Activation of the PI3K/AKT pathway in Merkel cell carcinoma

Comparison of Akt/mTOR/4E-BP1 pathway signal activation and mutations of PIK3CA in Merkel cell polyomavirus-positive and Merkel cell polyomavirus-negative carcinomas

Merkel cell polyomavirus (MCPyV) integrates monoclonally into the genomes of approximately 80% of Merkel cell carcinomas (MCCs), affecting their clinicopathological features. The molecular mechanisms underlying MCC development after MCPyV infection remain unclear. We investigated the association of MCPyV infection with activation of the Akt/mammalian target of rapamycin (mTOR)/4E-binding protein 1 (4E-BP1) signaling pathway in MCCs to elucidate the role of these signal transductions and to identify molecular targets for treatment. We analyzed the molecular and pathological characteristics of 41 MCPyV-positive and 27 MCPyV-negative MCCs. Expression of mTOR, TSC1, and TSC2 messenger RNA was significantly higher in MCPyV-negative MCCs, and Akt (T308) phosphorylation also was significantly higher (92% vs 66%; P = .019), whereas 4E-BP1 (S65 and T70) phosphorylation was common in both MCC types (92%-100%). The expression rates of most other tested signals were high (60%-100%) and not significantly correlated with MCPyV large T antigen expression. PIK3CA mutations were observed more frequently in MCPyV-positive MCCs (6/36 [17%] vs 2/20 [10%]). These results suggest that protein expression (activation) of most Akt/mTOR/4E-BP1 pathway signals was not significantly different in MCPyV-positive and MCPyV-negative MCCs, although these 2 types may differ in tumorigenesis, and MCPyV-negative MCCs showed significantly more frequent p-Akt (T308) activation. Therefore, certain Akt/mTOR/4E-BP1 pathway signals could be novel therapeutic targets for MCC regardless of MCPyV infection status.

Mutational analysis of merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine malignancy that is associated with a poor prognosis. The pathogenesis of MCC is not well understood, and despite a recent plethora of mutational analyses, we have yet to find a set of signature mutations implicated in the majority of cases. Mutations, including TP53, Retinoblastoma and PIK3CA, have been documented in subsets of patients. Other mechanisms are also likely at play, including infection with the Merkel cell polyomavirus in a subset of patients, dysregulated immune surveillance, epigenetic alterations, aberrant protein expression, posttranslational modifications and microRNAs. In this review, we summarize what is known about MCC genetic mutations and chromosomal abnormalities, and their clinical significance. We also examine aberrant protein function and microRNA expression, and discuss the therapeutic and prognostic implications of these findings. Multiple clinical trials designed to selectively target overexpressed oncogenes in MCC are currently underway, though most are still in early phases. As we accumulate more molecular data on MCC, we will be better able to understand its pathogenic mechanisms, develop libraries of targeted therapies, and define molecular prognostic signatures to enhance our clinicopathologic knowledge.

BET protein inhibitor JQ1 attenuates Myc-amplified MCC tumor growth in vivo

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin currently with no cure. In this study, we have first demonstrated that c-Myc overexpression is common in MCC. By targeting c-Myc, bromodomain inhibitors have demonstrated antitumor efficacy in several preclinical human cancer models. Thus, we interrogated the role of c-Myc inhibition in MCC with c-Myc amplification by using the BET inhibitor JQ1. We have uncovered that c-Myc can be regulated by JQ1 in MCC cells with pathologic c-Myc activation. Moreover, JQ1 potently abrogates c-Myc expression in MCC cells and causes marked G1 cell-cycle arrest. Mechanistically, JQ1-induced cell-cycle arrest coincides with downregulation of cyclin D1 and upregulation of p21, p27, and p57, whereas JQ1 exerts no effect on apoptosis in MCC cells. Further knockdown of p21, p27, or p57 by shRNA partially protects cells from JQ1-induced cell-cycle arrest. In addition, c-Myc knockdown by shRNA generates significant cell-cycle arrest, suggesting that c-Myc overexpression plays a role in MCC pathogenesis. Most importantly, JQ1 significantly attenuates tumor growth in xenograft MCC mouse models. Our results provide initial evidence, indicating the potential clinical utility of BET protein inhibitors in the treatment of MCC with pathologic activation of c-Myc.

