SKI pathways inducing progression of human melanoma

Overexpressed ski efficiently promotes neurorestoration, increases neuronal regeneration, and reduces astrogliosis after traumatic brain injury

Traumatic brain injury (TBI) survivors suffer from long-term disability and neuropsychiatric sequelae due to irreparable brain tissue destruction. However, there are still few efficient therapies to promote neurorestoration in damaged brain tissue. This study aimed to investigate whether the pro-oncogenic gene ski can promote neurorestoration after TBI. We established a ski-overexpressing experimental TBI mouse model using adenovirus-mediated overexpression through immediate injection after injury. Hematoxylin-eosin staining, MRI-based 3D lesion volume reconstruction, neurobehavioral tests, and analyses of neuronal regeneration and astrogliosis were used to assess neurorestorative efficiency. The effects of ski overexpression on the proliferation of cultured immature neurons and astrocytes were evaluated using imaging flow cytometry. The Ski protein level increased in the perilesional region at 3 days post injury. ski overexpression further elevated Ski protein levels up to 14 days post injury. Lesion volume was attenuated by approximately 36-55% after ski overexpression, with better neurobehavioral recovery, more newborn immature and mature neurons, and less astrogliosis in the perilesional region. Imaging flow cytometry results showed that ski overexpression elevated the proliferation rate of immature neurons and reduced the proliferation rate of astrocytes. These results show that ski can be considered a novel neurorestoration-related gene that effectively promotes neurorestoration, facilitates neuronal regeneration, and reduces astrogliosis after TBI.

Intra-Abdominal Malignant Melanoma: Challenging Aspects of Epidemiology, Clinical and Paraclinical Diagnosis and Optimal Treatment—A Literature Review

According to European consensus-based interdisciplinary guidelines for melanoma, cutaneous melanoma (CM) is the most deadly form of dermatological malignancy, accounting for 90% of the deaths of skin cancer patients. In addition to cutaneous melanoma, mucosal melanoma occurs in four major anatomical sites, including the upper respiratory tract, the conjunctiva, the anorectal region, and the urogenital area. As this cancer type metastasizes, a classification used in the current medical literature is the distinction between secondary lesions and primary malignant melanoma of the abdominal cavity. Given that malignant melanoma is the most common cancer that spreads to the gastrointestinal tract, different imaging modalities compete to diagnose the phenomenon correctly and to measure its extension. Treatment is primarily surgery-based, supported by immunotherapy, and prolongs survival, even when performed at stage IV illness. In the end, special forms of malignant melanoma are discussed, such as melanoma of the genito-urinary tract and amelanotic/achromic melanoma. The importance of this present literature review relies on yielding and grouping consistent and relevant, updated information on the many aspects and challenges that a clinician might encounter during the diagnosis and treatment of a patient with intra-abdominal melanoma.

Ski: Double roles in cancers

The Ski (Sloan-Kettering Institute) is an evolutionarily conserved protein that plays a dual role as an oncoprotein and tumor suppressor gene in the development of human cancer. The Ski oncogene was first identified as a transforming protein of the avian Sloan-Kettering retrovirus in 1986. Since its discovery, Ski has been identified as a carcinogenic regulator in a variety of malignant tumors. Later, it was reported that Ski regulates the occurrence and development of some cancers by acting as an oncogene. Ski mediates the proliferation, differentiation, metastasis, and invasion of numerous cancer cells through various mechanisms. Several studies have shown that Ski expression is correlated with the clinical characteristics of cancer patients and is a promising biomarker and therapeutic target for cancer. In this review, we summarize the mechanisms and potential clinical implications of Ski in dimorphism, cancer occurrence, and progression in various types of cancer.

Knockdown of Ski decreases osteosarcoma cell proliferation and migration by suppressing the PI3K/Akt signaling pathway

Ski, an evolutionary conserved protein, is involved in the development of a number of tumors, such as Barrett's esophagus, leukemia, colorectal cancer, gastric cancer, pancreatic cancer, hemangiomas and melanoma. However, studies on the functions of Ski in osteosarcoma (OS) are limited. In this study, firstly the differential expression of Ski in OS tissues and osteochondroma tissues was detected, and the expression of Ski in both human OS cell lines (MG63 and U2OS) and normal osteoblasts (hFoB1.19) was then detected. The results demonstrated that Ski expression was significantly upregulated in both human OS tissues and cell lines. The results led us to hypothesize that Ski may play an essential role in the pathological process of OS. Thus, Ski specific small interfere RNA (Ski-siRNA) was used. The results revealed that OS cell proliferation was markedly inhibited following the knockdown of Ski, which was identified by CCK8 assay, EdU staining and cell cycle analysis. In addition, OS cell migration was significantly suppressed following Ski knockdown, which was identified by wound healing assay. Moreover, the protein levels of p-PI3K and p-Akt in OS cells declined prominently following Ski knockdown. On the whole, the findings of this study revealed that Ski expression was significantly upregulated in OS tissue and OS cells. The knockdown of Ski decreased OS cell proliferation and migration, which was mediated by blocking the PI3K/Akt signaling pathway. Thus, Ski may act as a tumor promoter gene in tumorigenesis, and Ski may prove to be a potential therapeutic target for the treatment of OS.

