An ErbB receptor-mediated AP-1 regulatory network is modulated by STAT3 and c-MYC during calcium-dependent keratinocyte differentiation

Epidermal growth factor receptor-dependent stimulation of differentiation by human papillomavirus type 16 E5

Human papillomaviruses (HPVs) infect keratinocytes of stratified squamous epithelia, and persistent infection with high-risk HPV types, such as HPV16, may lead to the development of malignancies. HPV evades host immunity in part by linking its gene expression to the host differentiation program, and therefore relies on differentiation to complete its life cycle. Based on previous reports indicating that the HPV16 protein E5 is important in the late stages of the differentiation-dependent life cycle, we found that organotypic cultures harboring HPV16 genomes lacking E5 showed reduced markers of terminal differentiation compared to wild type HPV16-containing cultures. We found that epidermal growth factor receptor (EGFR) levels and activation were increased in an E5-depdendent manner in these tissues, and that EGFR promoted terminal differentiation and expression of the HPV16 L1 gene. These findings suggest a function for E5 in preserving the ability of HPV16 containing keratinocytes to differentiate, thus facilitating the production of new virus progeny.

The Desmosome-Keratin Scaffold Integrates ErbB Family and Mechanical Signaling to Polarize Epidermal Structure and Function

While classic cadherin-actin connections in adherens junctions (AJs) have ancient origins, intermediate filament (IF) linkages with desmosomal cadherins arose in vertebrate organisms. In this mini-review, we discuss how overlaying the IF-desmosome network onto the existing cadherin-actin network provided new opportunities to coordinate tissue mechanics with the positioning and function of chemical signaling mediators in the ErbB family of receptor tyrosine kinases. We focus in particular on the complex multi-layered outer covering of the skin, the epidermis, which serves essential barrier and stress sensing/responding functions in terrestrial vertebrates. We will review emerging data showing that desmosome-IF connections, AJ-actin interactions, ErbB family members, and membrane tension are all polarized across the multiple layers of the regenerating epidermis. Importantly, their integration generates differentiation-specific roles in each layer of the epidermis that dictate the form and function of the tissue. In the basal layer, the onset of the differentiation-specific desmosomal cadherin desmoglein 1 (Dsg1) dials down EGFR signaling while working with classic cadherins to remodel cortical actin cytoskeleton and decrease membrane tension to promote cell delamination. In the upper layers, Dsg1 and E-cadherin cooperate to maintain high tension and tune EGFR and ErbB2 activity to create the essential tight junction barrier. Our final outlook discusses the emerging appreciation that the desmosome-IF scaffold not only creates the architecture required for skin's physical barrier but also creates an immune barrier that keeps inflammation in check.

STAT3 maintains skin barrier integrity by modulating SPINK5 and KLK5 expression in keratinocytes

Skin barrier dysfunction induces skin inflammation. Signal transducer and activator of transcription 3 (STAT3) is known to be involved in Th17-mediated immune responses and barrier integrity in the cornea and intestine; however, its role in the skin barrier remains largely unknown. In this study, we elucidated the potential role of STAT3 in the skin barrier and its effect on kallikrein-related peptidase 5 (KLK5) and serine protease inhibitor Kazal-type 5 (SPINK5) expression using a mouse model with keratinocyte-specific ablation of STAT3. Keratinocyte-specific loss of STAT3 induced a cutaneous inflammatory phenotype with pruritus and intense scratching behaviour in mice. Transcriptomic analysis revealed that the genes associated with impaired skin barrier function, including KLK5, were upregulated. The effect of STAT3 on KLK5 expression in keratinocytes was not only substantiated by the increase in KLK5 expression following treatment with STAT3 siRNA but also by its decreased expression following STAT3 overexpression. Overexpression and IL-17A-mediated stimulation of STAT3 increased the expression of SPINK5, which was blocked by STAT3 siRNA. These results suggest that the expression of SPINK5 and KLK5 in keratinocytes could be dependent on STAT3 and that STAT3 might play an essential role in the maintenance of skin barrier homeostasis.