Molecular pathology of skin neoplasms of the head and neck

CONTEXT

Skin neoplasms include the most common malignancies affecting humans. Many show an ultraviolet (UV)-induced pathogenesis and often affect the head and neck region.

OBJECTIVE

To review literature on cutaneous neoplasms that show a predilection for the head and neck region and that are associated with molecular alterations.

DATA SOURCES

Literature review.

CONCLUSIONS

Common nonmelanoma skin cancers, such as basal and squamous cell carcinomas, show a UV-induced pathogenesis. Basal cell carcinomas are characterized by molecular alterations of the Hedgehog pathway, affecting patched and smoothened genes. While squamous cell carcinomas show UV-induced mutations in several genes, driver mutations are only beginning to be identified. In addition, certain adnexal neoplasms also predominantly affect the head and neck region and show interesting, recently discovered molecular abnormalities, or are associated with hereditary conditions whose molecular genetic pathogenesis is well understood. Furthermore, recent advances have led to an increased understanding of the molecular pathogenesis of melanoma. Certain melanoma subtypes, such as lentigo maligna melanoma and desmoplastic melanoma, which are more often seen on the chronically sun-damaged skin of the head and neck, show differences in their molecular signature when compared to the other more common subtypes, such as superficial spreading melanoma, which are more prone to occur at sites with acute intermittent sun damage. In summary, molecular alterations in cutaneous neoplasms of the head and neck are often related to UV exposure. Their molecular footprint often reflects the histologic tumor type, and familiarity with these changes will be increasingly necessary for diagnostic and therapeutic considerations.

Retinoblastoma gene mutations detected by whole exome sequencing of Merkel cell carcinoma

Merkel cell carcinoma is a highly aggressive cutaneous neuroendocrine tumor that has been associated with Merkel cell polyomavirus in up to 80% of cases. Merkel cell polyomavirus is believed to influence pathogenesis, at least in part, through expression of the large T antigen, which includes a retinoblastoma protein-binding domain. However, there appears to be significant clinical and morphological overlap between polyomavirus-positive and polyomavirus-negative Merkel cell carcinoma cases. Although much of the recent focus of Merkel cell carcinoma pathogenesis has been on polyomavirus, the pathogenesis of polyomavirus-negative cases is still poorly understood. We hypothesized that there are underlying human somatic mutations that unify Merkel cell carcinoma pathogenesis across polyomavirus status, and to investigate we performed whole exome sequencing on five polyomavirus-positive cases and three polyomavirus-negative cases. We found that there were no significant differences in the overall number of single-nucleotide variations, copy number variations, insertion/deletions, and chromosomal rearrangements when comparing polyomavirus-positive to polyomavirus-negative cases. However, we did find that the retinoblastoma pathway genes harbored a high number of mutations in Merkel cell carcinoma. Furthermore, the retinoblastoma gene (RB1) was found to have nonsense truncating protein mutations in all three polyomavirus-negative cases; no such mutations were found in the polyomavirus-positive cases. In all eight cases, the retinoblastoma pathway dysregulation was confirmed by immunohistochemistry. Although polyomavirus-positive Merkel cell carcinoma is believed to undergo retinoblastoma dysregulation through viral large T antigen expression, our findings demonstrate that somatic mutations in polyomavirus-negative Merkel cell carcinoma lead to retinoblastoma dysregulation through an alternative pathway. This novel finding suggests that the retinoblastoma pathway dysregulation leads to an overlapping Merkel cell carcinoma phenotype and that oncogenesis occurs through either a polyomavirus-dependent (viral large T antigen expression) or polyomavirus-independent (host somatic mutation) mechanism.

