FGF2 Induces Resistance to Nilotinib through MAPK Pathway Activation in KIT Mutated Melanoma.

KIT is a bona fide oncogene in a subset of melanoma and, ex vivo, KIT inhibitors are very efficient at killing KIT-mutant melanoma cell lines. However, KIT-mutant melanoma tumors tend to show a de novo resistance in most cases and a limited duration of response when response is achieved. We performed pharmacodynamic studies on patients with KIT-mutated melanoma treated with nilotinib, which suggested that the FGF2 axis may be a mechanism of resistance in this subset of melanoma. Using several melanoma cell lines, which are dependent on oncogenic KIT, we showed that although KIT inhibition markedly decreased cell viability in melanoma cell lines with distinct KIT mutations, this effect was lessened in the presence of FGF2 due to inhibition of BIM expression by MAPK pathway activation. Addition of a MEK inhibitor reversed the FGF2-driven resistance for all KIT mutants. We confirmed the expression of FGF2 and activation of MEK-ERK in melanoma patients using in situ data from a clinical trial. Therefore, the combined inhibition of KIT with FGFR or MEK may be a next-step effective clinical strategy in KIT-mutant melanoma.

TERT promoter mutations in melanoma render TERT expression dependent on MAPK pathway activation.

The mechanism of telomerase re-activation in cancer had remained elusive until the discovery of frequent mutations in the promoter of the TERT gene that encodes the catalytic reverse transcriptase subunit of telomerase. We investigated the regulation of TERT expression in melanoma cell lines and our results show that promoter mutations render TERT expression dependent on MAPK activation due to oncogenic BRAF or NRAS mutations. Mutations in the TERT promoter create binding sites for ETS transcription factors. ETS1, expressed in melanoma cell lines, undergoes activating phosphorylation by ERK at Thr38 residue as a consequence of constitutively activated MAPK pathway. We demonstrate that ETS1 binds on the mutated TERT promoter leading to the re-expression of the gene. The inhibition of ETS1 resulted in reduced TERT expression. We provide evidence that the TERT promoter mutations provide a direct link between TERT expression and MAPK pathway activation due to BRAF or NRAS mutations via the transcription factor ETS1.

PARKIN Inactivation Links Parkinson's Disease to Melanoma.

BACKGROUND: Melanoma incidence is higher in patients affected by Parkinson's disease (PD) and vice versa, but the genetic link shared by both diseases is unknown. As PARK2 is both a tumor suppressor gene and frequently mutated in young onset PD, we evaluated the role of PARK2 in melanoma predisposition and progression. METHODS: An in-depth PARK2 gene dosage analysis and sequencing was performed on 512 French case patients and 562 healthy control patients, as well as sporadic tumors and melanoma cell lines. The frequency of genetic alterations was compared between case patients and control patients using two-sided Fisher's exact tests and odds ratio (OR) calculations. We used western blotting to determine PARKIN expression in melanocytes and melanoma cell lines and transfection followed by clonogenic assays to evaluate the effect of PARKIN expression on cellular proliferation. All statistical tests were two-sided. RESULTS: Germline PARK2 mutations (including copy number variations, splicing, and putative deleterious missense mutations) were present in 25 case patients but only four control patients (OR = 3.95, 95% confidence interval = 1.34 to 15.75). Copy number variations (CNVs) and loss of heterozygosity were present in 60% and 74%, respectively, of primary tumors. PARKIN protein was expressed in melanocytes but not in most melanoma cell lines, and its expression decreased following melanocyte transformation by oncogenic NRAS. Re-expression of PARKIN in melanoma cell lines resulted in a drastic reduction of cell proliferation and inhibition of PARKIN in melanocytes stimulated their proliferation. CONCLUSION: Our results show an important role for PARK2 as a tumor suppressor both in melanoma predisposition and progression, which could explain the epidemiological association of these diseases.

RICTOR involvement in the PI3K/AKT pathway regulation in melanocytes and melanoma.

