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The increasing use of biologics is accompanied by a risk of hepatitis B (HBV) and C virus (HCV) reactivation.To determine the predictors of HBV and HCV reactivation in patients with psoriasis receiving biologics.This study screened 2060 patients with psoriasis (3562 treatment episodes) who were taking biologics from 2009 to 2018. There were 359 patients with psoriasis with HBV (561 treatment episodes) and 61 with HCV infection (112 treatment episodes).During 8809 and 1522 person-months of follow-up, 88 treatment episodes for HBV involved HBV reactivation, and 14 episodes of HCV involved reactivation. The reactivation rate was significantly higher in treatment episodes of chronic HBV infection than in that of occult HBV (34.3% vs 3.2%, P = .001) and resolved HBV (34.3% vs 5.0%, P .001). The multivariate analysis revealed that being hepatitis B surface antigen seropositive, being hepatitis B e-antigen seropositive, and tumor necrosis factor-α-inhibitor therapy were risk factors for HBV reactivation, whereas antiviral prophylaxis was effective in reducing the risk of HBV reactivation. No predictors were significantly associated with HCV reactivation.Observational design and a lack of a comparison group.Patients with psoriasis on biologics have a risk of HBV and HCV reactivations, particularly those who are seropositive for hepatitis B surface antigen and hepatitis B e-antigen and undergoing tumor necrosis factor-α-inhibitor therapy.

In Taiwan, the incidence and prevalence of psoriatic arthritis (PsA) have risen significantly in recent years. Moreover, data from the Taiwan National Health Insurance Research Database (NHIRD) show that more than 85% of PsA patients are treated with just non-steroidal anti-inflammatory drugs (NSAIDs) and/or conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs). Taiwanese clinicians have also expressed concerns regarding uncertainties in the diagnosis of PsA and the delayed, interrupted, and/or tapered use of biologics, as well as differences in therapeutic preferences between and within dermatologists and rheumatologists. To address these issues, the Taiwan Rheumatology Association and the Taiwanese Association for Psoriasis and Skin Immunology jointly convened a committee of 28 clinicians from the fields of rheumatology, dermatology, orthopedics, and rehabilitation, to develop evidence-based consensus recommendations for the practical management of PsA in Taiwan. A total of six overarching principles and 13 recommendations were developed and approved, as well as a treatment algorithm with four separate tracks for axial PsA, peripheral PsA, enthesitis, and dactylitis. Psoriasis (PsO) management was not discussed here, as the Taiwanese Dermatological Association has recently published a comprehensive consensus statement on the management of PsO. Together, these recommendations provide an up-to-date, evidence-based framework for PsA care in Taiwan.

UV irradiation can injure the epidermis, resulting in sunburn, inflammation, and cutaneous tissue disorders. Previous studies demonstrate that EGFR in keratinocytes can be activated by UVB and contributes to inflammation. Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme and plays an essential role in DNA repair under moderate stress. In this study, we set out to understand how PARP-1 regulates UVB irradiation-induced skin injury and interplays with EGFR to mediate the inflammation response. We found that PARP-1 deficiency exacerbated the UVB-induced inflammation, water loss, and back skin damage in mice. In human primary keratinocytes, UVB can activate PARP-1 and enhance DNA damage upon PARP-1 gene silencing. Moreover, PARP-1 silencing and PARP inhibitor olaparib can suppress UVB-induced COX-2 and MMP-1 expression, but enhance TNF-α and IL-8 expression. In addition, EGFR silencing or EGFR inhibition by gefitinib can decrease UVB-induced COX-2, TNF-α, and IL-8 expression, suggesting EGFR activation via paracrine action can mediate UVB-induced inflammation responses. Immunoblotting data revealed that PARP-1 inhibition decreases UVB-induced EGFR and p38 activation. Pharmacological inhibition of p38 also dramatically led to the attenuation of UVB-induced inflammatory gene expression. Of note, genetic ablation of PARP-1 or EGFR can attenuate UVB-induced ROS production, and antioxidant NAC can attenuate UVB-induced EGFR-p38 signaling axis and PARP-1 activation. These data suggest the regulatory loops among EGFR, PARP-1, and ROS upon UVB stress. PARP-1 not only serves DNA repair function but also orchestrates interactions to EGFR transactivation and ROS production, leading to p38 signaling for inflammatory gene expression in keratinocytes.

