ERAP1 and ERAP2 Gene Variants as Potential Clinical Biomarkers of Anti-IL-17A Response in Psoriasis Vulgaris.

BACKGROUND: Interleukin-17A (IL-17A) is a proinflammatory cytokine, playing an essential role in the development of psoriasis. Although treatment with anti-IL-17A monoclonal antibodies has demonstrated high efficacy in psoriasis patients, not all patients respond equally well, highlighting the need for biomarkers to predict treatment response. Specific single nucleotide polymorphisms (SNPs) in the endoplasmatic reticulum aminopeptidase (ERAP) 1 and 2 genes have been associated with psoriasis and other immune-mediated diseases. OBJECTIVES: We aimed to investigate the association between the ERAP1 and ERAP2 genotypes and response to secukinumab treatment in psoriasis patients. METHODS: A total of 75 patients with plaque psoriasis were included. All patients were genotyped for the ERAP1 rs27524, rs27044, rs30187, rs2287987, and rs26653 SNPs, the ERAP2 rs2248374 SNP, and human leukocyte antigen-C*06:02 (HLA-C*06:02) status. RESULTS: Our results demonstrated that individuals with specific ERAP1 and ERAP2 genotypes had a considerably lower response rate to secukinumab treatment. Patients with the ERAP2 rs2248374 G/G genotype had a more than 6-fold increased risk of treatment failure compared with patients with the rs2248374 A/G or -A/A genotypes. Stratifying for HLA-C*06:02 status, the ERAP2 G/G genotype pointed towards an increased risk of treatment failure among HLA-C*06:02-positive patients, although this was not statistically significant. CONCLUSION: Taken together, this unique study breaks new ground by identifying distinct ERAP1 and ERAP2 gene variants that may serve as potential biomarkers for predicting the treatment response to secukinumab in psoriasis patients. Notable, out data extends existing knowledge by linking specific ERAP1 and ERAP2 gene variants to treatment outcome.

Exploring treatment and antifungal resistance in an outbreak of tinea caused by Microsporum audouinii.

BACKGROUND: Microsporum audouinii has resurged recently. Infections with the dermatophyte are difficult to treat, which raises the question if we treat M. audouinii infections with the most effective antifungal (AF) agent. OBJECTIVES: The aims of this study was to investigate an outbreak of tinea capitis (TC) in Denmark, address the challenges in outbreak management and to conduct two reviews regarding previous outbreaks and minimal inhibitory concentration (MIC). METHODS: We used Wood's light, culture, direct microscopy, and PCR for screening and antifungal susceptibility testing (AFST) for treatment optimization. We performed two reviews to explore M. audouinii outbreaks and MIC values using broth microdilution method. RESULTS: Of 73 screened individuals, 10 had confirmed M. audouinii infections. Clinical resistance to griseofulvin was observed in 4 (66%) cases. While previous outbreaks showed high griseofulvin efficacy, our study favoured terbinafine, fluconazole and itraconazole in our hard-to-treat cases. AFST guided the choice of AF. Through the literature search, we identified five M. audouinii outbreaks, where differences in management included the use of Wood's light and prophylactic topical AF therapy. Terbinafine MIC values from the literature ranged from 0.002 to 0.125 mg/L. CONCLUSION: Use of Wood's light and preventive measurements were important for limiting infection. The literature lacked MIC data for griseofulvin against M. audouinii, but indicated sensitivity for terbinafine. The clinical efficacy for M. audouinii treatment was contradictory favouring both terbinafine and griseofulvin. AFST could have a key role in the treatment of difficult cases, but lack of standardisation of AFST and MIC breakpoints limits its usefulness.

Secukinumab and Dead Sea Climatotherapy Impact Resolved Psoriasis Skin Differently Potentially Affecting Disease Memory.