Several studies have highlighted the importance of the PI3K pathway in melanocytes and its frequent over-activation in melanoma. However, little is known about regulation of the PI3K pathway in melanocytic cells. We showed that normal human melanocytes are less sensitive to selective PI3K or mTOR inhibitors than to dual PI3K/mTOR inhibitors. The resistance to PI3K inhibitor was due to a rapid AKT reactivation limiting the inhibitor effect on proliferation. Reactivation of AKT was linked to a feedback mechanism involving the mTORC2 complex and in particular its scaffold protein RICTOR. RICTOR overexpression in melanocytes disrupted the negative feedback, activated the AKT pathway and stimulated clonogenicity highlighting the importance of this feedback to restrict melanocyte proliferation. We found that the RICTOR locus is frequently amplified and overexpressed in melanoma and that RICTOR over-expression in NRAS-transformed melanocytes stimulates their clonogenicity, demonstrating that RICTOR amplification can cooperate with NRAS mutation to stimulate melanoma proliferation. These results show that RICTOR plays a central role in PI3K pathway negative feedback in melanocytes and that its deregulation could be involved in melanoma development.

Driver KIT mutations in melanoma cluster in four hotspots.

There has been a great deal of interest in understanding the role of KIT in melanoma since the discovery of KIT mutations in a subset of melanoma. Although a significant proportion of these melanomas respond to KIT inhibitors, the presence of a KIT mutation does not guarantee a response to KIT inhibitors. Because recent data seem to indicate that only melanoma with specific KIT mutations respond to KIT inhibitors, we investigated which KIT mutations are driver mutations in melanoma and are therefore therapeutically relevant. We established that 70% of KIT mutations in melanoma are located in four hotspots (L576, K642, W557-V560, and D816-A829) and that these mutations are oncogenic in melanocytes and are bona-fide driver mutations. Testing for KIT mutations should therefore concentrate on these four hotspots, which can be targeted therapeutically.

Oncogene abnormalities in a series of primary melanomas of the sinonasal tract: NRAS mutations and cyclin D1 amplification are more frequent than KIT or BRAF mutations.

Primary malignant melanoma of sinonasal tract is a rare but severe form of melanoma. We retrospectively analyzed 17 cases and focused on the histologic presentation and the expression of c-Kit, epidermal growth factor receptor (EGFR), cyclin D1/Bcl-1, PS100, and HMB45 and searched for BRAF, NRAS, and KIT mutations that are known to be associated with melanoma subtypes, together with amplifications of KIT, cyclin D1, cyclin-dependent kinase 4, MDM2, and microphthalmia-associated transcription factor using quantitative polymerase chain reaction. In most cases (78%), an in situ component was evidenced. Invasive components were composed of diffuse areas of rhabdoid, epithelioid, or spindle cells and, in most cases, lacked inflammatory reaction, suggesting that an immune escape phenomenon probably develops when the disease progresses. EGFR was rarely and weakly expressed in the in situ component of 2 cases. None of the investigated case showed BRAF V600E, but 1 had a D594G mutation. NRAS mutations in exon 2 (G12D or G12A) were found in 3 cases (18%), and a KIT mutation in exon 11 (L576P), in 1, whereas c-Kit was expressed at the protein level in half of the cases. Amplifications of cyclin D1 were evidenced in 5 cases, confirmed in 3 by fluorescence in situ hybridization, but this was not always correlated with protein expression, found in 8 patients (62.5%), 3 having no significant amplification. In conclusion, primary malignant melanoma of sinonasal tract is not associated with BRAF V600E mutations. Instead, NRAS or KIT mutations and cyclin D1 amplification can be found in a proportion of cases, suggesting that primary malignant melanoma of sinonasal tract is heterogeneous at the molecular level and should not be sensitive to therapeutic approaches aiming at BRAF.

Genetic variation at KIT locus may predispose to melanoma.

As loss of KIT frequently occurs in melanoma progression, we hypothesized that KIT is implicated in predisposition to melanoma (MM). Thus, we sequenced the KIT coding region in 112 familial MM cases and 143 matched controls and genotyped tag single-nucleotide polymorphisms (SNPs) in two cohorts of melanoma patients and matched controls. Five rare KIT substitutions, all predicted possibly or probably deleterious, were identified in five patients, but none in controls [RR = 2.26 (1.26-2.26)]. Expressed in melanocyte lines, three substitutions inhibited KIT signaling. Comparison with exomes database (7020 alleles) confirmed a significant excess of rare deleterious KIT substitutions in patients. Additionally, a common SNP, rs2237028, was associated with MM risk, and 6 KIT variants were associated with nevus count. Our data strongly suggest that rare KIT substitutions predispose to melanoma and that common variants at KIT locus may also impact nevus count and melanoma risk.