The galectin family comprises β-galactoside-binding proteins widely expressed in many organisms. There are at least 16 family members, which can be classified into three groups based on their carbohydrate-recognition domains. Pleiotropic functions of different galectins in physiological and pathological processes through extracellular or intracellular actions have been revealed. In the skin, galectins are expressed in a variety of cells, including keratinocytes, melanocytes, fibroblasts, dendritic cells, lymphocytes, macrophages and endothelial cells. Expression of specific galectins is reported to affect cell status, such as activation or death, and regulate the interaction between different cell types or between cells and the extracellular matrix. In vitro cellular studies, in vivo animal studies and studies of human clinical material have revealed the pathophysiologic roles of galectins in the skin. The pathogenesis of diverse non-malignant skin disorders, such as atopic dermatitis, psoriasis, contact dermatitis and wound healing, as well as skin cancers, such as melanoma, squamous cell carcinoma, basal cell carcinoma and cutaneous haematologic malignancy can be regulated by different galectins. Revelation of biological roles of galectins in skin may pave the way to future development of galectin-based therapeutic strategies for skin diseases.

The efficacy and safety of secukinumab, a fully human anti-interleukin-17A monoclonal antibody, has been evaluated for moderate to severe plaque psoriasis in global trials which have included a low proportion of Asian subjects. We analyzed the efficacy and safety of secukinumab in Taiwanese patients in a phase III global clinical trial (ERASURE). Fifty-one Taiwanese patients were randomized into s.c. placebo, 150 and 300 mg secukinumab treatment groups. The proportions of patients who achieved 75% or more improvement in Psoriasis Area and Severity Index (PASI-75) at week 12 were 87.5% with 300 mg secukinumab, 70% with 150 mg secukinumab, 0% with placebo. Of the patients receiving 300 mg secukinumab, 68.8% achieved PASI-90 at week 12. Analysis of overall patients receiving 300 mg secukinumab for 12 weeks showed that the proportion of PASI-75 responders was less in patients with body mass index of 25 or more than less than 25. During the entire 52 weeks, the incidence of adverse events (AE) was consistent with the overall population in ERASURE. The most common AE (cases/per 100 patient-year) during the entire treatment period were upper respiratory tract infection and pruritus. The duration of upper respiratory tract infection per 100 patient-year was approximately 399 days in placebo, 1261 days in 150 mg secukinumab and 1805 days in 300 mg secukinumab. The safety and efficacy of secukinumab in Taiwanese patients was compatible with the global phase III study in the treatment of moderate to severe plaque psoriasis.

Background/Purpose Atopic dermatitis (AD) is a chronic inflammatory disease commonly seen in children and increasingly recognized in adults. With recent advances in the therapeutic development for AD, the Taiwanese Dermatological Association (TDA) established a committee to update the consensus for AD management in Taiwan. This report describes the 2020 updated consensus for the management of AD. Methods A panel of 11 core members was convened to review and discuss aspects of AD management and draft recommendation during the first two meetings. The 2015 TDA consensus and the 2017 European guideline, along with recent peer-reviewed articles, serve as the foundation for the update. In the third meeting, AD expert dermatologists selected on a national scale were invited to vote on the final statements. A total of 27 dermatologists attended the final meeting. The consensus was achieved when ratings of 7–9 (out of a total score of 9) accounted for ≥ 75% of the total votes. Results Consensus was achieved on the therapeutic options for AD by lines of treatment. A treatment algorithm was presented to illustrate the place of each modality in terms of basic care, acute disease control, and maintenance therapy. Special considerations for the pediatric population, as well as for women during pregnancy and lactation, are discussed. Conclusion Topical corticosteroids with long-term emollient-based therapies remain the cornerstone of AD treatment. Systemic treatments are indicated when topical therapies and phototherapy fail to control the disease. The recent approval of dupilumab and emerging targeted therapies are expected to bring significant clinical benefit for patients whose disease is inadequately managed by existing options.

