Epidermal growth factor (EGF)-mediated DNA-binding activity of AP-1 is attenuated in senescent human epidermal keratinocytes

Transcriptional responses consistent with perturbation in dermo-epidermal homeostasis in septic sole ulceration

The aim of this study was to evaluate transcriptional changes in sole epidermis and dermis of bovine claws with septic sole ulceration of the lateral claw. Assessment included changes in transcripts orchestrating epidermal homeostatic processes including epidermal proliferation, differentiation, inflammation, and cell signaling. Sole epidermis and dermis was removed from region 4 of lesion-bearing lateral and lesion-free medial claws of pelvic limbs in multiparous, lactating Holstein cows. Control sole epidermis and dermis was obtained from region 4 of lateral claws of normal pelvic limbs. Transcript abundances were evaluated by real-time QPCR and relative expression analyzed by ANOVA. Relative to normal lateral claws, sole epidermis and dermis in ulcer-bearing claws exhibited downregulation of genes associated with growth factors, growth factor receptors, activator protein 1 (AP-1) and proto-oncogene (CMYC) transcription components, cell cycle elements, lateral cell-to-cell signaling elements and structures of early and late keratinocyte differentiation. These changes were accompanied by upregulation of pro-inflammatory transcripts interleukin 1 α (IL1A), interleukin1 β (IL1B), interleukin 1 receptor 1 (IL1R1), inducible nitric oxide synthase (NOS2), the inflammasome components NOD like receptor protein 3 (NLRP3), pyrin and caspase recruitment domain (PYCARD), and caspase-1 interleukin converting enzyme (CASPASE), the matrix metalloproteinases (MMP2 and MMP9), and anti-inflammatory genes interleukin 1 receptor antagonist (IL1RN) and interleukin1 receptor 2 (IL1R2). Transcript abundance varied across epidermis and dermis from the ulcer center, margin and epidermis and dermis adjacent to the lesion. Sole epidermis and dermis of lesion-free medial claws exhibited changes paralleling those in the adjacent lateral claws in an environment lacking inflammatory transcripts and downregulated IL1A, interleukin 18 (IL18), tumor necrosis factor α (TNFA) and NOS2. These data imply perturbations in signal pathways driving epidermal proliferation and differentiation are associated with, but not inevitably linked to epidermis and dermis inflammation. Further work is warranted to better define the role of crushing tissue injury, sepsis, metalloproteinase activity, and inflammation in sole ulceration.

Insights into gene expression profiles induced by Socs3 depletion in keratinocytes

Specific deletion of suppressor of cytokine signaling 3 (Socs3) in keratinocytes can cause severe skin inflammation with infiltration of immune cells. The molecular mechanisms and key regulatory pathways involved in these processes remain elusive. To investigate the role of Socs3 in keratinocytes, we generated and analyzed global RNA-Seq profiles from Socs3 conditional knockout (cKO) mice of two different ages (2 and 10 weeks). Over 400 genes were significantly regulated at both time points. Samples from 2-week-old mice exhibited down-regulation of genes involved in keratin-related functions and up-regulation of genes involved in lipid metabolism. At week 10, multiple chemokine and cytokine genes were up-regulated. Functional annotation revealed that the genes differentially expressed in the 2-week-old mice play roles in keratinization, keratinocyte differentiation, and epidermal cell differentiation. By contrast, differentially expressed genes in the 10-week-old animals are involved in acute immune-related functions. A group of activator protein-1-related genes were highly up-regulated in Socs3 cKO mice of both ages. This observation was validated using qRT-PCR by SOCS3-depleted human keratinocyte-derived HaCaT cells. Our results suggest that, in addition to participating in immune-mediated pathways, SOCS3 also plays important roles in skin barrier homeostasis.

AP1 transcription factors in epidermal differentiation and skin cancer

AP1 (jun/fos) transcription factors (c-jun, junB, junD, c-fos, FosB, Fra-1, and Fra-2) are key regulators of epidermal keratinocyte survival and differentiation and important drivers of cancer development. Understanding the role of these factors in epidermis is complicated by the fact that each protein is expressed, at different levels, in multiple cells layers in differentiating epidermis, and because AP1 transcription factors regulate competing processes (i.e., proliferation, apoptosis, and differentiation). Various in vivo genetic approaches have been used to study these proteins including targeted and conditional knockdown, overexpression, and expression of dominant-negative inactivating AP1 transcription factors in epidermis. Taken together, these studies suggest that individual AP1 transcription factors have different functions in the epidermis and in cancer development and that altering AP1 transcription factor function in the basal versus suprabasal layers differentially influences the epidermal differentiation response and disease and cancer development.

