PKC-delta and -eta, MEKK-1, MEK-6, MEK-3, and p38-delta are essential mediators of the response of normal human epidermal keratinocytes to differentiating agents

MCPIP3 orchestrates the balance of epidermal proliferation and differentiation

BACKGROUND

Monocyte chemoattractant protein-induced protein 3 (MCPIP3), also called Regnase-3 and encoded by the ZC3H12C gene, is a member of the MCPIP family of RNases. Previous studies showed that MCPIP1 in keratinocytes plays a pivotal role in the maintenance of skin integrity and immunological function. Given that the expression of MCPIP3, similar to that of MCPIP1, is increased in psoriatic lesions compared with uninvolved skin, a role of MCPIP3 in the regulation of keratinocyte and epidermal biology was hypothesized.

METHODS

This study aimed to investigate the specific function of the MCPIP3 protein in the skin. The expression pattern of MCPIP3 was studied in normal human epidermal keratinocytes (NHEKs) subjected to in vitro differentiation and upon stimulation with proinflammatory factors. Mice with keratinocyte-specific deletion of MCPIP3 (Mcpip3loxP/loxPKrt14Cre; MCPIP3EKO) were generated and characterized. The response of the skin of MCPIP3EKO mice to imiquimod (IMQ) and 12-O-tetradecanoylphorbol-13-acetate (TPA) was investigated. The expression levels of key modulators of keratinocyte proliferation and differentiation were measured in MCPIP3EKO model mice and in NHEKs transiently transfected with MCPIP3-specific siRNA. Reporter assays were used to identify direct targets of MCPIP3 nucleolytic activity.

RESULTS

In human keratinocytes, the expression of ZC3H12C/MCPIP3 was rapidly induced by stimulation with TPA, IL-17a, IL-36α, and TNF-α. Although mice with keratinocyte-specific deletion of MCPIP3 (MCPIP3EKO) did not develop skin inflammation, they displayed abnormalities in skin morphology. Stimulation with IMQ and TPA exacerbated epidermal hyperplasia caused by keratinocyte-specific deficiency of MCPIP3 and led to abnormal epidermal differentiation. The expression levels of keratinocyte proliferation and differentiation markers, such as keratin-14, cyclin B1, involucrin, and the S100 calcium-binding proteins S100A7/A9, were increased in NHEKs in which MCPIP3 expression was silenced. MCPIP3 negatively regulates the level of cyclin B1 mRNA via direct nucleolytic cleavage within its 3' untranslated region.

CONCLUSIONS

The MCPIP3 protein modulates the balance of keratinocyte proliferation and differentiation and functions as a regulator of epidermal morphology in vivo.

A Novel Immune-Related Three-Gene Signature and Immune Infiltration Insights in Psoriasis and Chronic Kidney Disease

Purpose

There are significant inflammatory correlations and common immune dysregulation features between psoriasis and chronic kidney disease, however, the inflammatory mechanisms of these two diseases have not been clarified. The aim of this study was to screen immunologically related biomarkers for psoriasis and chronic kidney disease with the objective of identifying specific molecular markers to improve the accuracy and sensitivity of disease diagnosis.

Patients and Methods

To achieve this objective, common differentially expressed genes between psoriasis and chronic kidney disease were first identified. Through further functional analysis, these genes were found to be primarily involved in the activation of inflammation and innate immune responses. Subsequently, six hub genes were determined using five topological algorithms. The responses of these two diseases exhibited similar changes in immune reactions. By cross-analyzing these key genes with known immune genes, three Immunity-Related Hub Genes (IRHGs) were identified, including MX1, DDX58, and ISG20.

Results

ROC curve analysis validated the excellent discriminative ability of MX1 and ISG20 in both diseases. Furthermore, immune infiltration analysis revealed a higher abundance of T cells in samples from both psoriasis and chronic kidney disease, suggesting that T cell-driven immune responses may play a crucial role in the association of these two diseases. Lastly, single-cell analysis observed a significant increase in the cell abundance of T cells and endothelial cells in psoriasis and chronic kidney disease, respectively. The differential expression of MX1, DDX58, and ISG20 in these cells suggests that they may be involved to varying degrees in the pathogenic mechanisms of the two diseases.

Conclusion

This study provides a theoretical foundation for prognosis assessment and treatment of psoriasis and chronic kidney disease, contributing to a deeper understanding of the immune mechanisms underlying these conditions.

The impact of signaling pathways on the desmosome ultrastructure in pemphigus

Introduction

The autoantibody-driven disease pemphigus vulgaris (PV) impairs desmosome adhesion in the epidermis. In desmosomes, the pemphigus autoantigens desmoglein 1 (Dsg1) and Dsg3 link adjacent cells. Dsgs are clustered by plaque proteins and linked to the keratin cytoskeleton by desmoplakin (Dp). The aim of this study was to identify the impact of several PV-related signaling pathways on desmosome ultrastructure.

Methods

STED microscopy, Dispase-based dissociation assay.

Results

As observed using STED microscopy, pemphigus autoantibodies (PV-IgG) reduced desmosome number, decreased desmosome size, increased plaque distance and thickness and caused loss of adhesion. Decreased desmosome number, increased plaque distance and thickness and loss of adhesion correlate with features found for newly assembled immature desmosomes, observed after Ca2+ depletion and repletion. This was paralleled by plaque asymmetry, keratin filament retraction and fragmentation of Dsg1 and Dsg3 immunostaining. Inhibition of each individual signaling pathway investigated here prevented the loss of adhesion and ameliorated keratin retraction. In addition, inhibition of p38MAPK or PLC completely rescued all parameters of desmosomes ultrastructure and increased desmosome number under basal conditions. In contrast, inhibition of MEK1/2 was only partially protective for desmosome size and plaque thickness, whereas inhibition of Src or increase of cAMP decreased desmosome size but increased the desmosome number even in the presence of PV-IgG.

Discussion

Alterations of the desmosomal plaque ultrastructure are closely related to loss of adhesion and regulated differently by signaling pathways involved in pemphigus pathogenesis. This insight may allow identification of novel treatment options targeting specific steps of desmosome turn-over in the future.

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.

Mesothelioma cancer cells are glutamine addicted and glutamine restriction reduces YAP1 signaling to attenuate tumor formation

Glutamine addiction is an important phenotype displayed in some types of cancer. In these cells, glutamine depletion results in a marked reduction in the aggressive cancer phenotype. Mesothelioma is an extremely aggressive disease that lacks effective therapy. In this study, we show that mesothelioma tumors are glutamine addicted suggesting that glutamine depletion may be a potential therapeutic strategy. We show that glutamine restriction, by removing glutamine from the medium or treatment with inhibitors that attenuate glutamine uptake (V-9302) or conversion to glutamate (CB-839), markedly reduces mesothelioma cell proliferation, spheroid formation, invasion, and migration. Inhibition of the SLC1A5 glutamine importer, by knockout or treatment with V-9302, an SLC1A5 inhibitor, also markedly reduces mesothelioma cell tumor growth. A relationship between glutamine utilization and YAP1/TEAD signaling has been demonstrated in other tumor types, and the YAP1/TEAD signaling cascade is active in mesothelioma cells and drives cell survival and proliferation. We therefore assessed the impact of glutamine depletion on YAP1/TEAD signaling. We show that glutamine restriction, SLC1A5 knockdown/knockout, or treatment with V-9302 or CB-839, reduces YAP1 level, YAP1/TEAD-dependent transcription, and YAP1/TEAD target protein (e.g., CTGF, cyclin D1, COL1A2, COL3A1, etc.) levels. These changes are observed in both cells and tumors. These findings indicate that mesothelioma is a glutamine addicted cancer, show that glutamine depletion attenuates YAP1/TEAD signaling and tumor growth, and suggest that glutamine restriction may be useful as a mesothelioma treatment strategy.