Syk is a non-receptor tyrosine kinase involved in the signalling of immunoreceptors and growth factor receptors. Previously, we reported that Syk mediates epidermal growth factor receptor (EGFR) signalling and plays a negative role in the terminal differentiation of keratinocytes. To understand whether Syk is a potential therapeutic target of cancer cells, we further elucidated the role of Syk in disease progression of squamous cell carcinoma (SCC), which is highly associated with EGFR overactivation, and determined the combined effects of Syk and PARP1 inhibitors on SCC viability. We found that pharmacological inhibition of Syk could attenuate the EGF-induced phosphorylation of EGFR, JNK, p38 MAPK, STAT1, and STAT3 in A431, CAL27 and SAS cells. In addition, EGF could induce a Syk-dependent IL-8 gene and protein expression in SCC. Confocal microscopic data demonstrated the ability of the Syk inhibitor to change the subcellular distribution patterns of EGFR after EGF treatment in A431 and SAS cells. Moreover, according to Kaplan-Meier survival curve analysis, higher Syk expression is correlated with poorer patient survival rate and prognosis. Notably, both Syk and EGFR inhibitors could induce PARP activation, and synergistic cytotoxic actions were observed in SCC cells upon the combined treatment of the PARP1 inhibitor olaparib with Syk or the EGFR inhibitor. Collectively, we reported Syk as an important signalling molecule downstream of EGFR that plays crucial roles in SCC development. Combining Syk and PARP inhibition may represent an alternative therapeutic strategy for treating SCC.

Psoriasis is a common non-contagious chronic inflammatory skin lesion, with frequent recurrence. It mainly occurs due to aberrant regulation of the immune system leading to abnormal proliferation of skin cells. However, the pathogenic mechanisms of psoriasis are not fully understood. Although most of the current therapies are mostly efficient, the side effects can result in therapy stop, which makes the effectiveness of treatment strategies limited. Therefore, it is urgent and necessary to develop novel therapeutics. Here, we investigated the efficacy of chrysin, a plant flavonoid, which we previously reported to possess strong antioxidant and anti-inflammatory effects, against psoriasis-like inflammation. Our results revealed that chrysin significantly attenuated imiquimod-induced psoriasis-like skin lesions in mice, and improved imiquimod-induced disruption of skin barrier. Moreover, the TNF-α, IL-17A, and IL-22-induced phosphorylation of MAPK and JAK-STAT pathways, and activation of the NF-κB pathway were also attenuated by chrysin pretreatment of epidermal keratinocytes. Most importantly, chrysin reduced TNF-α-, IL-17A-, and IL-22-induced CCL20 and antimicrobial peptide release from epidermal keratinocytes. Thus, our findings indicate that chrysin may have therapeutic potential against inflammatory skin diseases. Our study provides a basis for further investigating chrysin as a novel pharmacologic agent and contributes to the academic advancement in the field of Chinese herbal medicine.

Background Galectin-3 is widely expressed in many immunocytes and epithelial cells including skin keratinocytes. Galectin-3 can regulate immunological or inflammatory processes and plays a proinflammatory role in some disease models. Galectin-3 has a role in disorders related to ultraviolet (UV) photodamage such as apoptosis, skin squamous cell carcinoma and basal cell carcinoma. However, the evidence of galectin-3 in UVB-induced skin inflammation is still limited and the underlying molecular mechanism remains elusive. Objective We aimed to investigate the effects of galectin-3 in human epidermal keratinocytes and in mice after UVB irradiation. Methods Primary human epidermal keratinocytes with galectin-3 knockdown were used as the in vitro model. ELISA, QPCR, and western blotting were applied to evaluate the released cytokine, mRNA and protein expression. Histologic analysis, measurement of erythema and transepidermal water loss (TEWL) were applied to evaluate UVB-induced skin damage in galectin-3 knockout mice. Results In UVB-irradiated human keratinocytes, galectin-3 knockdown downregulated the UVB-induced ASC crosslinking, cleavage of caspase-1, and formation of active IL-1β. Galectin-3 knockdown also decreased UVB-induced production of reactive oxygen species, p38 phosphorylation, and COX2 expression in human keratinocytes. After four days of UVB irradiation, galectin-3 knockout mice showed reduced gross erythema, histologic features of tissue inflammation, quantified levels of erythema and TEWL compared to wild type mice. The skin tissue lysate also showed less expression of active IL-1β and COX2 in galectin-3 knockout mice. Conclusion Galectin-3 may play a positive regulatory role in UVB-induced skin inflammation.