Suppression of AP1 transcription factor function in keratinocyte suppresses differentiation

Our previous study shows that inhibiting activator protein one (AP1) transcription factor function in murine epidermis, using dominant-negative c-jun (TAM67), increases cell proliferation and delays differentiation. To understand the mechanism of action, we compare TAM67 impact in mouse epidermis and in cultured normal human keratinocytes. We show that TAM67 localizes in the nucleus where it forms TAM67 homodimers that competitively interact with AP1 transcription factor DNA binding sites to reduce endogenous jun and fos factor binding. Involucrin is a marker of keratinocyte differentiation that is expressed in the suprabasal epidermis and this expression requires AP1 factor interaction at the AP1-5 site in the promoter. TAM67 interacts competitively at this site to reduce involucrin expression. TAM67 also reduces endogenous c-jun, junB and junD mRNA and protein level. Studies with c-jun promoter suggest that this is due to reduced transcription of the c-jun gene. We propose that TAM67 suppresses keratinocyte differentiation by interfering with endogenous AP1 factor binding to regulator elements in differentiation-associated target genes, and by reducing endogenous c-jun factor expression.

AP1 factor inactivation in the suprabasal epidermis causes increased epidermal hyperproliferation and hyperkeratosis but reduced carcinogen-dependent tumor formation

Activator protein one (AP1) (jun/fos) factors comprise a family of transcriptional regulators (c-jun, junB, junD, c-fos, FosB, Fra-1 and Fra-2) that are key controllers of epidermal keratinocyte survival and differentiation, and are important drivers of cancer development. Understanding the role of these factors in epidermis is complicated by the fact that each member is expressed in defined cell layers during epidermal differentiation, and because AP1 factors regulate competing processes (that is, proliferation, apoptosis and differentiation). We have proposed that AP1 factors function differently in basal versus suprabasal epidermis. To test this, we inactivated suprabasal AP1 factor function in mouse epidermis by targeted expression of dominant-negative c-jun (TAM67), which inactivates function of all AP1 factors. This produces increased basal keratinocyte proliferation, delayed differentiation and extensive hyperkeratosis. These findings contrast with previous studies showing that basal layer AP1 factor inactivation does not perturb resting epidermis. It is interesting that in spite of extensive keratinocyte hyperproliferation, susceptibility to carcinogen-dependent tumor induction is markedly attenuated. These novel observations strongly suggest that AP1 factors have distinct roles in the basal versus suprabasal epidermis, confirm that AP1 factor function is required for normal terminal differentiation, and suggest that AP1 factors have a different role in normal epidermis versus cancer progression.

Cigarette smoke extract induces expression of cell adhesion molecules in HUVEC via actin filament reorganization

Epidemiologic studies have shown a strong association between cigarette smoking and cardiovascular diseases. Various oxidative species and free radicals are produced during cigarette smoking and these lead to endothelial dysfunction and inflammation. Expression of adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1), E-selectin, and vascular cell adhesion molecule-1, and adhesion of leukocytes are present in atherosclerosis. We showed previously that a nonfractionated cigarette smoke extract (CSE) induces surface expression of ICAM-1 and E-selectin in human umbilical vein endothelial cells (HUVEC). We then investigated the role of the MAPKs (ERK1/2, JNK, and p38) and AP-1 and the role of actin cytoskeleton reorganization in the CSE-induced expression of ICAM-1 and E-selectin. Western blot analysis showed that CSE treatment rapidly and significantly caused phosphorylation of JNK and ERK1/2 but not of p38. Cytochalasin D (an actin filament disruptor) partially inhibited CSE-induced ICAM-1 and E-selectin surface expression. However, inhibitors of ERK1/2 (PD98059) and JNK (SP600125) did not attenuate the CSE-induced ICAM-1 and E-selectin surface expression. The results of electrophoretic mobility shift assay showed that CSE enhanced AP-1 binding activity. Therefore, CSE activated AP-1 and upregulated ICAM-1 and E-selectin surface expression in HUVEC seem to be via an MAPK-independent pathway. Moreover, the dynamic reorganization of the actin cytoskeleton seems to be required for the CSE-induced surface expression of ICAM-1 and E-selectin.

