Merkel cell carcinoma: if no breslow, then what?
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Carcinoma, Merkel Cell↗
Biomedical subjects
Paul Nghiem
Publications and source records attributed to Paul Nghiem.
The protective role of a small GTPase RhoE against UVB-induced DNA damage in keratinocytes.
RhoE, a p53 target gene, was identified as a critical factor for the survival of human keratinocytes in response to UVB. The Rho family of GTPases regulates many aspects of cellular behavior through alterations to the actin cytoskeleton, acting as molecular switches cycling between the active, GTP-bound and the inactive, GDP-bound conformations. Unlike typical Rho family proteins, RhoE (also known as Rnd3) is GTPase-deficient and thus expected to be constitutively active. In this study, we investigated the response of cultured human keratinocyte cells to UVB irradiation. RhoE protein levels increase upon exposure to UVB, and ablation of RhoE induction through small interfering RNA resulted in a significant increase in apoptosis and a reduction in the levels of the pro-survival targets p21, Cox-2, and cyclin D1, as well as an increase of reactive oxygen species levels when compared with control cells. These data indicate that RhoE is a pro-survival factor acting upstream of p38, JNK, p21, and cyclin D1. HaCat cells expressing small interfering RNA to p53 indicate that RhoE functions independently of its known associates, p53 and Rho-associated kinase I (ROCK I). Targeted expression of RhoE in epidermis using skin-specific transgenic mouse model resulted in a significant reduction in the number of apoptotic cells following UVB irradiation. Thus, RhoE induction counteracts UVB-induced apoptosis and may serve as a novel target for the prevention of UVB-induced photodamage regardless of p53 status.
Animals↗
Role of skin biopsy to confirm suspected acute graft-vs-host disease: results of decision analysis.
OBJECTIVE: To estimate the value of skin biopsy in the evaluation of suspected acute cutaneous graft-vs-host disease (GVHD) after allogeneic stem cell transplantation. DESIGN: Decision analysis using parameters specified by expert opinion for skin biopsy characteristics, prevalence of acute GVHD, and value of potential outcomes. One-, 2-, and 3-way sensitivity analyses were performed. SETTING: Major stem cell transplantation centers in the United States. PATIENTS: Hypothetical cohort of patients with suspected acute cutaneous GVHD after stem cell transplantation. INTERVENTIONS: The following 3 interventions were compared: treat immediately for GVHD without performing a skin biopsy, perform a skin biopsy and treat immediately but stop treatment if skin biopsy specimen findings are inconsistent with GVHD, and perform a skin biopsy and await results of the skin biopsy specimen before treating. MAIN OUTCOME MEASURES: Number of patients appropriately and inappropriately treated with each intervention, consistency of physician-reported behavior, individualized decision analyses, and preferred intervention based on the aggregate estimates of respondents. RESULTS: The decision to treat immediately for GVHD without performing a skin biopsy yielded the best clinical outcome for the specified clinical setting and under the parameters specified by expert opinion. One-way sensitivity analyses showed that these conclusions are robust if the prevalence of acute cutaneous GVHD in stem cell recipients with rash is greater than 50%, if the sensitivity of skin biopsy specimen is less than 0.8, and the specificity of skin biopsy specimen is less than 0.9. Only 25% of physicians interviewed chose an intervention consistent with their estimates of prevalence, test characteristics, and outcome evaluations, indicating an opportunity to improve management of this important clinical condition. CONCLUSIONS: This decision analysis modeling technique predicts that in patient populations in which the prevalence of GVHD is 30% or greater (typical for allogeneic stem cell transplantation), the best outcomes were obtained with treatment for GVHD and no skin biopsy. In populations with prevalence of GVHD of 30% or less, obtaining a skin biopsy specimen to guide treatment was predicted to provide the best patient outcomes.
Acute Disease↗
Sentinel lymph node biopsy for evaluation and treatment of patients with Merkel cell carcinoma: The Dana-Farber experience and meta-analysis of the literature.
OBJECTIVE: To determine the diagnostic accuracy and usefulness of sentinel lymph node biopsy (SLNB) and computed tomographic scans in the initial evaluation and treatment of patients with Merkel cell carcinoma (MCC). DESIGN: Single-institution case series and literature-based case-level meta-analysis. SETTING: Academic cutaneous oncology clinic.Patients Sixty-one adults with biopsy-proven MCC (30 who had undergone SLNB) plus 92 cases from the literature of patients who had undergone SLNB. MAIN OUTCOME MEASURES: Relapse-free survival. RESULTS: In 122 patients with no nodal disease found by physical examination, SLNB findings revealed nodal involvement in 39 cases (32%). At 3 years, the recurrence rate for those with a positive SLNB was 3 times (60%) higher than for those with a negative SLNB (20%; P = .03). Patients with a positive SLNB who received adjuvant nodal therapy had a relapse-free survival rate of 51% at 3 years (n = 26) compared with 0% for patients who did not receive nodal therapy (n = 3; P < .01). In contrast, among patients with a negative SLNB there was no significant difference in 3-year relapse-free survival rates for those who did (90%; n = 24) or did not (70%; n = 19; P = .26) receive adjuvant nodal therapy. Using SLNB plus clinical follow-up as a gold standard, computed tomographic scans had low sensitivity (20%) for detecting MCC that had spread to the lymph node basin and low specificity for distant disease (only 4 of 21 "positive" scans were confirmed during 6 months of follow-up). CONCLUSIONS: Sentinel lymph node biopsy detects MCC spread in one third of patients whose tumors would have otherwise been clinically and radiologically understaged and who may not have received treatment to the involved node bed. There was a significant benefit of adjuvant nodal therapy, but only when the SLNB was positive. Thus, SLNB is important for both prognosis and therapy and should be performed routinely for patients with MCC. In contrast, computed tomographic scans have poor sensitivity in detecting nodal disease as well as poor specificity in detecting distant disease.
