AATF/Che-1 acts as a phosphorylation-dependent molecular modulator to repress p53-driven apoptosis.

Following genotoxic stress, cells activate a complex signalling network to arrest the cell cycle and initiate DNA repair or apoptosis. The tumour suppressor p53 lies at the heart of this DNA damage response. However, it remains incompletely understood, which signalling molecules dictate the choice between these different cellular outcomes. Here, we identify the transcriptional regulator apoptosis-antagonizing transcription factor (AATF)/Che-1 as a critical regulator of the cellular outcome of the p53 response. Upon genotoxic stress, AATF is phosphorylated by the checkpoint kinase MK2. Phosphorylation results in the release of AATF from cytoplasmic MRLC3 and subsequent nuclear translocation where AATF binds to the PUMA, BAX and BAK promoter regions to repress p53-driven expression of these pro-apoptotic genes. In xenograft experiments, mice exhibit a dramatically enhanced response of AATF-depleted tumours following genotoxic chemotherapy with adriamycin. The exogenous expression of a phospho-mimicking AATF point mutant results in marked adriamycin resistance in vivo. Nuclear AATF enrichment appears to be selected for in p53-proficient endometrial cancers. Furthermore, focal copy number gains at the AATF locus in neuroblastoma, which is known to be almost exclusively p53-proficient, correlate with an adverse prognosis and reduced overall survival. These data identify the p38/MK2/AATF signalling module as a critical repressor of p53-driven apoptosis and commend this pathway as a target for DNA damage-sensitizing therapeutic regimens.

Mitotic rate in primary melanoma: interobserver and intraobserver reliability, analyzed using H&E sections and immunohistochemistry.

BACKGROUND: In 2009, the AJCC issued a revised melanoma staging system. In addition to tumor thickness and ulceration, the mitotic rate was introduced as the third major prognostic parameter for the classification of primary cutaneous melanoma. Given that, according to the 2009 AJCC classification, the detection of one or more dermal tumor mitoses leads to an upstaging - from stage Ia to Ib - of melanomas with a tumor thickness of ≤ 1.0 mm, we set out to investigate the reproducibility of this new parameter. METHODS: In order to assess interobserver reliability, 17 dermatopathologists und pathologists - all well versed in the diagnosis of cutaneous melanoma - analyzed the mitotic rate in 15 thin primary cutaneous melanomas (mean tumor thickness 0.91 mm) using identical slides. Mitotic rates were determined on H&E and phosphohistone H3 (Ser10)-stained samples. Without knowledge of their previous assessment, five of the aforementioned examiners reevaluated the samples after more than one year in order to ascertain intraobserver reliability. RESULTS: Interobserver reliability of the mitotic rate in thin primary melanomas is disappointing and independent of whether H&E or immunohistochemically stained samples are used (kappa value: 0.088 [H&E], 0.154 [IH], respectively). Kappa values improved to 0.345 (H&E) and 0.403 (IH) when using a cutoff of 0/1 vs. 2+ mitoses. Similarly unsatisfactory, kappa values for intraobserver reliability ranged from 0.18 and 0.348, depending on the individual examiner. DISCUSSION: Given the unsatisfactory reproducibility and large variations in assessing the mitotic rate, it remains a matter of debate whether this diagnostic parameter should play a role in therapeutic decisions.

Mitoserate beim primären Melanom: Interobserver- und Intraobserver-Reproduzierbarkeit am HE-Schnitt und in der Immunhistologie.