CDK9 activity switch associated with AFF1 and HEXIM1 controls differentiation initiation from epidermal progenitors

Progenitors in epithelial tissues, such as human skin epidermis, continuously make fate decisions between self-renewal and differentiation. Here we show that the Super Elongation Complex (SEC) controls progenitor fate decisions by directly suppressing a group of "rapid response" genes, which feature high enrichment of paused Pol II in the progenitor state and robust Pol II elongation in differentiation. SEC's repressive role is dependent on the AFF1 scaffold, but not AFF4. In the progenitor state, AFF1-SEC associates with the HEXIM1-containing inactive CDK9 to suppress these rapid-response genes. A key rapid-response SEC target is ATF3, which promotes the upregulation of differentiation-activating transcription factors (GRHL3, OVOL1, PRDM1, ZNF750) to advance terminal differentiation. SEC peptidomimetic inhibitors or PKC signaling activates CDK9 and rapidly induces these transcription factors within hours in keratinocytes. Thus, our data suggest that the activity switch of SEC-associated CDK9 underlies the initial processes bifurcating progenitor fates between self-renewal and differentiation.

Transglutaminase 2 enhances hepatocyte growth factor signaling to drive the mesothelioma cancer cell phenotype

Transglutaminase 2 (TG2) is an important mesothelioma cancer cell survival protein. However, the mechanism whereby TG2 maintains mesothelioma cell survival is not well understood. We present studies showing that TG2 drives hepatocyte growth factor (HGF)-dependent MET receptor signaling to maintain the aggressive mesothelioma cancer phenotype. TG2 increases HGF and MET messenger RNA and protein levels to enhance MET signaling. TG2 inactivation reduces MET tyrosine kinase activity to reduce cancer cell spheroid formation, invasion and migration. We also confirm that HGF/MET signaling is a biologically important mediator of TG2 action. Reducing MET level using genetic methods or treatment with MET inhibitors reduces spheroid formation, invasion and migration and this is associated with reduced MEK1/2 and ERK1/2. In addition, MEK1/2 and ERK1/2 inhibitors suppress the cancer phenotype. Moreover, MET knockout mesothelioma cells form 10-fold smaller tumors compared to wild-type cells and these tumors display reduced MET, MEK1/2, and ERK1/2 activity. These findings suggest that TG2 maintains HGF and MET levels in cultured mesothelioma cells and tumors to drive HGF/MET, MEK1/2, and ERK1/2 signaling to maintain the aggressive mesothelioma cancer phenotype.

Mammalian Epidermis: A Compendium of Lipid Functionality

Mammalian epidermis is a striking example of the role of lipids in tissue biology. In this stratified epithelium, highly specialized structures are formed that leverage the hydrophobic properties of lipids to form an impermeable barrier and protect the humid internal environment of the body from the dry outside. This is achieved through tightly regulated lipid synthesis that generates the molecular species unique to the tissue. Beyond their fundamental structural role, lipids are involved in the active protection of the body from external insults. Lipid species present on the surface of the body possess antimicrobial activity and directly contribute to shaping the commensal microbiota. Lipids belonging to a variety of classes are also involved in the signaling events that modulate the immune responses to environmental stress as well as differentiation of the epidermal keratinocytes themselves. Recently, high-resolution methods are beginning to provide evidence for the involvement of newly identified specific lipid molecules in the regulation of epidermal homeostasis. In this review we give an overview of the wide range of biological functions of mammalian epidermal lipids.

GRHL3 Promotes Tumor Growth and Metastasis via the MEK Pathway in Colorectal Cancer

GRHL3 is a factor associated with a tumor, of which the molecular mechanism remains a further investigation. We explored the underlying mechanism of tumor-promoting effect of GRHL3 in colorectal cancer (CRC), which is involved in the MEK1/2 pathway. The expression of GRHL3 was measured in CRC and adjacent normal tissue using qPCR and immunohistochemical staining. Lentivirus-mediated knockdown expression of GRHL3 was performed in the CRC cell line HT29. Cell proliferation and metastasis were assayed in vitro, and tumorigenicity was investigated in vivo. We found higher GRHL3 expression in colorectal cancer, which was negatively correlated with patients' prognosis. Results from studies in vitro and in vivo indicated that downregulation of GRHL3 expression inhibited tumor growth and metastasis and inhibited the activation of the MEK1/2 pathway. The effect of GRHL3 downexpression was the same as that of MEK1/2 antagonists on suppression of tumor growth and metastasis. Our results suggested that GRHL3 may act as an oncogene to promote tumor growth and metastasis via the MEK pathway in colorectal cancer.

ACTL6A suppresses p21Cip1 tumor suppressor expression to maintain an aggressive mesothelioma cancer cell phenotype

Mesothelioma is a poor prognosis cancer of the mesothelial lining that develops in response to exposure to various agents including asbestos. Actin-Like Protein 6A (ACTL6A, BAF53a) is a SWI/SNF regulatory complex protein that is elevated in cancer cells and has been implicated as a driver of cancer cell survival and tumor formation. In the present study, we show that ACTL6A drives mesothelioma cancer cell proliferation, spheroid formation, invasion, and migration, and that these activities are markedly attenuated by ACTL6A knockdown. ACTL6A expression reduces the levels of the p21^Cip1 cyclin-dependent kinase inhibitor and tumor suppressor protein. DNA binding studies show that ACTL6A interacts with Sp1 and p53 binding DNA response elements in the p21^Cip1 gene promoter and that this is associated with reduced p21^Cip1 promoter activity and p21^Cip1 mRNA and protein levels. Moreover, ACTL6A suppression of p21^Cip1 expression is required for maintenance of the aggressive mesothelioma cancer cell phenotype suggesting that p21^Cip1 is a mediator of ACTL6A action. p53, a known inducer of p21^Cip1 expression, is involved ACTL6A in regulation of p21^Cip1 in some but not all mesothelioma cells. In addition, ACTL6A knockout markedly reduces tumor formation and this is associated with elevated tumor levels of p21^Cip1. These findings suggest that ACTL6A suppresses p21^Cip1 promoter activity to reduce p21^Cip1 protein as a mechanism to maintain the aggressive mesothelioma cell phenotype.

Transglutaminase 2 Maintains Hepatocyte Growth Factor Signaling to Enhance the Cancer Cell Phenotype

Transglutaminase 2 (TG2) is a key epidermal squamous cell carcinoma cancer cell survival protein. However, how TG2 maintains the aggressive cancer phenotype is not well understood. The present studies show that TG2, which is highly expressed in epidermal cancer stem-like cells (ECS cells), maintains hepatocyte growth factor (HGF) signaling to drive an aggressive ECS cell cancer phenotype. Inhibiting TG2 reduces MET tyrosine kinase receptor expression and activity and attenuates the cancer cell phenotype. Moreover, inhibition of TG2 or HGF/MET function reduces downstream MEK1/2 and ERK1/2 activity, and this is associated with reduced cancer cell spheroid formation, invasion, and migration, and reduced stem and EMT marker expression. Treatment of TG2 knockdown cells with HGF partially restores the aggressive cancer phenotype, confirming that MET signaling is downstream of TG2. MET knockout reduces ERK1/2 signaling, doubles the time to initial tumor appearance, and reduces overall tumor growth. These findings suggest that TG2 maintains HGF/MET and MAPK (MEK1/2 and ERK1/2) signaling to drive the aggressive ECS cell cancer phenotype and tumor formation, and that TG2-dependent MET signaling may be a useful anti-cancer target. IMPLICATIONS: TG2 is an important epidermal squamous cell carcinoma stem cell survival protein. We show that TG2 activates an HGF/MET, MEK1/2 ERK1/2 signaling cascade that maintains the aggressive cancer phenotype.

