Involvement of FKHRL1 in melanoma cell survival and death

International audienceMelanoma is a highly aggressive tumour characterized by a strong resistance to apoptotic stimuli that give rise to a selective advantage for tumour progression and metastasis formation. Therefore, it is of paramount importance to better understand the mechanisms involved in this resistance to apoptosis. In this report, we focused our attention on FKHRL1, a member of the forkhead family of transcription factors, which controls expression of genes involved in cell cycle progression and apoptosis. In melanoma cells, we show that IGF1, which exerts pro-survival properties, induces the phosphorylation and nuclear exclusion of FKHRL1 in a PI3K/AKT-dependent pathway. Moreover, we observe that over-expression of a non-phosphorylable mutant of FKHRL1 (FKHRL1-TM), constitutively localized to the nucleus, promotes apoptotic cell death of melanoma cells. Finally, we find that FKHRL1-TM decreases the expression of survivin, a member of the inhibitor of apoptosis protein and that survivin re-expression partially rescues the deleterious effects of FKHRL1. Taken together, these findings reveal, in melanoma cells, that endogenous FKHRL1 is a downstream target of the PI3K/AKT pathway and suggest that the phosphorylation of this transcription factor may be involved in the pro-survival effects of growth factors such as IGF1. On the other hand, forced nuclear localization of FKHRL1 decreases melanoma cell growth and may serve as a therapeutic strategy against melanoma

Aurora B Is Regulated by the Mitogen-activated Protein Kinase/Extracellular Signal-regulated Kinase (MAPK/ERK) Signaling Pathway and Is a Valuable Potential Target in Melanoma Cells

International audienceMetastatic melanoma is a deadly skin cancer and is resistant to almost all existing treatment. Vemurafenib, which targets the BRAFV600E mutation, is one of the drugs that improves patient outcome, but the patients next develop secondary resistance and a return to cancer. Thus, new therapeutic strategies are needed to treat melanomas and to increase the duration of v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) inhibitor response. The ERK pathway controls cell proliferation, and Aurora B plays a pivotal role in cell division. Here, we confirm that Aurora B is highly expressed in metastatic melanoma cells and that Aurora B inhibition triggers both senescence-like phenotypes and cell death in melanoma cells. Furthermore, we show that the BRAF/ERK axis controls Aurora B expression at the transcriptional level, likely through the transcription factor FOXM1. Our results provide insight into the mechanism of Aurora B regulation and the first molecular basis of Aurora B regulation in melanoma cells. The inhibition of Aurora B expression that we observed in vemurafenib-sensitive melanoma cells was rescued in cells resistant to this drug. Consistently, these latter cells remain sensitive to the effect of the Aurora B inhibitor. Noteworthy, wild-type BRAF melanoma cells are also sensitive to Aurora B inhibition. Collectively, our findings, showing that Aurora B is a potential target in melanoma cells, particularly in those vemurafenib-resistant, may open new avenues to improve the treatment of metastatic melanoma

Ciglitazone negatively regulates CXCL1 signaling through MITF to suppress melanoma growth: Negative regulation of MITF/CXCL1 axis by ciglitazone

International audienceWe have previously demonstrated that the thiazolidinedione ciglitazone inhibited, independently of PPAR activation, melanoma cell growth. Further investigations now show that ciglitazone effects are mediated through the regulation of secreted factors. Q-PCR screening of several genes involved in melanoma biology reveals that ciglitazone inhibits expression of the CXCL1 chemokine gene. CXCL1 is overexpressed in melanoma and contributes to tumorigenicity. We show that ciglitazone induces a diminution of CXCL1 level in different human melanoma cell lines. This effect is mediated by the down regulation of microphthalmia-associated transcription factor, MITF, the master gene in melanocyte differentiation and involved in melanoma development. Further, recombinant CXCL1 protein is sufficient to abrogate thiazolidinedione effects such as apoptosis induction, while extinction of the CXCL1 pathway mimics phenotypic changes observed in response to ciglitazone. Finally, inhibition of human melanoma tumor development in nude mice treated with ciglitazone is associated with a strong decrease in MITF and CXCL1 levels. Our results demonstrate that anti-melanoma effects of thiazolidinediones involve an inhibition of the MITF/CXCL1 axis and highlight the key role of this specific pathway in melanoma malignancy