Secukinumab and Dead Sea treatment result in clear skin for many psoriasis patients, through distinct mechanisms. However, recurrence in the same areas after treatments suggests the existence of a molecular scar. We aimed to compare the molecular and genetic differences in psoriasis patients who achieved complete response from secukinumab and Dead Sea climatotherapy treatments. We performed quantitative immunohistochemical and transcriptomic analysis, in addition to digital spatial profiling of skin punch biopsies. Histologically, both treatments resulted in a normalization of the lesional skin to a level resembling nonlesional skin. Interestingly, the transcriptome was not normalized by either treatments. We revealed 479 differentially expressed genes between secukinumab and Dead Sea climatotherapy at the end of treatment, with a psoriasis panel identifying SERPINB4, SERPINB13, IL36G, IL36RN, and AKR1B10 as upregulated in Dead Sea climatotherapy compared with secukinumab. Using digital spatial profiling, pan-RAS was observed to be differentially expressed in the microenvironment surrounding CD103+ cells, and IDO1 was differentially expressed in the dermis when comparing the two treatments. The differences observed between secukinumab and Dead Sea climatotherapy suggest the presence of a molecular scar, which may stem from mechanistically different pathways and potentially contribute to disease recurrence. This may be important for determining treatment response duration and disease memory.

Transcriptomic Analysis of Hidradenitis Suppurativa: A Unique Molecular Signature with Broad Immune Activation.

Hidradenitis suppurativa is a chronic inflammatory skin disease with limited treatment options. The poorly understood pathogenesis hinders the development of effective treatments; therefore, a pressing need exists to further elucidate the molecular mechanisms in hidradenitis suppurativa. This study investigated the underlying inflammatory pathways and cell types in hidradenitis suppurativa using transcriptomic approaches with RNA sequencing of lesional and non-lesional skin biopsies from hidradenitis suppurativa, which was jointly analyzed with previously published transcriptomic data from atopic dermatitis and psoriasis patients. The differential expression and pathway enrichment analyses demonstrated the activation of multiple inflammatory processes, including the innate and adaptive immune systems, implicated in the hidradenitis suppurativa pathogenesis. In agreement, hidradenitis suppurativa exhibited a unique and heterogeneous cell type signature involving lymphoid and myeloid cells such as B cells and macrophages. Furthermore, hidradenitis suppurativa displayed increased expression of TH1/2/17 signatures with no predominant TH signatures unlike psoriasis (TH1/17) and atopic dermatitis (TH2). In summary, our study provides molecular insights into the pathomechanisms in hidradenitis suppurativa, revealing a strong and widespread immune activation, which may benefit from treatment strategies offering a broad immunomodulation of various key inflammatory pathways. Our data not only corroborate previously reported findings but also enhance our understanding of the immune dysregulation in hidradenitis suppurativa, uncovering novel and potential therapeutic targets.

Climatotherapy at the Dead Sea for psoriasis is a highly effective anti-inflammatory treatment in the short term: An immunohistochemical study.

Climatotherapy is a well-described treatment of psoriasis. Dead Sea climatotherapy (DSC) in Israel consists of intensive sun and Dead Sea bathing and is very effective in improving clinical and patient-reported outcomes. However, the effect of DSC has not been widely studied. We aimed to investigate the effect of DSC on psoriasis skin using quantitative immunohistochemistry techniques and analysis of blood samples. Skin punch biopsies from 18 psoriasis patients from a previous cohort study were used. Biopsies were obtained from non-lesional skin and from a psoriasis target lesion at baseline. A biopsy was acquired from the target lesion after DSC. Among patients who achieved complete visual clearance, a biopsy was also obtained at relapse. Blood samples were obtained at the same time points. We performed haematoxylin and eosin staining and quantitative immunohistochemical analysis of CD3, CD4, CD8, CD11c, CD103, CD163, CD207, forkhead box P3, Ki67 and myeloperoxidase. We performed blood tests of cholesterol, c-reactive protein, glucose, haemoglobin A1c and triglycerides. All skin biomarkers except for CD207 were decreased after DSC. At relapse, none of the biomarkers were significantly different from the baseline lesional measurements. Total CD207 staining correlated with psoriasis area and severity index at baseline while CD163 staining correlated with psoriasis area and severity index at EOT. No changes were observed in selected blood tests during the study. Consistent with clinical results, DSC is highly effective in the short term almost normalising all investigated biomarkers. However, at relapse, biomarkers were upregulated to the baseline level.