VGLL4 inhibits YAP1/TEAD signaling to suppress the epidermal squamous cell carcinoma cancer phenotype

Epidermal squamous cell carcinoma (SCC) develops in response to ultraviolet light exposure and is among the most common cancers. The transglutaminase 2 cancer cell survival protein stimulates the activity of the YAP1/TEAD transcription complex to drive the expression of genes that promote aggressive epidermal SCC cell invasion, migration, and tumor formation. Therefore, we are interested in mechanisms that may inhibit these events. Vestigial-like protein-4 (VGLL4) is a transcription cofactor/tumor suppressor that inhibits several pro-cancer pathways including YAP1 signaling. Our present studies show that VGLL4 inhibits YAP1/TEAD-dependent transcription to reduce the expression of YAP1 target genes (CCND1, CYR61, and CTGF) and pro-cancer collagen genes (COL1A2 and COL3A1). We further show that loss of these YAP1 regulated genes is required for VGLL4 suppression of the cancer cell phenotype, as forced CCND1 or COL1A2 expression partially restores the aggressive cancer phenotype in VGLL4 expressing cells. Consistent with these findings, VGLL4 expression reduces tumor formation, and this is associated with reduced CCND1, CYR61, CTGF, COL1A2, and COL1A3 mRNA and protein levels, and reduced EMT marker expression. These findings indicate that VGLL4 suppresses the malignant epidermal SCC cancer phenotype by inhibiting YAP1/TEAD-dependent pro-cancer signaling.

Sulforaphane inhibits PRMT5 and MEP50 function to suppress the mesothelioma cancer cell phenotype

Mesothelioma is a highly aggressive cancer of the mesothelial lining that is caused by exposure to asbestos. Surgical resection followed by chemotherapy is the current treatment strategy, but this is marginally successful and leads to drug-resistant disease. We are interested in factors that maintain the aggressive mesothelioma cancer phenotype as therapy targets. Protein arginine methyltransferase 5 (PRMT5) functions in concert with the methylosome protein 50 (MEP50) cofactor to catalyze symmetric dimethylation of key arginine resides in histones 3 and 4 which modifies the chromatin environment to alter tumor suppressor and oncogene expression and enhance cancer cell survival. Our studies show that PRMT5 or MEP50 loss reduces H4R3me2s formation and that this is associated with reduced cancer cell spheroid formation, invasion, and migration. Treatment with sulforaphane (SFN), a diet-derived anticancer agent, reduces PRMT5/MEP50 level and H4R3me2s formation and suppresses the cancer phenotype. We further show that SFN treatment reduces PRMT5 and MEP50 levels and that this reduction is required for SFN suppression of the cancer phenotype. SFN treatment also reduces tumor formation which is associated with reduced PRMT5/MEP50 expression and activity. These findings suggest that SFN may be a useful mesothelioma treatment agent that operates, at least in part, via suppression of PRMT5/MEP50 function.

Effects of Aloe vera Flower Extract and Its Active Constituent Isoorientin on Skin Moisturization via Regulating Involucrin Expression: In Vitro and Molecular Docking Studies

Skin moisturization is very crucial for maintaining the flexibility, viscoelasticity, and differentiation of the epidermis and its deprivation causes several diseases from dry skin to dermatitis. Aloe vera, a miracle plant having diverse medicinal properties including skin moisturization effects. This study investigated for the first time the molecular mechanism targeting skin moisturization effects of the Aloe vera flower and its major active constituent. By treating human epidermal keratinocytes (HaCaT cells) with Aloe vera flower water extract (AFWE), we found that AFWE upregulated epidermal involucrin by activating the expression of protein kinase C, p38, and ERK 1/2. Additionally, it modulated filaggrin, increased aquaporin expression, and hyaluronan synthesis via a balanced regulation of HAS1 and HYAL1 protein. Similarly, it was able to protect UVB-induced photodamage. Western blot analysis, ELISA, and qRT- PCR were performed to evaluate various epidermal differentiation markers and moisturization-related factors on human epidermal keratinocytes (HaCaT cells). TLC and HPLC were used to detect and analyze the chemical constituents. Among them, we found that an active component of Aloe vera flower, isoorientin (IO) has a high binding affinity to all of its targeted proteins such as involucrin, PKC, P38, etc. through molecular docking assay. This study indicated that the Aloe vera flower and its active constituent, IO can be used as a prominent ingredient to enhance skin barrier function and improve its related pathologies.

ACTL6A suppresses p21Cip1 expression to enhance the epidermal squamous cell carcinoma phenotype

Epidermal squamous cell carcinoma (SCC) is a common and highly invasive form of cancer. SCC arises due to ultraviolet light exposure and is associated with increased expression of pro-cancer genes and reduced expression of cancer suppressors. Actin-Like Protein 6A (ACTL6A, BAF53a) is an important protein subunit of the SWI/SNF epigenetic chromatin regulatory complex. ACTL6A is elevated in cancer cells and has been implicated as a driver of cancer cell proliferation and tumor growth. In the present study, we show that ACTL6A drives SCC cell proliferation, spheroid formation, invasion and migration, and that these activities are markedly reduced by ACTL6A knockdown. We further show that ACTL6A expression is associated with reduced levels of the p21^Cip1 cyclin-dependent kinase inhibitor and tumor suppressor protein. Molecular studies show that ACTL6A interacts with p53 DNA response elements in the p21^Cip1 gene promoter to suppress p21^Cip1 promoter activity and mRNA and protein level. Additional studies show that an increase in p21^Cip1 expression in ACTL6A knockdown cells is required for suppression of the SCC cell phenotype, suggesting that p21^Cip1 is a mediator of ACTL6A action. We further show that this regulation is p53 independent. These findings suggest that ACTL6A suppresses p21^Cip1 promoter activity to reduce p21^Cip1 protein as a mechanism to maintain the aggressive epidermal SCC phenotype.

Protein kinases involved in epidermal barrier formation: The AKT family and other animals

Formation of a stratified epidermis is required for the performance of the essential functions of the skin; to act as an outside-in barrier against the access of microorganisms and other external factors, to prevent loss of water and solutes via inside-out barrier functions and to withstand mechanical stresses. Epidermal barrier function is initiated during embryonic development and is then maintained throughout life and restored after injury. A variety of interrelated processes are required for the formation of a stratified epidermis, and how these processes are both temporally and spatially regulated has long been an aspect of dermatological research. In this review, we describe the roles of multiple protein kinases in the regulation of processes required for epidermal barrier formation.