Progress of the Plasma Centerpost for the PROTO-SPHERA Spherical Tokamak

Plasma properties can be useful in a wide spectrum of applications. Experimental projects on controlled nuclear fusion are the most challenging of these applications and, at the same time, the best way to approach plasma science. Since nuclear fusion reactors can ensure a large-scale, safe, environmentally-friendly and virtually inexhaustible source of energy, several fusion-oriented megaprojects and innovative companies are appearing all over the world. PROTO-SPHERA (Spherical Plasma for HElicity Relaxation Assessment) is the first plasma project with a simply connected configuration, namely not requiring additional objects inside the plasma volume. This is obtained by a plasma arc, shaped as a screw pinch, acting as the centerpost of a spherical torus with minimal aspect ratio. Due to its intrinsic physical, engineering and economic advantages, this new approach is attractive also on an industrial scale and with several developments that still needs to be explored. This paper presents the PROTO-SPHERA basic principles, its first encouraging results and its expected and potential evolutions

Interleukin-1-inducible genes in endothelial cells. Cloning of a new gene related to C-reactive protein and serum amyloid P component

Differential screening of a cDNA library constructed from human umbilical vein endothelial cells exposed for 1 h to interleukin-1 beta (IL-1 beta) has led to the identification of a novel gene (PTX3) related to pentaxins (C-reactive protein and serum amyloid P component in man), a subclass of acute phase proteins. Sequencing of the full-length cDNA clone and RNase mapping revealed that the PTX3 transcript is 1861 base pairs long and has a unique transcription start site. The predicted protein sequence of 381 amino acids is highly similar to pentaxins in its COOH-terminal half where it also contains a typical 8-amino acid "pentaxin signature" sequence. The NH2-terminal half of PTX3 shows no similarity to any known protein sequence and initiates with a putative signal peptide indicating that PTX3 is secreted. The genome of PTX3 is organized into three exons. Interestingly, the region of homology between PTX3 and pentaxins corresponds to the third PTX3 exon. The PTX3 gene has been localized on human chromosome 3 band q25 by Southern blots of somatic cell hybrids and by in situ hybridization. The PTX3 mRNA is induced in endothelial, hepatic, and fibroblastic cells by IL-1 beta and tumor necrosis factor alpha but not by IL-6 and interferon-gamma. PTX3 may represent a novel marker of inflammatory reactions, particularly those involving the vessel wall

Centromere sliding on a mammalian chromosome

The centromere directs the segregation of chromosomes during mitosis and meiosis. It is a distinct genetic locus whose identity is established through epigenetic mechanisms that depend on the deposition of centromere-specific centromere protein A (CENP-A) nucleosomes. This important chromatin domain has so far escaped comprehensive molecular analysis due to its typical association with highly repetitive satellite DNA. In previous work, we discovered that the centromere of horse chromosome 11 is completely devoid of satellite DNA; this peculiar feature makes it a unique model to dissect the molecular architecture of mammalian centromeres. Here, we exploited this native satellite-free centromere to determine the precise localization of its functional domains in five individuals: We hybridized DNA purified from chromatin immunoprecipitated with an anti CENP-A antibody to a high resolution array (ChIP-on-chip) of the region containing the primary constriction of horse chromosome 11. Strikingly, each individual exhibited a different arrangement of CENP-A binding domains. We then analysed the organization of each domain using a single nucleotide polymorphism (SNP)-based approach and single molecule analysis on chromatin fibres. Examination of the ten instances of chromosome 11 in the five individuals revealed seven distinct 'positional alleles', each one extending for about 80-160 kb, were found across a region of about 500 kb. Our results demonstrate that CENP-A binding domains are autonomous relative to the underlying DNA sequence and are characterized by positional instability causing the sliding of centromere position. We propose that this dynamic behaviour may be common in mammalian centromeres and may determine the establishment of epigenetic alleles