Antibiotics inhibit tumor and disease activity in cutaneous T-cell lymphoma.

It has been proposed that CD4 T-cell responses to Staphylococcus aureus (SA) can inadvertently enhance neoplastic progression in models of skin cancer and cutaneous T-cell lymphoma (CTCL). In this prospective study, we explored the effect of transient antibiotic treatment on tumor cells and disease activity in 8 patients with advanced-stage CTCL. All patients experienced significant decrease in clinical symptoms in response to aggressive, transient antibiotic treatment. In some patients, clinical improvements lasted for more than 8 months. In 6 of 8 patients, a malignant T-cell clone could be identified in lesional skin, and a significant decrease in the fraction of malignant T cells was observed following antibiotics but an otherwise unchanged treatment regimen. Immunohistochemistry, global messenger RNA expression, and cell-signaling pathway analysis indicated that transient aggressive antibiotic therapy was associated with decreased expression of interleukin-2 high-affinity receptors (CD25), STAT3 signaling, and cell proliferation in lesional skin. In conclusion, this study provides novel evidence suggesting that aggressive antibiotic treatment inhibits malignant T cells in lesional skin. Thus, we provide a novel rationale for treatment of SA in advanced CTCL.

Suppressed microRNA-195-5p expression in mycosis fungoides promotes tumor cell proliferation.

BACKGROUND: Several cancers, including mycosis fungoides (MF), have reported dysregulation of miR-195-5p. miR-195-5p plays a role in cell cycle regulation in several malignant diseases. OBJECTIVES: This study aimed to investigate: (a) the expression level of miR-195-5p in lesional MF skin biopsies and (b) the potential regulatory roles of miR-195-5p in MF. METHODS: Quantitative real-time polymerase chain reaction (RT-qPCR) was used to determine miR-195-5p expression in MF skin biopsies and cell lines. The effect of miR-195-5p and ADP-ribosylation factor-like protein 2 (ARL2) on cell cycle and apoptosis was measured by flow cytometry assays. Changes in ARL2 expression were determined by RT-qPCR and Western blotting (WB). RESULTS: We found lower expression levels of miR-195-5p in lesional skin from MF patients compared with non-lesional MF skin and skin from healthy volunteers. Additionally, miR-195-5p showed lower expression levels in the skin from patients with disease progression compared with patients with stable disease. In vitro studies showed that overexpression of miR-195-5p induced a cell cycle arrest in G0G1. Using microarray analysis, we identified several genes that were regulated after miR-195-5p overexpression. The most downregulated gene after miR-195-5p mimic transfection was ARL2. RT-qPCR and WB analyses confirmed downregulation of ARL2 following transfection with miR-195-5p mimic. Lastly, transfection with siRNA against ARL2 also induced a G0G1 arrest. CONCLUSION: Upregulation of miR-195-5p in MF inhibits cycle arrest by downregulation of ARL2. miR-195-5p may thus function as a tumor suppressor in MF and low miR-195-5p expression in lesional MF skin may promote disease progression.

The HSP90 inhibitor RGRN-305 exhibits strong immunomodulatory effects in human keratinocytes.