T Cell Leukemia/Lymphoma 1A is essential for mouse epidermal keratinocytes proliferation promoted by insulin-like growth factor 1

T Cell Leukemia/Lymphoma 1A is expressed during B-cell differentiation and, when over-expressed, acts as an oncogene in mouse (Tcl1a) and human (TCL1A) B-cell chronic lymphocytic leukemia (B-CLL) and T-cell prolymphocytic leukemia (T-PLL). Furthermore, in the murine system Tcl1a is expressed in the ovary, testis and in pre-implantation embryos, where it plays an important role in blastomere proliferation and in embryonic stem cell (ESC) proliferation and self-renewal. We have also observed that Tcl1-/- adult mice exhibit alopecia and deep ulcerations. This finding has led us to investigate the role of TCL1 in mouse skin and hair follicles. We have found that TCL1 is expressed in the proliferative structure (i.e. the secondary hair germ) and in the stem cell niche (i.e. the bulge) of the hair follicle during regeneration phase and it is constitutively expressed in the basal layer of epidermis where it is required for the correct proliferative–differentiation program of the keratinocytes (KCs). Taking advantage of the murine models we have generated, including the Tcl1-/- and the K14-TCL1 transgenic mouse, we have analysed the function of TCL1 in mouse KCs and the molecular pathways involved. We provide evidence that in the epidermal compartment TCL1 has a role in the regulation of KC proliferation, differentiation, and apoptosis. In particular, the colony-forming efficiency (CFE) and the insulin-like growth factor 1 (IGF1)-induced proliferation are dramatically impaired, while apoptosis is increased, in KCs from Tcl1-/- mice when compared to WT. Moreover, the expression of differentiation markers such as cytokeratin 6 (KRT6), filaggrin (FLG) and involucrin (IVL) are profoundly altered in mutant mice (Tcl1-/-). Importantly, by over-expressing TCL1A in basal KCs of the K14-TCL1 transgenic mouse model, we observed a significant rescue of cell proliferation, differentiation and apoptosis of the mutant phenotype. Finally, we found TCL1 to act, at least in part, via increasing phospho-ERK1/2 and decreasing phospho-P38 MAPK. Hence, our data demonstrate that regulated levels of Tcl1a are necessary for the correct proliferation and differentiation of the interfollicular KCs.

Role of FGFR2b expression and signaling in keratinocyte differentiation: sequential involvement of PKCδ and PKCα

The tumor suppressor epithelial isoform of the fibroblast growth factor receptor 2 (FGFR2b) induces human keratinocyte early differentiation. Moreover, protein kinases C (PKCs) are known to regulate the differentiation program in several cellular contexts, including keratinocytes. Therefore, in this paper we propose to clarify if FGFR2b could play a role also in the late steps of keratinocyte differentiation and to assess if this receptor-induced process would sequentially involve PKCδ and PKCα isoforms. Immunofluorescence, biochemical, and molecular approaches, performed on 2D cultures or 3D organotypic rafts of human keratinocytes overexpressing FGFR2b by stable transduction, showed that receptor signaling induced the precocious onset and an accelerated progression of keratinocyte differentiation, indicating that FGFR2b is a crucial regulator of the entire program of keratinocyte differentiation. In addition, the use of specific inhibitors and gene silencing approaches through specific siRNA demonstrated that PKCδ controls the onset of FGFR2b-triggered differentiation, while PKCα plays a role restricted to the terminal stages of the process. Molecular analysis revealed that the two PKC isoforms sequentially act via induction of KLF4 and DLX3, two transcription factors linked by negative loops to p63, suggesting that p63 would represent the hub molecule at the crossroad of an intricate signaling network downstream FGFR2b, involving multiple PKC-induced transcription factors.

Threonine 454 phosphorylation in Grainyhead-like 3 is important for its function and regulation by the p38 MAPK pathway

The mammalian Grainyhead-like 3 (GRHL3) transcription factor is essential for epithelial development and plays a protective role against squamous cell carcinoma of the skin and of the oral cavity. A single nucleotide polymorphism (SNP) in GRHL3, rs141193530 (p.P455A), is associated with non-melanoma skin cancer in human patients. Moreover, it is known that this SNP, as well as another variant, rs41268753 (p.T454M), are associated with nonsyndromic cleft palate and that rs41268753 negatively affects GRHL3 transcriptional activity. These SNPs are located in adjacent codons of the GRHL3 gene, and the occurrence of either SNP abolishes a putative threonine-proline phosphorylation motif at T454 in the encoded protein. The role of phosphorylation in regulating mammalian GRHL function is currently unknown. In this work we show that GRHL3 is phosphorylated at several residues in a human keratinocyte cell line, among them at T454. This site is essential for the full transcriptional activity of GRHL3. The T454 residue is phosphorylated by p38 MAPK in vitro and activation of p38 signaling in cells causes an increase in GRHL3 activity. The regulation of GRHL3 function by this pathway is dependent on T454, as the substitution of T454 with methionine inhibits the activation of GRHL3. Taken together, our results show that T454 is one of the phosphorylated residues in GRHL3 in keratinocytes and this residue is important for the upregulation of GRHL3 transcriptional activity by the p38 pathway.

Sulforaphane suppresses PRMT5/MEP50 function in epidermal squamous cell carcinoma leading to reduced tumor formation

Protein arginine methyltransferase 5 (PRMT5) cooperates with methylosome protein 50 (MEP50) to arginine methylate histone H3 and H4 to silence gene expression, and increased PRMT5 activity is associated with enhanced cancer cell survival. We have studied the role of PRMT5 and MEP50 in epidermal squamous cell carcinoma. We show that knockdown of PRMT5 or MEP50 results in reduced H4R3me2s formation, and reduced cell proliferation, invasion, migration and tumor formation. We further show that treatment with sulforaphane (SFN), a cancer preventive agent derived from cruciferous vegetables, reduces PRMT5 and MEP50 level and H4R3me2s formation, and this is associated with reduced cell proliferation, invasion and migration. The SFN-dependent reduction in PRMT5 and MEP50 level requires proteasome activity. Moreover, SFN-mediated responses are partially reversed by forced PRMT5 or MEP50 expression. SFN treatment of tumors results in reduced MEP50 level and H4R3me2s formation, confirming that that SFN impacts this complex in vivo. These studies suggest that the PRMT5/MEP50 is required for tumor growth and that reduced expression of this complex is a part of the mechanism of SFN suppression of tumor formation.

Polymorphisms associated with etanercept response in moderate-to-severe plaque psoriasis

AIM

Few studies have evaluated the influence of pharmacogenetics in psoriatic patients treated with etanercept.

MATERIALS & METHODS

We evaluated the association between 124 polymorphisms with the response to etanercept in patients with moderate-to-severe plaque psoriasis at 3 months (n = 78) and 6 months of treatment (n = 68).

RESULTS

The results of the multivariate analysis showed an association between polymorphisms rs13437088 (HLA-B/MICA), rs96844 (MAP3K1), rs2431697 (PTTG1), rs9304742 (ZNF816A) and the response to etanercept at 3 months. Besides polymorphisms rs928655 (GBP6) and rs2546890 (IL12B) were associated to response at 6 months.

CONCLUSIONS

Nevertheless, these biomarkers should be validated in large-scale studies before its implementation in clinical practice.