Promoter hypomethylation of SKI in autoimmune pancreatitis

The relationship between methylation abnormality and autoimmune pancreatitis (AIP)-a representative IgG4-related disease-has not yet been elucidated. We identified SKI might have a significant methylation abnormality in AIP through methylation array analysis using the Illumina Infinium Human Methylation 450K BeadChip array, and investigated the relationship of SKI with AIP clinicopathological features. The methylation rate of SKI was assessed by quantitative SYBR green methylation-specific PCR, and the degree of SKI expression in tissue specimens was assessed by immunohistochemistry in 10 AIP cases, 14 cases of obstructive pancreatitis area in pancreatic ductal adenocarcinoma (PDA) without a history of AIP, and 9 normal pancreas (NP) cases. The SKI methylation ratio was significantly lower in AIP than in PDA and NP. Additionally, the immunohistochemical staining-index (SI) score for SKI was significantly higher in AIP than NP, although there was no significant difference between AIP and PDA. There was a strong negative correlation between SI score and SKI methylation ratio, and between the serum concentrations of IgG4 and the SKI methylation ratio. There was a moderate positive correlation between the serum concentrations of IgG4 and SI. SKI is thought to be an oncogene indicating that SKI hypomethylation and carcinogenesis might be linked to AIP. Furthermore, the correlation between serum concentrations of IgG4 and SKI methylation levels suggest SKI might be involved in the pathogenesis of AIP. However, the role of SKI has not been clearly elucidated. Further studies are needed to understand further the function of SKI.

Translocation of BBAP from the cytoplasm to the nucleus reduces the metastatic ability of vemurafenib-resistant SKMEL28 cells

To the best of our knowledge, the present study is the first to demonstrate that treatment of vemurafenib-resistant SKMEL28 (SKMEL28-R) cells with paclitaxel leads to a shift in localization of the E3-ligase BBAP from the cytoplasm to the nucleus, consequently decreasing the metastatic ability of this cell line. The present study revealed that the movement of BBAP from the cytoplasm to nucleus initiated a change in cell morphology. In addition, the translocation of BBAP led to a decrease of metastatic characteristics in SKMEL28‑R cells, including migration and invasion via downregulation of the phosphorylated form of focal adhesion kinase and N‑cadherin, as well as an upregulation of p21 and E-cadherin. The results of the present study suggested that BBAP may not only be a novel biomarker for melanoma, but also a novel therapeutic target for treatment of metastatic melanoma.

MiR-1908 promotes scar formation post-burn wound healing by suppressing Ski-mediated inflammation and fibroblast proliferation

The cell biological basis for scar formation is mainly via excessive fibroblast proliferation accompanied by hypernomic Col I accumulation and inflammation. The role of miR-1908 in scar formation has not been investigated. In this study, we found that miR-1908 expression was inversely associated with the scar suppressor Ski in normal, burn-wounded, healing and scar dermal tissues in humans. Bioinformatics and luciferase reporter gene assays confirmed that miR-1908 targeted the 3'UTR region of Ski mRNA and suppressed Ski expression. Next, human scar epidermal fibroblasts were isolated and the miR-1908 oligonucleotide mimic and inhibitor were respectively transfected into the cells. Western blot analysis proved that Ski expression was sharply reduced by the miR-1908 mimic. MTT and Cell Counting Kit-8 analyses showed that miR-1908 mimic transfection promoted cell proliferation. Simultaneously, data on real-time qPCR analysis indicated that expression of the fibrotic master gene TGF-β1, Ski-suppressing gene Meox2, Col I and proinflammatory markers IL-1α and TNF-α, were all significantly upregulated. In contrast, the miR-1908 inhibitor had a completely opposite effect on cell proliferation and gene expression. The mimic and inhibitor were locally injected into rats with abdominal burn-wounded scars during a 180-day, post-healing experiment. The miR-1908 mimic injection significantly reduced Ski expression, as well as the area, volume and fibrosis of scars in vivo. And, in contrast, the miR-1908 inhibitor injection had an opposite effect to that of the miR-1908 mimic injection. In conclusion, miR-1908 had a positive role in scar formation by suppressing Ski-mediated inflammation and fibroblast proliferation in vitro and in vivo.

Novel regulation of Ski protein stability and endosomal sorting by actin cytoskeleton dynamics in hepatocytes

TGF-β-induced antimitotic signals are highly regulated during cell proliferation under normal and pathological conditions, such as liver regeneration and cancer. Up-regulation of the transcriptional cofactors Ski and SnoN during liver regeneration may favor hepatocyte proliferation by inhibiting TGF-β signals. In this study, we found a novel mechanism that regulates Ski protein stability through TGF-β and G protein-coupled receptor (GPCR) signaling. Ski protein is distributed between the nucleus and cytoplasm of normal hepatocytes, and the molecular mechanisms controlling Ski protein stability involve the participation of actin cytoskeleton dynamics. Cytoplasmic Ski is partially associated with actin and localized in cholesterol-rich vesicles. Ski protein stability is decreased by TGF-β/Smads, GPCR/Rho signals, and actin polymerization, whereas GPCR/cAMP signals and actin depolymerization promote Ski protein stability. In conclusion, TGF-β and GPCR signals differentially regulate Ski protein stability and sorting in hepatocytes, and this cross-talk may occur during liver regeneration.

Genome-wide DNA methylation profile of leukocytes from melanoma patients with and without CDKN2A mutations

Melanoma is a highly aggressive cancer, accounting for up to 75% of skin cancer deaths. A small proportion of melanoma cases can be ascribed to the presence of highly penetrant germline mutations, and approximately 40% of hereditary melanoma cases are caused by CDKN2A mutations. The current study sought to investigate whether the presence of germline CDKN2A mutations or the occurrence of cutaneous melanoma would result in constitutive genome-wide DNA methylation changes. The leukocyte methylomes of two groups of melanoma patients (those with germline CDKN2A mutations and those without CDKN2A mutations) were analyzed together with the profile of a control group of individuals. A pattern of DNA hypomethylation was detected in the CDKN2A-negative patients relative to both CDKN2A-mutated patients and controls. Additionally, we delineated a panel of 90 CpG sites that were differentially methylated in CDKN2A-mutated patients relative to controls. Although we identified a possible constitutive epigenetic signature in CDKN2A-mutated patients, the occurrence of reported SNPs at the detected CpG sites complicated the data interpretation. Thus, further studies are required to elucidate the impact of these findings on melanoma predisposition and their possible effect on the penetrance of CDKN2A mutations.

