The ARE-binding protein Tristetraprolin (TTP) is a novel target and mediator of calcineurin tumor suppressing function in the skin.

An increased incidence of skin inflammatory diseases is frequently observed in organtransplanted patients being treated with calcineurin inhibitor-based immunosuppressive agents. The mechanism of increased skin inflammation in this context has however not yet been clarified. Here we report an increased inflammation following inhibition of calcineurin signaling seen in both chemically induced mouse skin tumors and in tumors grafted from H-rasV12 expressing primary human keratinocytes (HKCs). Following UVB or TPA treatment, we specifically found that deletion of the calcineurin gene in mouse keratinocytes (MKCs) resulted in increased inflammation, and this was accompanied by the enhanced production of pro-inflammatory cytokines, such as TNFα, IL-8 and CXCL1. Furthermore, expression of the RNA-binding protein, tristetraprolin (TTP) was down-regulated in response to calcineurin inhibition, wherein TTP was shown to negatively regulate the production of pro-inflammatory cytokines in keratinocytes. The induction of TTP following TPA or UVB treatment was attenuated by calcineurin inhibition in keratinocytes, and correspondingly, disruption of calcineurin signaling down-regulated the amounts of TTP in both clinical and H-rasV12-transformed keratinocyte tumor models. Our results further demonstrated that calcineurin positively controls the stabilization of TTP in keratinocytes through a proteasome-dependent mechanism. Reducing the expression of TTP functionally promoted tumor growth of H-rasV12 expressing HKCs, while stabilizing TTP expression counteracted the tumor-promoting effects of calcineurin inhibition. Collectively these results suggest that calcineurin signaling, acting through TTP protein level stabilization, suppresses keratinocyte tumors by downregulating skin inflammation.

Prevalence of Actinic Keratosis in Patients Attending General Practitioners in Switzerland.

BACKGROUND: Most of the data concerning the prevalence of actinic keratosis (AK) originate from the USA and Australia, and recently from Austria and Spain, but are based on populations in dermatology practices. Switzerland is the leading country with skin cancer incidence in Europe. AK prevalence among the Swiss population is therefore an important public health issue. OBJECTIVE: To assess the prevalence of AK in the outpatient Swiss population in general practice. METHODS: General practitioners captured AK diagnosis stage and localization in consecutive patients, who attended the physician for any reason. RESULTS: A total of 2,844 consecutive patients (55.7% female) were enrolled in 59 general practitioners' offices. AK prevalence was 25.3% and increased steadily with age; 33% of men and 19% of women were diagnosed with AK. Every second AK patient declared leisure-related UV exposure, while only 23% were exposed to UV occupationally; 16% of the patients were UV exposed both occupationally and during leisure. AK distribution among sun-exposed body sites and extent of disease varied by sex. CONCLUSION: In Switzerland AK is a common diagnosis in dermatology practices. Since up to 5% of AK may progress to invasive squamous cell carcinoma (SCC), prevention of AK, as well as education of patients and general practitioners, may play a critical role for subsequent SCC development. This is the first study on AK prevalence in Switzerland identifying patients most affected by AK. These results will help to define future approaches to target general practitioners for education, screening, and specific intervention in patients with AK.

CYFIP1 is directly controlled by NOTCH1 and down-regulated in cutaneous squamous cell carcinoma.

Squamous cell carcinoma of the skin (SCC) represents one of the most common cancers in the general population and is associated with a substantial risk of metastasis. Previous work uncovered the functional role of CYFIP1 in epithelial tumors as an invasion inhibitor. It was down-regulated in some cancers and correlated with the metastatic properties of these malignant cells. We investigated its role and expression mechanisms in SCC. We analyzed the expression of CYFIP1 in patient derived SCC, primary keratinocytes and SCC cell lines, and correlated it to the differentiation and NOTCH1 levels. We analyzed the effects of Notch1 manipulation on CYFIP1 expression and confirmed the biding of Notch1 to the CYFIP1 promoter. CYFIP1 expression was down-regulated in SCC and correlated inversely with histological differentiation of tumors. As keratinocyte differentiation depends on Notch1 signaling, we investigated the influence of Notch1 on CYFIP1 expression. CYFIP1 mRNA was highly increased in human Notch1-overexpressing keratinocytes. Further manipulation of the Notch1 pathway in keratinocytes impacted CYFIP1 levels and chromatin immunoprecipitation assay confirmed the direct binding of Notch1 to the CYFIP1 promoter. CYFIP1 may be a link between loss of differentiation and invasive potential in malignant keratinocytes of cutaneous squamous cell carcinoma.

TLR4 as a negative regulator of keratinocyte proliferation.

TLR4 is an innate immune receptor with expression in human skin, keratinocytes as well as squamous cell carcinoma (SCC) of the skin. In the present study we investigate the role of TLR4 as a negative regulator of keratinocyte proliferation. We present here that the expression of TLR4 increased with the differentiation of cultured keratinocytes in a passage-dependent manner or under calcium-rich conditions. Moreover, the down-regulation of TLR4 by specific knockdown increased the proliferation of HaCaT keratinocytes in vitro. In addition, subcutaneously injected HaCaT keratinocytes with shTLR4 formed growing tumors in nude mice. In contrast, we observed lower proliferation and increased migration in vitro of the SCC13 cell line stably overexpressing TLR4 in comparison to SCC13 TLR4 negative cells. In vivo, SCC13 TLR4-overexpressing tumors showed delayed growth in comparison to TLR4 negative tumors. The overexpression of TLR4 in SCC13 tumor cells was followed by phosphorylation of ERK1/2 and JNK and increased expression of ATF3. In gene expression arrays, the overexpression of TLR4 in tumor cells correlated with gene expression of ATF-3, IL-6, CDH13, CXCL-1 and TFPI. In summary, TLR4 negatively regulates the proliferation of keratinocytes and its overexpression reduces tumor growth of SCC cells.

