Merkel Cell Polyomavirus Large T Antigen is Dispensable in G2 and M-Phase to Promote Proliferation of Merkel Cell Carcinoma Cells.

Merkel cell carcinoma (MCC) is an aggressive skin cancer frequently caused by the Merkel cell polyomavirus (MCPyV), and proliferation of MCPyV-positive MCC tumor cells depends on the expression of a virus-encoded truncated Large T antigen (LT) oncoprotein. Here, we asked in which phases of the cell cycle LT activity is required for MCC cell proliferation. Hence, we generated fusion-proteins of MCPyV-LT and parts of geminin (GMMN) or chromatin licensing and DNA replication factor1 (CDT1). This allowed us to ectopically express an LT, which is degraded either in the G1 or G2 phase of the cell cycle, respectively, in MCC cells with inducible T antigen knockdown. We demonstrate that LT expressed only in G1 is capable of rescuing LT knockdown-induced growth suppression while LT expressed in S and G2/M phases fails to support proliferation of MCC cells. These results suggest that the crucial function of LT, which has been demonstrated to be inactivation of the cellular Retinoblastoma protein 1 (RB1) is only required to initiate S phase entry.

Unknown primary Merkel cell carcinoma with cutaneous spread.

The authors present the case of a woman in the seventh decade of life with medical history of: left nephrectomy for renal tuberculosis and non-Hodgkin's lymphoma treated with chemotherapy (QT) and radiotherapy. She presented with a 2-month history of non-tender, left inguinal lymph node enlargement. Positron Emission Tomography (PET)-CT -scanshowed hypermetabolic inguinal and retroperitoneal lymphadenopathies, no primary tumour. On the second dermatological examination a pink, 2 cm plaque on the anterior left knee was noted. The histopathological analysis revealed Merkel cell carcinoma. The patient underwent two lines of systemic QT, with life-threatening toxicities limiting treatment. Followed overwhelming disease progression with lymphoedema and numerous skin metastases in the left lower limb. The patient received palliative care until death. The rare incidence of such neoplasia and its uncommon clinical presentation justifies reporting this case and highlights the importance of multidisciplinary teams in the management of cancer patients.

Spontaneous regression of Merkel cell carcinoma.

A 96-year-old woman presented with a rapidly enlarging lesion overlying the suprasternal notch. The lesion originated as a small, erythematous, scaly macule that rapidly increased in size over 8 weeks and became an ulcerated nodule measuring 5 cm in diameter and 4.5 cm in thickness. A 4-mm punch biopsy showed a poorly differentiated tumor with cells that were positive for CAM 5.2 and cytokeratin 20 in a dotlike paranuclear pattern and negative for cytokeratin 5/6, human melanoma black 45, and leukocyte common antigen. Two weeks after the punch biopsy, the lesion noticeably decreased in size, and within 8 weeks of the biopsy the tumor had completely resolved with no further intervention. Regression of Merkel cell carcinoma (MCC) is a very rare event, with as few as 30 cases reported. The mechanism of this phenomenon remains unclear; however, T-cell-mediated immunity and apoptosis appear to play a major role.

Merkel cell carcinoma with seborrheic keratosis: A unique association.

Merkel cell carcinoma (MCC) is a rare, clinically aggressive neuroendocrine carcinoma of the skin; MCC is 40 times less common as compared to melanoma. The most frequently reported sites have been the head and neck, extremities, and trunk. Potential mimics include malignant melanoma, lymphoma, or metastatic small cell (neuroendocrine) carcinomas. Histopathology of MCC resembles small cell carcinoma both morphologically and on IHC. The possible cell of origin was proposed as the Merkel cell, which functions as a mechanoreceptor. It has a high chance of local recurrence, regional and distant spread. In recent times, Merkel cell polyomavirus has been implicated as the causative agent for this tumor. The same agent has a reported etiologic association with other skin lesions, including seborrheic keratosis.

Merkel cell carcinoma cardiac metastasis causing cardiac tamponade.