Akt and p53R2, partners that dictate the progression and invasiveness of cancer

The serine/threonine kinase or the so-called "Akt" is a key regulatory molecule of signaling pathway that regulates various cellular processes. Many intracellular proteins are involved in the activation or inhibition of Akt signaling and the hyperactivation of Akt signaling pathway is found to be frequently involved in various types of human cancers. Furthermore, while p53R2, a p53-inducible peptide involved in the synthesis of dNTPs normally works toward suppression of cancer through elimination of reactive oxygen species (ROS), inhibition of MAPK/ERK pathway and providing dNTPs for DNA repair, the overexpression of p53R2 is reported to be associated with cancer progression and resistance to therapy. In this review article, we will discuss the situation in which cancer cells with hyperactive PI3K/Akt signaling can recruit p53R2 in favor of cancer progression and resistance to therapy. In the hyperactive state of PI3K/Akt signaling (which happens in the absence of deactivation or excess of activation), p53R2 can be used by cancer cells to promote proliferation. Therefore, the hyperactivity of PI3K/Akt pathway and elevated levels of p53R2 can give rise to highly invasive cancers.

Merkel cell carcinoma - recent advances in the biology, diagnostics and treatment

Merkel cell carcinoma (MCC) is an uncommon primary cutaneous carcinoma with neuroendocrine differentiation. Since recent discovery of MCCs strong association with Merkel cell polyomavirus (MCPyV), there has been a rapid increase in the understanding of the carcinomas genetics, molecular biology and pathogenesis. In our study, we reviewed recent advances and controversies concerning MCC histogenesis, epidemiology, diagnostic and prognostic markers. We analyzed the association of MCPyV with MCC and the possible new targets for therapy. We also examined English-based literature regarding MCC pathogenesis published between 2008 and 2013, which lead to a deeper understanding of the topic. Our study showed that the association of MCPyV strongly influences the course of MCC. Additionally, it has been shown that a immunological response to MCPyV may in the future give hope to identify new therapeutic strategies in treatment of this fatal malignancy. This article is part of a Directed Issue entitled: Rare Cancers.

Characterization of the Merkel Cell Carcinoma miRNome

MicroRNAs have been implicated in various skin cancers, including melanoma, squamous cell carcinoma, and basal cell carcinoma; however, the expression of microRNAs and their role in Merkel cell carcinoma (MCC) have yet to be explored in depth. To identify microRNAs specific to MCC (MCC-miRs), next-generation sequencing (NGS) of small RNA libraries was performed on different tissue samples including MCCs, other cutaneous tumors, and normal skin. Comparison of the profiles identified several microRNAs upregulated and downregulated in MCC. For validation, their expression was measured via qRT-PCR in a larger group of MCC and in a comparison group of non-MCC cutaneous tumors and normal skin. Eight microRNAs were upregulated in MCC: miR-502-3p, miR-9, miR-7, miR-340, miR-182, miR-190b, miR-873, and miR-183. Three microRNAs were downregulated: miR-3170, miR-125b, and miR-374c. Many of these MCC-miRs, the miR-183/182/96a cistron in particular, have connections to tumorigenic pathways implicated in MCC pathogenesis. In situ hybridization confirmed that the highly expressed MCC-miR, miR-182, is localized within tumor cells. Furthermore, NGS and qRT-PCR reveal that several of these MCC-miRs are highly expressed in the patient-derived MCC cell line, MS-1. These data indicate that we have identified a set of MCC-miRs with important implications for MCC research.

Merkel Cell Carcinoma: Epidemiology, Target, and Therapy

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin with a rising incidence. MCC has metastatic potential regardless the size of the primary tumor and a 5-year disease associated mortality rate is 46 %. Surgery and radiation are the mainstays of management for primary MCC. There is no evidence-based effective chemotherapy for recurrent or metastatic diseases to date. In-depth mechanistic studies in MCC have uncovered important cellular events and the association with a polyomavirus, which has provided direct evidence for molecular targeted and immunotherapy. Further perspective studies and clinical trials are warranted to provide reliable evidence of possible pitfalls and effectiveness of molecular targeted immunotherapy alone or in combination with chemotherapy in MCC.