ADAM17/EGFR axis promotes transglutaminase-dependent skin barrier formation through phospholipase C γ1 and protein kinase C pathways

The vitally important skin barrier is formed by extensive cross-linking activity of transglutaminases (TGs) during terminal epidermal differentiation. We have previously shown that epidermal deficiency of a disintegrin and metalloproteinase 17 (ADAM17), the principal EGFR ligand sheddase, results in postnatal skin barrier defects in mice due to impeded TG activity. However, the mechanism by which ADAM17/EGFR signalling maintains TG activity during epidermal differentiation remains elusive. Here we demonstrate that ADAM17-dependent EGFR signalling promotes TG activity in keratinocytes committed to terminal differentiation by direct induction of TG1 expression. Restored TG1 expression of EGF-stimulated differentiated Adam17-/- keratinocytes was strongly repressed by inhibitors for PLCγ1 or protein kinase C (PKC) pathways, while treatment with the PKC stimulator 12-O-tetradecanoylphorbol-13-acetate restored TG activity in the epidermis of keratinocyte-specific Adam17-/- (AD17ΔKC) mice. Further investigations emphasized the expression of PKCη, a mediator of TGM1 transcription, to be sensitive to EGFR activation. In agreement, topical skin application of cholesterol sulfate, an activator of PKCη, significantly improved TG activity in epidermis of AD17ΔKC mice. Our results suggest ADAM17/EGFR-driven PLCγ1 and PKC pathways as important promoters of TG1 expression during terminal keratinocyte differentiation. These findings may help to identify new therapeutic targets for inflammatory skin diseases related to epidermal barrier defects.

Ingenol Disoxate: A Novel 4-Isoxazolecarboxylate Ester of Ingenol with Improved Properties for Treatment of Actinic Keratosis and Other Non-Melanoma Skin Cancers

Introduction

Ingenol mebutate gel (Picato^®, LEO Pharma A/S) is approved for the field treatment of actinic keratosis and is characterized by high sustained clearance of actinic lesions. The inherent propensity of ingenol mebutate towards chemical rearrangement necessitates refrigeration of the final product. We sought to identify novel ingenol derivatives with enhanced chemical stability and similar or improved in vitro potency and in vivo efficacy.

Methods

A number of ingenol esters were synthesized with full regiocontrol from ingenol. Chemical stability was determined in aqueous buffer at physiological pH and hydroalcoholic gel at lower pH. Acute cytotoxicity was determined in HeLa or HSC-5 cells. Keratinocyte proliferation, viability and caspase 3/7 activation was measured in primary epidermal keratinocytes. Relative gene expression levels were determined by real-time quantitative PCR. Evaluation of in vivo tumor ablating potential was performed in the murine B16 melanoma mouse model and in the UV-induced skin carcinogenesis model in hairless SKH-1 mice following topical treatment for two consecutive days with test compounds formulated at 0.1% in a hydroalcoholic gel.

Results

This work resulted in the identification of ingenol disoxate (LEO 43204) displaying increased stability in a clinically relevant formulation and in aqueous buffer with minimal pH-dependent acyl migration degradation. Ingenol disoxate exhibited a significantly higher cytotoxic potency relative to ingenol mebutate. Likewise, cell growth arrest in normal human keratinocyte was more potently induced by ingenol disoxate, which was accompanied by protein kinase C dependent transcription of markers of keratinocyte differentiation. Most notably, ingenol disoxate possessed a superior antitumor effect in a B16 mouse melanoma model and significantly increased median survival time relative to ingenol mebutate. A significant effect on tumor ablation was also observed in a murine model of ultraviolet irradiation-induced skin carcinogenesis.

Conclusion

These data illustrate that the favorable in vitro and in vivo pharmacological properties driving ingenol mebutate efficacy are either preserved or improved in ingenol disoxate. In combination with improved chemical stability to potentially facilitate storage of the final product at ambient temperatures, these features support further development of ingenol disoxate as a convenient and efficacious treatment modality of non-melanoma skin cancers.

Funding

LEO Pharma A/S.

Electronic supplementary material

The online version of this article (doi:10.1007/s13555-016-0137-2) contains supplementary material, which is available to authorized users.

Type II transglutaminase stimulates epidermal cancer stem cell epithelial-mesenchymal transition

Type II transglutaminase (TG2) is a multifunctional protein that has recently been implicated as having a role in ECS cell survival. In the present study we investigate the role of TG2 in regulating epithelial mesenchymal transition (EMT) in ECS cells. Our studies show that TG2 knockdown or treatment with TG2 inhibitor, results in a reduced EMT marker expression, and reduced cell migration and invasion. TG2 has several activities, but the most prominent are its transamidase and GTP binding activity. Analysis of a series of TG2 mutants reveals that TG2 GTP binding activity, but not the transamidase activity, is required for expression of EMT markers (Twist, Snail, Slug, vimentin, fibronectin, N-cadherin and HIF-1α), and increased ECS cell invasion and migration. This coupled with reduced expression of E-cadherin. Additional studies indicate that NF&#ξ03BA;B signaling, which has been implicated as mediating TG2 impact on EMT in breast cancer cells, is not involved in TG2 regulation of EMT in skin cancer. These studies suggest that TG2 is required for maintenance of ECS cell EMT, invasion and migration, and suggests that inhibiting TG2 GTP binding/G-protein related activity may reduce skin cancer tumor survival.

Polyphenol compounds and PKC signaling

BACKGROUND

Naturally occurring polyphenols found in food sources provide huge health benefits. Several polyphenolic compounds are implicated in the prevention of disease states, such as cancer. One of the mechanisms by which polyphenols exert their biological actions is by interfering in the protein kinase C (PKC) signaling pathways. PKC belongs to a superfamily of serine-threonine kinase and are primarily involved in phosphorylation of target proteins controlling activation and inhibition of many cellular processes directly or indirectly.

SCOPE OF REVIEW

Despite the availability of substantial literature data on polyphenols' regulation of PKC, no comprehensive review article is currently available on this subject. This article reviews PKC-polyphenol interactions and its relevance to various disease states. In particular, salient features of polyphenols, PKC, interactions of naturally occurring polyphenols with PKC, and future perspective of research on this subject are discussed.

MAJOR CONCLUSIONS

Some polyphenols exert their antioxidant properties by regulating the transcription of the antioxidant enzyme genes through PKC signaling. Regulation of PKC by polyphenols is isoform dependent. The activation or inhibition of PKC by polyphenols has been found to be dependent on the presence of membrane, Ca(2+) ion, cofactors, cell and tissue types etc. Two polyphenols, curcumin and resveratrol are in clinical trials for the treatment of colon cancer.

GENERAL SIGNIFICANCE

The fact that 74% of the cancer drugs are derived from natural sources, naturally occurring polyphenols or its simple analogs with improved bioavailability may have the potential to be cancer drugs in the future.

MEP50/PRMT5 Reduces Gene Expression by Histone Arginine Methylation and this Is Reversed by PKCδ/p38δ Signaling

PKCδ and p38δ are key proteins in a cascade that stimulates keratinocyte differentiation. This cascade activates transcription of involucrin (hINV) and other genes associated with differentiation. Protein arginine methyltransferase 5 (PRMT5) is an arginine methyltransferase that symmetrically dimethylates arginine residues. This protein interacts with a cofactor, MEP50, and symmetrically dimethylates arginine eight of histone 3 (H3R8me2s) and arginine three of histone 4 (H4R3me2s) to silence gene expression. We use the involucrin gene as a tool to understand the relationship between PKCδ/p38δ and PRMT5/MEP50 signaling. MEP50 suppresses hINV mRNA level and promoter activity. This is associated with increased arginine dimethylation of hINV gene-associated H3/H4. We further show that the PKCδ/p38δ keratinocyte differentiation cascade reduces PRMT5 and MEP50 expression, association with the hINV gene promoter, and H3R8me2s and H4R2me2s formation. We propose that PRMT5/MEP50-dependent methylation is an epigenetic mechanism that assists in silencing of hINV expression, and that PKCδ signaling activates gene expression by directly activating transcription and by suppressing PRMT5/MEP50 dependent arginine dimethylation of promoter associated histones. This is an example of crosstalk between PKCδ/p38δ signaling and PRMT5/MEP50 epigenetic silencing.