Adult↗
A robust small-molecule microarray platform for screening cell lysates.
Herein we report the expanded functional group compatibility of small-molecule microarrays to include immobilization of primary alcohols, secondary alcohols, phenols, carboxylic acids, hydroxamic acids, thiols, and amines on a single slide surface. Small-molecule "diversity microarrays" containing nearly 10,000 known bioactive small molecules, natural products, and small molecules originating from several diversity-oriented syntheses were produced by using an isocyanate-mediated covalent capture strategy. Selected printed bioactive compounds were detected with antibodies against compounds of interest. The new surface of the diversity microarrays is highly compatible with approaches involving cellular lysates. This feature has enabled a robust, optimized screening methodology using cellular lysates, allowing the detection of specific interactions with a broad range of binding affinity by using epitope-tagged or chimeric fluorescent proteins without prior purification. We believe that this expanded research capability has considerable promise in biology and medicine.
Cell Line↗
Tissue eosinophils and the perils of using skin biopsy specimens to distinguish between drug hypersensitivity and cutaneous graft-versus-host disease.
Graft-versus-host disease (GvHD) is a frequent and serious complication of bone-marrow transplantation (BMT), and carries a high morbidity and mortality if not promptly recognized and treated. The rash of acute GvHD is often difficult to distinguish clinically from a drug eruption, and skin biopsies are often performed in an attempt to render a diagnosis. Histologically, eosinophils are classically associated with hypersensitivity reactions, and their presence in inflamed tissue is considered suggestive of a drug-induced dermatitis. We present 3 cases of acute exanthema in BMT recipients in whom the presence of eosinophils on skin biopsy specimen led to an initial diagnosis of drug eruption over GvHD. As a result, these patients experienced delays in the institution of definitive immunosuppressive therapy for GvHD. We review the growing literature suggesting that no single or combined histologic feature, including tissue eosinophils, is useful in differentiating GvHD from drug eruptions in BMT recipients. Indeed, in most cases, the cause of a new-onset blanchable erythematous rash in a BMT recipient is most accurately determined by close examination and follow-up of the clinical features without a skin biopsy.
Adult↗
Human immunodeficiency virus type 1 Vpr-mediated G2 arrest requires Rad17 and Hus1 and induces nuclear BRCA1 and gamma-H2AX focus formation.
Eukaryotic cells have evolved a complex mechanism for sensing DNA damage during genome replication. Activation of this pathway prevents entry into mitosis to allow for either DNA repair or, in the event of irreparable damage, commitment to apoptosis. Under conditions of replication stress, the damage signal is initiated by the ataxia-telangiectasia-mutated and Rad3-related kinase ATR. We recently demonstrated that the human immunodeficiency virus type 1 (HIV-1) gene product viral protein R (Vpr) arrests infected cells in the G(2) phase via the activation of ATR. In the present study, we show that the activation of ATR by Vpr is analogous to activation by certain genotoxic agents, both mechanistically and in its downstream consequences. Specifically, we show a requirement for Rad17 and Hus1 to induce G(2) arrest as well as Vpr-induced phosphorylation of histone 2A variant X (H2AX) and formation of nuclear foci containing H2AX and breast cancer susceptibility protein 1. These results demonstrate that G(2) arrest mediated by the HIV-1 gene product Vpr utilizes the cellular signaling pathway whose physiological function is to recognize replication stress. These findings should contribute to a greater understanding of how HIV-1 manipulates the CD4(+)-lymphocyte cell cycle and apoptosis induction in the progressive CD4(+)-lymphocyte depletion characteristic of HIV-1 pathogenesis.
Animals↗
Activation of the ATR-mediated DNA damage response by the HIV-1 viral protein R.
DNA damage is a universal inducer of cell cycle arrest at the G2 phase. Infection by the human immunodeficiency virus type 1 (HIV-1) also blocks cellular proliferation at the G2 phase. The HIV-1 accessory gene vpr encodes a conserved 96-amino acid protein (Vpr) that is necessary and sufficient for the HIV-1-induced block of cellular proliferation. In the present study, we examined a recently identified DNA damage-signaling protein, the ATM- and Rad3-related protein, ATR, for its potential role in the induction of G2 arrest by Vpr. We show that inhibition of ATR by pharmacological inhibitors, by expression of the dominant-negative form of ATR, or by RNA interference inhibits Vpr-induced cell cycle arrest. As with DNA damage, activation of ATR by Vpr results in phosphorylation of Chk1. This study provides conclusive evidence of activation of the ATR-initiated DNA damage-signaling pathway by a viral gene product. These observations are important toward understanding how HIV infection promotes cell cycle disruption, cell death, and ultimately, CD4+ lymphocyte depletion.