Ski protein levels increase during in vitro progression of HPV16-immortalized human keratinocytes and in cervical cancer

We compared the levels of the Ski oncoprotein, an inhibitor of transforming growth factor-beta (TGF-β) signaling, in normal human keratinocytes (HKc), HPV16 immortalized HKc (HKc/HPV16), and differentiation resistant HKc/HPV16 (HKc/DR) in the absence and presence of TGF-β. Steady-state Ski protein levels increased in HKc/HPV16 and even further in HKc/DR, compared to HKc. TGF-β treatment of HKc, HKc/HPV16, and HKc/DR dramatically decreased Ski. TGF-β-induced Ski degradation was delayed in HKc/DR. Ski and phospho-Ski protein levels are cell cycle dependent with maximal Ski expression and localization to centrosomes and mitotic spindles during G2/M. ShRNA knock down of Ski in HKc/DR inhibited cell proliferation. More intense nuclear and cytoplasmic Ski staining and altered Ski localization were found in cervical cancer samples compared to adjacent normal tissue in a cervical cancer tissue array. Overall, these studies demonstrate altered Ski protein levels, degradation and localization in HPV16-transformed human keratinocytes and in cervical cancer.

Differential role of Sloan-Kettering Institute (Ski) protein in Nodal and transforming growth factor-beta (TGF-β)-induced Smad signaling in prostate cancer cells

Transforming growth factor-beta (TGF-β) signaling pathways contain both tumor suppressor and tumor promoting activities. We have demonstrated that Nodal, another member of the TGF-β superfamily, and its receptors are expressed in prostate cancer cells. Nodal and TGF-β exerted similar biological effects on prostate cells; both inhibited proliferation in WPE, RWPE1 and DU145 cells, whereas neither had any effect on the proliferation of LNCaP or PC3 cells. Interestingly, Nodal and TGF-β induced migration in PC3 cells, but not in DU145 cells. TGF-β induced predominantly phosphorylation of Smad3, whereas Nodal induced phosphorylation of only Smad2. We also determined the expression and differential role of Ski, a corepressor of Smad2/3, in Nodal and TGF-β signaling in prostate cancer cells. Similar levels of Ski mRNA were found in several established prostate cell lines; however, high levels of Ski protein were only detected in prostate cancer cells and prostate cancer tissue samples. Exogenous Nodal and TGF-β had no effects on Ski mRNA levels. On the other hand, TGF-β induced a rapid degradation of Ski protein mediated by the proteasomal pathway, whereas Nodal had no effect on Ski protein. Reduced Ski levels correlated with increased basal and TGF-β-induced Smad2/3 phosphorylation. Knockdown of endogenous Ski reduced proliferation in DU145 cells and enhanced migration of PC3 cells. We conclude that high levels of Ski expression in prostate cancer cells may be responsible for repression of TGF-β and Smad3 signaling, but Ski protein levels do not influence Nodal and Smad2 signaling.

BMP2 signals loss of epithelial character in epicardial cells but requires the Type III TGFβ receptor to promote invasion

Coronary vessel development depends on a subpopulation of epicardial cells that undergo epithelial to mesenchymal transformation (EMT) and invade the subepicardial space and myocardium. These cells form the smooth muscle of the vessels and fibroblasts, but the mechanisms that regulate these processes are poorly understood. Mice lacking the Type III Transforming Growth Factor β Receptor (TGFβR3) die by E14.5 due to failed coronary vessel development accompanied by reduced epicardial cell invasion. BMP2 signals via TGFβR3 emphasizing the importance of determining the relative contributions of the canonical BMP signaling pathway and TGFβR3-dependent signaling to BMP2 responsiveness. Here we examined the role of TGFβR3 in BMP2 signaling in epicardial cells. Whereas TGFβ induced loss of epithelial character and smooth muscle differentiation, BMP2 induced an ALK3-dependent loss of epithelial character and modestly inhibited TGFβ-stimulated differentiation. Tgfbr3(-/-) cells respond to BMP2 indicating that TGFβR3 is not required. However, Tgfbr3(-/-) cells show decreased invasion in response to BMP2 and overexpression of TGFβR3 in Tgfbr3(-/-) cells rescued invasion. Invasion was dependent on ALK5, ALK2, ALK3, and Smad4. Expression of TGFβR3 lacking the 3 C-terminal amino acids required to interact with the scaffolding protein GIPC (GAIP-interacting protein, C terminus) did not rescue. Knockdown of GIPC in Tgfbr3(+/+) or Tgfbr3(-/-) cells rescued with TGFβR3 decreased BMP2-stimulated invasion confirming a requirement for TGFβR3/GIPC interaction. Our results reveal the relative roles of TGFβR3-dependent and TGFβR3-independent signaling in the actions of BMP2 on epicardial cell behavior and demonstrate the critical role of TGFβR3 in mediating BMP2-stimulated invasion.

A two-gene signature, SKI and SLAMF1, predicts time-to-treatment in previously untreated patients with chronic lymphocytic leukemia

We developed and validated a two-gene signature that predicts prognosis in previously-untreated chronic lymphocytic leukemia (CLL) patients. Using a 65 sample training set, from a cohort of 131 patients, we identified the best clinical models to predict time-to-treatment (TTT) and overall survival (OS). To identify individual genes or combinations in the training set with expression related to prognosis, we cross-validated univariate and multivariate models to predict TTT. We identified four gene sets (5, 6, 12, or 13 genes) to construct multivariate prognostic models. By optimizing each gene set on the training set, we constructed 11 models to predict the time from diagnosis to treatment. Each model also predicted OS and added value to the best clinical models. To determine which contributed the most value when added to clinical variables, we applied the Akaike Information Criterion. Two genes were consistently retained in the models with clinical variables: SKI (v-SKI avian sarcoma viral oncogene homolog) and SLAMF1 (signaling lymphocytic activation molecule family member 1; CD150). We optimized a two-gene model and validated it on an independent test set of 66 samples. This two-gene model predicted prognosis better on the test set than any of the known predictors, including ZAP70 and serum β2-microglobulin.