HINTERGRUND: Die Melanomklassifikation wurde 2009 durch die AJCC revidiert. Für die Klassifizierung primärer Melanome wurde als dritte Größe neben Tumordicke und Ulzeration die Angabe der Mitoserate neu eingeführt. Gemäß der AJCC-2009-Klassifikation des Melanoms führt der Nachweis nur einer oder mehrerer dermaler Tumormitosen bei Melanomen ≤ 1,0 mm Tumordicke zu einer Umgruppierung des Tumors von T1a nach T1b. Dies erklärt, wie wichtig die Frage nach der Reproduzierbarkeit dieses neuen Parameters ist. METHODEN: Zur Prüfung der Interobserver-Reproduzierbarkeit der Mitoserate haben 17 Dermatopathologen und Pathologen, die in der Befundung des kutanen Melanoms sehr erfahren sind, die Mitoserate in 15 dünnen Melanomen mit einer mittleren Tumordicke von 0,91 mm an demselben Tumorschnitt bestimmt. Die Mitoserate wurde am HE-Schnitt und immunhistologisch (IH) mittels des mitosespezifischen Antikörpers Phospho-Histon-H3 (Ser10) bestimmt. Fünf Befunder wiederholten die Bestimmung nach mehr als einem Jahr ohne Kenntnis ihres Vorbefundes zur Ermittlung der Intraobserver-Reproduzierbarkeit. ERGEBNISSE: Die Interobserver-Reproduzierbarkeit der Mitoserate bei dünnen Melanomen ist unbefriedigend und unabhängig davon, ob die Mitoserate am HE-Schnitt oder am immungefärbten Schnitt bestimmt wird (κ-Werte: 0,088 [HE] bzw. 0,154 [IH]). Bei einer Diskriminationsschwelle von 0/1 vs. 2+ Mitosen verbesserte sich der κ-Wert auf 0,345 (HE) bzw. 0,403 (IH). Die Intraobserver-Reproduzierbarkeit lag mit κ-Werten zwischen 0,18 und 0,348 je nach Befunder ebenfalls im unbefriedigenden Bereich. DISKUSSION: Wegen der unbefriedigenden Reproduzierbarkeit und der großen Variation der Befunde zur Mitoserate bleibt es zweifelhaft, ob dieser Befund als Grundlage für Therapieentscheidungen herangezogen werden kann.

Proteolytic processing regulates placental growth factor activities.

Placental growth factor (PlGF) is a critical mediator of blood vessel formation, yet mechanisms of its action and regulation are incompletely understood. Here we demonstrate that proteolytic processing regulates the biological activity of PlGF. Specifically, we show that plasmin processing of PlGF-2 yields a protease-resistant core fragment comprising the vascular endothelial growth factor receptor-1 binding site but lacking the carboxyl-terminal domain encoding the heparin-binding domain and an 8-amino acid peptide encoded by exon 7. We have identified plasmin cleavage sites, generated a truncated PlGF118 isoform mimicking plasmin-processed PlGF, and explored its biological function in comparison with that of PlGF-1 and -2. The angiogenic responses induced by the diverse PlGF forms were distinct. Whereas PlGF-2 increased endothelial cell chemotaxis, vascular sprouting, and granulation tissue formation upon skin injury, these activities were abrogated following plasmin digestion. Investigation of PlGF/Neuropilin-1 binding and function suggests a critical role for heparin-binding domain/Neuropilin-1 interaction and its regulation by plasmin processing. Collectively, here we provide new mechanistic insights into the regulation of PlGF-2/Neuropilin-1-mediated tissue vascularization and growth.

Mast cells play a protumorigenic role in primary cutaneous lymphoma.

Primary cutaneous lymphomas (PCLs) are clonal T- or B-cell neoplasms, which originate in the skin. In recent years, mast cells were described as regulators of the tumor microenvironment in different human malignancies. Here, we investigated the role of mast cells in the tumor microenvironment of PCL. We found significantly increased numbers of mast cells in skin biopsies from patients with cutaneous T-cell lymphoma (CTCL) and cutaneous B-cell lymphoma (CBCL). Mast cell infiltration was particularly prominent in the periphery, at lymphoma rims. Interestingly, CTCL and CBCL patients with a progressive course showed higher mast cell counts than stable patients, and mast cell numbers in different stages of CTCL correlated positively with disease progression. In addition, mast cell numbers positively correlated with microvessel density. Incubating primary CTCL cells with mast cell supernatant, we observed enhanced proliferation and production of cytokines. In line with our in vitro experiments, in a mouse model of cutaneous lymphoma, tumor growth in mast cell-deficient transgenic mice was significantly decreased. Taken together, these experiments show that mast cells play a protumorigenic role in CTCL and CBCL. Our data provide a rationale for exploiting tumor-associated mast cells as a prognostic marker and therapeutic target in PCL.