Melanoma represents less than 5% of skin cancers, but is the most lethal, mainly because of its high-metastatic potential and resistance to various therapies. Therefore, it is important to develop effective treatments, especially chemotherapeutic drugs with cytotoxicity, anti-metastaticity, and few side effects. One such natural product is hispidulin, a flavone distributed in plants of the Asteraceae. Previous studies have demonstrated that hispidulin has various pharmacological benefits, such as anti-tumor, anti-inflammation, and anti-allergic effects. This study aims to explore the effects of hispidulin against melanoma in vitro and in vivo. Results revealed that hispidulin selectively decreased the cell viability of A2058 cells in a dose- and time-dependent manner. Hispidulin induced cells accumulated in the sub-G1 phase via activating caspase 8 and 9, increased cleaved caspase 3, and cleaved PARP expression. Hispidulin was able to decrease AKT and ERK phosphorylation, which facilitated cell growth and survival. Moreover, hispidulin promoted reactive oxygen species generation in cells and suppressed cell migration through downregulated matrix metalloproteinase-2 expression. Hispidulin significantly inhibited tumor growth in a xenograft model. Based on these results, hispidulin produces its anti-melanoma effects by inducing cancer cell apoptosis and reducing its migration. Therefore, we suggest hispidulin as a potent therapeutic candidate for melanoma treatment.

Solar ultraviolet (UV) light has been recognized as the important environmental hazard and contributes to diverse skin damage such as cell death, photoageing and even carcinogenesis. Revelation of harmful responses attributed to UVA radiation has promoted the development of photoprotective agents against UVA-induced skin damage. In the present study, we tried to evaluate the potential protective effects of a synthetic green fluorescent protein (GFP) chromophore derivative, 4-chlorobenzyldene-1, 2-dimethylimidazolinone (Cl-BDI, called TC-22) on UVA- and UVB- induced stress responses in skin. The HaCaT keratinocytes were used to evaluate the cellular effects. Zebrafish (Danio rerio), which is regarded as a useful and cost-effective alternative to some mammalian models, was applied as the in vivo animal model. In HaCaT keratinocytes, TC-22 was able to obviously decrease UVA-induced cell death. Dissection of the UVA-induced signalling pathways revealed that TC-22 could suppress the activation of JNK and caspase 3, but not of ERK and p38. Reduction of UVA-induced cleavage of caspase 3 and sub-G1 phase accumulation by pretreatment of TC-22 was also observed. In zebrafish, we showed that UVA irradiation could decrease the survival and hatching rate, suppress heart beats of embryos and enhance the pigmentation of larvae. Pretreatment of TC-22 could significantly reverse UVA-induced the suppression in hatching of eggs and heart beating of embryos and also lowered the UVA-induced pigmentation in zebrafish. Collectively, we demonstrate that TC-22, a GFP chromophore derivative, can ameliorate the UVA-induced stress responses in both epidermal keratinocytes and zebrafish, suggesting the potential use of TC-22 in photoprotection in the future.

Ethnopharmacological relevance Numerous epidemiological and clinical studies have demonstrated the protective role of dietary isoflavones against development of several chronic diseases. ISO-1, one fraction of isoflavone powders derived from soybean cake, is reported to attenuate inflammation and photodamage. Aim of the study Contact dermatitis is a common inflammatory skin disease, which accounts for most occupational skin disorders. Instead of oral administration, we aimed to explore the effects of topical ISO-1 application on contact dermatitis by using 2,4-dinitrochlorobenzene (DNCB)-stimulated HaCaT keratinocytes and DNCB-induced mouse dermatitis as models. Materials and methods In the in vitro study, we first evaluated the biologic effects of DNCB on HaCaT keratinocytes. HaCaT keratinocytes were treated with 2,4-dinitrochlorobenzene (DNCB), and cell viability was measured by MTT assay. Then, we detect the prominent induction of IL-8 mRNA expression after DNCB and ISO-1 treatment by reverse transcription polymerase chain reaction (RT-PCR), and release of IL-8 from HaCaT keratinocytes was measured by ELISA assay. HaCaT keratinocytes were pretreated with ISO-1 and then treated with DNCB, phosphorylation of JNK, p38, ERK and IκBα was analyzed by western blot. In the in vivo study, the hairless mice were used for an induced contact dermatitis model. The surface changes in the dorsal skin after DNCB and ISO-1 treatment were recorded using photography, and TEWL, erythema were measured using an MPA-580 cutometer. Blood was also collected from mice for measurement of white blood cell counts. Results Results showed ISO-1 inhibited DNCB-induced IL-8 production and also suppressed DNCB-induced phosphorylation of JNK and p38, and IκBα in HaCaT. In the animal model of DNCB-induced contact dermatitis, topical ISO-1 treatment significantly decreased DNCB-induced erythema and transepidermal water loss (TEWL) in mouse skin. ISO-1 also reduced DNCB-induced skin thickening and increase of white blood cell count. Conclusions ISO-1 is promising for improvement of DNCB-induced inflammation and skin barrier impairment, suggesting the potential application of topical ISO-1 for inflammatory dermatoses.