C-H Oxidation of Ingenanes Enables Potent and Selective Protein Kinase C Isoform Activation

Ingenol derivatives with varying degrees of oxidation were prepared by two-phase terpene synthesis. This strategy has allowed access to analogues that cannot be prepared by semisynthesis from natural ingenol. Complex ingenanes resulting from divergent C-H oxidation of a common intermediate were found to interact with protein kinase C in a manner that correlates well with the oxidation state of the ingenane core. Even though previous work on ingenanes has suggested a strong correlation between potential to activate PKCδ and induction of neutrophil oxidative burst, the current study shows that the potential to activate PKCβII is of key importance while interaction with PKCδ is dispensable. Thus, key modifications of the ingenane core allowed PKC isoform selectivity wherein PKCδ-driven activation of keratinocytes is strongly reduced or even absent while PKCβII-driven activation of neutrophils is retained.

Effect of PKCα expression on Bcl-2 phosphorylation and cell death by hypericin

In order to explain the contribution of the protein kinase Cα (PKCα) in apoptosis induced by photo-activation of hypericin (Hyp), a small interfering RNA was used for post-transcriptional silencing of pkcα gene expression. We have evaluated the influence of Hyp photo-activation on cell death in non-transfected and transfected (PKCα(-)) human glioma cells (U-87 MG). No significant differences were detected in cell survival between non-transfected and transfected PKCα(-) cells. However, the type of cell death was notably affected by silencing the pkcα gene. Photo-activation of Hyp strongly induced apoptosis in non-transfected cells, but the level of necrotic cells in transfected PKCα(-) cells increased significantly. The differences in cell death after Hyp photo-activation are demonstrated by changes in: (i) reactive oxygen species production, (ii) Bcl-2 phosphorylation on Ser70 (pBcl-2(Ser70)), (iii) cellular distributions of pBcl-2(Ser70) and (iv) cellular distribution of endogenous anti-oxidant glutathione and its co-localization with mitochondria. In summary, we suggest that post-transcriptional silencing of the pkcα gene and the related decrease of PKCα level considerably affects the anti-apoptotic function and the anti-oxidant function of Bcl-2. This implies that PKCα, as Bcl-2 kinase, indirectly protects U-87 MG cells against oxidative stress and subsequent cell death.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Methylosome Protein 50 and PKCδ/p38δ Protein Signaling Control Keratinocyte Proliferation via Opposing Effects on p21Cip1 Gene Expression

Protein arginine methyltransferase 5 (PRMT5) is a key epigenetic regulator that symmetrically dimethylates arginine residues on histones H3 and H4 to silence gene expression. PRMT5 is frequently observed in a complex with the cofactor methylosome protein 50 (MEP50), which is required for PRMT5 activity. PKCδ/p38δ signaling, a key controller of keratinocyte proliferation and differentiation, increases p21(Cip1) expression to suppress keratinocyte proliferation. We now show that MEP50 enhances keratinocyte proliferation and survival via mechanisms that include silencing of p21(Cip1) expression. This is associated with enhanced PRMT5-MEP50 interaction at the p21(Cip1) promoter and enhanced arginine dimethylation of the promoter-associated histones H3 and H4. It is also associated with a MEP50-dependent reduction in the level of p53, a key controller of p21(Cip1) gene expression. We confirm an important biological role for MEP50 and PRMT5 in regulating keratinocyte proliferation using a stratified epidermal equivalent model that mimics in vivo epidermal keratinocyte differentiation. In this model, PRMT5 or MEP50 knockdown results in reduced keratinocyte proliferation. We further show that PKCδ/p38δ signaling suppresses MEP50 expression, leading to reduced H3/H4 arginine dimethylation at the p21(Cip1) promoter, and that this is associated with enhanced p21(Cip1) expression and reduced cell proliferation. These findings describe an opposing action between PKCδ/p38δ MAPK signaling and PRMT5/MEP50 epigenetic silencing mechanisms in regulating cell proliferation.

PKCη Regulates the TGFβ3-induced Chondevrepogenic Differentiation of Human Mesenchymal Stem Cell

Transforming growth factor (TGF) family is well known to induce the chondevrepogenic differentiation of mesenchymal stem cells (MSC). However, the precise signal transduction pathways and underlying factors are not well known. Thus the present study aims to evaluate the possible role of C2 domain in the chondevrepogenic differentiation of human mesenchymal stem cells. To this end, 145 C2 domains in the adenovirus were individually transfected to hMSC, and morphological changes were examined. Among 145 C2 domains, C2 domain of protein kinase C eta (PKCη) was selected as a possible chondevrepogenic differentiation factor for hMSC. To confirm this possibility, we treated TGFβ3, a well known chondevrepogenic differentiation factor of hMSC, and examined the increased-expression of glycosaminoglycan (GAG), collagen type II (COL II) as well as PKCη using PT-PCR, immunocytochemistry and Western blot analysis. To further evaluation of C2 domain of PKCη, we examined morphological changes, expressions of GAG and COL II after transfection of PKCη -C2 domain in hMSC. Overexpression of PKCη-C2 domain induced morphological change and increased GAG and COL II expressions. The present results demonstrate that PKCη involves in the TGF-β3-induced chondevrepogenic differentiation of hMSC, and C2 domain of PKCη has important role in this process.

Transglutaminase Is Required for Epidermal Squamous Cell Carcinoma Stem Cell Survival

Cancer stem cells are thought to be responsible for rapid tumor growth, metastasis, and enhanced tumor survival following drug treatment. For this reason, there is a major emphasis on identifying proteins that can be targeted to kill cancer stem cells or control their growth, and transglutaminase type II (TGM2/TG2) is such a target in epidermal squamous cell carcinoma. TG2 was originally described as a transamidase in the extracellular matrix that crosslinks proteins by catalyzing ε-(γ-glutamyl)lysine bonds. However, subsequent studies have shown that TG2 is a GTP-binding protein that plays an important role in cell signaling and survival. In the present study, TG2 shows promise as a target for anticancer stem cell therapy in human squamous cell carcinoma. TG2 was determined to be highly elevated in epidermal cancer stem cells (ECS cells), and TG2 knockdown or suppression of TG2 function with inhibitors reduced ECS cell survival, spheroid formation, Matrigel invasion, and migration. The reduction in survival is associated with activation of apoptosis. Mechanistic studies, using TG2 mutants, revealed that the GTP-binding activity is required for maintenance of ECS cell growth and survival, and that the action of TG2 in ECS cells is not mediated by NF-κB signaling.