Allogeneic stem cell transplantation versus conventional therapy for advanced primary cutaneous T-cell lymphoma.

BACKGROUND: Primary cutaneous T-cell lymphomas (CTCL) belong to the group of non-Hodgkin lymphomas and usually run an indolent course. However, some patients progress to advanced tumour or leukaemic stages. To date, there is no cure for those cases. In the last few years, several publications reported durable responses in some patients following allogeneic stem cell transplantation (alloSCT). This is an update of a Cochrane review first published in 2011 and updated in 2013. OBJECTIVES: To compare the efficacy and safety of conventional therapies with allogeneic stem cell transplantation in patients with advanced primary cutaneous T-cell lymphomas. SEARCH METHODS: We searched the Cochrane Central Register of Controlled Trials (CENTRAL, Issue 1), MEDLINE (1950 to January 2013), Internet-databases of ongoing trials, conference proceedings of the American Society of Clinical Oncology (ASCO, 2009 to July 2013) and the American Society of Hematology (ASH, 2009 to July 2013). We also contacted members of the European Organisation for Research and Treatment of Cancer (EORTC) Cutaneous Lymphoma Task Force to check for ongoing study activities. We handsearched citations from identified trials and relevant review articles. In addition, we handsearched randomised controlled trials from the European Group for Blood and Marrow Transplantation (EBMT) and International Conference on Cutaneous T-cell Lymphoma, ASCO and ASH up to July 2013. SELECTION CRITERIA: Trials eligible for inclusion were genetically randomised controlled trials (RCTs) comparing alloSCT plus conditioning therapy (regardless of agents) with conventional therapy as treatment for advanced CTCL. DATA COLLECTION AND ANALYSIS: Two review authors would have extracted data from eligible studies and assessed their quality. The primary outcome measure was overall survival; secondary outcomes were time to progression, response rate, treatment-related mortality, adverse events and quality of life. MAIN RESULTS: We did not identify any randomised controlled trials from the updated search in January 2013. In 2011, we found 2077 citations but none were relevant genetically or non-genetically randomised controlled trials. All 41 studies that were thought to be potentially suitable were excluded after full text screening for being non-randomised, not including CTCL or being review articles. AUTHORS' CONCLUSIONS: We planned to report evidence from genetically or non-genetically randomised controlled trials comparing conventional therapy and allogeneic stem cell transplantation. However, we did not identify any randomised controlled trials addressing this question. Nevertheless, prospective genetically randomised controlled trials need to be initiated to evaluate the precise role of alloSCT in advanced CTCL.

Treatment of advanced cutaneous T-cell lymphomas with non-pegylated liposomal doxorubicin--consensus of the lymphoma group of the Working Group Dermatologic Oncology.

BACKGROUND: Systemic treatment with pegylated liposomal doxorubicin is an established second-line treatment of advanced cutaneous T-cell lymphoma. Pegylated liposomal doxorubicin (PLD) is currently unavailable, therefore, clinical studies investigating the efficacy of non-pegylated liposomal formula (NPLD) have been analyzed. METHODS: Since clinical trials comparing PLD and NPLD in CTCL do not exist, the clinical use of NPLD including safety and efficiency profile in other types of non-Hodgkin lymphoma were analyzed. RESULTS: Clinical trials show a comparable efficacy of NPLD and PLD in non-Hodgkin lymphoma. The dosage of NPLD used in the treatment of systemic lymphoma within polychemotherapy regimens was 50 mg/m2 every three weeks. Overall response was 75-95%, including a complete remission rate of 65-80% and 2- and 3-year overall survival rates of 55-75%. These data indicate that the non-pegylated formula of doxorubicin has a similar antitumor effect as the pegylated one but shows reduced cardiotoxicity. The palmoplantar erythrodysesthesia frequently observed in PLD has not been observed with the use of the NPLD. CONCLUSIONS: The clinical use of NPLD in the treatment of CTCL is reasonable. In analogy to the clinical trials of NPLD in non-Hodgkin lymphoma a dosage of 50 mg/m(2) every three weeks is recommended for the treatment of CTCL.