Antineoplastic Agents↗
Merkel cell carcinoma treatment with radiation: a good case despite no prospective studies.
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Carcinoma, Merkel Cell↗
Integration of growth factor and nutrient signaling: implications for cancer biology.
Signaling networks that promote cell growth are frequently dysregulated in cancer. One regulatory network, which converges on effectors such as 4EBP1 and S6K1, leads to growth by promoting protein synthesis. Here, we discuss how this network is regulated by both extracellular signals, such as growth factors, and intracellular signals, such as nutrients. We discuss how mutations amplifying either type of signal can lead to tumor formation. In particular, we focus on the recent discovery that a tumor suppressor complex whose function is lost in tuberous sclerosis patients regulates the nutrient signal carried by the critical signaling protein TOR to the effectors 4EBP1 and S6K1. Finally, we describe how the small molecule rapamycin, which inhibits TOR and thereby the activation of these effectors, could be useful to treat tumors that have become dependent upon this pathway for growth.
Adaptor Proteins, Signal Transducing↗
ATR regulates fragile site stability.
Conditions that partially inhibit DNA replication induce expression of common fragile sites. These sites form gaps and breaks on metaphase chromosomes and are deleted and rearranged in many tumors. Yet, the mechanism of fragile site expression has been elusive. We demonstrate that the replication checkpoint kinase ATR, but not ATM, is critical for maintenance of fragile site stability. ATR deficiency results in fragile site expression with and without addition of replication inhibitors. Thus, we propose that fragile sites are unreplicated chromosomal regions resulting from stalled forks that escape the ATR replication checkpoint. These findings have important implications for understanding both the mechanism of fragile site instability and the consequences of stalled replication in mammalian cells.
2-Aminopurine↗
The standard of care for Merkel cell carcinoma should include adjuvant radiation and lymph node surgery.
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Carcinoma, Merkel Cell↗
Tacrolimus and pimecrolimus: from clever prokaryotes to inhibiting calcineurin and treating atopic dermatitis.
Tacrolimus ointment, a topical inhibitor of the phosphatase calcineurin, has recently been approved in the United States for use in the treatment of atopic dermatitis. It is the first topical immune suppressant that is not one of the hydrocortisone derivatives, important allies in dermatology for nearly 50 years. Although tacrolimus is less able to penetrate thick skin than glucocorticoids, it does not cause dermal atrophy, an important advantage over the hydrocortisone class. Pimecrolimus (ASM 981), a newer calcineurin inhibitor closely related to tacrolimus, is also being developed for atopic dermatitis therapy. Pimecrolimus has an altered skin penetration profile but the same mechanism of action as tacrolimus. In this review we chronicle the discovery of the calcineurin inhibitors, their presumed evolutionary role as a bacterial "smart bomb" against fungi, molecular and cellular mechanisms of action in the immune system, systemic and topical side effects, efficacy in atopic dermatitis, and future applications within the specialty of dermatology. Particular attention is given to the issues of systemic absorption of tacrolimus, the conditions in which absorption can become a concern, efficacy relative to glucocorticoids, and the choice of 0.03% or 0.1% tacrolimus ointment for use in adults and children.
Administration, Topical↗
ATR is not required for p53 activation but synergizes with p53 in the replication checkpoint.
ATR (ataxia telangiectasia and Rad-3-related) is a protein kinase required for survival after DNA damage. A critical role for ATR has been hypothesized to be the regulation of p53 and other cell cycle checkpoints. ATR has been shown to phosphorylate p53 at Ser(15), and this damage-induced phosphorylation is diminished by expression of a catalytically inactive (ATR-kd) mutant. p53 function could not be examined directly in prior studies of ATR, however, because p53 was mutant or because cells expressed the SV40 large T antigen that blocks p53 function. To test the interactions of ATR and p53 directly we generated human U2OS cell lines inducible for either wild-type or kinase-dead ATR that also have an intact p53 pathway. Indeed, ATR-kd expression sensitized these cells to DNA damage and caused a transient decrease in damage-induced serine 15 phosphorylation of p53. However, we found that the effects of ATR-kd expression do not result in blocking the response of p53 to DNA damage. Specifically, prior ATR-kd expression had no effect on DNA damage-induced p53 protein up-regulation, p53-DNA binding, p21 mRNA up-regulation, or G(1) arrest. Instead of promoting survival via p53 regulation, we found that ATR protects cells by delaying the generation of mitotic phosphoproteins and inhibiting premature chromatin condensation after DNA damage or hydroxyurea. Although p53 inhibition (by E6 or MDM2 expression) had little effect on premature chromatin condensation, when combined with ATR-kd expression there was a marked loss of the replication checkpoint. We conclude that ATR and p53 can function independently but that loss of both leads to synergistic disruption of the replication checkpoint.
Ataxia Telangiectasia Mutated Proteins↗