We describe an unusual presentation of Merkel cell carcinoma (MCC), a rare neuroendocrine cutaneous tumour. A 59-year-old man presented with a 2-week history of dyspnoea on a background of MCC of the left elbow that was diagnosed after an axillary lymph node metastasis had appeared. He was clinically diagnosed with cardiac tamponade and received urgent pericardiocentesis. Thoracic CT imaging revealed a large infiltrating mass within the inferior aspect of the heart, confirmed to be MCC via immunohistochemistry of the pericardial fluid. On review of prior fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) imaging, avid uptake was evident at the corresponding site of disease. This case has several important illustrative aspects, including the clinical manifestations of cardiac metastases, the challenges of MCC histopathological diagnosis and the role of imaging (in particular FDG-PET) in this aggressive disease.

Merkel cell polyomavirus infection and Merkel cell carcinoma.

Merkel cell polyomavirus is the only polyomavirus discovered to date that is associated with a human cancer. MCPyV infection is highly prevalent in the general population. Nearly all healthy adults asymptomatically shed MCPyV from their skin. However, in elderly and immunosuppressed individuals, the infection can lead to a lethal form of skin cancer, Merkel cell carcinoma. In the last few years, new findings have established links between MCPyV infection, host immune response, and Merkel cell carcinoma development. This review discusses these recent discoveries on how MCPyV interacts with host cells to achieve persistent infection and, in the immunocompromised population, contributes to MCC development.

Merkel cell carcinoma in a vein graft donor site.

The development of malignancies in graft donor sites is rare and may be caused by de novo malignancies as well as metastatic and iatrogenic spread. Malignancies in graft donor sites are distinguished from Marjolin ulcers by some investigators because they occur in healed surgical wounds rather than in chronic wounds or unstable scars and tend to occur sooner after injury. We present a unique case of Merkel cell carcinoma (MCC) developing in a vein graft donor site 18 years after vein harvesting.

Emerging differential roles of the pRb tumor suppressor in trichodysplasia spinulosa-associated polyomavirus and Merkel cell polyomavirus pathogeneses.

BACKGROUND: Merkel cell carcinoma (MCC) and trichodysplasia spinulosa (TS) are two proliferative cutaneous diseases caused by the Merkel cell polyomavirus (MCPyV) and trichodysplasia spinulosa-associated polyomavirus (TSPyV) respectively. Recently, studies have elucidated a key role of the small tumor (sT) antigen in the proliferative pathogenic mechanisms of MCPyV and likely TSPyV. While both sT antigens have demonstrated a capacity in regulating cellular pathways, it remains unknown whether MCPyV and TSPyV sT antigens contribute similarly or differentially to cell proliferation. OBJECTIVES: The present study aims to explore the proliferative potential of MCPyV and TSPyV sT antigens by investigating their regulatory effects on the retinoblastoma protein (pRb) tumor suppressor. STUDY DESIGN: Inducible cell lines expressing MCPyV sT or TSPyV sT were created using a lentiviral packaging system. Cellular proteins were extracted and subjected to SDS-PAGE followed by Western blot detection and densitometric analysis. RESULTS: Expression of TSPyV sT markedly enhanced the phosphorylation of pRb in Western blot experiments. In contrast, expression of MCPyV sT did not alter pRb phosphorylation under the same experimental conditions. Densitometric analysis revealed that TSPyV sT antigen expression nearly doubled the ratio of phosphorylated to total pRb (P<0.001, Student's T-test), while MCPyV sT antigen expression did not cause significant change in pRb phosphorylation status. CONCLUSION: Given that hyperphosphorylation of pRb is associated with dysregulation of the cell cycle, S-phase induction, and increased cell proliferation, our findings support an important role of TSPyV-mediated pRb deactivation in the development of TS. The observation that the pRb tumor suppressor is inactivated by TSPyV sT but not MCPyV sT provides further insights into the distinct pathobiological mechanisms of MCC and TS.

How does the Merkel polyomavirus lead to a lethal cancer? Many answers, many questions, and a new mouse model.

