Mitf dosage as a primary determinant of melanocyte survival after ultraviolet irradiation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75008/1/j.1755-148X.2009.00551.x.pd

Increased sensitivity to TRAIL-induced apoptosis occurs during the adenoma to carcinoma transition of colorectal carcinogenesis

The death ligand TRAIL (Apo2L) has potential for cancer therapy, since tumour cells are thought to be more sensitive than normal cells. We investigated whether sensitivity to TRAIL increases during the adenoma to carcinoma transition of colorectal carcinogenesis. Under the same culture conditions, we compared the extent of TRAIL-induced apoptosis in four premalignant adenoma and three carcinoma cell lines. Although TRAIL induced some apoptosis in adenoma cultures, the carcinoma cell lines were significantly more sensitive (P<0.001). This finding was recapitulated in an in vitro model of tumour progression in which conversion of the adenoma cell line AA/C1 to a tumorigenic phenotype was associated with increased TRAIL sensitivity (P<0.001). Increased TRAIL sensitivity during colorectal carcinogenesis has been previously attributed to changes in the balance between TRAIL receptors TRAIL-R1 and -R2 and ‘decoy' receptors TRAIL-R3 and -R4 during malignant progression. To address this, cell surface receptor expression was measured by flow cytometry. In summary, during colorectal carcinogenesis, there is a marked increase in sensitivity to TRAIL-induced apoptosis associated with progression from benign to malignant tumour that could be exploited for colon cancer therapy, but alterations in cell surface TRAIL receptor expression may not be the primary reason for this change

Metformin inhibits melanoma development through autophagy and apoptosis mechanisms

Metformin is the most widely used antidiabetic drug because of its proven efficacy and limited secondary effects. Interestingly, recent studies have reported that metformin can block the growth of different tumor types. Here, we show that metformin exerts antiproliferative effects on melanoma cells, whereas normal human melanocytes are resistant to these metformin-induced effects. To better understand the basis of this antiproliferative effect of metformin in melanoma, we characterized the sequence of events underlying metformin action. We showed that 24 h metformin treatment induced a cell cycle arrest in G0/G1 phases, while after 72 h, melanoma cells underwent autophagy as demonstrated by electron microscopy, immunochemistry, and by quantification of the autolysosome-associated LC3 and Beclin1 proteins. In addition, 96 h post metformin treatment we observed robust apoptosis of melanoma cells. Interestingly, inhibition of autophagy by knocking down LC3 or ATG5 decreased the extent of apoptosis, and suppressed the antiproliferative effect of metformin on melanoma cells, suggesting that apoptosis is a consequence of autophagy. The relevance of these observations were confirmed in vivo, as we showed that metformin treatment impaired the melanoma tumor growth in mice, and induced autophagy and apoptosis markers. Taken together, our data suggest that metformin has an important impact on melanoma growth, and may therefore be beneficial in patients with melanoma

The inhibition of Bid expression by Akt leads to resistance to TRAIL-induced apoptosis in ovarian cancer cells

Epithelial ovarian cancer (EOC) cells often show increased activity of the PI3K/Akt pathway. In addition, we have previously shown that EOC ascites induce Akt activation in the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-sensitive EOC cell line, CaOV3, leading to TRAIL-mediated apoptosis inhibition. In this study, we investigated the role of Akt in intrinsic resistance to TRAIL, which is common in EOC cells. We report that Akt activation reduces the sensitivity of EOC cells to TRAIL. TRAIL-resistant SKOV3ip1 and COV2 cells were sensitized to TRAIL-induced apoptosis by PI3K or Akt inhibitors although inhibition of PI3K/Akt signaling pathway did not interfere with the recruitment and processing of caspase-8 to the death-inducing signaling complex. Conversely, overexpression of Akt1 in TRAIL-sensitive cells promoted resistance to TRAIL. Although the fact that TRAIL-induced caspase-8 activation was observed in both sensitive and resistant cell lines, Bid cleavage occurred only in sensitive cells or in SKOV3ip1 cells treated with LY294002. Bid expression was low in resistant cells and Akt activation downregulated its expression. Depletion of Bid by siRNA in OVCAR3 cells was associated with a decrease in TRAIL-mediated apoptosis. Overexpression of Bid only in SKOV3ip1 cells enhanced TRAIL-induced apoptosis. Simultaneous blockade of Akt pathway further increased TRAIL-induced apoptosis. Thus, Akt acts upstream of mitochondria and inhibits TRAIL-induced apoptosis by decreasing Bid protein levels and possibly inhibiting its cleavage