Skin tumors induced by sorafenib; paradoxic RAS-RAF pathway activation and oncogenic mutations of HRAS, TP53, and TGFBR1.

PURPOSE: The emergence of skin tumors in patients treated with sorafenib or with more recent BRAF inhibitors is an intriguing and potentially serious event. We carried out a clinical, pathologic, and molecular study of skin lesions occurring in patients receiving sorafenib. EXPERIMENTAL DESIGN: Thirty-one skin lesions from patients receiving sorafenib were characterized clinically and pathologically. DNA extracted from the lesions was screened for mutation hot spots of HRAS, NRAS, KiRAS, TP53, EGFR, BRAF, AKT1, PI3KCA, TGFBR1, and PTEN. Biological effect of sorafenib was studied in vivo in normal skin specimen and in vitro on cultured keratinocytes. RESULTS: We observed a continuous spectrum of lesions: from benign to more inflammatory and proliferative lesions, all seemingly initiated in the hair follicles. Eight oncogenic HRAS, TGFBR1, and TP53 mutations were found in 2 benign lesions, 3 keratoacanthomas (KA) and 3 KA-like squamous cell carcinoma (SCC). Six of them correspond to the typical UV signature. Treatment with sorafenib led to an increased keratinocyte proliferation and a tendency toward increased mitogen-activated protein kinase (MAPK) pathway activation in normal skin. Sorafenib induced BRAF-CRAF dimerization in cultured keratinocytes and activated CRAF with a dose-dependent effect on MAP-kinase pathway activation and on keratinocyte proliferation. CONCLUSION: Sorafenib induces keratinocyte proliferation in vivo and a time- and dose-dependent activation of the MAP kinase pathway in vitro. It is associated with a spectrum of lesions ranging from benign follicular cystic lesions to KA-like SCC. Additional and potentially preexisting somatic genetic events, like UV-induced mutations, might influence the evolution of benign lesions to more proliferative and malignant tumors.

ERK and PDE4 cooperate to induce RAF isoform switching in melanoma.

Melanocytes use BRAF to activate the MAP kinase (MAPK) pathway because CRAF is inhibited by the cyclic AMP (cAMP) pathway in these cells. By contrast, melanomas harboring Ras mutations use CRAF to activate the MAPK pathway. We describe the molecular mechanism of Raf isoform switching and cAMP pathway disruption, which take place during melanocyte transformation. We show that overactivation of the MAPK pathway, induced by the oncogenic Ras in melanoma, induces constitutive phosphorylation of BRAF on Ser151 by ERK, which inhibits NRAS-BRAF interaction . We also demonstrate that melanoma cells have elevated cAMP phosphodiesterase activity owing to overexpression of the cAMP-specific phosphodiesterase-4 enzymes; this activity inhibits cAMP signaling and allows CRAF reactivation in these cells. Reactivating the cAMP pathway inhibits proliferation and induces apoptosis of Ras-mutated melanoma cells, suggesting a new therapeutic approach for treating melanomas harboring Ras mutations.

Cloning of the human GLI2 Promoter: transcriptional activation by transforming growth factor-beta via SMAD3/beta-catenin cooperation.

