SIRT1 promotes proliferation and inhibits the senescence-like phenotype in human melanoma cells

SIRT1 operates as both a tumor suppressor and oncogenic factor depending on the cell context. Whether SIRT1 plays a role in melanoma biology remained poorly elucidated. Here, we demonstrate that SIRT1 is a critical regulator of melanoma cell proliferation. SIRT1 suppression by genetic or pharmacological approaches induces cell cycle arrest and a senescence-like phenotype. Gain and loss of function experiments show that M-MITF regulates SIRT1 expression, thereby revealing a melanocyte-specific control of SIRT1. SIRT1 over-expression relieves the senescence-like phenotype and the proliferation arrest caused by MITF suppression, demonstrating that SIRT1 is an effector of MITF-induced proliferation in melanoma cells. Interestingly, SIRT1 level and activity are enhanced in the PLX4032-resistant BRAF(V600E)-mutated melanoma cells compared with their sensitive counterpart. SIRT1 inhibition decreases melanoma cell growth and rescues the sensibility to PLX4032 of PLX4032-resistant BRAF(V600E)-mutated melanoma cells. In conclusion, we provide the first evidence that inhibition of SIRT1 warrants consideration as an anti-melanoma therapeutic option

Activity, certainty, optimism, and realism: The verbal style in televised presidential campaign commercials.

Presidential campaign commercials have been analyzed to determine their effectiveness with respect to length and style. However, to this point, no study has attempted to count and categorize the words used in the commercials. The current study analyzed 1178 televised presidential campaign commercials in terms of their activity, certainty, optimism, and realism.These variables identify a verbal style and differences between winners and losers, and between incumbents and nonincumbents, with respect to the words used in their campaign commercials. Most striking in the findings was the overall low use of certainty words in the advertisements. This indicates that DICTION may not provide the correct variables for analyzing and interpreting campaign commercials. It is suggested that other variables be designed to measure the persuasiveness of presidential campaign commercials.The commercials were transcribed from video tapes to computer disk. The transcriptions were then submitted to a computer content analysis to count and categorize the words with respect to the four major variables. The four variables were constructed using the formulas prescribed by Hart (1984)

[Insulin receptor and action mechanism of the hormone].

International audienceThe first step in insulin action consists in binding of the hormone to specific cell surface receptors. This receptor displays two functional domains: an extracellular alpha-subunit containing the majority or the totality of the hormone binding site, and an transmembrane beta-subunit possessing insulin-stimulated tyrosine kinase activity. A general consensus has been reached in favor of the idea that this receptor enzymic function is essential for generation of the metabolic and growth promoting effects of insulin. Concerning the mechanism of transmembrane signalling we like to think that interaction of insulin with the receptor alpha-subunit triggers a conformational change, which is propagated to the beta-subunit and activates it. The active receptor kinase leads then to phosphorylation of cellular protein substrates, which are likely to belong to two broad categories, those generating metabolic effects of insulin, and those resulting in growth-promoting effects. The phosphorylated and active substrates generate then the final effects of insulin

Pathways from senescence to melanoma: focus on MITF sumoylation

International audienceCutaneous melanoma is a deadly skin cancer that originates from melanocytes. The development of cutaneous melanoma involves a complex interaction between environmental factors, mainly ultraviolet radiation from sunlight, and genetic alterations. Melanoma can also occur from a pre-existing nevus, a benign lesion formed from melanocytes harboring oncogenic mutations that trigger proliferative arrest and senescence entry. Senescence is a potent barrier against tumor progression. As such, the acquisition of mutations that suppress senescence and promote cell division is mandatory for cancer development. This topic appears central to melanoma development because, in humans, several somatic and germline mutations are related to the control of cellular senescence and proliferative activity. Consequently, primary melanoma can be viewed as a paradigm of senescence evasion. In support of this notion, a sumoylation-defective germline mutation in microphthalmia-associated transcription factor (MITF), a master regulator of melanocyte homeostasis, is associated with the development of melanoma. Interestingly, this MITF variant has also been recently reported to negatively impact the program of senescence. This article reviews the genetic alterations that have been shown to be involved in melanoma and that alter the process of senescence to favor melanoma development. Then, the transcription factor MITF and its sumoylation-defective mutant are described. How sumoylation misregulation can change MITF activity and impact the process of senescence is discussed. Finally, the contribution of such information to the development of anti-malignant melanoma strategies is evaluated

Regulation of tyrosinase gene expression by cAMP in B16 melanoma cells involves two CATGTG motifs surrounding the TATA box: implication of the microphthalmia gene product.