Keratinocytes are the key cellular target for IL-17A-mediated effects in psoriasis and HSP90 is important for IL-17A-mediated signalling. RGRN-305 is a novel HSP90 inhibitor reported to reduce psoriatic phenotypes in preclinical animal models. The aim of this study was to investigate the effect of RGRN-305 on a psoriasis-like inflammatory response in human keratinocytes in vitro. Using RT-qPCR, we demonstrated a significantly increased expression of the HSP90 isoforms HSP90AB1, HSP90B1 and TRAP1 in lesional compared with non-lesional psoriatic skin. In a psoriasis-like setting where keratinocytes were stimulated with TNFα and/or IL-17A, we analysed the mRNA expression using the NanoString nCounter technology and demonstrated that the HSP90 inhibitor RGRN-305 significantly reduced the IL-17A- and TNFα-induced gene expression of a number of proinflammatory genes, including the psoriasis-associated genes CCL20, NFKBIZ, IL36G and IL23A. In agreement with the mRNA data, the protein level of CCL20, IκBζ and IL-36γ were inhibited by RGRN-305 as demonstrated by western blotting and ELISA. Interestingly, when keratinocytes were stimulated with a TLR3 agonist, RGRN-305 also demonstrated potent immunomodulatory effects, significantly inhibiting poly(I:C)-induced expression of the proinflammatory genes TNFα, IL1B, IL6 and IL23A. Taken together, our data support a role for HSP90 not only in the pathogenesis of psoriasis, but also in broader immune responses. Therefore, HSP90 provides an attractive target for the treatment of psoriasis and other diseases where the innate immune system plays an important role.

IkBζ is a Key Regulator of Tumour Necrosis Factor-a and Interleukin-17A-mediated Induction of Interleukin-36g in Human Keratinocytes.

The interleukin (IL)-36 cytokine family plays an essential role in inflammatory processes in the skin and is implicated in the pathogenesis of psoriasis. This study explored the role of IL-36 in psoriasis and investigated the molecular mechanism involved in tumour necrosis factor-α (TNFα)/IL-17A-mediated IL-36 induction. In human keratinocytes IL-36 expression was strongly upregulated by combined TNFα and IL-17A stimulation. Moreover, IκBζ, encoded by NFKBIZ, was identified as a key regulator required for TNFα/IL-17A-induced IL-36γ expression. TNFα/IL-17A-induced IL-36γ expression also involved the nuclear factor κB (NF-κB), p38 mitogen-activated protein kinase and ERK1/2 signalling pathways. Furthermore, a specific NF-κB DNA-binding site in the promoter region of IL36G responsible for the TNFα/IL-17A-induced IL36G gene expression was identified. Finally, in a cohort of patients with psoriasis receiving anti-IL-17A treatment, a positive correlation was found between the expression of NFKBIZ and IL36G. In conclusion, these data reveal a novel crucial regulatory mechanism by which TNFα and IL-17A regulate IL-36γ expression.

IκBζ is a key player in the antipsoriatic effects of secukinumab.

BACKGROUND: IκBζ plays a key role in psoriasis by mediating IL-17A-driven effects, but the molecular mechanism by which IL-17A regulates IκBζ expression is not clarified. OBJECTIVE: We sought to explore the molecular transformation in patients with psoriasis during anti-IL-17A (secukinumab) treatment with a focus on IκBζ. METHODS: The study was an open-label, single-arm, single-center secukinumab treatment study that included 14 patients with plaque psoriasis. Skin biopsy specimens and blood samples were collected on days 0, 4, 14, 42, and 84 and processed for microarray gene expression analysis. Furthermore, in vitro experiments with human keratinocytes and synovial fibroblasts were conducted. RESULTS: Secukinumab improved clinical scores and histologic psoriasis features. Moreover, secukinumab altered the skin transcriptome. The major transcriptional shift appeared between day 14 and day 42 after treatment initiation, although 80 genes were differentially expressed already at day 4. Expression of nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor (IκB) ζ (NFKBIZ, the gene encoding IκBζ) was reduced already after 4 days of treatment in the skin. NFKBIZ expression correlated to Psoriasis Area and Severity Index score, and NFKBIZ mRNA levels in the skin decreased during anti-IL-17A treatment. Moreover, specific NFKBIZ signature genes were significantly altered during anti-IL-17A treatment. Finally, we identified NF-κB activator 1 (Act1), p38 mitogen-activated protein kinase (MAPK), Jun NH2-terminal kinase (JNK), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) as key signaling pathways in NFKBIZ/IκBζ regulation. CONCLUSION: Our results define a crucial role for IκBζ in the antipsoriatic effect of secukinumab. Because IκBζ signature genes were regulated already after 4 days of treatment, this strongly indicates that IκBζ plays a crucial role in the antipsoriatic effects mediated by anti-IL-17A treatment.