Differential effect of the expression of TGF-β pathway inhibitors, Smad-7 and Ski, on invasive breast carcinomas: relation to biologic behavior

The aim of our study was to investigate the expression of Smad-7 and Ski proteins in invasive breast carcinomas, to determine their clinicopathological value and their influence on carcinomas biologic behavior. Immunohistochemistry was applied on 150 invasive breast carcinomas to detect the expression of Smad-7 and Ski. Their correlation to clinicopathologic parameters and markers of metastasis was statistically processed using chi-squared test. Overall and disease-free survival was assessed using Kaplan-Meier test and log-rank statistics. Smad-7 was immunodetected in the cytoplasm of cancer cells in 60%, whereas Ski was immunodetected in the cytoplasm and nuclei in 44.5% and 17.6% of the cases, respectively. Smad-7 expression was positively correlated with tumor size, stage, matrix metalloproteinase (MMP)-9, and MMP-14. Cytoplasmic Ski expression was negatively associated with tumor size, stage, and lymph node status, and its nuclear expression was negatively related to histologic grade. Cytoplasmic Ski expression was associated with longer overall and disease-free survival. It appears that two negative regulators of the transforming growth factor-β pathway, Smad-7 and Ski, behave differentially in invasive breast carcinomas. Smad-7 appears to be related with an aggressive phenotype, whereas Ski expression is related to a less aggressive behavior and positively influences patients' survival.

Preparation of novel anti-ski monoclonal antibodies

Ski is an avian sarcoma virus oncogene homolog best known for inhibiting TGF beta signaling through its association with the SMAD proteins. Anti-Ski antibodies (MAbs) of high titer were prepared by immunizing BALB/c mice with multifocal intradermal injections and fusing high titer antibody producing spleen cells with myeloma cells of SP2/0 origin. Three MAbs were selected for further characterization as classes and subclasses. Antibodies were produced by these three clones with high affinities ranging from 10(9) to 10(11)/m. These clones were found to be of the immunoglobulin IgG1 and IgG2b subclass with kappa light chain. They could recognize Ski as determined by Western blot analysis. The produced MAbs will be a useful tool for further investigation of Ski functions in organisms.

Lentigo Maligna: Melanoma In Situ on Chronically Sun-Damaged Skin

Context.—Cutaneous primary invasive malignant melanoma often is classified by its histologic appearance. Major recognized histologic subtypes of melanoma include superficial spreading, lentigo maligna melanoma, nodular, and acral lentiginous. More recently, it has been shown that most primary invasive melanomas harbor nonrandom genetic or biochemical aberrations that correlate with anatomic site or with the amount of cutaneous exposure to sunlight. It also is generally accepted that most primary invasive melanomas are preceded by an intraepidermal atypical melanocytic proliferation that lacks invasive capability (melanoma in situ).

Objective.—To focus on lentigo maligna, the preinvasive/in situ form of melanoma located on chronically sun-damaged skin.

Data Sources.—Review of the literature and the authors' personal experiences.

Conclusions.—A better understanding of the earliest stage of melanoma progression, including the contribution of chronic exposure to ultraviolet radiation, may lead to improved classification schemes that direct more effective targeted or personalized therapies for patients.

MicroRNA-155 targets the SKI gene in human melanoma cell lines

The SKI protein is a transcriptional coregulator over-expressed in melanoma. Experimentally induced down-regulation of SKI inhibits melanoma cell growth in vitro and in vivo. MicroRNAs (miRNAs) negatively modulate gene expression and have been implicated in oncogenesis. We previously showed that microRNA-155 (miR-155) is down-regulated in melanoma cells as compared with normal melanocytes and that its ectopic expression impairs proliferation and induces apoptosis. Here, we investigated whether miR-155 could mediate melanoma growth inhibition via SKI gene silencing. Luciferase reporter assays demonstrated that miR-155 interacted with SKI 3'UTR and impaired gene expression. Transfection of melanoma cells with miR-155 reduced SKI levels, while inhibition of endogenous miR-155 up-regulated SKI expression. Specifically designed small interfering RNAs reduced SKI expression and inhibited proliferation. However, melanoma cells over-expressing a 3'UTR-deleted SKI were still susceptible to the antiproliferative effect of miR-155. Our data demonstrate for the first time that SKI is a target of miR-155 in melanoma. However, impairment of SKI expression is not the leading mechanism involved in the growth-suppressive effect of miR-155 found in this malignancy.

SnoN: bridging neurobiology and cancer biology

The transcriptional regulator SnoN has been the subject of growing interest due to its diverse functions in normal and pathological settings. A large body of evidence has established a fundamental role for SnoN as a modulator of signaling and responses by the transforming growth beta (TGFbeta) family of cytokines, though how SnoN regulates TGFbeta responses remains incompletely understood. In accordance with the critical and complex roles of TGFbeta in tumorigenesis and metastasis, SnoN may act as a tumor promoter or suppressor depending on the stage and type of cancer. Beyond its role in cancer, SnoN has also been implicated in the control of axon morphogenesis in postmitotic neurons in the mammalian brain. Remarkably, signaling pathways that control SnoN functions in the divergent cycling cells and postmitotic neurons appear to be conserved. Identification of novel SnoN regulatory and effector mechanisms holds the promise of advances at the interface of cancer biology and neurobiology.

Efficient TGF-β/SMAD signaling in human melanoma cells associated with high c-SKI/SnoN expression

Background

SKI and SnoN proteins have been shown to inhibit TGF-β signaling, acting both as transcriptional co-repressors in the cell nucleus, and as sequestrators of SMAD proteins in the cytoplasm. TGF-β, on the other hand, induces rapid, proteasome-mediated, degradation of both proteins. How elevated SKI and SnoN protein levels co-exist with active autocrine TGF-β signaling in cancer cells is yet to be understood.