Integrin α3β1 Is a Key Regulator of Several Protumorigenic Pathways during Skin Carcinogenesis

Integrin α3β1 plays a crucial role in tumor formation in the two-stage chemical carcinogenesis model (DMBA and TPA treatment). However, the mechanisms whereby the expression of α3β1 influences key oncogenic drivers of this established model are not known yet. Using an in vivo mouse model with epidermal deletion of α3β1 and in vitro Matrigel cultures of transformed keratinocytes, we demonstrate the central role of α3β1 in promoting the activation of several protumorigenic signaling pathways during the initiation of DMBA/TPA‒driven tumorigenesis. In transformed keratinocytes, α3β1-mediated focal adhesion kinase/Src activation leads to in vitro growth of spheroids and to strong Akt and STAT 3 activation when the α3β1-binding partner tetraspanin CD151 is present to stabilize cell‒cell adhesion and promote Smad2 phosphorylation. Remarkably, α3β1 and CD151 can support Akt and STAT 3 activity independently of α3β1 ligation by laminin-332 and as such control the essential survival signals required for suprabasal keratin-10 expression during keratinocyte differentiation. These data demonstrate that α3β1 together with CD151 regulate the signaling pathways that control the survival of differentiating keratinocytes and provide a mechanistic understanding of the essential role of α3β1 in early stages of skin cancer development.

Emerging Laminin-332‒Dependent and ‒Independent Roles for Integrin α3 in Protumorigenic Signaling

The epidermal integrin α3β1 promotes skin tumorigenesis in experimental models; yet, the underlying molecular mechanisms remain mostly unclear. In their article, Ramovs et al. (2020a) identify two spatially separated α3β1-dependent signaling branches fostering skin tumor outgrowth. In basal keratinocytes, α3β1/laminin (LN)-332 drives FAK/Src activation, whereas in suprabasal layers, junctional α3β1 and the tetraspanin CD151 mediate signal transducer and protein kinase B (Akt)‒dependent survival that is independent of LN-332 binding.

Immunohistochemical study of janus kinase 1/signal transducer and activator of transcription 3 in psoriasis vulgaris

Background: Human JAKs are responsible for generating docking sites for human SSTAT phosphorylation. The role of JAKs in psoriasis pathogenesis has not been clearly explained. Aim: To investigate the role of JAK1 in psoriasis pathogenesis and to assess if this role is mediated through STAT3 or not, through evaluation of their immunohistochemical expression in the skin of psoriatic patients. Methods: This case-control study was carried out on 26 patients presenting with psoriasis vulgaris versus 26 age- and sex-matched apparently healthy volunteers. Psoriasis Area and Severity Index (PASI) scores were used to evaluate psoriasis severity. From all controls and cases (lesional and perilesional), skin biopsies were taken for histopathological and immunohistochemical JAK1 and STAT3 evaluation. Results: There was significant stepwise upregulation of JAK1 from controls to perilesional to lesional psoriatic skin of the patient group in both epidermis and dermis (P≤0.001 for both). Dermal JAK1 H-score was significantly associated with psoriasis severity (P=0.01). STAT3 was significantly overexpressed in lesional psoriatic skin over nonlesional skin (P<0.001). There were significant positive correlations between lesional H-scores for STAT3 and Psoriasis Area and Severity Index scores in epidermis (r=0.63, P<0.001), and in dermis (r=0.47, P=0.04). There was a significant positive correlation between JAK1 and STAT3 expression in epidermal lesional psoriatic skin (r=0.44, P=0.03). Conclusion: JAK1 has a proinflammatory effect in psoriasis pathogenesis, which could be mediated through increasing STAT3 expression in psoriasis. JAK1 and STAT3 tissue expression could be markers of psoriasis severity. JAK1 may be used as a target for immunotherapy in psoriasis-management programs.