Malignant melanoma S3-guideline "diagnosis, therapy and follow-up of melanoma".

This first German evidence-based guideline for cutaneous melanoma was developed under the auspices of the German Dermatological Society (DDG) and the Dermatologic Cooperative Oncology Group (DeCOG) and funded by the German Guideline Program in Oncology. The recommendations are based on a systematic literature search, and on the consensus of 32 medical societies, working groups and patient representatives. This guideline contains recommendations concerning diagnosis, therapy and follow-up of melanoma. The diagnosis of primary melanoma based on clinical features and dermoscopic criteria. It is confirmed by histopathologic examination after complete excision with a small margin. For the staging of melanoma, the AJCC classification of 2009 is used. The definitive excision margins are 0.5 cm for in situ melanomas, 1 cm for melanomas with up to 2 mm tumor thickness and 2 cm for thicker melanomas, they are reached in a secondary excision. From 1 mm tumor thickness, sentinel lymph node biopsy is recommended. For stages II and III, adjuvant therapy with interferon-alpha should be considered after careful analysis of the benefits and possible risks. In the stage of locoregional metastasis surgical treatment with complete lymphadenectomy is the treatment of choice. In the presence of distant metastasis mutational screening should be performed for BRAF mutation, and eventually for CKIT and NRAS mutations. In the presence of mutations in case of inoperable metastases targeted therapies should be applied. Furthermore, in addition to standard chemotherapies, new immunotherapies such as the CTLA-4 antibody ipilimumab are available. Regular follow-up examinations are recommended for a period of 10 years, with an intensified schedule for the first three years.

Allogeneic stem cell transplantation versus conventional therapy for advanced primary cutaneous T-cell lymphoma.

BACKGROUND: Primary cutaneous T-cell lymphomas (CTCL) belong to the group of non-Hodgkin lymphomas and usually run an indolent course. However, some patients progress to advanced tumour or leukaemic stages. Up to now, no curative treatment has been established for those cases. In the last few years, several publications have reported durable responses in some patients following allogeneic stem cell transplantation (alloSCT). OBJECTIVES: To compare the efficacy and safety of conventional therapies with allogeneic stem cell transplantation in patients with advanced primary cutaneous T-cell lymphomas. SEARCH METHODS: The search strategy included the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1950 to May 2011), Internet-databases of ongoing trials (www.controlled-trials.com; www.clinicaltrials.gov), conference proceedings of the American Society of Clinical Oncology (ASCO, 2009 to present) and the American Society of Hematology (ASH, 2009 to present). We also contacted members of the European Organisation for Research and Treatment of Cancer (EORTC) Cutaneous Lymphoma Task Force to check for ongoing study activities. We handsearched citations from identified trials and relevant review articles. In addition, randomised controlled trials from the European Group for Blood and Marrow Transplantation (EBMT) and International Conference on Cutaneous T-cell Lymphoma, ASCO and ASH up to 2010 were handsearched. SELECTION CRITERIA: Genetically randomised controlled trials (RCT) comparing alloSCT plus conditioning therapy regardless of agents with conventional therapy as treatment for advanced CTCL were eligible to be included. DATA COLLECTION AND ANALYSIS: From eligible studies data would have been extracted by two review authors and assessed for quality. Primary outcome measures were overall survival, secondary criteria were time to progression, response rate, treatment-related mortality, adverse events and quality of life. MAIN RESULTS: We found 2077 citations but none were relevant genetically or non-genetically randomised controlled trials. All 41 studies that were thought to be potentially suitable were excluded after full text screening for being non-randomised, not including CTCL or being review articles. AUTHORS' CONCLUSIONS: We planned to report evidence from genetically or non-genetically randomised controlled trials comparing conventional therapy and allogeneic stem cell transplantation. However, no randomised trials addressing this question were identified. Nevertheless, prospective genetically randomised controlled trials need to be initiated to evaluate the precise role of alloSCT in advanced CTCL.

