing the expression of p38 mitogen-activated protein kinase (MAPK), p44/42 MAPK and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK). The expression of filaggrin, p38 MAPK, p44/42 MAPK and SAPK/JNK, caspase-14, keratin1and keratin2 were detected by western blot. 
Results:In filaggrin-deficient NHEKs, the expression of p38, p44/42 MAPK and SAPK/JNK and caspase-14 were significantly decreased. The inhibition of p38 and SAPK/JNK reduced the expression of caspase-14, while the p44/42 MAPK showed no consistent effects. Moreover, the filaggrin knockdown decreased the expression of keratin2, but had no effects on the level of keratin1.
Conclusion: The decreased expression of caspase-14 in filaggrin-deficient NHEKs may be induced by the inactivation of MAPK signaling pathway. These provide a novel perspective to understand the mechanism for the protective effects of filaggrin and caspase-14 on skin barrier function.


1. Madison KC. Barrier function of the skin:“la raison d'etre” of the epidermis. J Investig Dermatol 2003; 121:231-241.
2. Oji V, Traupe H. Ichthyoses: differential diagnosis and molecular genetics. Eur J Dermatol 2006; 16:349-359.
3. Akdis CA, Akdis M, Bieber T, Bindslev-Jensen C, Boguniewicz M, Eigenmann P, et al. Diagnosis and treatment of atopic dermatitis in children and adults: European Academy of Allergology and Clinical Immunology/American Academy of Allergy, Asthma and Immunology/PRACTALL Consensus Report. Allergy 2006; 61:969-987.
4. Griffiths CE, Barker JN. Pathogenesis and clinical features of psoriasis. Lancet 2007; 370: 263-271.
5. Mildner M, Jin J, Eckhart L, Kezic S, Gruber F, Barresi C, et al. Knockdown of filaggrin impairs diffusion barrier function and increases UV sensitivity in a human skin model. J Invest Dermatol 2010; 130:2286-2294.
6. Eckhart L, Ban J, Fischer H, Tschachler E. Caspase-14: analysis of gene structure and mRNA expression during keratinocyte differentiation. Biochem Biophys Res Commun 2000; 277:655-659.
7. Eckhart L, Declercq W, Ban J, Rendl M, Lengauer B, Mayer C, et al. Terminal differentiation of human keratinocytes and stratum corneum formation is associated with caspase-14 activation. J Investig Dermatol 2000; 115:1148-1151.
8. Lippens S, Kockx M, Knaapen M, Mortier L, Polakowska R, Verheyen A, et al. Epidermal differentiation does not involve the pro-apoptotic executioner caspases, but is associated with caspase-14 induction and processing. Cell Death Differ 2000; 7:1218-1224.
9. Denecker G, Ovaere P, Vandenabeele P, Declercq W. Caspase-14 reveals its secrets. J Cell Biol 2008; 180:451-458.
10. Hoste E, Kemperman P, Devos M, Denecker G, Kezic S, Yau N, et al. Caspase-14 is required for filaggrin degradation to natural moisturizing factors in the skin. J Investig Dermatol 2011; 131:2233-2241.
11. Hsu S, Dickinson D, Borke J, Walsh DS, Wood J, Qin H, et al. Green tea polyphenol induces caspase 14 in epidermal keratinocytes via MAPK pathways and reduces psoriasiform lesions in the flaky skin mouse model. Exp Dermatol 2007; 16:678-684.
12. Dang N, Pang S, Song H, Bian H, Zhang X, An L,              et al. Knockdown of filaggrin influences the epidermal terminal differentiation via MAPK pathway in normal human epidermal keratinocytes. Mol Biol Rep 2014; 6:6.
13. Palmer CN, Irvine AD, Terron-Kwiatkowski A, Zhao Y, Liao H, Lee SP, et al. Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis. Nat Genet 2006; 38:441-446.
14. Kezic S, O’Regan GM, Lutter R, Jakasa I, Koster ES, Saunders S, et al. Filaggrin loss-of-function mutations are associated with enhanced expression of IL-1 cytokines in the stratum corneum of patients with atopic dermatitis and in a murine model of filaggrin deficiency. J Allergy Clin Immunol 2012; 129:1031-1039. e1031.
15. Levin J, Friedlander SF, Del Rosso JQ. Atopic dermatitis and the stratum corneum: part 1: the role of filaggrin in the stratum corneum barrier and atopic skin. J Clin Aesthet Dermatol 2013; 6:16-22.
16. Handa S. Filaggrin mutations and the skin. Indian J Dermatol Venereol Leprol 2012; 78: 545.
17. Dang N, Pang S, Song H, An L, Ma X. Filaggrin silencing by shRNA directly impairs the skin barrier function of normal human epidermal keratinocytes and then induces an immune response. Braz J Med Biol Res 2015; 48:39-45.
18. Eckert R, Efimova T, Dashti SR, Balasubramanian S, Deucher A, Crish JF, et al. Keratinocyte survival, differentiation, and death: many roads lead to mitogen-activated protein kinase.  J Investig Derma-tol Symp Proc 2002; 7:36-40.
19. Denecker G, Hoste E, Gilbert B, Hochepied T, Ovaere P, Lippens S, et al. Caspase-14 protects against epidermal UVB photodamage and water loss. Nat Cell Biol 2007; 9:666-674.
20. Rendl M, Ban J, Mrass P, Mayer C, Lengauer B, Eckhart L, et al. Caspase-14 expression by epidermal keratinocytes is regulated by retinoids in a differentiation-associated manner. J Invest Dermatol 2002; 119:1150-1155.
21. Bayo P, Sanchis A, Bravo A, Cascallana JL, Buder K, Tuckermann J, et al. Glucocorticoid receptor is required for skin barrier competence. Endocrinology 2008; 149:1377-1388.
22. Lippens S, Kockx M, Denecker G, Knaapen M, Verheyen A, Christiaen R, et al. Vitamin D3 induces caspase-14 expression in psoriatic lesions and enhances caspase-14 processing in organotypic skin cultures. Am J Pathol 2004; 165:833-841.
23. Hsu S, Yamamoto T, Borke J, Walsh DS, Singh B, Rao S, et al. Green tea polyphenol-induced epidermal keratinocyte differentiation is associated with coordinated expression of p57/KIP2 and caspase 14. J Pharmacol Exp Ther 2005; 312: 884-890.
24. McGrath JA, Uitto J. The filaggrin story: novel insights into skin-barrier function and disease. Trends Mol Med 2008; 14:20-27.
25. Popp T, Egea V, Kehe K, Steinritz D, Schmidt A, Jochum M, et al. Sulfur mustard induces differentiation in human primary keratinocytes: opposite roles of p38 and ERK1/2 MAPK. Toxicol Lett 2011; 204:43-51.
26. Efimova T, Broome AM, Eckert RL. A regulatory role for p38 delta MAPK in keratinocyte differentiation. Evidence for p38 delta-ERK1/2 complex formation. J Biol Chem 2003; 278:34277-34285.
27. Jonak C, Mildner M, Klosner G, Paulitschke V, Kunstfeld R, Pehamberger H, et al. The hsp27kD heat shock protein and p38-MAPK signaling are required for regular epidermal differentiation. J Dermatol Sci 2011; 61:32-37.
28. Gazel A, Banno T, Walsh R, Blumenberg M. Inhibition of JNK promotes differentiation of epidermal keratinocytes. J Biol Chem 2006; 281:20530-20541.
29. Sandilands A, Sutherland C, Irvine AD, McLean WI. Filaggrin in the frontline: role in skin barrier function and disease. J Cell Sci 2009; 122:1285-1294.