Results

In this study, we found elevated SKI and SnoN protein levels in a panel of melanoma cell lines, as compared to normal melanocytes. There was no correlation between SKI protein content and the capacity of melanoma cells to invade Matrigel™, to form subcutaneous tumors, or to metastasize to bone after intracardiac inoculation into nude mice. Nor did we find a correlation between SKI expression and histopathological staging of human melanoma. TGF-β induced a rapid and dose-dependent degradation of SKI protein, associated with SMAD3/4 specific transcriptional response and induction of pro-metastatic target genes, partially prevented by pharmacologic blockade of proteasome activity. SKI knockdown in 1205Lu melanoma cells did not alter their invasive capacity or transcriptional responses to TGF-β, and did not allow p21 expression in response to TGF-β or reveal any growth inhibitory activity of TGF-β.

Conclusions

Despite high expression in melanoma cells, the role of SKI in melanoma remains elusive: SKI does not efficiently interfere with the pro-oncogenic activities of TGF-β, unless stabilized by proteasome blockade. Its highly labile nature makes it an unlikely target for therapeutic intervention.

A global genomic view on LNX siRNA-mediated cell cycle arrest

LNX protein is the first described PDZ domain-containing member of the RING finger-type E3 ubiquitin ligase family. Studies have approved that LNX could participate in signal transduction, such as Notch pathway, and play an important role in tumorigenesis. In this study, we found that down-regulation of LNX resulted in G0/G1 cell cycle arrest in G0/G1 phase in HEK293 cells. To explore the molecular mechanism of this phenomenon, we employed expression microarray to comparatively analyze the genome-wide expression between the LNX-knockdown cells and the normal cells. We also used quantitative real-time PCR to further confirm the differential expression patterns of 25 transcripts involved in cell cycle. Combined with known information about genic functions, signal pathways and cell cycle machinery, we analyzed the role of endogenous LNX in cell cycle. The results suggest that down-regulation of LNX could result in cell cycle arrest in G0/G1 phase through inhibition of β-catenin, MAPK, NFκB, c-Myc-dependent pathway and activation of p53, TGF-β-dependent pathway. This study provides new perspectives on LNX's pleiotropic activities, especially its essential role in cell proliferation and cell cycle.

The oncoprotein c-ski functions as a direct antagonist of the transforming growth factor-{beta} type I receptor

The oncoprotein c-Ski has been implicated in the negative regulation of transforming growth factor-β (TGF-β) signaling owing to its ability to repress Smad transcriptional activity via recruitment of a transcriptional corepressor complex containing histone deacetylases. However, c-Ski has also been shown to localize to the cytoplasm, raising the interesting possibility that it might disable TGF-β signaling through alternative mechanisms. Here, we provide evidence that c-Ski can restrict TGF-β signaling by interacting directly with the activated TGF-β type I receptor (TβRI). We explored the physiologic relevance of the c-Ski/TβRI interaction and found that it can culminate in a constitutive association of TβRI with a nonfunctional R-Smad/Smad4 complex. Based on these findings, we hypothesize that the interaction between c-Ski and TβRI might interfere with nuclear translocation of the R-Smad/Smad4 complex, thereby attenuating TGF-β signaling. Such a mechanism may play a crucial role in tumor progression, because many tumors that express high levels of c-Ski also display impaired nuclear accumulation of Smads.

Biomarkers of metastatic melanoma

Melanoma, one of the most aggressive forms of human cancer, has undergone an alarming increase in incidence in recent years. Early detection is a prerequisite for proper diagnosis and therapy orientation. Soluble biomarkers are an important tool for early diagnosis. Markers that are associated with melanocyte functions imply the enzymes involved in melanin synthesis and the melanin-related metabolites. Proteins such as autocrine melanocyte cell growth factor and melanoma metastasis suppressor have gained attention in the biomarkers domain. The antimelanoma immune response elicited in patients can not only provide new biomarkers but important therapeutic approaches in specific treatments. All the molecules generated during the metastasis process, invasion of neighboring tissue, angiogenesis, invading lymphatic/blood vessels and establishing new tumors at a distant site, are targets for biomarker discovery.

SKI promotes Smad3 linker phosphorylations associated with the tumor-promoting trait of TGFbeta

The transcriptional co-regulator SKI is a potent inhibitor of TGFbeta-growth inhibitory signals. SKI binds to receptor-activated Smads in the nucleus, forming repressor complexes containing HDACs, mSin3, NCoR, and other protein partners. Alternatively, SKI binds to activated Smads in the cytoplasm, preventing their nuclear translocation. SKI is necessary for anchorage-independent growth of melanoma cells in vitro, and most important, for human melanoma xenograft growth in vivo. We recently identified a novel role of SKI in TGFbeta signaling. SKI promotes the switch of Smad3 from repressor of proliferation to activator of oncogenesis by facilitating phosphorylations in the linker domain. High levels of endogenous SKI are required by the tumor promoting trait of TGFbeta to induce expression of the plasminogen-activator inhibitor-1 (PAI-1), sustained expression of C-Myc and for aborting upregulation of p21(Waf-1). Here we discuss how SKI diversifies and amplifies its functions by associating with multiple protein partners and by promoting Smad3 linker phosphorylation(s) in response to TGFbeta signaling in melanoma cells.

Differential Expression of SKI Oncogene Protein in Hemangiomas

OBJECTIVE: The pathogenesis for benign tumorigenesis in hemangiomas is unknown. Oncogene proteins may be influential in this process. SKI proteins have been previously described in various malignancies. We investigated the differential expression of the SKI (sarcoma viral oncogene) protein in hemangiomas.

STUDY DESIGN: Prospective basic science study.