Chronic mTOR activation promotes cell survival in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive skin cancer with rising incidence. In this study, we demonstrate that mTOR activation and suppressed autophagy is common in MCCs. mTOR inhibition in two primary human MCC cell lines induces autophagy and cell death that is independent of caspase activation but can be attenuated by autophagy inhibition. This is the first study to evaluate mTOR and autophagy in MCC. Our data suggests a potential role of autophagic cell death upon mTOR inhibition and thus uncovers a previously underappreciated role of mTOR signaling and cell survival, and merits further studies for potential therapeutic targets.

Emerging and mechanism-based therapies for recurrent or metastatic Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine skin cancer with a disease-specific mortality of approximately 40 %. The association of MCC with a recently discovered polyomavirus, combined with the increased incidence and mortality of MCC among immunocompromised patients, highlight the importance of the immune system in controlling this cancer. Initial management of MCC is summarized within the NCCN guidelines and in recently published reviews. The high rate of recurrent and metastatic disease progression in MCC, however, presents a major challenge in a cancer that lacks mechanism-based, disease-specific therapies. Traditional treatment approaches have focused on cytotoxic chemotherapy that, despite frequent initial efficacy, rarely provides durable responses and has high morbidity among the elderly. In addition, the immunosuppressive nature of chemotherapy is of concern when treating a virus-associated cancer for which survival is unusually tightly linked to immune function. With a median survival of 9.6 months after development of an initial metastasis (n = 179, described herein), and no FDA-approved agents for this cancer, there is an urgent need for more effective treatments. We review diverse management options for patients with advanced MCC, with a focus on emerging and mechanism-based therapies, some of which specifically target persistently expressed viral antigens. These treatments include single-dose radiation and novel immunotherapies, some of which are in clinical trials. Due to their encouraging efficacy, low toxicity, and lack of immune suppression, these therapies may offer viable alternatives to traditional cytotoxic chemotherapy.

Expression of anaplastic lymphoma kinase in Merkel cell carcinomas

This study examines the presence of anaplastic lymphoma kinase protein and anaplastic lymphoma kinase gene rearrangements in Merkel cell carcinomas. A total of 32 cases of Merkel cell carcinomas and 12 cases of small cell lung carcinomas were analyzed. Immunohistochemistry was performed using 3 different anaplastic lymphoma kinase antibody clones (D5F3, 5A4, and anaplastic lymphoma kinase 1). Tumors were divided into high (intensity score 2-3+ in ≥25% of the tumor cells) and low expressors (all other positive expression patterns). Anaplastic lymphoma kinase reactivity in Merkel cell carcinoma was observed in 93.8% (30/32) with clone D5F3, 87.5% (28/32) with clone 5A4, and 12.5% (4/32) with clone anaplastic lymphoma kinase 1. One small cell lung carcinoma (1/12; 8.3%) showed anaplastic lymphoma kinase low expression with clone D5F3. Anaplastic lymphoma kinase high expression was observed in 81.3% (26/32) of the Merkel cell carcinomas with clone D5F3, 71.9% (23/32) with clone 5A4, and none with clone anaplastic lymphoma kinase 1. The specificity of anaplastic lymphoma kinase expression in Merkel cell carcinoma versus small cell lung carcinoma was 91.7% with clone D5F3 and 100% with the clones 5A4 and anaplastic lymphoma kinase 1. Interphase fluorescence in situ hybridization with the anaplastic lymphoma kinase dual-color, break-apart rearrangement probe was performed on 10 randomly selected Merkel cell carcinoma anaplastic lymphoma kinase high expressors. No rearrangement or other cytogenetic aberration of the anaplastic lymphoma kinase gene locus was identified. In conclusion, the anaplastic lymphoma kinase protein was detected with high frequency in Merkel cell carcinomas and was useful in distinguishing Merkel cell carcinoma from small cell lung carcinoma. No correlation with anaplastic lymphoma kinase rearrangement was found. Our findings could have important therapeutic consequences for patients, but the role of anaplastic lymphoma kinase in the pathogenesis of Merkel cell carcinoma needs to be further elucidated.