GLI2 (GLI-Kruppel family member 2), a zinc finger transcription factor that mediates Hedgehog signaling, is implicated in the progression of an ever-growing number of human malignancies, including prostate and pancreatic cancer, as well as basal cell carcinoma of the skin. Its expression is up-regulated by transforming growth factor-beta (TGF-beta) in a variety of cell types, both normal and transformed. We report herein that TGF-beta-driven GLI2 expression is transcriptional and does not result from stabilization of GLI2 transcripts. We describe the characterization of the 5'-flanking sequence of human GLI2 mRNA, the identification of a transcription start site, the cloning of approximately 1,600 bp of the regulatory promoter region and the identification and functional analysis of a TGF-beta-responsive region mapped to a 91-bp sequence between nucleotides -119 and -29 of the promoter. This region harbors SMAD and lymphoid enhancer factor/T cell factor binding sites that allow functional cooperation between SMAD3 and beta-catenin, recruited to the promoter in response to TGF-beta to drive GLI2 gene transcription.

c-Fos accelerates hepatocyte conversion to a fibroblastoid phenotype through ERK-mediated upregulation of paxillin-Serine178 phosphorylation.

Transforming growth factor beta (TGF-beta) exerts an important role in the late steps of carcinogenesis by cooperating with Ras to induce cell motility and tumor invasion. The transcription complex AP-1 has been implicated in the regulation of genes involved in motility and invasion, by mechanisms not yet delineated. We utilized a model of immortalized human hepatocytes (IHH) overexpressing c-Fos (IHH-Fos) or not (IHH-C) to investigate the role of c-Fos on cell motility in response to a prolonged treatment with TGF-beta, EGF or a combination of both. Cotreatment with EGF and TGF-beta, but neither cytokine alone, induced the conversion of hepatocytes to a fibroblastoid phenotype and increased their motility in Boyden chambers. EGF/TGF-beta cotreatment induced a higher effect on ERK phosphorylation compared to TGF-beta treatment alone. It also induced an increase in total and phosphorylated Ser(178) paxillin, a protein previously implicated in cell motility. This response was inhibited by two specific MEK inhibitors, indicating the involvement of the ERK pathway in paxillin activation. Overexpression of c-Fos correlated with increased cell scattering and motility, higher levels of ERK activation and phospho Ser(178) paxillin, increased levels of EGF receptor (EGF-R) mRNA and higher EGF-R phosphorylation levels following EGF/TGF-beta cotreatment. Conversely, siRNA-mediated invalidation of c-Fos delayed the appearance of fibroblastoid cells, decreased EGF-R mRNA and downregulated ERK and Ser(178) paxillin phosphorylations, indicating that c-Fos activates hepatocyte motility through an EGF-R/ERK/paxillin pathway. Since c-Fos is frequently overexpressed in hepatocarcinomas, this newly identified mechanism might be involved in the progression of hepatic tumors in vivo.

Induction of sonic hedgehog mediators by transforming growth factor-beta: Smad3-dependent activation of Gli2 and Gli1 expression in vitro and in vivo.

Hedgehog (Hh) and transforming growth factor-beta (TGF-beta) family members are involved in numerous overlapping processes during embryonic development, hair cycle, and cancer. Herein, we show that TGF-beta induces the expression of the Hh signaling molecules Gli1 and Gli2 in various human cell types, including normal fibroblasts and keratinocytes, as well as various cancer cell lines. Gli2 induction by TGF-beta is rapid, independent from Hh receptor signaling, and requires a functional Smad pathway. Gli1 expression is subsequently activated in a Gli2-dependent manner. In transgenic mice overexpressing TGF-beta1 in the skin, Gli1 and Gli2 expression is also elevated and depends on Smad3. In pancreatic adenocarcinoma cell lines resistant to Hh inhibition, pharmacologic blockade of TGF-beta signaling leads to repression of cell proliferation accompanied with a reduction in Gli2 expression. We thus identify TGF-beta as a potent transcriptional inducer of Gli transcription factors. Targeting the cooperation of Hh and TGF-beta signaling may provide new therapeutic opportunities for cancer treatment.

Stable overexpression of Smad7 in human melanoma cells impairs bone metastasis.