Psoriasis is a common inflammatory disease. It affects 1–3% of the population worldwide and is associated with increasing medical costs every year. Typical psoriatic skin lesions are reddish, thick, scaly plaques that can occur on multiple skin sites all over the body. Topical application of imiquimod (IMQ), a toll-like receptor (TLR)7 agonist and potent immune system activator, can induce and exacerbate psoriasis. Previous studies have demonstrated that isoflavone extract has an antioxidant effect which may help decrease inflammation and inflammatory pain. Through in vivo studies in mice, we found that the topical application to the shaved back and right ear of mice of isoflavone extract prior to IMQ treatment significantly decreased trans-epidermal water loss (TEWL), erythema, blood flow speed, and ear thickness, while it increased surface skin hydration, and attenuated epidermal hyperplasia and inflammatory cell infiltration. Through in vitro experiments, we found that isoflavone extract can reduce IL-22, IL-17A, and TNF-α-induced MAPK, NF-κB, and JAK-STAT activation in normal human epidermal keratinocytes. At the mRNA level, we determined that isoflavone extract attenuated the increased response of the TNF-α-, IL-17A-, and IL-22- related pathways. These results indicate that isoflavone extract has great potential as an anti-psoriatic agent and in the treatment of other inflammatory skin diseases.

Background B lymphocyte-induced maturation protein-1 (BLIMP1) is a transcriptional repressor, and plays a crucial role in the regulation of development and functions of various immune cells. Currently, there is limited understanding about the regulation of BLIMP1 expression in keratinocytes and crosstalk between EGFR and BLIMP1 in skin homeostasis. Objective The aim of the study was to investigate the regulation and functional link between EGFR and BLIMP1 in human epidermal keratinocytes. Methods Immunoblotting and Q-PCR were used to determine the molecular mechanism of BLIMP1 expression induced by EGFR in primary human epidermal keratinocytes (NHEK) and HaCaT cells. In functional assay, effects of BLIMP1 knockdown on EGFR-mediated cytokine production, differentiation, and migration in NHEK were evaluated by Q-PCR, ELISA, immunoblotting, and/or wound-healing assay. Results EGFR activation by EGFR ligands could upregulate the protein and mRNA levels of BLIMP1 in NHEK and HaCaT cells. This effect was dependent on PKC, p38, and ERK activation. Additionally, the stability of BLIMP1 protein was under the control of the proteasome and lysosome degradation systems. EGF could also upregulate BLIMP1 expression in skin squamous cell carcinomas. In addition, BLIMP1 knockdown enhanced the EGFR-mediated IL8, CXCL5 and IL6 gene expression and keratinocyte migration, but reduced the EGFR-mediated suppression of differentiation marker K10. Conclusions Our findings shed new insights into the regulation of BLIMP1 expression by EGFR-mediated gene transcription and proteasome/lysosome-mediated degradation in keratinocytes. Functionally, BLIMP1 is a negative regulator of EGF-induced inflammation and migration in keratinocytes, and exerts a gene-specific regulation on keratinocyte differentiation.

Diverse nanoparticles have been widely applied in different fields, including industries and biomedical sciences. Recent developments in nanotechnology have broadened the potential applications of nanotechnology in clinical diagnosis and medical therapy of malignant and non-malignant diseases. Gold nanoparticles (AuNPs) have been reported to possess unique physico-chemical properties; they have been investigated in studies on tumor growth and metastasis. Here, we explored the possible pharmacological functions of AuNPs on the mouse melanoma cell line, B16F10. We demonstrated that AuNPs of sizes 1–3, 3–5, and 10–15 nm exerted dose-dependent cytotoxic effects after 72-h treatments. AuNPs (4 and 10 ppm) of 1–3 and 3–5 nm were more cytotoxic than those of 10–15 nm. However, AuNPs of 1–3 nm were more cytotoxic against benign HaCaT keratinocytes than those of 3–5 nm. Thus, 4 ppm of AuNPs of 3–5 nm was considered relatively safe and an ideal candidate for this study. Further investigations revealed that AuNPs could induce sub-G1 phase accumulation, cleavage of caspase-3 and poly-(ADP-ribose) polymerase, and activation of JNK/p38. The expression of pro-apoptotic protein, Bax, was also induced. Furthermore, platelet-derived growth factor BB-induced migration and motility of melanoma cells were reduced after pretreatment with AuNPs of 3–5 nm. Adhesion assay showed that AuNPs of 3–5 nm could significantly suppress the adhesion of melanoma cells to collagen. In summary, AuNPs of 3–5 nm might be potential anti-tumor agents, as they were selectively cytotoxic against and inhibited motility of melanoma cells.