Tissue-Resident Memory T Cells in Skin Diseases: A Systematic Review.

In health, the non-recirculating nature and long-term persistence of tissue-resident memory T cells (TRMs) in tissues protects against invading pathogens. In disease, pathogenic TRMs contribute to the recurring traits of many skin diseases. We aimed to conduct a systematic literature review on the current understanding of the role of TRMs in skin diseases and identify gaps as well as future research paths. EMBASE, PubMed, SCOPUS, Web of Science, Clinicaltrials.gov and WHO Trials Registry were searched systematically for relevant studies from their inception to October 2020. Included studies were reviewed independently by two authors. This study was conducted in accordance with the PRISMA-S guidelines. This protocol was registered with the PROSPERO database (ref: CRD42020206416). We identified 96 studies meeting the inclusion criteria. TRMs have mostly been investigated in murine skin and in relation to infectious skin diseases. Pathogenic TRMs have been characterized in various skin diseases including psoriasis, vitiligo and cutaneous T-cell lymphoma. Studies are needed to discover biomarkers that may delineate TRMs poised for pathogenic activity in skin diseases and establish to which extent TRMs are contingent on the local skin microenvironment. Additionally, future studies may investigate the effects of current treatments on the persistence of pathogenic TRMs in human skin.

The kinases MSK1 and MSK2 act as negative regulators of Toll-like receptor signaling.

The kinases MSK1 and MSK2 are activated 'downstream' of the p38 and Erk1/2 mitogen-activated protein kinases. Here we found that MSK1 and MSK2 were needed to limit the production of proinflammatory cytokines in response to stimulation of primary macrophages with lipopolysaccharide. By inducing transcription of the mitogen-activated protein kinase phosphatase DUSP1 and the anti-inflammatory cytokine interleukin 10, MSK1 and MSK2 exerted many negative feedback mechanisms. Deficiency in MSK1 and MSK2 prevented the binding of phosphorylated transcription factors CREB and ATF1 to the promoters of the genes encoding interleukin 10 and DUSP1. Mice doubly deficient in MSK1 and MSK2 were hypersensitive to lipopolysaccharide-induced endotoxic shock and showed prolonged inflammation in a model of toxic contact eczema induced by phorbol 12-myristate 13-acetate. Our results establish MSK1 and MSK2 as key components of negative feedback mechanisms needed to limit Toll-like receptor-driven inflammation.

Prognostic miRNA classifier in early-stage mycosis fungoides: development and validation in a Danish nationwide study.