Induction of durable responses by oral etoposide monochemotherapy in patients with metastatic Merkel cell carcinoma.

Merkel cell carcinoma (MCC) is an aggressive, rare tumour of the skin. For advanced cases with distant organ metastases several different regimens of chemotherapeutics have been described. Disease specific 5-year survival rates for these patients are approximately 11%. In this case series we report our experience with orally administered etoposide (100 mg at days 1 to 10 in a 31 day cycle) in 4 patients. We treated two male and two female patients with a median age of 68.5 years. In our four treated patients the disease control rate (complete remission, partial remission, stable disease) was 100%. Three out of four patients reached complete remission. Promisingly, two of our patients had long lasting, durable responses which, until now, have lasted for 16 and 36 months, respectively. The mean follow up time after start of therapy was 14.25 months (range 1-36 months). Etoposide treatment was generally well tolerated, the most common side effect was neutropenia, in one case CTC grade 3. In conclusion, orally administered etoposide in metastatic Merkel cell carcinoma was highly effective and well tolerated.

Histopathological diagnostics of malignant melanoma in accordance with the recent AJCC classification 2009: Review of the literature and recommendations for general practice.

BACKGROUND: TNM classifications are the basis for diagnostic and therapeutic procedures in oncology. Histopathological reports have to enable a proper indexing of tumor specific findings into recent classifications. METHODS: A systematic review of the literature was performed to identify reports dealing with the assessment of mitotic rate and the processing and evaluation of sentinel node biopsies in malignant melanoma. On the basis of this review an expert panel of dermatopathologists and general pathologists discussed and agreed recommendations for general practice. RESULTS: Following recommendations were agreed with a broad consensus (93-100 % agreement): The determination of the mitotic rate in primary melanoma is performed on HE slides. The evaluation of an area of 1 mm(2) is sufficient. Only dermal mitoses are considered. The counted number of mitoses is provided as an integer value. The mitotic rate shall be determined in primary melanomas of ≤1.00 mm vertical tumor thickness according to the hot-spot method and provided as an integer value in relation to an area of 1 mm(2) . The determination of the mitotic rate in the case of thicker primary melanomas is desirable. In general, for the evaluation of each sentinel lymph node, 4 slides should be prepared. For diagnostic purposes, immunohistochemistry (preferably with antibodies against S100ß, Melan A and HMB-45) should be performed in addition to HE staining. The pathology report should provide information about micro-metastases and their longest extension (one-tenth of a millimeter). CONCLUSIONS: These recommendations are suitable for standardizing the histopathological diagnosis of malignant melanoma and for providing a common basis for clinical decisions and scientific research.

Primary perforating granulomatous folliculitis--scarring deep type.

Perforating folliculitis is characterized by asymptomatic skin-coloured or erythematous scattered and aggregated follicular papules with a central keratotic plug. Histologically, a superficial type can be distinguished from the profound type where perforations and rupture of the follicular wall take place at different levels of the hair follicle. This goes along with a granulomatous reaction of the entire pilary complex with destruction of the follicle epithelium and sebaceous gland. Often cases are associated with systemic disorders such as renal diseases or diabetes mellitus. We describe two patients with the profunda type of perforating folliculitis with scarring that manifested in early adulthood without any underlying disorders.

Use of complementary and alternative medicine: A multicenter cross-sectional study in 1089 melanoma patients.