A cornucopia of human polyomaviruses

During the past 6 years, focused virus hunting has led to the discovery of nine new human polyomaviruses, including Merkel cell polyomavirus, which has been linked to Merkel cell carcinoma, a lethal skin cell cancer. The discovery of so many new and highly divergent human polyomaviruses raises key questions regarding their evolution, tropism, latency, reactivation, immune evasion and contribution to disease. This Review describes the similarities and differences among the new human polyomaviruses and discusses how these viruses might interact with their human host.

Merkel cell polyomavirus: a newly discovered human virus with oncogenic potential

A marked escalation in the rate of discovery of new types of human polyomavirus has occurred over the last five years largely owing to recent technological advances in their detection. Among the newly discovered viruses, Merkel Cell Polyomavirus (MCPyV or MCV) has gained the most attention due to its link with a rare human cancer. Infection with MCPyV is common in the human population, and the virus is detected in several anatomical locations, but most frequently in skin. Study of MCPyV molecular virology has been complicated by the lack of straightforward cell culture models, but recent in vitro studies are making strides towards understanding the virus life cycle, its cellular tropism, and mode of transmission. While MCPyV shares several traditional traits with other human polyomaviruses, the burst of research since its discovery reveals insight into a virus with many unique genetic and mechanistic features. The evidence for a causal link between MCPyV and the rare neuroendocrine cancer, Merkel Cell Carcinoma (MCC), is compelling. A majority of MCCs contain clonally integrated viral DNA, express viral T antigen transcripts and protein, and exhibit an addiction to the viral large T and small t antigen oncoproteins. The MCPyV large T antigen contains MCC tumor-specific mutations that ablate its replication capacity but preserve its oncogenic functions, and the small t antigen promotes an environment favorable for cap-dependent translation. The mechanisms of MCPyV-induced transformation have not been fully elucidated, but the likely etiological role of this new polyomavirus in human cancer provides a strong opportunity to expand knowledge of virus-host interactions and viral oncology.

A Proteomic Study of Human Merkel Cell Carcinoma

Merkel Cell Carcinoma (MCC) is an aggressive neuroendocrine cancer of the skin. The incidence has been quadrupled with a 5-year mortality rate of 46%, presently there is no cure for metastatic disease. Despite the contribution of Merkel cell polyomavirus, the molecular events of MCC carcinogenesis are poorly defined. To better understand MCC carcinogensis, we have performed the first quantitative proteomic comparison of formalin-fixed, paraffin-embedded (FFPE) MCC tissues using another neuroendocrine tumor (carcinoid tumor of the lung) as controls. Bioinformatic analysis of the proteomic data has revealed that MCCs carry distinct protein expression patterns. Further analysis of significantly over-expressed proteins suggested the involvement of MAPK, PI3K/Akt/mTOR, wnt, and apoptosis signaling pathways. Our previous study and that from others have shown mTOR activation in MCCs. Therefore, we have focused on two downstream molecules of the mTOR pathway, lactate dehydrogenase B (LDHB) and heterogeneous ribonucleoprotein F (hnRNPF). We confirm over-expression of LDHB and hnRNPF in two primary human MCC cell lines, 16 fresh tumors, and in the majority of 80 tissue microarray samples. Moreover, mTOR inhibition suppresses LDHB and hnRNPF expression in MCC cells. The results of the current study provide insight into MCC carcinogenesis and provide rationale for mTOR inhibition in pre-clinical studies.

Merkel cell carcinoma: 30-year experience from a single institution

BACKGROUND

Merkel cell carcinoma (MCC) is a rare cutaneous malignancy. Few single-institution series have been reported.