IMPLICATIONS

This study suggests that TG2 has an important role in maintaining cancer stem cell survival, invasive, and metastatic behavior and is an important therapeutic target to reduce survival of cancer stem cells in epidermal squamous cell carcinoma.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Receptor-interacting protein kinase 4 and interferon regulatory factor 6 function as a signaling axis to regulate keratinocyte differentiation

Receptor-interacting protein kinase 4 (RIPK4) and interferon regulatory factor 6 (IRF6) are critical regulators of keratinocyte differentiation, and their mutation causes the related developmental epidermal disorders Bartsocas-Papas syndrome and popliteal pterygium syndrome, respectively. However, the signaling pathways in which RIPK4 and IRF6 operate to regulate keratinocyte differentiation are poorly defined. Here we identify and mechanistically define a direct functional relationship between RIPK4 and IRF6. Gene promoter reporter and in vitro kinase assays, coimmunoprecipitation experiments, and confocal microscopy demonstrated that RIPK4 directly regulates IRF6 trans-activator activity and nuclear translocation. Gene knockdown and overexpression studies indicated that the RIPK4-IRF6 signaling axis controls the expression of key transcriptional regulators of keratinocyte differentiation, including Grainyhead-like 3 and OVO-like 1. Additionally, we demonstrate that the p.Ile121Asn missense mutation in RIPK4, which has been identified recently in Bartsocas-Papas syndrome, inhibits its kinase activity, thereby preventing RIPK4-mediated IRF6 activation and nuclear translocation. We show, through mutagenesis-based experiments, that Ser-413 and Ser-424 in IRF6 are important for its activation by RIPK4. RIPK4 is also important for the regulation of IRF6 expression by the protein kinase C pathway. Therefore, our findings not only provide important mechanistic insights into the regulation of keratinocyte differentiation by RIPK4 and IRF6, but they also suggest one mechanism by which mutations in RIPK4 may cause epidermal disorders (e.g. Bartsocas-Papas syndrome), namely by the impaired activation of IRF6 by RIPK4.

The nanoscale geometrical maturation of focal adhesions controls stem cell differentiation and mechanotransduction

We show that the nanoscale adhesion geometry controls the spreading and differentiation of epidermal stem cells. We find that cells respond to such hard nanopatterns similarly to their behavior on soft hydrogels. Cellular responses were seen to stem from local changes in diffusion dynamics of the adapter protein vinculin and associated impaired mechanotransduction rather than impaired recruitment of proteins involved in focal adhesion formation.

p38δ regulates p53 to control p21Cip1 expression in human epidermal keratinocytes

PKCδ suppresses keratinocyte proliferation via a mechanism that involves increased expression of p21(Cip1). However, the signaling mechanism that mediates this regulation is not well understood. Our present studies suggest that PKCδ activates p38δ leading to increased p21(Cip1) promoter activity and p21(Cip1) mRNA/protein expression. We further show that exogenously expressed p38δ increases p21(Cip1) mRNA and protein and that p38δ knockdown or expression of dominant-negative p38 attenuates this increase. Moreover, p53 is an intermediary in this regulation, as p38δ expression increases p53 mRNA, protein, and promoter activity, and p53 knockdown attenuates the activation. We demonstrate a direct interaction of p38δ with PKCδ and MEK3 and show that exogenous agents that suppress keratinocyte proliferation activate this pathway. We confirm the importance of this regulation using a stratified epidermal equivalent model, which mimics in vivo-like keratinocyte differentiation. In this model, PKCδ or p38δ knockdown results in reduced p53 and p21(Cip1) levels and enhanced cell proliferation. We propose that PKCδ activates a MEKK1/MEK3/p38δ MAPK cascade to increase p53 levels and p53 drives p21(Cip1) gene expression.

An optimized yeast cell-free lysate system for in vitro translation of human virus mRNA

Yeast (Saccharomyces cerevisiae) as a model organism has long been established to study various aspects of eukaryotic cellular and molecular biology. Cell-free lysates prepared from different yeast strains have been used as a powerful tool to study eukaryotic protein expression in vitro. Recently, we established a yeast cell-free lysate system for in vitro translation long and short L1 capsid gene mRNAs of human papillomavirus type 58. We were able to significantly improve the translation efficiencies of the viral mRNAs in the established system by optimizing the concentrations of potassium and magnesium and controlling the physiological status of the yeast cells used for lysate preparation. We proved that a single specific amino acid can be rate limiting for translation of a target mRNA. Here, we describe the materials, method, and technique used for the development of an efficient yeast cell-free translation system.

Loss of p38δ mitogen-activated protein kinase expression promotes oesophageal squamous cell carcinoma proliferation, migration and anchorage-independent growth

Oesophageal cancer is an aggressive tumour which responds poorly to both chemotherapy and radiation therapy and has a poor prognosis. Thus, a greater understanding of the biology of oesophageal cancer is needed in order to identify novel therapeutic targets. Among these targets p38 MAPK isoforms are becoming increasingly important for a variety of cellular functions. The physiological functions of p38α and -β are now well documented in contrast to -γ and -δ which are comparatively under-studied and ill-defined. A major obstacle to deciphering the role(s) of the latter two p38 isoforms is the lack of specific chemical activators and inhibitors. In this study, we analysed p38 MAPK isoform expression in oesophageal cancer cell lines as well as human normal and tumour tissue. We observed specifically differential p38δ expression. The role(s) of p38δ and active (phosphorylated) p38δ (p-p38δ) in oesophageal squamous cell carcinoma (OESCC) was delineated using wild-type p38δ as well as active p-p38δ, generated by fusing p38δ to its upstream activator MKK6b(E) via a decapeptide (Gly-Glu)₅ linker. OESCC cell lines which are p38δ-negative (KE-3 and -8) grew more quickly than cell lines (KE-6 and -10) which express endogenous p38δ. Re-introduction of p38δ resulted in a time-dependent decrease in OESCC cell proliferation which was exacerbated with p-p38δ. In addition, we observed that p38δ and p-p38δ negatively regulated OESCC cell migration in vitro. Finally both p38δ and p-p38δ altered OESCC anchorage-independent growth. Our results suggest that p38δ and p-p38δ have a role in the suppression of OESCC. Our research may provide a new potential target for the treatment of oesophageal cancer.

Protein kinase C δ increases Kruppel-like factor 4 protein, which drives involucrin gene transcription in differentiating keratinocytes

KLF4 is a member of the Kruppel-like factor family of transcriptional regulators. KLF4 has been shown to be required for normal terminal differentiation of keratinocytes, but the molecular mechanism whereby KLF4 regulates genes associated with the differentiation process has not been studied. In the present study, we explore the impact of KLF4 on expression of involucrin, a gene that is specifically expressed in differentiated keratinocytes. KLF4 overexpression and knockdown studies show that involucrin mRNA and protein level correlates directly with KLF4 level. Moreover, studies of mutant KLF4 proteins indicate that transcriptionally inactive forms do not increase involucrin expression. PKCδ is a regulator of keratinocyte differentiation that increases expression of differentiation-associated target genes, including involucrin. Overexpression of KLF4 augments the PKCδ-dependent increase in involucrin expression, whereas KLF4 knockdown attenuates this response. The KLF4 induction of human involucrin (hINV) promoter activity is mediated via KLF4 binding to a GC-rich element located in the hINV promoter distal regulatory region, a region of the promoter required for in vivo involucrin expression. Mutation of the GC-rich element, an adjacent AP1 factor binding site, or both sites severely attenuates the response. Moreover, loss of KLF4 in an epidermal equivalent model of differentiation results in loss of hINV expression. These studies suggest that KLF4 is part of a multiprotein complex that interacts that the hINV promoter distal regulatory region to drive differentiation-dependent hINV gene expression in epidermis.

Biochemistry of epidermal stem cells

BACKGROUND

The epidermis is an important protective barrier that is essential for maintenance of life. Maintaining this barrier requires continuous cell proliferation and differentiation. Moreover, these processes must be balanced to produce a normal epidermis. The stem cells of the epidermis reside in specific locations in the basal epidermis, hair follicle and sebaceous glands and these cells are responsible for replenishment of this tissue.