EGF-recruited JunD/c-fos complexes activate CD2AP gene promoter and suppress apoptosis in renal tubular epithelial cells

CD2-associated protein (CD2AP) plays a critical role in the maintenance of the kidney filtration barrier. In this study, we showed that epidermal growth factor (EGF) led to an increase of the CD2AP protein and mRNA in the human renal proximal tubular epithelial cell line HK-2 cells, which was due to the elevation of CD2AP promoter activity. Upon deletion and mutation analysis, electrophoretic mobility shift assays and chromatin immunoprecipitation, an AP-1-like element within CD2AP promoter was characterized, by which EGF recruited c-fos and JunD, two components of AP-1, to the human CD2AP gene promoter and suppressed angiotensin II-induced apoptosis in HK-2 cells. Specific siRNA was synthesized to knock down the human CD2AP gene in HK-2 cells. We found that CD2AP deficiency attenuated the inhibitory effects of EGF and predisposed the renal tubular epithelial cells to undergo angiotensin II-induced apoptosis. Furthermore, EGF-induced increases of CD2AP protein and mRNA expressions in HK-2 cells were significantly inhibited by the transfection of dominant negative JunD or c-fos vector, which was in parallel with a marked reduction of antiapoptotic effect of EGF. These results indicated that the antiapoptotic effect of EGF/CD2AP signal transduction was mediated by JunD and c-fos, at least partially. This study defined a new EGF/AP-1/CD2AP mediated cell-survival signaling, which might be useful to clarify the molecular mechanisms responsible for CD2AP associated kidney diseases.

EGFR intron 1 dinucleotide repeat polymorphism is associated with the occurrence of skin rash with gefitinib treatment

BACKGROUND

Skin rash is the most common toxicity of epidermal growth factor receptor (EGFR)-targeted therapy. This study investigated the clinical and genetic factors associated with this skin rash.

METHODS

Fifty-two non-small cell lung cancer patients enrolled in a clinical trial of first-line gefitinib treatment were genotyped for EGFR intron 1 CA repeat ([CA]n) polymorphism and single nucleotide polymorphisms at G-216T, C-191A, and R521K. The severity of skin rash was correlated with the genotypic and clinicopathological features.

RESULTS

Seventeen patients (32.7%) developed grade 2-3 skin rashes within 4 weeks of treatment (early G2/3 rash). In the multivariate logistic regression analysis, only the [CA]n genotype was correlated with early G2/3 rash; and this relationship was modified by age. Early G2/3 rash developed in 21% of patients with homozygous long allele (19-22 repeats, L) genotype, 31% with heterozygous short allele (15-18 repeats, S)/L genotype, and 71% with S/S genotype, respectively. The estimated logarithm of odds ratio (lnOR) for early G2/3 rash, as compared to S/S genotype, for S/L genotype was -0.038 multiplied by age (P=0.011); and the lnOR for L/L genotype was -0.050 multiplied by age (P=0.004). Early G2/3 rash was correlated with tumor response in the multiple logistic regression analysis (P=0.027). However, the [CA]n genotype was not significantly correlated with tumor response (P=0.35).

CONCLUSIONS

EGFR [CA]n genotype appears to be a useful predictive marker of the development of skin rashes with gefitinib treatment.

The combination of ubiquitous transcription factors AP-1 and Sp1 directs keratinocyte-specific and differentiation-specific gene expression in vitro

Previous studies of epidermal-specific gene promoters suggested that a limited set of transcription factors regulate keratinocyte-specific and differentiation-specific gene expression in the epidermis. In the present study, we investigated the functional importance of AP-1- and Sp1-binding elements in the determination of cell type-specific and differentiation-specific gene expression by transient transfection into undifferentiated and differentiated keratinocytes as well as into various non-epidermal cell lines. Synthesized short AP-1- and/or Sp1-binding elements were inserted into a minimal reporter vector, and the artificial promoter containing both AP-1 and Sp1 elements showed high levels of transcriptional activity only when transfected into differentiated keratinocytes. Promoters containing either the AP-1 or the Sp1 motif alone showed little activity in any of the cells examined. We also found that close proximity of the Sp1 and AP-1 sites is essential for transcriptional activity, suggesting that the physical interaction between Sp1 and AP-1 factors is important for functional activity. These results clearly demonstrate that the combination of ubiquitously expressed transcription factors AP-1 and Sp1 confers keratinocyte specificity and differentiation specificity on the gene expression. Our findings also provide a simple model of the mechanisms underlying regulation of cell type-specific and cell differentiation-specific gene expression by ubiquitously expressed transcription factors.