The Merkel cell polyomavirus (MCPyV), discovered in 2008, drives the development of most Merkel cell carcinomas (MCCs) through several canonical mechanisms. A glaring gap in our knowledge remains the basis by which MCPyV, among all 12 human polyomaviruses, is the only one that causes cancer in humans. Moreover, initial attempts by numerous groups have failed to reproduce MCC in mice using oncoproteins from this polyomavirus. Verhaegen et al. report MCPyV small T-antigen-expressing transgenic mice that now provide insight into in vivo transformation mechanisms.

Merkel cell polyomavirus small T antigen is oncogenic in transgenic mice.

Merkel cell carcinoma (MCC) is a rare and deadly neuroendocrine skin tumor frequently associated with clonal integration of a polyomavirus, Merkel cell polyomavirus (MCPyV), and MCC tumor cells express putative polyomavirus oncoprotein small T antigen (sTAg) and truncated large T antigen. Here, we show robust transforming activity of sTAg in vivo in a panel of transgenic mouse models. Epithelia of preterm sTAg-expressing embryos exhibited hyperplasia, impaired differentiation, increased proliferation, and apoptosis, and activation of a DNA damage response. Epithelial transformation did not require sTAg interaction with the protein phosphatase 2A protein complex, a tumor suppressor in some other polyomavirus transformation models, but was strictly dependent on a recently described sTAg domain that binds Fbxw7, the substrate-binding component of the Skp1/Cullin1/F-box protein ubiquitin ligase complex. Postnatal induction of sTAg using a Cre-inducible transgene also led to epithelial transformation with development of lesions resembling squamous cell carcinoma in situ and elevated expression of Fbxw7 target proteins. Our data establish that expression of MCPyV sTAg alone is sufficient for rapid neoplastic transformation in vivo, implicating sTAg as an oncogenic driver in MCC and perhaps other human malignancies. Moreover, the loss of transforming activity following mutation of the sTAg Fbxw7 binding domain identifies this domain as crucial for in vivo transformation.

Merkel cell polyomavirus large T antigen has growth-promoting and inhibitory activities.

Merkel cell carcinoma (MCC) is a rare and aggressive form of skin cancer. In at least 80% of all MCC, Merkel cell polyomavirus (MCPyV) DNA has undergone clonal integration into the host cell genome, and most tumors express the MCPyV large and small T antigens. In all cases of MCC reported to date, the integrated MCPyV genome has undergone mutations in the large T antigen. These mutations result in expression of a truncated large T antigen that retains the Rb binding or LXCXE motif but deletes the DNA binding and helicase domains. However, the transforming functions of full-length and truncated MCPyV large T antigen are unknown. We compared the transforming activities of full-length, truncated, and alternatively spliced 57kT forms of MCPyV large T antigen. MCPyV large T antigen could bind to Rb but was unable to bind to p53. Furthermore, MCPyV-truncated large T antigen was more effective than full-length and 57kT large T antigen in promoting the growth of human and mouse fibroblasts. In contrast, expression of the MCPyV large T antigen C-terminal 100 residues could inhibit the growth of several different cell types. These data imply that the deletion of the C terminus of MCPyV large T antigen found in MCC serves not only to disrupt viral replication but also results in the loss of a distinct growth-inhibitory function intrinsic to this region.

Carcinoma de células de Merkel. A propósito de un caso / Merkel cell carcinoma. A case report

El Carcinoma de Células de Merkel (CCM) es un tumor inusual de rápido crecimiento y potencial metastático, que presenta una mortalidad elevada (30%) y cuya incidencia está en aumento. Principalmente afecta a las personas de avanzada edad, inmunodeprimidos e historia de fotoexposición prolongada. En el 2008 se estableció su asociación con el Poliomavirus de las células de Merkel (MCPyV) lo que ha supuesto un nuevo campo de investigación. Su manejo está en continua discusión ya que la mayoría de las guías se basan en estudios restrospectivos. Presentamos un caso de CCM en mejilla derecha, en una paciente de 85 años. Esta revisión pretende actualizar los conocimientos de este tumor poco frecuente pero muy agresivo (AU)