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Antiphosphotyrosine antibodies modulate insulin receptor kinase activity and insulin action.

International audienceInsulin elicits the autophosphorylation of the beta-subunit of its receptor on tyrosine residues: this effect appears to be the earliest post-binding event involved in insulin action. In the present study we have raised highly specific antibodies to phosphotyrosine residues, and we have taken advantage of these antibodies to further evaluate the role of the insulin receptor tyrosine kinase in the generation of insulin's biological responses. Using a cell-free phosphorylation assay, we show here that these antibodies increase the tyrosine kinase activity of the receptor, and its phosphorylation on tyrosine residues. In contrast, the antibodies do not interfere with dephosphorylation of the insulin receptor. Introduction of the same antibodies in living Fao hepatoma cells enhances the effect of insulin on both glucose transport and aminoacid uptake. As a whole our data indicate that the insulin receptor kinase is involved in the generation of an early (glucose transport) and late (aminoacid uptake) response to insulin. Further, conformational changes in phosphotyrosine containing domains of the insulin receptor appear to modulate insulin's biological effects. Finally, the injection of antibodies in intact cells provides us with a novel and promising tool to search for cellular substrates for the insulin receptor tyrosine kinase

Direct regulation of the Microphthalmia promoter by Sox10 links Waardenburg-Shah syndrome (WS4)-associated hypopigmentation and deafness to WS2.

The transcription factor Sox10 is genetically linked with Waardenburg syndrome 4 (WS4) in humans and the Dominant megacolon (Dom) mouse model for this disease. The pigmentary defects observed in the Dom mouse and WS4 are reminiscent of those associated with mutations in the microphthalmia (Mitf) gene, which encodes a transcription factor essential for the development of the melanocyte lineage. We demonstrate here that wild type Sox10 directly binds and activates transcription of the MITF promoter, whereas a mutant form of the Sox10 protein genetically linked with WS4 acts as a dominant-negative repressor of MITF expression and can reduce endogenous MITF protein levels. The ability of Sox10 to activate transcription of the MITF promoter implicates Sox10 in the regulation of melanocyte development and provides a molecular basis for the hypopigmentation and deafness associated with WS4

Rapid increase of the human IFN-gamma receptor phosphorylation in response to human IFN-gamma and phorbol myristate acetate. Involvement of different serine/threonine kinases

Various cell surface receptors are phosphorylated upon binding of their ligand, and this phosphorylation seems to be involved in the signal transduction or in the feedback regulation of this signal. The possibility of a phosphorylation of the human IFN-gamma receptor (hu-IFN-gamma-R) has been investigated with 32P-labeled whole Raji cells and receptor purification either by immunoprecipitation with an anti-hu-IFN-gamma-R polyclonal antiserum or by affinity chromatography. The hu-IFN-gamma-R was found to be phosphorylated at a basal level. Upon incubation of the cells with recombinant hu-IFN-gamma, a dose-dependent two-fold increase of this phosphorylation was observed. Phosphoamino acid analysis by TLC showed that the same amino acids, serine and threonine, are phosphorylated at a basal level and after incubation with hu-IFN-gamma. Protein kinase C and Ca2+/calmodulin-dependent kinase pathways have been reported in some cases to be involved in the signal transduction pathway of hu-IFN-gamma. Both pathways involved the activation of a serine/threonine kinase and therefore we have investigated the possibility of hu-IFN-gamma-R phosphorylation by these kinases. PMA, an activator of protein kinase C, induced a rapid increase of the receptor phosphorylation in Raji cells, whereas the Ca2+ ionophore A23187 did not. PMA-induced hu-IFN-gamma-R phosphorylation was not associated with any effect on expression or inactivation of the receptor. PMA alone did not mimic the hu-IFN-gamma effect in Raji cells as measured by induction of IP-10 gene expression, a high specific marker of hu-IFN-gamma response. But the protein kinase C inhibitors, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7) and staurosporine, reduced this IFN-gamma-induced expression. However, H7 and staurosporine treatment as well as protein kinase C depletion suppressed PMA-induced receptor phosphorylation, whereas constitutive and hu-IFN-gamma-induced phosphorylation remained unchanged. Our results suggest that the serine/threonine kinase involved in the hu-IFN-gamma-R phosphorylation induced by IFN-gamma is different from protein kinase C