Daniela Alotto

New p63 targets in keratinocytes identified by a genome‐wide approach

p63 is a developmentally regulated transcription factor related to p53. It is involved in the development of ectodermal tissues, including limb, skin and in general, multilayered epithelia. The ΔNp63α isoform is thought to play a ‘master’ role in the asymmetric division of epithelial cells. It is also involved in the pathogenesis of several human diseases, phenotypically characterized by ectodermal dysplasia. Our understanding of transcriptional networks controlled by p63 is limited, owing to the low number of bona fide targets. To screen for new targets, we employed chromatin immunoprecipitation from keratinocytes (KCs) coupled to the microarray technology, using both CpG islands and promoter arrays. The former revealed 96 loci, the latter yielded 85 additional genes. We tested 40 of these targets in several functional assays, including: (i) in vivo binding by p63 in primary KCs; (ii) expression analysis in differentiating HaCaT cells and in cells overexpressing ΔNp63α; (iii) promoter transactivation and (iv) immunostaining in normal tissues, confirming their regulation by p63. We discovered several new specific targets whose functional categorization links p63 to cell growth and differentiation.

Preparation and Characterization of a Novel Skin Substitute

Autologous epidermal cell cultures (CEA) represent a possibility to treat extensive burn lesions, since they allow a significative surface expansion which cannot be achieved with other surgical techniques based on autologous grafting. Moreover currently available CEA preparations are difficult to handle and their take rate is unpredictable. This study aimed at producing and evaluating a new cutaneous biosubstitute made up of alloplastic acellular glycerolized dermis (AAGD) and CEA to overcome these difficulties. A procedure that maintained an intact basement membrane was developed, so as to promote adhesion and growth of CEA on AAGD. Keratinocytes were seeded onto AAGD and cultured up to 21 days. Viability tests and immunohistochemical analysis with specific markers were carried out at 7, 14, and 21 days, to evaluate keratinocyte adhesion, growth, and maturation. Our results support the hypothesis that this newly formed skin substitute could allow its permanent engraftment in clinical application.

Imbalance between activin A and follistatin drives postburn hypertrophic scar formation in human skin

Abstract:  Hypertrophic scarring is a skin disorder characterized by persistent inflammation and fibrosis that may occur after wounding or thermal injury. Altered production of cytokines and growth factors, such as TGF‐β, play an important role in this process. Activin A, a member of the TGF‐β family, shares the same intra‐cellular Smad signalling pathway with TGF‐β, but binds to its own specific transmembrane receptors and to follistatin, a secreted protein that inhibits activin by sequestration. Recent studies provide evidences of a novel role of activin A in inflammatory and repair processes. The aim of this study was to evaluate the importance of activin A and follistatin expression in the different phases of scar evolution. Immunostaining of sections obtained from active phase hypertrophic scars (AHS) revealed the presence of a high number of α‐SMA+ myofibroblasts and DC‐SIGN+ dendritic cells coexpressing activin A. Ex‐vivo AHS fibroblasts produced more activin and less follistatin than normal skin or remission phase hypertrophic scar (HS) fibroblasts, both in basal conditions and upon TGF‐βs stimulation. We demonstrate that fibroblasts do express activin receptors, and that this expression is not affected by TGF‐βs. Treatment of HS fibroblasts with activin A induced Akt phosphorylation, promoted cell proliferation, and enhanced α‐SMA and type I collagen expression. Follistatin reduced proliferation and suppressed activin‐induced collagen expression. These results indicate that the activin/follistatin interplay has a role in HS formation and evolution. The impact of these observations on the understanding of wound healing and on the identification of new therapeutic targets is discussed.

Identification of new p63 targets in human keratinocytes.

p63 is a transcription factor involved in the development of ectodermal tissues, including limb, skin and, in general, multilayered epithelia. We identified both activated and repressed genes in human keratinocytes via gene expression profiling of p63-depleted cells and validated 21 new primary targets by RT-PCR and ChIP location analysis. The p63 isoforms differentially activate or repress selected promoters. ChIPs in primary keratinocytes indicate that p63 targets are generally shared with p53, but some are p63-specific. Several growth suppressors are among repressed genes. The newly identified genes belong to pathways of growth and differentiation and are regulated in HaCaT differentiation and in stratification of human skin.