Exosomes Released from Tumor-Associated Macrophages Transfer miRNAs That Induce a Treg/Th17 Cell Imbalance in Epithelial Ovarian Cancer

The immune microenvironment is crucial for epithelial ovarian cancer (EOC) progression and consists of tumor-associated macrophages (TAM) and T lymphocytes, such as regulatory T cells (Treg) and T helper 17 (Th17) cells. In this study, the Treg/Th17 ratio was significantly higher in EOC in situ and in metastatic peritoneal tissues than in benign ovarian tumors and benign peritoneum. The Treg/Th17 ratio was associated with histologic grade and was an independent prognostic factor for overall survival of EOC patients. On the basis of microarray analysis of exosomes derived from TAMs, we identified miRNAs enriched in the exosomes, including miR-29a-3p and miR-21-5p. When the two miRNA mimics were transfected into CD4⁺ T cells, they directly suppressed STAT3 and regulated Treg/Th17 cells, inducing an imbalance, and they had a synergistic effect on STAT3 inhibition. Taken together, these results indicate that exosomes mediate the interaction between TAMs and T cells, generating an immune-suppressive microenvironment that facilitates EOC progression and metastasis. These findings suggest that targeting these exosomes or their associated miRNAs might pave the way for the development of novel treatments for EOC.

SIRT2 as a new player in epigenetic programming of keratinocyte differentiation and a candidate tumor suppressor

Epidermal keratinocytes undergo a continuous process of terminal differentiation, which is accompanied by a dramatic change in the expression and composition of keratins. This complex and carefully orchestrated process is regulated by a large number of signal transduction events and transcriptional factors as well as by epigenetic regulatory mechanisms, namely by histone methylation/acetylation and DNA methylation. In a recent issue of Exp Dermatol, Ming et al. provide evidence that sirtuin-2 (SIRT2), a NAD+-dependent deacetylase, inhibits the expression of keratin 15 and keratin 19, epidermal stem cell markers, while it stimulates the expression of loricrin, a marker of terminal keratinocyte differentiation. Human skin cancer cells show downregulation of SIRT2, and its deletion increases tumor growth in mice. Overall, these findings suggest that this deacetylase is involved in the epigenetic regulation of keratinocyte differentiation and exerts intracutaneous tumor suppressor functions.

Genetic Network Inference Using Hierarchical Structure

Many methods for inferring genetic networks have been proposed, but the regulations they infer often include false-positives. Several researchers have attempted to reduce these erroneous regulations by proposing the use of a priori knowledge about the properties of genetic networks such as their sparseness, scale-free structure, and so on. This study focuses on another piece of a priori knowledge, namely, that biochemical networks exhibit hierarchical structures. Based on this idea, we propose an inference approach that uses the hierarchical structure in a target genetic network. To obtain a reasonable hierarchical structure, the first step of the proposed approach is to infer multiple genetic networks from the observed gene expression data. We take this step using an existing method that combines a genetic network inference method with a bootstrap method. The next step is to extract a hierarchical structure from the inferred networks that is consistent with most of the networks. Third, we use the hierarchical structure obtained to assign confidence values to all candidate regulations. Numerical experiments are also performed to demonstrate the effectiveness of using the hierarchical structure in the genetic network inference. The improvement accomplished by the use of the hierarchical structure is small. However, the hierarchical structure could be used to improve the performances of many existing inference methods.

Six1 overexpression at early stages of HPV16-mediated transformation of human keratinocytes promotes differentiation resistance and EMT

Previous studies in our laboratory discovered that SIX1 mRNA expression increased during in vitro progression of HPV16-immortalized human keratinocytes (HKc/HPV16) toward a differentiation-resistant (HKc/DR) phenotype. In this study, we explored the role of Six1 at early stages of HPV16-mediated transformation by overexpressing Six1 in HKc/HPV16. We found that Six1 overexpression in HKc/HPV16 increased cell proliferation and promoted cell migration and invasion by inducing epithelial-mesenchymal transition (EMT). Moreover, the overexpression of Six1 in HKc/HPV16 resulted in resistance to serum and calcium-induced differentiation, which is the hallmark of the HKc/DR phenotype. Activation of MAPK in HKc/HPV16 overexpressing Six1 is linked to resistance to calcium-induced differentiation. In conclusion, this study determined that Six1 overexpression resulted in differentiation resistance and promoted EMT at early stages of HPV16-mediated transformation of human keratinocytes.