Melanoma has a propensity to metastasize to bone, where it is exposed to high concentrations of transforming growth factor-beta (TGF-beta). Because TGF-beta promotes bone metastases from other solid tumors, such as breast cancer, we tested the role of TGF-beta in melanoma metastases to bone. 1205Lu melanoma cells, stably transfected to overexpress the natural TGF-beta/Smad signaling inhibitor Smad7, were studied in an experimental model of bone metastasis whereby tumor cells are inoculated into the left cardiac ventricle of nude mice. All mice bearing parental and mock-transfected 1205Lu cells developed osteolytic bone metastases 5 weeks post-tumor inoculation. Mice bearing 1205Lu-Smad7 tumors had significantly less osteolysis on radiographs and longer survival compared with parental and mock-transfected 1205Lu mice. To determine if the reduced bone metastases observed in mice bearing 1205Lu-Smad7 clones was due to reduced expression of TGF-beta target genes known to enhance metastases to bone from breast cancer cells, we analyzed gene expression of osteolytic factors, parathyroid hormone-related protein (PTHrP) and interleukin-11 (IL-11), the chemotactic receptor CXCR4, and osteopontin in 1205Lu cells. Quantitative reverse transcription-PCR analysis indicated that PTHrP, IL-11, CXCR4, and osteopontin mRNA steady-state levels were robustly increased in response to TGF-beta and that Smad7 and the TbetaRI small-molecule inhibitor, SB431542, prevented such induction. In addition, 1205Lu-Smad7 bone metastases expressed significantly lower levels of IL-11, connective tissue growth factor, and PTHrP. These data suggest that TGF-beta promotes osteolytic bone metastases due to melanoma by stimulating the expression of prometastatic factors via the Smad pathway. Blockade of TGF-beta signaling may be an effective treatment for melanoma metastasis to bone.

Stable overexpression of Smad7 in human melanoma cells inhibits their tumorigenicity in vitro and in vivo.

We previously identified constitutive Smad signaling in human melanoma cells despite resistance to transforming growth factor-beta (TGF-beta) control of cell proliferation. This led us to investigate the effect of inhibitory Smad7 overexpression on melanoma cell behavior. Using the highly metastatic cell line, 1205-Lu, we thus generated melanoma cell clones constitutively expressing Smad7, and their mock-transfected counterparts. Stable expression of Smad7 resulted in an inhibition of constitutive Smad2/3 phosphorylation, and in a reduced TGF-beta response of Smad3/Smad4-driven gene transactivation, as measured using transfected Smad3/4-specific reporter gene constructs. Smad7 overexpression, however, did not alter their proliferative capacity and resistance to TGF-beta-driven growth inhibition. On the other hand, expression of Smad7 efficiently reduced the capacity of human melanoma cells to invade Matrigel in Boyden migration chambers, while not affecting their motility and adhesion to collagen and laminin. Gelatin zymography identified reduced MMP-2 and MMP-9 secretion by Smad7-expressing melanoma cells as compared with their control counterparts. Smad7-expressing melanoma cells exhibited a dramatically reduced capacity to form colonies under anchorage-independent culture conditions, and, when injected subcutaneously into nude mice, were largely delayed in their ability to form tumors. These results suggest that TGF-beta production by melanoma cells not only affects the tumor environment but also directly contributes to tumor cell aggressiveness through autocrine activation of Smad signaling.

Leptin: a potential marker of placental insufficiency.

To investigate placental leptin production in placental insufficiency, placental leptin production was measured in women with severe preeclampsia (group 1) and in normotensive pregnancies associated with intrauterine growth restriction (group 2), compared to controls (group 3). Placental leptin content was increased 3-fold in group 1 compared to group 2 (192.5.1 +/- 39.5 vs. 67.8 +/- 10.6 ng/g) and 8-fold in group 1 compared to group 3 (192.5.1 +/- 39.5 vs. 25.4 +/- 6.9 ng/g). Placental leptin content was positively correlated with maternal leptin/BMI ratio (r = 0.62) and the resistance index of the umbilical artery (r = 0.60). These data demonstrate that placental insufficiency is associated with a dramatic increase in placental leptin production. This results in a rise in maternal leptinemia that may be taken as an early index of placental dysfunction.

Leptin receptor-deficient obese Zucker rats reduce their food intake in response to a systemic supply of calories from glucose.