SUBJECTS AND METHODS: Paraffin-embedded hemangioma tissues were obtained from the senior author from 2005 to 2006. We created the first vascular tissue array composed of 12 hemangioma specimens at various stages of growth and anatomic location. Two cores were taken from each sample. Controls were also included. Immunohistochemical studies were performed using SKI, CD31, and Ki67.

RESULTS: All 12 hemangioma tissues overexpressed the SKI protein. The staining pattern was perinuclear within the endothelial cells. The intensity of staining was inversely proportional to the growth stage. The endothelial cells that were SKI-positive were involved in active cell division.

CONCLUSION: SKI oncogene protein is differentially and specifically expressed in hemangioma tissues. SKI acts as a transcriptional co-repressor and inhibits the TGF-β pathway, thus leading to uncontrolled cellular proliferation and transformation. All vascular controls were negative for SKI staining.

CLINICAL SIGNIFICANCE OF STUDY: The SKI oncogene protein is upregulated by hemangiomas and may play a role in hemangioma tumorigenesis.

Epigenetics of cutaneous melanoma

Tumorigenesis is traditionally thought to be caused by the imbalance between oncogenes and tumor-suppressor genes. Epigenetics is a recently described phenomenon that uses an alternative mechanism to explain the transcriptional inactivation of tumor-suppressor genes predominantly by hypermethylation of the promoter regions. Hypermethylation of these regions has been described extensively in many neoplasms, including cutaneous melanoma. Histone modification, primarily by acetylation and deacetylation, is a current potential target for melanoma therapy, but more research is required to understand the mechanisms involved and the therapeutic effectiveness of regimens involving these agents. These mechanisms not only are important for understanding the origin and progression of neoplasms but also have important potential therapeutic implications. Understanding the epigenetic mechanisms involved in melanoma can provide valuable information with significant implications in diagnosis, treatment, and prevention.

Ski and SnoN, potent negative regulators of TGF-beta signaling

Ski and the closely related SnoN were discovered as oncogenes by their ability to transform chicken embryo fibroblasts upon overexpression. While elevated expressions of Ski and SnoN have also been reported in many human cancer cells and tissues, consistent with their pro-oncogenic activity, emerging evidence also suggests a potential anti-oncogenic activity for both. In addition, Ski and SnoN have been implicated in regulation of cell differentiation, especially in the muscle and neuronal lineages. Multiple cellular partners of Ski and SnoN have been identified in an effort to understand the molecular mechanisms underlying the complex roles of Ski and SnoN. In this review, we summarize recent findings on the biological functions of Ski and SnoN, their mechanisms of action and how their levels of expression are regulated.

Inhibition of PAX3 by TGF-beta modulates melanocyte viability

The protein encoded by paired-box homeotic gene 3 (PAX3) is a key regulator of the microphthalmia-associated transcription factor (Mitf) in the melanocyte lineage. Here, we show that PAX3 expression in skin is directly inhibited by TGF-beta/Smads. UV irradiation represses TGF-beta in keratinocytes, and the repression of TGF-beta/Smads upregulates PAX3 in melanocytes, which is associated with a UV-induced melanogenic response and consequent pigmentation. Furthermore, the TGF-beta-PAX3 signaling pathway interacts with the p53-POMC/MSH-MC1R signaling pathway, and both are crucial in melanogenesis. The activation of p53-POMC/MSH-MC1R signaling is required for the UV-induced melanogenic response because PAX3 functions in synergy with SOX10 in a cAMP-response element (CRE)-dependent manner to regulate the transcription of Mitf. This study will provide a rich foundation for further research on skin cancer prevention by enabling us to identify targeted small molecules in the signaling pathways of the UV-induced melanogenic response that are highly likely to induce naturally protective pigmentation.

Deciphering the melanoma interactome

Late-stage malignant melanoma continues to pose a significant therapeutic challenge, despite numerous recent advances in our understanding of the molecular and genetic pathways leading to tumor development and progression. Dr Scott McNutt was among the first researchers to employ the cutting edge technology, electron microscopy, to the study of cutaneous neoplasms. This work provided the foundation for more recent studies using molecular pathology to examine disease in the context of aberrant interactions between cellular signaling pathways in the so-called 'interactome'. Understanding the functional interrelationships of aberrant signaling networks in melanoma may lead to the development of novel therapies for advanced disease. This mini review will focus on few of the proteins that likely significantly contribute to the melanoma disease interactome.

Clinical significance of the expression of c-Ski and SnoN, possible mediators in TGF-beta resistance, in primary cutaneous melanoma

BACKGROUND

Loss of TGF-beta growth control is considered as a hallmark of several human neoplasms including melanoma. Resistance of cancer cells to TGF-beta has been linked to mutations in proteins involved in the TGF-beta pathway. In melanoma such mutations have not been observed. C-Ski and SnoN, two structurally and functionally highly homologous proteins, are known as negative regulators in the TGF-beta signaling pathway. C-Ski and SnoN expression levels and subcellular localization have been associated with clinicopathological parameters and tumour progression in several human malignancies. In melanoma cell lines, high c-Ski and SnoN expression levels have been described.

OBJECTIVE

The objective of this study was to evaluate the clinical value of c-Ski and SnoN expression in primary cutaneous melanoma.

METHODS

We evaluated c-Ski and SnoN expression by immunohistochemical staining in 120 primary melanomas. Possible associations between c-Ski and SnoN staining patterns and clinicopathological parameters were analyzed.

RESULTS

Nuclear c-Ski expression was significantly associated with thicker and ulcerated tumours. The percentage of SnoN positivity was higher in ulcerated tumours and in the sentinel node positive group.

CONCLUSION

These results suggest that c-Ski and SnoN, mediators in TGF-beta resistance, might be implicated in melanoma growth and progression.