Mycosis fungoides (MF) is the most frequent form of cutaneous T-cell lymphoma. The disease often takes an indolent course, but in approximately one-third of the patients, the disease progresses to an aggressive malignancy with a poor prognosis. At the time of diagnosis, it is impossible to predict which patients develop severe disease and are in need of aggressive treatment. Accordingly, we investigated the prognostic potential of microRNAs (miRNAs) at the time of diagnosis in MF. Using a quantitative reverse transcription polymerase chain reaction platform, we analyzed miRNA expression in diagnostic skin biopsies from 154 Danish patients with early-stage MF. The patients were subdivided into a discovery cohort (n = 82) and an independent validation cohort (n = 72). The miRNA classifier was built using a LASSO (least absolute shrinkage and selection operator) Cox regression to predict progression-free survival (PFS). We developed a 3-miRNA classifier, based on miR-106b-5p, miR-148a-3p, and miR-338-3p, which successfully separated patients into high-risk and low-risk groups of disease progression. PFS was significantly different between these groups in both the discovery cohort and the validation cohort. The classifier was stronger than existing clinical prognostic factors and remained a strong independent prognostic tool after stratification and adjustment for these factors. Importantly, patients in the high-risk group had a significantly reduced overall survival. The 3-miRNA classifier is an effective tool to predict disease progression of early-stage MF at the time of diagnosis. The classifier adds significant prognostic value to existing clinical prognostic factors and may facilitate more individualized treatment of these patients.

MicroRNA-106b Regulates Expression of the Tumour Suppressors p21 and TXNIP and Promotes Tumour Cell Proliferation in Mycosis Fungoides.

A prognostic 3-miRNA classifier for early-stage mycosis fungoides has been developed recently, with miR-106b providing the strongest prognostic power. The aim of this study was to investigate the molecular function of miR-106b in mycosis fungoides disease progression. The cellular localization of miR-106b in mycosis fungoides skin biopsies was determined by in situ hybridization. The regulatory role of miR-106b was assessed by transient miR-106b inhibitor/mimic transfection of 2 mycosis fungoides derived cell lines, followed by quantitative real-time PCR (RT-qPCR), western blotting and a proliferation assay. MiR-106b was found to be expressed by dermal T-lymphocytes in mycosis fungoides skin lesions, and miR-106b expression increased with advancing mycosis fungoides stage. Transfection of miR-106b in 2 mycosis fungoides derived cell lines showed that miR-106b represses the tumour suppressors cyclin-dependent kinase inhibitor 1 (p21) and thioredoxin-interacting protein (TXNIP) and promotes mycosis fungoides tumour cell proliferation. In conclusion, these results substantiate that miR-106b has both a functional and prognostic role in progression of mycosis fungoides.

The MicroRNA Expression Profile Differs Between Erythrodermic Mycosis Fungoides and Sézary Syndrome.

It is difficult to distinguish erythrodermic mycosis fungoides from Sézary syndrome due to their similar clinical and histological features. The main purpose of this study was to investigate whether microRNA expression profiles in lesional skin could discriminate patients with erythrodermic mycosis fungoides from those with Sézary syndrome. A further aim was to assess whether the microRNA expression profiles in erythrodermic mycosis fungoides skin was more comparable to microRNA expression profiles of Sézary syndrome or early-stage mycosis fungoides. RNA was extracted from diagnostic skin biopsies, followed by quantitative reverse transcription polymerase chain reaction analysis of 383 microRNAs. Twenty-seven microRNAs were significantly differentially expressed between erythro-dermic mycosis fungoides and Sézary syndrome. More-over, erythrodermic mycosis fungoides showed microRNA features overlapping with Sézary syndrome and early-stage mycosis fungoides, although hierarchical cluster analysis co-clustered erythrodermic mycosis fungoides with early-stage mycosis fungoides rather than with Sézary syndrome. These findings underscore that erythrodermic mycosis fungoides and Sézary syndrome are different diseases.

The human IL-17A/F heterodimer regulates psoriasis-associated genes through IκBζ.