It has been established that leptin exerts a negative control on food intake, allowing one to maintain stable caloric intake over time. The aim of the present study was to investigate whether leptin regulates food intake when a supply of calories is provided by the systemic route. Experiments were carried out in leptin receptor-deficient obese fa/fa rats and lean Fa/fa controls. In both groups, 48 h of glucose infusion reduced food intake in proportion to caloric supply, resulting in virtually no change in total caloric intake as compared to before the infusion. This hypophagic response was reproduced without adding systemic calories, but by increasing glucose and insulin concentrations specifically in the brain through carotid artery infusion. Concomitant intracerebroventricular administration of 5-(tetradecyloxy)-2-furoic acid, an acetyl CoA carboxylase inhibitor that precludes malonyl-CoA synthesis, abolished the restriction of feeding in carotid-infused lean and obese rats. These data indicate that a supply of calories via glucose infusion induces a hypophagic response independent of leptin signaling in the rat, and support the hypothesis that a rise in central malonyl-CoA, triggered by increased glucose and insulin concentrations, participates in this adaptation. This process could contribute to the limiting of hyperphagia, primarily when leptin signaling is altered, as in the obese state.

Hypoxia-inducible factor 1 transactivates the human leptin gene promoter.

Increased placental leptin has been demonstrated in preeclampsia, a pregnancy disorder associated with placental hypoxia. This suggests that leptin gene expression is enhanced in response to oxygen deficiency in this organ. In support of this hypothesis, we have previously shown that hypoxia activates the leptin promoter in trophoblast-derived BeWo cells. Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric HIF-1alpha/HIF-1beta complex that regulates the transcription of hypoxia-responsive genes. To test whether this factor is involved in hypoxia-induced leptin promoter activation, BeWo cells were transiently transfected with a HIF-1alpha expression vector. Exogenous HIF-1alpha markedly increased luciferase reporter activity driven by the leptin promoter when HIF-1beta was co-expressed in the same cells. This effect was similar to that elicited by CoCl2, an agent known to stabilize endogenous HIF-1alpha. These data suggest that HIF-1alpha/HIF-1beta dimers are involved in the effect of CoCl2 to activate the leptin promoter. To confirm the implication of HIF-1, the cells were transfected with a dominant negative form of HIF-1alpha producing transcriptionally inactive HIF-1beta/HIF-1alpha dimers. This mutant HIF-1alpha protein abolished CoCl2 activation of the leptin promoter, providing direct evidence that the effect of CoCl2 is mediated by endogenous HIF-1alpha. Deletion analysis and site-specific mutagenesis demonstrated that a HIF-1 consensus binding site (HRE) spanning -120 to -116 bp relative to the start site was required for CoCl2 and exogenous HIF-1alpha induction of leptin promoter activity. Electrophoretic mobility shift assays performed with in vitro-translated HIF-1alpha and HIF-1beta proteins demonstrated binding to this HRE and not to mutated sequences only when both subunits were used together. These data demonstrate that leptin is a new hypoxia-inducible gene, which is stimulated in a placental cell line through HIF-1 interaction with a consensus HRE site located at -116 in the proximal promoter.

Specific increase in leptin production in obese (falfa) rat adipose cells.

In the obese state, enlarged adipose cells display an altered gene-expression profile and metabolic capacity. The aim of this study was to gain insight into their secretory function, by assessing two secreted proteins, leptin and angiotensinogen, in adipose cells of obese (fa/fa) Zucker rats. A marked and co-ordinate increase in leptin mRNA, gene transcription and promoter activity was observed in obese compared with lean (Fa/fa) rat adipose cells, and this resulted in increased leptin release in culture. Two sets of observations suggest that this effect is due to the fa mutation. First, adipose-cell leptin release was higher in heterozygous (Fa/fa) than in homozygous (Fa/Fa) lean rats. Second, leptin release was not enhanced in enlarged adipose cells of FalFa rats fed a high-fat diet for 15 days. At variance with leptin, angiotensinogen production was not significantly increased in the obese cells. Dexamethasone stimulated both leptin and angiotensinogen release in lean and obese rat adipose cells. The magnitude of leptin stimulation was higher in fa/fa than in Fa/fa rats, whereas angiotensinogen release was increased to the same extent in both genotypes. These observations suggest that leptin production is specifically enhanced in enlarged adipose cells of obese Zucker rats and that cell hypertrophy is not the sole determinant of this feature. Increased leptin production might be related to disruption of leptin signalling by the fa mutation.