Overexpression of SnoN/SkiL, amplified at the 3q26.2 locus, in ovarian cancers: a role in ovarian pathogenesis

High-resolution array comparative genomic hybridization of 235 serous epithelial ovarian cancers demonstrated a regional increase at 3q26.2 encompassing SnoN/SkiL, a coregulator of SMAD/TGFbeta signaling. SnoN RNA transcripts were elevated in approximately 80% of advanced stage serous epithelial ovarian cancers. In both immortalized normal (TIOSE) and ovarian carcinoma cell lines (OVCA), SnoN RNA levels were increased by TGFbeta stimulation and altered by LY294002 and JNK II inhibitor treatment suggesting that the PI3K and JNK signaling pathways may regulate TGFbeta-induced increases in SnoN RNA. In TIOSE, SnoN protein levels were reduced 15min post TGFbeta-stimulation, likely by proteosome-mediated degradation. In contrast, in OVCA, SnoN levels were elevated 3h post-stimulation potentially as a result of inhibition of the proteosome. To elucidate the role of SnoN in ovarian tumorigenesis, we explored the effects of both increasing and decreasing SnoN levels. In both TIOSE and OVCA, SnoN siRNA decreased cell growth between 20 and 50% concurrent with increased p21 levels. In TIOSE, transient expression of SnoN repressed TGFbeta induction of PAI-1 promoters with little effect on the p21 promoter or resultant cell growth. In contrast to the effects of transient expression, stable expression of SnoN in TIOSE led to growth arrest through induction of senescence. Collectively, these results implicate SnoN levels in multiple roles during ovarian carcinogenesis: promoting cellular proliferation in ovarian cancer cells and as a positive mediator of cell cycle arrest and senescence in non-transformed ovarian epithelial cells.

Understanding signaling cascades in melanoma

Understanding regulatory pathways involved in melanoma development and progression has advanced significantly in recent years. It is now appreciated that melanoma is the result of complex changes in multiple signaling pathways that affect growth control, metabolism, motility and the ability to escape cell death programs. Here we review the major signaling pathways currently known to be deregulated in melanoma with an implication to its development and progression. Among these pathways are Ras, B-Raf, MEK, PTEN, phosphatidylinositol-3 kinase (PI3Ks) and Akt which are constitutively activated in a significant number of melanoma tumors, in most cases due to genomic change. Other pathways discussed in this review include the [Janus kinase/signal transducer and activator of transcription (JAK/STAT), transforming growth factor-beta pathways which are also activated in melanoma, although the underlying mechanism is not yet clear. As a paradigm for remodeled signaling pathways, melanoma also offers a unique opportunity for targeted drug development.

Epigenetic events in malignant melanoma

Irreversible changes in the DNA sequence, including chromosomal deletions or amplification, activating or inactivating mutations in genes, have been implicated in the development and progression of melanoma. However, increasing attention is being turned towards the participation of 'epigenetic' events in melanoma progression that do not affect DNA sequence, but which nevertheless may lead to stable inherited changes in gene expression. Epigenetic events including histone modifications and DNA methylation play a key role in normal development and are crucial to establishing the correct program of gene expression. In contrast, mistargeting of such epigenetic modifications can lead to aberrant patterns of gene expression and loss of anti-cancer checkpoints. Thus, to date at least 50 genes have been reported to be dysregulated in melanoma by aberrant DNA methylation and accumulating evidence also suggests that mistargetting of histone modifications and altered chromatin remodeling activities will play a key role in melanoma. This review gives an overview of the many different types of epigenetic modifications and their involvement in cancer and especially in melanoma development and progression.

Suppression of FHL2 expression induces cell differentiation and inhibits gastric and colon carcinogenesis

BACKGROUND AND AIMS

FHL2 (4-1/2 LIM protein 2) is an adapter and modifier in protein interactions that is expressed mainly in the heart and ovary. It functions in a cell type- or promoter-specific manner. The aims of this study were to examine its expression in gastrointestinal cancers and to determine its role in cell differentiation and tumorigenesis.

METHODS

FHL2 expression in cancerous and normal gastrointestinal cells was detected by reverse-transcription polymerase chain reaction, immunoblotting, and immunohistochemistry. The effect of FHL2 suppression by both antisense and siRNA methods on cell differentiation and growth were evaluated in vitro and in vivo.

RESULTS

FHL2 expression was up-regulated in gastrointestinal cancer, compared with matched normal tissues. Stable transfection of gastric cancer cell line, AGS, and colon cancer cell line, Lovo, with antisense FHL2 induced lengthened or shuttle-shape morphologic changes with long or dendritic-like cytoplasmic processes and decreased the nuclear:cytoplasmic ratio. FHL2 antisense induced expressions of carcinoembryonic antigen and E-cadherin and the maturation of F-actin. Furthermore, FHL2 antisense inhibited the transcriptions of some oncogenes including cox-2, survivin, c-jun, and hTERT, and suppressed the promoter activity of activator protein-1 and hTERT. Suppression of FHL2 inhibited serum-dependent, anchorage-dependent and -independent cell growth, and suppressed de novo tumor formation in nude mice xenograft.

CONCLUSIONS

Suppression of FHL2 induces cell differentiation and inhibits tumorigenesis. Antisense or siRNA methods targeting FHL2 is a promising strategy for treatment of gastrointestinal cancers.