BACKGROUND: About half of patients with cancer use complementary and alternative medicine (CAM). So far, data on melanoma patients are missing. OBJECTIVE: The aim of our study was to evaluate the prevalence and predictors for the use of CAM in this patient group. METHODS: All patients with melanoma being attended at one of 7 skin cancer centres in Germany between March 2012 and March 2013 were invited to take part in a survey using a structured questionnaire on CAM. The physicians filled in a second part on the diagnosis, state and former and current therapy. RESULTS: Nearly half of the 1089 participants (41.0%) used CAM and half of those using CAM (56.8%) marked that this made them feel better. Biological-based CAMs which consists of substances taken were used by 25.9% of all patients (63.1% of those using CAM). Predictors of CAM use were education, psychological support, interest in CAM and previous CAM use. CAM users show higher physical activity, more often use psychosocial help and have contact with a self-help group. Family and friends (41.0%) as well as print media (41.7%) are the main sources of information. Most important reasons to use CAM are to strengthen one's own forces (57.7%) or the immune system (63.4%) and to be able to do something for oneself (53.7%). CONCLUSION: Communication on CAM should become a regular topic in counselling melanoma patients. To increase safety, patients and physicians must have access to evidence-based information on these methods and their interactions with modern cancer treatments.

Interactions from complementary and alternative medicine in patients with melanoma.

Biological-based (BbCAM) methods from complementary and alternative medicine (CAM) may interact with cancer treatments, reduce efficacy, or enhance adverse effects. Although CAM usage has been evaluated well in other cancer entities, data on melanoma patients are still missing. The aim of this study was to determine CAM usage of melanoma patients using a standardized questionnaire to identify potential interactions with established and new systemic melanoma therapies. This multicenter study was carried out in seven German skin cancer centers. During routine care contact, CAM usage of former and current melanoma treatment was assessed in melanoma patients. The probability of interaction was classified into four categories ranging from 'interaction unlikely' (I), 'possible' (II), 'likely' (III), or 'no data' (IV). The questionnaire was filled out by 1157 patients, of whom 1089 were eligible for evaluation. CAM usage was reported by 41% of melanoma patients, of whom 63.1% took BbCAM such as vitamins, trace elements, supplements, or phytotherapeuticals. Of 335 patients with former or current therapy, 28.1% used BbCAM. The melanoma treatment included interferon, radiotherapy, chemotherapy, BRAF-inhibitor, or other tyrosine kinase inhibitors and ipilimumab. On the basis of our model of likelihood of interaction, we found that 23.9% of those on cancer therapy and 85.1% of those also using BbCAM were at some risk of interactions. The main limitation of our study is that no reliable and comprehensive database on clinical relevant interactions with CAM in oncology exists. Most patients receiving a melanoma-specific treatment and using BbCAM methods are at risk for interactions, which raises concerns on the safety and treatment efficacy of these patients. To protect melanoma patients from potential harm by the combination of their cancer treatment and CAM usage, patients should systematically be encouraged to report their CAM use, while oncologists should be trained on evidence of CAM, and patient guidance for saver CAM use.

Melanoma cell-derived vascular endothelial growth factor induces endothelial tubulogenesis within fibrin gels by a metalloproteinase-mediated mechanism.

Angiogenesis is a process required not only for embryonal development but is encountered in wound healing and in pathological situations such as tumour growth. In vitro, formation of capillary-like structures can be induced by seeding human microvascular endothelial cells (HDMECs) on top of a fibrin matrix in the presence of phorbol 12-myristate 13-acetate (PMA) as a stimulating agent. In this study, we show that supernatants collected from high-invasive melanoma cells (BLM) induce the formation of tubular structures similar to PMA treatment whereas supernatants from low-invasive cells (WM164) did not. Analysis of proteins secreted into the supernatant of both melanoma cell lines identified differential expression of several pro-angiogenic proteins in high- and low-invasive melanoma cells. Vascular endothelial growth factor (VEGF) was strongly expressed by high- but not by low-invasive melanoma cells. Neutralisation of VEGF as well as inhibition of matrix metalloproteases (MMPs) using the broad spectrum MMP inhibitor 1,10-phenanthroline, both strongly reduced the melanoma-induced tube formation. PMA treatment of HDMECs on a fibrin matrix stimulated MT1-MMP synthesis, indicating that this protease is involved in PMA-induced angiogenesis. In addition, stimulation of HDMECs by supernatants of BLM melanoma cells resulted in a strong induction of ADAM-15, which is known to act as a metalloproteinase. In conclusion, these results show that VEGF released by melanoma cells is an important mediator of neo-vascularisation and that this process depends on the presence of metalloproteinases.