Gene expression changes in long-term culture of T-cell clones: genomic effects of chronic antigenic stress in aging and immunosenescence

The adaptive immune response requires waves of T-cell clonal expansion on contact with altered self and contraction after elimination of antigen. In the case of persisting antigen, as occurs for example in cytomegalovirus or Epstein–Barr virus infection, this critical process can become dysregulated and responding T-cells enter into a dysfunctional senescent state. Longitudinal studies suggest that the presence of increased numbers of such T-cells is a poor prognostic factor for survival in the very elderly. Understanding the nature of the defects in these T-cells might facilitate intervention to improve immunity in the elderly. The process of clonal expansion under chronic antigenic stress can be modelled in vitro using continuously cultured T-cells. Here, we have used cDNA array technology to investigate differences in gene expression in a set of five different T-cell clones at early, middle and late passage in culture. Differentially expressed genes were confirmed by real-time polymerase chain reaction, and relationships between these assessed using Ingenuity Systems evidence-based association analysis. Several genes and chemokines related to induction of apoptosis and signal transduction pathways regulated by transforming growth factor β (TGFβ), epidermal growth factor (EGF), fos and β-catenin were altered in late compared to early passage cells. These pathways and affected genes may play a significant role in driving the cellular senescent phenotype and warrant further investigation as potential biomarkers of aging and senescence. These genes may additionally provide targets for intervention.

Resveratrol inhibits proliferation of human epidermoid carcinoma A431 cells by modulating MEK1 and AP-1 signalling pathways

Resveratrol (trans-3,4',5-trihydroxystilbene) is a naturally occurring polyphenolic phytoalexin found in grapes, and has been shown to inhibit the growth of various types of cancer cells. We investigated the mechanism of the antiproliferative effect of resveratrol in A431-transformed keratinocytes harbouring mutant p53, and show that it is accompanied by G1 cell cycle arrest, which coincides with a marked inhibition of G1 cell cycle regulatory proteins, including cyclins A and D1 and cyclin-dependent kinase (CDK)6 and p53-independent induction of p21WAF1. Cell cycle arrest was also associated with the accumulation of hypophosphorylated Rb and p27KIP1. Resveratrol inhibited mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)1 > extracellular signal-regulated protein kinase (ERK)1/2 signalling, downregulated c-Jun, and suppressed activating protein (AP)-1 DNA-binding and promoter activity. In addition, the inhibition of MEK1 > ERK1/2 signalling appears to be independent of retinoblastoma protein (pRb) hypophosphorylation in A431 cells, as PD098059 did not suppress pRb phosphorylation. Our results demonstrate that resveratrol affects multiple cellular targets in A431 cells, and that the downregulation of both AP-1 and pRb contributes to its antiproliferative activity in these cells.

Stat3 activation is required for cell proliferation and tumorigenesis but not for cell viability in cutaneous squamous cell carcinoma cell lines

Signal transducer and activator of transcription 3 (Stat3), a cytoplasmic transcription factor, is constitutively activated in various types of cancer. Previous investigations have demonstrated that Stat3 plays important roles in cell growth, survival, differentiation, and transformation. The constitutive activation of Stat3 in human malignancies is an important key to maintain the characteristics of a malignant tumor, such as the rate of proliferation and/or immortalization, and inhibition of Stat3 function could be a potent therapeutic approach. In order to elucidate the role of Stat3 in tumors, cutaneous squamous cell carcinoma (SCC) cells, which have constitutive activation of Stat3 in vivo and in vitro, were used for this study. To investigate the effect of specific inhibition of Stat3 in SCC cells, we developed small interfering RNAs (siRNAs) that target Stat3, and which effectively prevent its expression in vitro. Introduction of Stat3 siRNA into SCC cells led to inhibition of growth and changes in morphology but did not induce apoptosis. Stat3 siRNA-transfected SCC cells had impaired tumor growth in nude mice. These findings demonstrate that Stat3 plays a critical role in the tumorigenesis, but not in the cell survival, of SCC cells and suggest that additional pro-apoptotic signals are necessary for the induction of apoptosis.