SCOPE OF REVIEW

A great deal of effort has gone into identifying protein epitopes that mark stem cells, in identifying stem cell niche locations, and in understanding how stem cell populations are related. We discuss these studies as they apply to understanding normal epidermal homeostasis and skin cancer.

MAJOR CONCLUSIONS

An assortment of stem cell markers have been identified that permit assignment of stem cells to specific regions of the epidermis, and progress has been made in understanding the role of these cells in normal epidermal homeostasis and in conditions of tissue stress. A key finding is the multiple stem cell populations exist in epidermis that give rise to different structures, and that multiple stem cell types may contribute to repair in damaged epidermis.

GENERAL SIGNIFICANCE

Understanding epidermal stem cell biology is likely to lead to important therapies for treating skin diseases and cancer, and will also contribute to our understanding of stem cells in other systems. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Two mechanisms regulate keratin K15 expression in keratinocytes: role of PKC/AP-1 and FOXM1 mediated signalling

Background

Keratin 15 (K15) is a type I keratin that is used as a marker of stem cells. Its expression is restricted to the basal layer of stratified epithelia, and the bulge in hair follicles. However, in certain clinical situations including oral lichen planus, K15 is induced in suprabasal layers, which is inconsistent with the role of a stem cell marker. This study provides insights into the mechanisms of K15 expression in the basal and differentiating keratinocytes.

Methodology/Principal Findings

Human keratinocytes were differentiated by three different methods; suspension in methylcellulose, high cell density and treatment with phorbol ester. The expression of mRNA was determined by quantitative PCR and protein by western blotting and immunostaining. Keratinocytes in suspension suppressed β1-integrin expression, induced differentiation-specific markers and K15, whereas FOXM1 (a cell cycle regulated protein) and K14 were downregulated. Rescuing β1-integrin by either fibronectin or the arginine-glycine-aspartate peptide suppressed K15 but induced K14 and FOXM1 expression. Specific inhibition of PKCδ, by siRNA, and AP-1 transcription factor, by TAM67 (dominant negative c-Jun), suppressed K15 expression, suggesting that PKC/AP-1 pathway plays a role in the differentiation-specific expression of K15. The basal cell-specific K15 expression may involve FOXM1 because ectopic expression of the latter is known to induce K15. Using chromatin immunoprecipitation, we have identified a single FOXM1 binding motif in the K15 promoter.

Conclusions/Significance

The data suggests that K15 is induced during terminal differentiation mediated by the down regulation of β1-integrin. However, this cannot be the mechanism of basal/stem cell-specific K15 expression in stratified epithelia, because basal keratinocytes do not undergo terminal differentiation. We propose that there are two mechanisms regulating K15 expression in stratified epithelia; differentiation-specific involving PKC/AP-1 pathway, and basal-specific mediated by FOXM1, and therefore the use of K15 expression as a marker of stem cells must be viewed with caution.

An RCT on the effects of topical CGP on surgical wound appearance and residual scarring in bilateral total-knee arthroplasty patients

OBJECTIVE

To test the hypothesis that topically applied calcium glycerophosphate (CGP) would improve the appearance of the wound following bilateral knee replacement.

METHOD

Healthy patients, aged 45-75 years, scheduled for bilateral total-knee replacement surgery were recruited into the study. One knee was randomly assigned to the treatment group, while the contralateral knee was designated the control (standard care). Subjects were instructed to apply a preparation of 10% CGP in an aqueous lotion to the treated knee once daily for 42 days, starting at the third postoperative day. Functional sealing and cosmetic appearance of the incision were evaluated by two surgeons by direct examination of the patient and then by two experienced assessors from photographs. The investigators qualitatively scored the intensity and extent of erythema along the incision and over the entire knee, the appearance of visible oedema along the incision and over the knee, and the overall clinical impression of wound healing. All four assessors were blinded to the subjects' allocation and the latter two assessors to the initial investigators' assessments. Subjects were also followed up for an additional 46 weeks, giving a total study duration of 12 months.

RESULTS

Twenty patients completed the study. Statistical analysis showed that both the area and intensity of erythema along the incision were significantly reduced in the treated vs untreated knee over the entire study period. The analysis further showed that treatment significantly reduced oedema, both along the incision and across the entire knee. The differences were most marked at the seventh postoperative day and diminished with time. No adverse effects were observed for any patient, in either treated or untreated knees.

CONCLUSION

These data demonstrate that postoperative application of 10% CGP could improve the appearance of the wound following total knee arthroplasty.

The black box illuminated: signals and signaling

Unraveling the signaling pathways that transmit information from the cell surface to the nucleus has been a major accomplishment of modern cell and molecular biology. The benefit to humans is seen in the multitude of new therapeutics based on the illumination of these pathways. Although considerable insight has been gained in understanding homeostatic and pathological signaling in the epidermis and other skin compartments, the translation into therapy has been lacking. This review will outline advances made in understanding fundamental signaling in several of the most prominent pathways that control cutaneous development, cell-fate decisions, and keratinocyte growth and differentiation with the anticipation that this insight will contribute to new treatments for troubling skin diseases.

Disruption of spectrin-like cytoskeleton in differentiating keratinocytes by PKCδ activation is associated with phosphorylated adducin

Spectrin is a central component of the cytoskeletal protein network in a variety of erythroid and non-erythroid cells. In keratinocytes, this protein has been shown to be pericytoplasmic and plasma membrane associated, but its characteristics and function have not been established in these cells. Here we demonstrate that spectrin increases dramatically in amount and is assembled into the cytoskeleton during differentiation in mouse and human keratinocytes. The spectrin-like cytoskeleton was predominantly organized in the granular and cornified layers of the epidermis and disrupted by actin filament inhibitors, but not by anti-mitotic drugs. When the cytoskeleton was disrupted PKCδ was activated by phosphorylation on Thr505. Specific inhibition of PKCδ^(Thr505) activation with rottlerin prevented disruption of the spectrin-like cytoskeleton and the associated morphological changes that accompany differentiation. Rottlerin also inhibited specific phosphorylation of the PKCδ substrate adducin, a cytoskeletal protein. Furthermore, knock-down of endogenous adducin affected not only expression of adducin, but also spectrin and PKCδ, and severely disrupted organization of the spectrin-like cytoskeleton and cytoskeletal distribution of both adducin and PKCδ. These results demonstrate that organization of a spectrin-like cytoskeleton is associated with keratinocytes differentiation, and disruption of this cytoskeleton is mediated by either PKCδ^(Thr505) phosphorylation associated with phosphorylated adducin or due to reduction of endogenous adducin, which normally connects and stabilizes the spectrin-actin complex.

New Insights into the p38γ and p38δ MAPK Pathways

The mammalian p38 mitogen-activated protein kinases (MAPKs) family is composed of four members (p38α, p38β, p38γ, and p38δ), which are very similar in amino acid sequence but differ in their expression patterns. This suggests that they may have specific functions in different organs. In the last years most of the effort has been centred on the study of the function of the p38α isoform, which is widely referred to as p38 in the literature. However, the role that other p38 isoforms play in cellular functions and their implication in some of the pathological conditions have not been precisely defined so far. In this paper we highlight recent advances made in defining the functions of the two less studied alternative p38MAPKs, p38γ and p38δ. We describe that these p38MAPKs show similarities to the classical p38α isoform, although they may play central and distinct role in certain physiological and pathological processes.