Étude de mécanismes moléculaires impliqués dans la régulation de la survie et de l'apoptose des cellules mélanocytaires

Le mélanome, qui est la forme la plus agressive des cancers de la peau est un problème majeur de santé publique. Cette tumeur touche des sujets jeunes et son incidence a doublé en trente ans. Il y a donc un besoin urgent de mieux comprendre les mécanismes entraînant la transformation du mélanocyte en mélanome, et notamment les processus qui conduisent à l'altération des voies apoptotiques et l'acquisition d'une résistance aux traitements thérapeutiques existants. Au cours de ma thèse, j'ai étudié les mécanismes moléculaires qui sont impliqués dans la régulation de la survie et de la mort des mélanocytes et de leur contrepartie transformée les mélanomes. Ainsi, j'ai montré que le SCF (Stem Cell Factor), un facteur de croissance des mélanocytes protège ces cellules de l'apoptose induite par Trail ou la staurosporine. Le SCF est capable d'activer à la fois la voie Ras/Raf/MAPK et la voie PI3K/AKT qui sont fréquemment mutées et constitutivement activées dans les mélanomes. Cependant, j'ai observé que la protection de l'apoptose par le SCF est majoritairement médiée par la voie PI3K/AKT et que l'activation de cette voie seule est suffisante pour bloquer l'apoptose. De plus, le rôle clé de la voie PI3K/AKT dans la transformation mélanocytaire a récemment été mis en évidence dans une étude qui montre que la PI3K active, contrairement à Ras actif, peut induire une hyperprolifération mélanocytaire invasive. Donc, dans la peau, une surproduction de SCF pourrait prévenir, via la voie PI3K/AKT, l'apoptose des mélanocytes et favoriser leur survie et leur transformation. L'approfondissement de cette étude m'a permis de montrer une diminution d'expression de MITF (MIcrophthalmia-associated Transcription Factor), un facteur de transcription spécifique des mélanocytes, au cours de l'apoptose induite par Trail. J'ai démontré que cette perte d'expression de MITF est la conséquence d'un clivage par les caspases qui génère un grand fragment N-terminal et un petit fragment C-terminal. Le rôle physiologique de ce processus est d'amplifier le signal apoptotique. En effet, un mutant non-clivable de MITF rend les mélanomes résistants à l'apoptose. De plus, la surexpression du petit fragment C-terminal induit l'apoptose par elle-même. Donc, ces résultats révèlent l'existence d'un mécanisme apoptotique spécifique des mélanocytes et dépendant de MITF. Ceci met en évidence la dualité fonctionnelle de MITF qui contribue à la survie en contrôlant l'expression de Bcl-2 et à la mort cellulaire en libérant, après son clivage par les caspases, un fragment pro-apoptotique.NICE-BU Sciences (060882101) / SudocSudocFranceF

Retrospective Side Effect Profiling of the Metastatic Melanoma Combination Therapy Ipilimumab-Nivolumab Using Adverse Event Data

Recent studies suggest that combining nivolumab with ipilimumab is a more effective treatment for melanoma patients, compared to using ipilimumab or nivolumab alone. However, treatment with these immunotherapeutic agents is frequently associated with increased risk of toxicity, and (auto-) immune-related adverse events. The precise pathophysiologic mechanisms of these events are not yet clear, and evidence from clinical trials and translational studies remains limited. Our retrospective analysis of ~7700 metastatic melanoma patients treated with ipilimumab and/or nivolumab from the FDA Adverse Event Reporting System (FAERS) demonstrates that the identified immune-related reactions are specific to ipilimumab and/or nivolumab, and that when the two agents are administered together, their safety profile combines reactions from each drug alone. While more prospective studies are needed to characterize the safety of ipilimumab and nivolumab, the present work constitutes perhaps the first effort to examine the safety of these drugs and their combination based on computational evidence from real world post marketing data

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