The Merkel cell carcinoma (MCC) is an unusual, rapidly growing tumour and potentially metastatic, presenting a high mortality rate (30%), and whose incidence is increasing. It mainly affects people of advanced age, immunodepressed, and with a history of prolonged exposure to the sun. In 2008, an association with Merkel cell polyomavirus (MCPyV) was established, which has led to a new field of research. Its management is under continuous discussion, as most guidelines are based on retrospective studies. We report a case of MCC on the right cheek, in an 85 year old patient. The aim of this report is to update knowledge of this uncommon but very aggressive tumour (AU)

Tumor de Merkel en atención primaria / Merkel cell carcinoma in primary care

El tumor de células de Merkel es una neoplasia maligna cutánea de origen neuroendocrino muy poco frecuente. Afecta principalmente a mujeres mayores de cincuenta años, se localiza por lo general en zonas fotoexpuestas, suele ser asintomático y de rápido crecimiento, presenta un elevado porcentaje de recurrencias y metástasis, siendo el lugar más frecuente de diseminación la piel, seguido por los ganglios regionales. Su tratamiento está aún en controversia. Presentamos el caso clínico de una mujer de 76 años con un nódulo eritematoso en antebrazo derecho que presenta una evolución tórpida siendo el diagnóstico final un tumor de Merkel y que tras el tratamiento mantiene una buena evolución (AU)

Merkel cell tumour is a rare malignant cutaneous neoplasm of neuroendocrine origin. It mainly affects women over 50, is generally located in photo-exposed areas, is normally asymptomatic and of rapid growth. It has a high percentage of recurrences and metastasis, with the most frequent sites of dissemination being the skin, followed by the regional lymph nodes. Its treatment is still controversial. We report a clinical case of a 76-year-old woman with erythematous nodule in the right forearm that was not responding to treatment. The final diagnosis was a Merkel tumour and after the treatment it shows good progress (AU)

Recent advances in the biology of Merkel cell carcinoma.

Recent outstanding research has rapidly revealed new aspects of the biology, etiology, and clinicopathology of Merkel cell carcinoma, a rare but highly aggressive neuroendocrine skin malignancy that affects the elderly and immunosuppressed patients. Molecular biological studies, especially the discovery of Merkel cell polyomavirus, have shed new light on the pathogenesis of the disease. Increasing evidence strongly suggests that this virus is causally related to the development of Merkel cell carcinoma. On the other hand, many studies have also indicated that a subset (approximately 20%) of Merkel cell carcinomas are not likely to be associated with the virus. Tumors with and without the virus have been shown to be significantly different in prognosis, oncogene expression, and histologic appearance, suggesting that they have different etiologies. Moreover, studies on the histopathology, immunohistochemistry, and cytogenetics have revealed several biological factors that are related to the clinical behavior and prognosis of the disease. This review summarizes the advances in the molecular biology of Merkel cell carcinoma based on recent study results. Although the exact molecular pathway of the pathogenesis of Merkel cell carcinoma remains unclear, further understanding of the pathophysiology of this tumor is expected to result in novel therapeutic approaches for management of the disease and contribute to better patient outcomes.

Tumor de células de merkel: revisión de la literatura / Merkel cell tumor: review of literature

El carcinoma de Merkel es un carcinoma primario cutáneo infrecuente. Es una enfermedad potencialmente fatal, con escasa sobrevida en los casos avanzados. Recientemente Feng y col. (2008) identificaron ADN de un nuevo poliomavirus clonalmente integrado en varios casos de carcinoma de Merkel. Esto apoya la posibilidad que dicho virus se encuentre implicado al menos en algunos casos de esta patología. El carcinoma de Merkel carece de características clínicas distintivas, aunque un dato significativo es su rápido crecimiento. Afecta principalmente áreas fotoexpuestas (la mitad de los tumores se localizan en cabeza y cuello) de pacientes añosos. La gran mayoría de ellos se presentan con enfermedad localizada hasta un 30% tiene compromiso de ganglios linfáticos regionales. A pesar de la resección local, las metástasis linfáticas regionales y a distancia son frecuentes y generalmente ocurren en los primeros 2 años del diagnóstico. El tratamiento óptimo aún es incierto, pero los mejores resultados se alcanzan con un manejo interdisciplinario.