METHODS

Review of MCC patients treated at our institution between 1980 and 2010. Patient, tumor, and treatment variables were analyzed to determine MCC-specific outcomes.

RESULTS

We identified 161 patients with MCC. There was a 2.5-fold increase in cases over the last decade. Median length of follow-up was 36 months. Stage at diagnosis was I in 35 %, II in 21 %, IIIa in 12 %, IIIb in 23 %, and IV in 9 %. The 5-year MCC-specific survival rates were 87, 63, 42, and 0 % for stages I, II, III, and IV, respectively. Death from the disease occurred in 10 % of patients with T1 and in 50 % with larger lesions. One-third of patients presented with nodal disease. Sentinel lymph node biopsy (SLNB) identified micrometastases in 9 out of 27 (33 %) early-stage patients. Recurrence developed in 56 % of SLNB-positive and 39 % of SLNB-negative patients. Half of patients recurred after a median time of 9 months. Proportions of first recurrence location were distant (52 %), nodal (27 %), and local (21 %). Adjuvant treatments did not improve recurrence or survival rates. One-third of patients died of the disease.

CONCLUSIONS

SLNB identifies micrometastasis in one-third of early-stage patients. Negative SLNB may predict for improved but not necessarily favorable outcome. Initial tumor size and clinical nodal disease predict for poor outcome. High recurrence rates warrant the development of more effective adjuvant therapies, and better markers of recurrence and treatment response for MCC are needed.

Improved detection suggests all Merkel cell carcinomas harbor Merkel polyomavirus

A human polyomavirus was recently discovered in Merkel cell carcinoma (MCC) specimens. The Merkel cell polyomavirus (MCPyV) genome undergoes clonal integration into the host cell chromosomes of MCC tumors and expresses small T antigen and truncated large T antigen. Previous studies have consistently reported that MCPyV can be detected in approximately 80% of all MCC tumors. We sought to increase the sensitivity of detection of MCPyV in MCC by developing antibodies capable of detecting large T antigen by immunohistochemistry. In addition, we expanded the repertoire of quantitative PCR primers specific for MCPyV to improve the detection of viral DNA in MCC. Here we report that a novel monoclonal antibody detected MCPyV large T antigen expression in 56 of 58 (97%) unique MCC tumors. PCR analysis specifically detected viral DNA in all 60 unique MCC tumors tested. We also detected inactivating point substitution mutations of TP53 in the two MCC specimens that lacked large T antigen expression and in only 1 of 56 tumors positive for large T antigen. These results indicate that MCPyV is present in MCC tumors more frequently than previously reported and that mutations in TP53 tend to occur in MCC tumors that fail to express MCPyV large T antigen.

Fatty acid synthase regulates proliferation and migration of colorectal cancer cells via HER2-PI3K/Akt signaling pathway

Recent evidence suggests that fatty acid synthase mediating de novo fatty acid synthesis plays a crucial role in the carcinogenesis process of various cancers. Moreover, HER2 and related PI3K/Akt signaling pathway, which links intimately with cellular metabolism, influence cancer biological behavior. However, it remains unknown whether malignant phenotype of colorectal cancer cells is regulated by the HER2-PI3K/Akt-FASN signaling pathway. In this study, Caco-2 cells were selected for functional characterization, and treated with ZSTK474, followed by RT-qPCR and Western blot assays examining PI3K, Akt, HER2, and FASN expression. The MTT and colony formation assays were used to assess proliferation. The migration was investigated by transwell, apoptosis, and cell-cycle analysis. We found that the blockade of PI3K/Akt signaling pathway by ZSTK474 treatment led to downregulation of PI3K, Akt, HER2, and FASN expression. The proliferation was decreased upon treatment which was consistent with an increased percentage of G(1) arrested cells instead of apoptosis. The migration of Caco-2 cells was also impaired by ZSTK474 treatment. Inhibition of HER2-PI3K/Akt signaling pathway suppresses FASN expression of Caco-2 cells, and inhibition of FASN expression changes malignant phenotype of Caco-2 cells.