S100A8/A9 stimulates keratinocyte proliferation in the development of squamous cell carcinoma of the skin via the receptor for advanced glycation-end products.

Squamous cell carcinoma (SCC) is the most common neoplasm in organ transplant recipients (OTR) on long-term immunosuppression and occurs 60- to 100-fold more frequently than in the general population. Here, we present the receptor for advanced glycation end products (RAGE) and S100A8/A9 as important factors driving normal and tumor keratinocyte proliferation. RAGE and S100A8/A9 were transcriptionally upregulated in SCC compared to normal epidermis, as well as in OTR compared to immunocompetent patients (IC) with SCC. The proliferation of normal and SCC keratinocytes was induced by exposure to exogenous S100A8/A9 which in turn was abolished by blocking of RAGE. The migratory activities of normal and SCC keratinocytes were also increased upon exposure to S100A8/A9. We demonstrated that exogenous S100A8/A9 induces phosphorylation of p38 and SAPK/JNK followed by activation of ERK1/2. We hypothesize that RAGE and S100A8/A9 contribute to the development of human SCC by modulating keratinocyte growth and migration. These processes do not seem to be impaired by profound drug-mediated immunosuppression in OTR.

The oncogene ATF3 is potentiated by cyclosporine A and ultraviolet light A.

Cutaneous squamous cell carcinoma (SCC) represents the most important cutaneous complication following organ transplantation. It develops mostly on sun-exposed areas. A recent study showed the role of activating transcription factor 3 (ATF3) in SCC development following treatment with calcineurin inhibitors. It has been reported that ATF3, which may act as an oncogene, is under negative calcineurin/nuclear factor of activated T cells (NFAT) control and is upregulated by calcineurin inhibitors. Still, these findings do not fully explain the preferential appearance of SCC on chronically sun-damaged skin. We analyzed the influence of UV radiation on ATF3 expression and its potential role in SCC development. We found that ATF3 is a specifically induced AP1 member in SCC of transplanted patients. Its expression was strongly potentiated by combination of cyclosporine A and UVA treatment. UVA induced ATF3 expression through reactive oxygen species-mediated nuclear factor erythroid 2-related factor 2 (NRF2) activation independently of calcineurin/NFAT inhibition. Activated NRF2 directly binds to ATF3 promoter, thus inducing its expression. These results demonstrate two mechanisms that independently induce and, when combined together, potentiate the expression of ATF3, which may then force SCC development. Taking into account the previously defined role of ATF3 in the SCC development, these findings may provide an explanation and a mechanism for the frequently observed burden on SCCs on sun-exposed areas of the skin in organ transplant recipients treated by calcineurin inhibitors.

Organ transplantation and skin--principles and concepts.

Solid organ transplantation influences the biology of the skin profoundly. In the wake of transplantation, inflammatory, infectious and neoplastic disorders arise, often with atypical clinical presentation. Inflammatory disorders mainly relate to pathogen-driven conditions such as seborrheic dermatitis and pityrosporum folliculitis and to drug reactions. Infectious disorders are dominated by viral infections of human papilloma virus and by infections and reactivations of herpes family members. Neoplastic disorders are greatly increased with squamous cell carcinoma of the skin as most relevant clinical problem which is increased 65- to 100-fold following transplantation. This dramatic increase in cutaneous carcinogenesis results from the isolated effect of ultraviolet light on the skin with immunosuppression and DNA damage and of immunosuppressants which drive skin cancer formation by properties unrelated to immunosuppression and from the combined effect of UV light and immunosuppressive drugs on immunomodulation which results in impaired antitumor response as well as chronic tumorigenic inflammation.

The expression levels of microRNA-361-5p and its target VEGFA are inversely correlated in human cutaneous squamous cell carcinoma.

Vascular endothelial growth factor A (VEGFA) plays a key role in the angiogenesis of human skin. Elevated levels of VEGFA are associated with several pathological conditions, including chronic inflammatory skin diseases and several types of skin cancer. In particular, squamous cell carcinoma (SCC) of the skin, the second most common skin cancer in the general population, is characterized by invasive growth, pronounced angiogenesis and elevated levels of VEGFA. The processing, turnover and production of VEGFA are extensively regulated at the post-transcriptional level, both by RNA-binding proteins and microRNAs (miRNAs). In the present study, we identified a new miRNA recognition element in a downstream conserved region of the VEGFA 3'-UTR. We confirmed the repressive effect of miR-361-5p on this element in vitro, identifying the first target for this miRNA. Importantly, we found that miR-361-5p levels are inversely correlated with VEGFA expression in SCC and in healthy skin, indicating that miR-361-5p could play a role in cancers.