Risk of interactions between complementary and alternative medicine and medication for comorbidities in patients with melanoma.

Complementary and alternative medicine (CAM) is used widely among cancer patients. Beside the risk of interaction with cancer therapies, interactions with treatment for comorbidities are an underestimated problem. The aim of this study was to assess prevalence of interactions between CAM and drugs for comorbidities from a large CAM usage survey on melanoma patients and to classify herb-drug interactions with regard to their potential to harm. Consecutive melanoma outpatients of seven skin cancer centers were asked to complete a standardized CAM questionnaire including questions to their CAM use and their taken medication for comorbidities and cancer. Each combination of conventional drugs and complementary substances was evaluated for their potential of interaction. 1089 questionnaires were eligible for evaluation. From these, 61.6% of patients reported taking drugs regularly from which 34.4% used biological-based CAM methods. Risk evaluation for interaction was possible for 180 CAM users who listed the names or substances they took for comorbidities. From those patients, we found 37.2% at risk of interaction of their co-consumption of conventional and complementary drugs. Almost all patients using Chinese herbs were at risk (88.6%). With a high rate of CAM usage at risk of interactions between CAM drugs and drugs taken for comorbidities, implementation of a regular assessment of CAM usage and drugs for comorbidities is mandatory in cancer care.

Endothelial progenitor cell sprouting in spheroid cultures is resistant to inhibition by osteoblasts: a model for bone replacement grafts.

Survival of tissue transplants generated in vitro is strongly limited by the slow process of graft vascularization in vivo. A method to enhance graft vascularization is to establish a primitive vascular plexus within the graft prior to transplantation. Endothelial cells (EC) cultured as multicellular spheroids within a collagen matrix form sprouts resembling angiogenesis in vitro. However, osteoblasts integrated into the graft suppress EC sprouting. This inhibition depends on direct cell-cell-interactions and is characteristic of mature ECs isolated from preexisting vessels. In contrast, sprouting of human blood endothelial progenitor cells is not inhibited by osteoblasts, making these cells suitable for tissue engineering of pre-vascularized bone grafts.

Downregulation of STRA6 expression in epidermal keratinocytes leads to hyperproliferation-associated differentiation in both in vitro and in vivo skin models.

Retinoids are known to affect skin cell proliferation and differentiation and are key molecules that target retinoid and retinoic acid receptors (RXRs and RARs), leading to physiological and pharmacologic effects. Our aim was to elucidate the role of the retinol-binding protein receptor STRA6, mediating cellular uptake of retinol, on skin structure and function. Our results indicate that STRA6 is constitutively expressed in human epidermal keratinocytes and dermal fibroblasts and is regulated via RAR/RXR-mediated pathways. HaCaT (Human adult low Calcium high Temperature) cells with stable STRA6 knockdown (STRA6KD) showed increased proliferation. Consistently, human organotypic 3D skin models using stable STRA6KD HaCaT cells showed a significantly thicker epidermis and enhanced expression of activation, differentiation, and proliferation markers. The effects were reversible after treatment with free retinol. Human skin reconstitution employing STRA6KD HaCaT cells leads to massive epithelial thickening under in vivo conditions in SCID mice. We propose that STRA6KD could lead to cellular vitamin A deficiency in keratinocytes. Consequently, STRA6 has a role for regulating retinoid homeostasis and in helping to program signaling that drives proliferation and differentiation of human skin cells. By its influence on hyperproliferation-associated differentiation, STRA6 could also have a role in skin regeneration and could be a target for pharmacological approaches to improve wound healing.