Antagonists of IL-17A and its receptor have proven to be highly effective in the treatment of psoriasis. However, many of the underlying molecular mechanisms involved in the pathogenesis of psoriasis are still to be determined. IκBζ (encoded by the NFKBIZ gene) plays a key role in the development of psoriasis by mediating IL-17A- and IL-17F-driven effects. Both IL-17A and IL-17F expression are increased in lesional psoriatic skin. IL-17A/A and IL-17F/F homodimers as well as the IL-17A/F heterodimer signal through the same receptors. The aim of this study was to characterize the role of the IL-17A/F heterodimer in the regulation of NFKBIZ expression and in the regulation of selected psoriasis-associated genes. We demonstrated that IL-17A/F stimulation of human keratinocytes significantly induced NFKBIZ expression. Moreover, silencing IκBζ by siRNA revealed that IκBζ is a key regulator of IL-17A/F-inducible psoriasis-associated genes, including CCL20, DEFB4, IL-8, CHI3L1 and S100A7. In addition, IL-17A/F-induced NFKBIZ expression was mediated by a mechanism involving the p38 MAPK and NF-κB signalling pathways. In conclusion, we present IκBζ as a novel key regulator of IL-17A/F-driven effects in psoriasis. Thus, antagonists to IL-17A/F or IκBζ may present a targeted approach for treating psoriasis.

IκBζ is a key driver in the development of psoriasis.

Psoriasis is a common immune-mediated, chronic, inflammatory skin disease characterized by hyperproliferation and abnormal differentiation of keratinocytes and infiltration of inflammatory cells. Although TNFα- and IL-17A-targeting drugs have recently proven to be highly effective, the molecular mechanism underlying the pathogenesis of psoriasis remains poorly understood. We found that expression of the atypical IκB member IκB (inhibitor of NF-κB) ζ, a selective coactivator of particular NF-κB target genes, was strongly increased in skin of patients with psoriasis. Moreover, in human keratinocytes IκBζ was identified as a direct transcriptional activator of TNFα/IL-17A-inducible psoriasis-associated proteins. Using genetically modified mice, we found that imiquimod-induced psoriasis-like skin inflammation was completely absent in IκBζ-deficient mice, whereas skin inflammation was still inducible in IL-17A- and TNFα-deficient mice. IκBζ deficiency also conferred resistance against IL-23-induced psoriasis. In addition, local abrogation of IκBζ function by intradermal injection of IκBζ siRNA abolished psoriasis-like skin inflammation. Taken together, we identify IκBζ as a hitherto unknown key regulator of IL-17A-driven effects in psoriasis. Thus, targeting IκBζ could be a future strategy for treatment of psoriasis, and other inflammatory diseases for which IL-17 antagonists are currently tested in clinical trials.

IL-17F regulates psoriasis-associated genes through IκBζ.

Psoriasis is a common chronic inflammatory and immune-mediated skin disease. Antagonists of TNF-α and, recently, IL-17 have proven to be highly effective in the treatment for psoriasis; however, the molecular mechanisms involved in the pathogenesis of psoriasis are poorly understood. Recently, we presented evidence that IκBζ is a key regulator in the development of psoriasis through its role in mediating IL-17A-driven effects. Like IL-17A, IL-17F is produced by a variety of immune cells, and the expression of IL-17F is increased in psoriatic skin. The purpose of this study was to characterize the role of IL-17F in the regulation of IκBζ expression and to investigate whether IL-17F regulates psoriasis-associated genes in human keratinocytes through IκBζ. Here, we demonstrate that IL-17F stimulation induces IκBζ expression at both the mRNA and the protein levels in normal human keratinocytes. Moreover, silencing IκBζ by siRNA revealed that IκBζ is a key regulator of specific IL-17F-inducible psoriasis-associated genes and proteins, including DEFB4/hBD2, S100A7, CCL20, IL-8 and CHI3L1. In addition, IL-17F-induced IκBζ expression is mediated by a mechanism involving the p38 MAPK and NF-κB signalling pathways, as shown by the clear reduction in IL-17F-mediated expression of IκBζ during chemical inhibition of these two signalling pathways. In summary, we present IκBζ as a novel key regulator of IL-17F-driven effects in psoriasis. Thus, antagonists to IκBζ could potentially provide a more targeted approach for treating psoriasis as well as for treating the other inflammatory and immune-mediated diseases for which IL-17-targeting drugs have recently been approved.