Activin A induces Langerhans cell differentiation in vitro and in human skin explants.

Langerhans cells (LC) represent a well characterized subset of dendritic cells located in the epidermis of skin and mucosae. In vivo, they originate from resident and blood-borne precursors in the presence of keratinocyte-derived TGFβ. Ιn vitro, LC can be generated from monocytes in the presence of GM-CSF, IL-4 and TGFβ. However, the signals that induce LC during an inflammatory reaction are not fully investigated. Here we report that Activin A, a TGFβ family member induced by pro-inflammatory cytokines and involved in skin morphogenesis and wound healing, induces the differentiation of human monocytes into LC in the absence of TGFβ. Activin A-induced LC are Langerin+, Birbeck granules+, E-cadherin+, CLA+ and CCR6+ and possess typical APC functions. In human skin explants, intradermal injection of Activin A increased the number of CD1a+ and Langerin+ cells in both the epidermis and dermis by promoting the differentiation of resident precursor cells. High levels of Activin A were present in the upper epidermal layers and in the dermis of Lichen Planus biopsies in association with a marked infiltration of CD1a+ and Langerin+ cells. This study reports that Activin A induces the differentiation of circulating CD14+ cells into LC. Since Activin A is abundantly produced during inflammatory conditions which are also characterized by increased numbers of LC, we propose that this cytokine represents a new pathway, alternative to TGFβ, responsible for LC differentiation during inflammatory/autoimmune conditions.

p63 regulates the caspase-8-FLIP apoptotic pathway in epidermis.

The transcription factor p63, member of the p53 family, is crucial for epithelial development. An RNAi screening identified the apoptotic gene Procaspase-8 as a target activated by p63. The caspase-8 inhibitor FLIP is also under p63 control. We analysed and detailed the direct transactivation through the use of RNAi, reporter assays, ChIPs, western blots, confocal studies in HaCat, as well as in primary human keratinocytes. The direct ΔNp63 regulation of these targets was confirmed in vivo using transgenic ΔNp63 mice under the K5 promoter, as compared with p63 knockout mice, and in vitro in normal human primary keratinocytes following UV irradiation. Lowering the steady state of p63 protein levels changes the relative ratio of FLIP isoforms, causing the activation of the expressed, inactive Procaspase-8, into the active isoform thus triggering the proapoptotic cascade. Therefore, p63 fine-tunes the Procaspase-8-FLIP pro- and antiapoptotic pathway in keratinocytes.

Reciprocal regulation of p63 by C/EBP delta in human keratinocytes

BackgroundGenetic experiments have clarified that p63 is a key transcription factor governing the establishment and maintenance of multilayered epithelia. Key to our understanding of p63 strategy is the identification of target genes. We perfomed an RNAi screening in keratinocytes for p63, followed by profiling analysis.ResultsC/EBPδ, member of a family with known roles in differentiation pathways, emerged as a gene repressed by p63. We validated C/EBPδ as a primary target of ΔNp63α by RT-PCR and ChIP location analysis in HaCaT and primary cells. C/EBPδ is differentially expressed in stratification of human skin and it is up-regulated upon differentiation of HaCaT and primary keratinocytes. It is bound to and activates the ΔNp63 promoter. Overexpression of C/EBPδ leads to alteration in the normal profile of p63 isoforms, with the emergence of ΔNp63β and γ, and of the TA isoforms, with different kinetics. In addition, there are changes in the expression of most p63 targets. Inactivation of C/EBPδ leads to gene expression modifications, in part due to the concomitant repression of ΔNp63α. Finally, C/EBPδ is found on the p63 targets in vivo by ChIP analysis, indicating that coregulation is direct.ConclusionOur data highlight a coherent cross-talk between these two transcription factors in keratinocytes and a large sharing of common transcriptional targets.