Ultraviolet (UV) radiation, particularly ultraviolet A (UVA), is known to play a major role in photoaging of the human skin. Many studies have demonstrated that UV exposure causes the skin cells to generate reactive oxygen species and activates the mitogen-activated protein kinase (MAPK) pathway. Previous studies have also demonstrated that cycloheterophyllin has an antioxidant effect and can effectively scavenge free radicals. Extending the aforementioned investigations, in this study, human dermal fibroblasts were used to investigate the protective effect of cycloheterophyllin against UV-induced damage. We found that cycloheterophyllin not only significantly increased cell viability, but also attenuated the phosphorylation of MAPK after UVA exposure. Furthermore, cycloheterophyllin could reduce hydrogen peroxide (H2O2) generation and down-regulate H2O2-induced MAPK phosphorylation. In the in vivo studies, the topical application of cycloheterophyllin before UVA irradiation significantly decreased trans-epidermal water loss (TEWL), erythema, and blood flow rate. These results indicate that cycloheterophyllin is a photoprotective agent that inhibits UVA-induced oxidative stress and damage, and could be used in the research on and prevention of skin photoaging.

Licorice (Glycyrrhiza) species have been widely used as a traditional medicine and a natural sweetener in foods. The 18β-glycyrrhetinic acid (18β-GA) is a bioactive compound in licorice that exhibits potential anti-cancer, anti-inflammatory, and anti-microbial activities. Many synthesized derivatives of 18β-GA have been reported to be cytotoxic and suggested for the treatment of malignant diseases. In this study, we explored the possible pharmacological roles of an 18β-GA derivative in skin biology using primary human dermal fibroblasts and HaCaT keratinocytes as cell models. We found that this 18β-GA derivative did not cause cell death, but significantly enhanced the proliferation of dermal fibroblasts and HaCaT keratinocytes. A scratch wound healing assay revealed that the 18β-GA derivative promoted the migration of fibroblasts. Due to the important role of aquaporin-3 in cell migration and proliferation, we also investigated the expression of aquaporin-3 and found this compound up-regulated the expression of aquaporin-3 in dermal fibroblasts and HaCaT keratinocytes. In dermal fibroblasts, the 18β-GA derivative induced the phosphorylation of Akt, ERK, and p38. The inhibitor of Akt predominantly suppressed the 18β-GA derivative-induced expression of aquaporin-3. Collectively, this compound had a positive effect on the proliferation, migration, and aquaporin-3 expression of skin cells, implying its potential role in the treatment of skin diseases characterized by impaired wound healing or dermal defects.

Spleen tyrosine kinase (Syk), a nonreceptor tyrosine kinase, was initially identified as a crucial regulator in proximal immunoreceptor signaling. Additional studies have revealed its pleiotropic roles, and drugs targeting Syk are under development for inflammatory diseases. Syk expression in the skin has been detected, but its functions in the skin are still unknown. Here, we found that Syk phosphorylation and expression in primary human keratinocytes decreased gradually along with terminal differentiation. Human skin specimens showed similar in vivo patterns. Syk inhibitors or knockdown of Syk increased the expression of differentiation markers under in vitro differentiation models. Furthermore, EGFR activation prominently induced Syk phosphorylation, which could be inhibited by the EGFR inhibitor gefitinib or knockdown of EGFR. The Src inhibitor also partially attenuated EGF-induced phosphorylation of Syk. However, Syk inhibition suppressed EGF-induced phosphorylation of EGFR. Immunoprecipitation and confocal microscopy further revealed the increased molecular interaction between EGFR and Syk after EGF stimulation. This study unravels the role of Syk in EGFR-mediated signaling and reveals regulatory roles of Syk in keratinocyte differentiation, suggesting the clinical potential of topical or systemic Syk inhibitors in the treatment of skin diseases with aberrant differentiation.