Drosophila SnoN modulates growth and patterning by antagonizing TGF-beta signalling

Signalling by TGF-beta ligands through the Smad family of transcription factors is critical for developmental patterning and growth. Disruption of this pathway has been observed in various cancers. In vertebrates, members of the Ski/Sno protein family can act as negative regulators of TGF-beta signalling, interfering with the Smad machinery to inhibit the transcriptional output of this pathway. In some contexts ski/sno genes function as tumour suppressors, but they were originally identified as oncogenes, whose expression is up-regulated in many tumours. These growth regulatory effects and the normal physiological functions of Ski/Sno proteins have been proposed to result from changes in TGF-beta signalling. However, this model is controversial and may be over-simplified, because recent findings indicate that Ski/Sno proteins can affect other signalling pathways. To address this issue in an in vivo context, we have analyzed the function of the Drosophila Ski/Sno orthologue, SnoN. We found that SnoN inhibits growth when overexpressed, indicating a tumour suppressor role in flies. It can act in multiple tissues to selectively and cell autonomously antagonise signalling by TGF-beta ligands from both the BMP and Activin sub-families. By contrast, analysis of a snoN mutant indicates that the gene does not play a global role in TGF-beta-mediated functions, but specifically inhibits TGF-beta-induced wing vein formation. We propose that SnoN normally functions redundantly with other TGF-beta pathway antagonists to finely adjust signalling levels, but that it can behave as an extremely potent inhibitor of TGF-beta signalling when highly expressed, highlighting the significance of its deregulation in cancer cells.

Influence of melanoma inhibitory activity on transforming growth factor-beta signaling in malignant melanoma

Melanoma cells escape transforming growth factor-beta (TGFbeta)-mediated growth inhibition by expressing the Smad (mothers against decapentaplegic homolog, Drosophila) inhibitors Ski and Sno. Here, we demonstrate that melanoma inhibitory activity (MIA) influences the expression of these inhibitors. A Smad responsive reporter construct was activated after TGFbeta1 treatment in the MIA-deficient cell clones but not in the parental cell line. According to this finding, the TGFbeta target genes JunB and Id-1 showed a strong induction of expression. Additional analyses revealed that Ski and Sno, repressors of TGFbeta/SMAD signaling, are not expressed in the MIA-deficient cells but in the parental cell line HMB2 and the mock control. Further investigation showed that Ski and Sno expression might be regulated via the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling cascade. Treatment of HMB2 cells with a MEK inhibitor revealed a reduction of Ski and Sno expression, which leads to the conclusion that, in our melanoma cell model, Ski and Sno expression is regulated via MAPK/ERK signaling.

Involvement of the c-Ski oncoprotein in cell cycle arrest and transformation during nurse cell formation after Trichinella spiralis infection

The role of c-Ski, an oncoprotein encoded by the oncogene, c-ski, in Trichinella spiralis-infected muscle tissues during nurse cell formation, was investigated by following the expression kinetics and distribution of c-Ski (both protein and mRNA) in the infected muscle cell, as well as the expression kinetics of the transforming growth factor beta (TGF-beta) signaling pathway factor genes (TGF-beta, Smad2 and Smad4) which cooperate with c-Ski. Immunohistochemical analysis using an anti-c-Ski antibody indicated that in the early stages of infection (13 and 18 days post-infection (p.i.)) the increased expression of the c-Ski protein was limited to the eosinophilic cytoplasm and not the enlarged nuclei or basophilic cytoplasm. At a later stage of infection (23 and 28 days p.i.) the c-Ski protein was limited to the enlarged nuclei in the basophilic cytoplasm, rather than the eosinophilic cytoplasm. At 48 days p.i., the c-Ski protein was barely detectable. Real-time PCR analysis showed that expression of the c-ski gene increased from 13 days p.i., reached a peak at 23-28 days p.i. and then decreased to a low level by 48 days p.i. Expression kinetics for the TGF-beta signaling pathway factor genes (TGF-beta, Smad2 and Smad4) were similar to that of c-ski. These findings provide evidence that the c-Ski protein is involved in nurse cell formation through the TGF-beta signaling pathway process in the host cell nucleus.

Pocket protein function in melanocyte homeostasis and neoplasia

Melanoma is the most lethal of human skin cancers and its incidence is increasing worldwide [L.K. Dennis (1999). Arch. Dermatol. 135, 275; C. Garbe et al. (2000). Cancer 89, 1269]. Melanomas often metastasize early during the course of the disease and are then highly intractable to current therapeutic regimens [M.F. Demierre and G. Merlino (2004). Curr. Oncol. Rep. 6, 406]. Consequently, understanding the factors that maintain melanocyte homeostasis and prevent their neoplastic transformation into melanoma is of utmost interest from the perspective of therapeutic interdiction. This review will focus on the role of the pocket proteins (PPs), Rb1 (retinoblastoma protein), retinoblastoma-like 1 (Rbl1 also known as p107) and retinoblastoma-like 2 (Rbl2 also known as p130), in melanocyte homeostasis, with particular emphasis on their functions in the cell cycle and the DNA damage repair response. The potential mechanisms of PP deregulation in melanoma and the possibility of PP-independent pathways to melanoma development will also be considered. Finally, the role of the PP family in ultraviolet radiation (UVR)-induced melanoma and the precise contribution that each PP family member makes to melanocyte homeostasis will be discussed in the context of a number of genetically engineered mouse models.

Bone morphogenetic proteins and their antagonists

Skeletal homeostasis is determined by systemic hormones and local factors. Bone morphogenetic proteins (BMPs) are unique because they induce the commitment of mesenchymal cells toward cells of the osteoblastic lineage and also enhance the differentiated function of the osteoblast. BMP activities in bone are mediated through binding to specific cell surface receptors and through interactions with other growth factors. BMPs are required for skeletal development and maintenance of adult bone homeostasis, and play a role in fracture healing. BMPs signal by activating the mothers against decapentaplegic (Smad) and mitogen activated protein kinase (MAPK) pathways, and their actions are tempered by intracellular and extracellular proteins. The BMP antagonists block BMP signal transduction at multiple levels including pseudoreceptor, inhibitory intracellular binding proteins, and factors that induce BMP ubiquitination. A large number of extracellular proteins that bind BMPs and prevent their binding to signaling receptors have emerged. The extracellular antagonists are differentially expressed in cartilage and bone tissue and exhibit BMP antagonistic as well as additional activities. Both intracellular and extracellular antagonists are regulated by BMPs, indicating the existence of local feedback mechanisms to modulate BMP cellular activities.