Ligand-independent epidermal growth factor receptor hyperactivation increases sebaceous gland size and sebum secretion in mice

The epidermal growth factor receptor (EGFR) system is an established regulator of the development and homeostasis of the hair follicle and interfollicular epidermis. Here, we evaluated EGFR actions on the sebaceous glands (SGs) by employing Dsk5 mice, a mutant line in which the EGFR is constitutively activated in a ligand-independent manner. Compared to control littermates, Dsk5 mice showed increased sebum levels and enlarged SGs, which contained a higher number of cells and showed stronger proliferation. c-myc transcript levels were increased in Dsk5 skin, suggesting that c-myc mediates the proliferative stimuli of the EGFR in the SG. Analysis of differentiation markers revealed deregulated expression of Scd1 and Scd3, indicating that sebaceous lipogenesis is affected in Dsk5 mice. In conclusion, our study indicates that the EGFR is an important regulator of presebocyte proliferation, contributing to the final cell number, to the size and to the lipid output of SGs.

Studies of Jak/STAT3 expression and signalling in psoriasis identifies STAT3-Ser727 phosphorylation as a modulator of transcriptional activity

Jak/Tyk proteins have recently aroused as possible therapeutic targets for the treatment of psoriasis. In psoriasis, these proteins signal through STAT molecules including STAT3, and STAT3 expression and activation has been shown augmented in psoriatic lesions. Here, we characterized the expression of Jak/Tyk proteins in lesional compared with non-lesional psoriatic skin. Jak1, Jak2 mRNA and protein and Tyk2 mRNA appeared to be downregulated, whereas Jak3 mRNA expression was increased. Moreover, STAT3 expression and activation was examined in psoriasis. STAT3 is activated at two phosphorylation sites: Tyr705 and Ser727. Both phosphorylation sites were phosphorylated in lesional psoriatic skin. The activation of STAT3 by Jak/Tyk proteins was studied in cultured normal human keratinocytes. Tyr705 phosphorylation was induced by IL-6 and IL-20 in a Jak2-dependent manner, and moreover, phosphorylation of Tyr705 produced a strong increase in STAT3 transcriptional activity. TNFα, 12-O-Tetradecanoylphorbol 13-acetate (TPA) and UVB irradiation induced Ser727 phosphorylation of STAT3 in an ERK1/2- and p38 MAPK-dependent manner, which resulted in a modulatory effect on STAT3 transcriptional activity. Our results demonstrate how different signalling pathways can integrate and lead to regulation of STAT3 transcriptional activity.

Pulsed electric current induces the differentiation of human keratinocytes

Although normal human keratinocytes are known to migrate toward the cathode in a direct current (DC) electric field, other effects of the electric stimulation on keratinocyte activities are still unclear. We have investigated the keratinocyte differentiation under monodirectional pulsed electric stimulation which reduces the electrothermal and electrochemical hazards of a DC application. When cultured keratinocytes were exposed to the electric field of 3 V (ca. 100 mV/mm) or 5 V (ca. 166 mV/mm) at a frequency of 4,800 Hz for 5 min a day for 5 days, cell growth under the 5-V stimulation was significantly suppressed as compared with the control culture. Expression of mRNAs encoding keratinocyte differentiation markers such as keratin 10, involucrin, transglutaminase 1, and filaggrin was significantly increased in response to the 5-V stimulation, while the 3-V stimulation induced no significant change. After the 5-V stimulation, enhanced immunofluorescent stainings of involucrin and filaggrin were observed. These results indicate that monodirectional pulsed electric stimulation induces the keratinocyte differentiation with growth arrest.