Mutant p53 subverts p63 control over KLF4 expression in keratinocytes

Genetic experiments established that p63 is crucial for the development and maintenance of pluri-stratified epithelia and KLF4 for the barrier function of the skin. KLF4 is one of the factors that reprogram differentiated cells to iPS. We investigated the relationship between p63 and KLF4 using RNA interference, overexpression, chromatin immunoprecipitation and transient transfections with reporter constructs. We find that p63 directly represses KLF4 in normal keratinocytes (KCs) by binding to upstream promoter sites. Unlike p63, KLF4 levels are high in the upper layers of human skin and increase upon differentiation of KCs in vitro. In HaCaT KCs, which harbor two mutant alleles of p53, inactivation of p63 and of mutant p53 leads to KLF4 repression. p63 and p53 mutants are bound to sites in the KLF4 core promoter. Importantly, expression of the H179Y and R282Q p53 mutants in primary KCs is sufficient to activate endogenous KLF4. Finally, immunohistochemical analysis of tissue arrays confirms increased coexpression of KLF4 and mutant p53 in squamous cell carcinomas. Our data indicate that suppression of KLF4 is part of the growth-promoting strategy of p63 in the lower layers of normal epidermis, and that tumor-predisposing p53 mutations hijack p63 to a different location on the promoter, turning it into an activator of this reprogramming factor.

C/EBPδ gene targets in human keratinocytes.

C/EBPs are a family of B-Zip transcription factors -TFs- involved in the regulation of differentiation in several tissues. The two most studied members -C/EBPα and C/EBPβ- play important roles in skin homeostasis and their ablation reveals cells with stem cells signatures. Much less is known about C/EBPδ which is highly expressed in the granular layer of interfollicular epidermis and is a direct target of p63, the master regular of multilayered epithelia. We identified C/EBPδ target genes in human primary keratinocytes by ChIP on chip and profiling of cells functionally inactivated with siRNA. Categorization suggests a role in differentiation and control of cell-cycle, particularly of G2/M genes. Among positively controlled targets are numerous genes involved in barrier function. Functional inactivation of C/EBPδ as well as overexpressions of two TF targets -MafB and SOX2- affect expression of markers of keratinocyte differentiation. We performed IHC on skin tumor tissue arrays: expression of C/EBPδ is lost in Basal Cell Carcinomas, but a majority of Squamous Cell Carcinomas showed elevated levels of the protein. Our data indicate that C/EBPδ plays a role in late stages of keratinocyte differentiation.

Adipose Derived-Mesenchymal Stem Cells Viability and Differentiating Features for Orthopaedic Reparative Applications: Banking of Adipose Tissue

Osteoarthritis is characterized by loss of articular cartilage also due to reduced chondrogenic activity of mesenchymal stem cells (MSCs) from patients. Adipose tissue is an attractive source of MSCs (ATD-MSCs), representing an effective tool for reparative medicine, particularly for treatment of osteoarthritis, due to their chondrogenic and osteogenic differentiation capability. The treatment of symptomatic knee arthritis with ATD-MSCs proved effective with a single infusion, but multiple infusions could be also more efficacious. Here we studied some crucial aspects of adipose tissue banking procedures, evaluating ATD-MSCs viability, and differentiation capability after cryopreservation, to guarantee the quality of the tissue for multiple infusions. We reported that the presence of local anesthetic during lipoaspiration negatively affects cell viability of cryopreserved adipose tissue and cell growth of ATD-MSCs in culture. We observed that DMSO guarantees a faster growth of ATD-MSCs in culture than trehalose. At last, ATD-MSCs derived from fresh and cryopreserved samples at −80°C and −196°C showed viability and differentiation ability comparable to fresh samples. These data indicate that cryopreservation of adipose tissue at −80°C and −196°C is equivalent and preserves the content of ATD-MSCs in Stromal Vascular Fraction (SVF), guaranteeing the differentiation ability of ATD-MSCs.