Notch signaling promotes growth and invasion in uveal melanoma

PURPOSE

To determine whether uveal melanoma, the most common primary intraocular malignancy in adults, requires Notch activity for growth and metastasis.

EXPERIMENTAL DESIGN

Expression of Notch pathway members was characterized in primary tumor samples and in cell lines, along with the effects of Notch inhibition or activation on tumor growth and invasion.

RESULTS

Notch receptors, ligands, and targets were expressed in all five cell lines examined and in 30 primary uveal melanoma samples. Interestingly, the three lines with high levels of baseline pathway activity (OCM1, OCM3, and OCM8) had their growth reduced by pharmacologic Notch blockade using the γ-secretase inhibitor (GSI) MRK003. In contrast, two uveal melanoma lines (Mel285 and Mel290) with very low expression of Notch targets were insensitive to the GSI. Constitutively active forms of Notch1 and Notch2 promoted growth of uveal melanoma cultures and were able to rescue the inhibitory effects of GSI. MRK003 treatment also inhibited anchorage-independent clonogenic growth and cell invasion and reduced phosphorylation levels of STAT3 and extracellular signal-regulated kinase (Erk)1/2. Suppression of canonical Notch activity using short hairpin RNA targeting Notch2 or CBF1 was also able to reduce tumor growth and invasion. Finally, intraocular xenograft growth was significantly decreased by GSI treatment.

CONCLUSION

Our findings suggest that Notch plays an important role in inducing proliferation and invasion in uveal melanoma and that inhibiting this pathway may be effective in preventing tumor growth and metastasis.

Abstract 1415: The Notch ligand Jag 2 promotes growth and invasion in uveal melanoma cells

Uveal melanoma is the most common primary intraocular cancer in the adults, and up to 50% of patients die from hematogenous visceral metastases which are extremely resistant to chemotherapy. Using oligonucleotide expression array analysis of mRNA from primary uveal melanomas, we found that the Jag 2 ligand was 1.9 fold more expressed in tumors which metastasized than those which did not. Other Notch pathway members were also significantly induced in the metastatic cohort. We then used quantitative RT PCR to analyze mRNA extracted from a second cohort of 30 snap-frozen primary tumors, and confirmed that elevated Jag 2 mRNA levels were significantly associated (p = 0.048) with the metastatic Class 2 signature as compared to non-metastatic Class 1 uveal melanoma. To directly examine the importance of Jag 2 in driving cellular growth and invasion, we introduced the ligand into a uveal melanoma cell line, Mel 290, which has low baseline levels of Notch activity as measured by expression of the pathway targets Hes1, Hey1 and Hey2. The Jag 2-GFP-MSCV-infected cells showed a 2.5 to 6 fold induction of Notch targets Hey 1 and Hes1, indicating that pathway activity had been induced. While overall growth of the Jag 2-GFP-MSCV infected cultures as measured by MTT increased only slightly, overexpression of Jag 2 induced an approximately 3 fold increase in clonogenic growth in soft agar. Finally, we assayed the migratory properties of the cells using a wound-healing (“scratch”) assay, as well as their ability to invade Matrigel. Jag 2 expressing cells showed increased motility in both of these tests, with a significant (p = 0.0003) approximately 2 fold induction of transwell invasion capacity. Our data suggest that expression of the Notch ligand Jag 2 may play an important role in uveal melanoma growth and metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1415. doi:10.1158/1538-7445.AM2011-1415

Abstract 4141: Notch signaling: A new potential target in the treatment of uveal melanoma

Uveal melanoma is the most common primary intra-ocular malignancy in adults, and causes significant mortality due to its propensity to metastasize. Our aim is to investigate the role of Notch signaling in promoting uveal melanoma proliferation and invasion. We examined five established uveal melanoma cell lines, and found using qPCR that the Notch 1-2-3 receptors, Jag1-2 ligands and the pathway target Hes1 were expressed to varying degrees in all lines. We then blocked Notch signaling using the gamma-secretase inhibitor (GSI) MRK003, and found that only three of the lines (OCM1, OCM3, OCM8) had their growth inhibited by the drug. Interestingly, these three lines had significantly higher levels of Hes1 mRNA as compared to the two lines resistant to GSI treatment (Mel 285, Mel 290). GSI treatment induced a dose-dependent reduction of anchorage-independent clonogenic growth, with 50% inhibition in OCM1, 70% in OCM3, and 40% in OCM8, as well as a significant reduction in Hes1 mRNA and protein levels. Apoptosis, as measured by cleavage and activation of caspase-9, was also induced. Finally, we observed inhibition of cellular invasion in GSI treated cultures using transwell migration and scratch assays. Preliminary studies of snap-frozen primary tumors indicate that Notch pathway components are expressed in primary uveal melanoma in vivo at levels as high or higher than those in our cell line models. In addition, oligonucleotide microarray analysis showed a significant increase in Jag2 and Notch3 expression levels in primary uveal melanomas that metastasized as compared to those that did not. Our findings suggest that the Notch pathway plays an important role in inducing cellular proliferation and invasion in uveal melanoma, and that inhibiting this pathway using pharmacological agents may be effective in preventing tumor growth and metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4141.

Nuclear-targeting of mutant huntingtin fragments produces Huntington's disease-like phenotypes in transgenic mice

Huntington's disease (HD) results from the expansion of a glutamine repeat near the N-terminus of huntingtin (htt). At post-mortem, neurons in the central nervous system of patients have been found to accumulate N-terminal fragments of mutant htt in nuclear and cytoplasmic inclusions. This pathology has been reproduced in transgenic mice expressing the first 171 amino acids of htt with 82 glutamines along with losses of motoric function, hypoactivity and abbreviated life-span. The relative contributions of nuclear versus cytoplasmic mutant htt to the pathogenesis of disease have not been clarified. To examine whether pathogenic processes in the nucleus disproportionately contribute to disease features in vivo, we fused a nuclear localization signal (NLS) derived from atrophin-1 to the N-terminus of an N171-82Q construct. Two lines of mice (lines 8A and 61) that were identified expressed NLS-N171-82Q at comparable levels and developed phenotypes identical to our previously described HD-N171-82Q mice. Western blot and immunohistochemical analyses revealed that NLS-N171-82Q fragments accumulate in nuclear, but not cytoplasmic, compartments. These data suggest that disruption of nuclear processes may account for many of the disease phenotypes displayed in the mouse models generated by expressing mutant N-terminal fragments of htt.

Environmental, pharmacological, and genetic modulation of the HD phenotype in transgenic mice

The HD-N171-82Q (line 81) mouse model of Huntington's disease (HD), expresses an N-terminal fragment of mutant huntingtin (htt), loses motor function, displays HD-related pathological features, and dies prematurely. In the present study, we compare the efficacy with which environmental, pharmacological, and genetic interventions ameliorate these abnormalities. As previously reported for the R6/2 mouse model of HD, housing mice in enriched environments improved the motor skills of N171-82Q mice. However, life expectancy was not prolonged. Significant improvements in motor function, without prolonging survival, were also observed in N171-82Q mice treated with Coenzyme Q10 (CoQ10, an energy metabolism enhancer). Several compounds were not effective in either improving motor skills or prolonging life, including Remacemide (a glutamate antagonist), Celecoxib (a COX-2 inhibitor), and Chlorpromazine (a prion inhibitor); Celecoxib dramatically shortened life expectancy. We also tested whether raising cellular antioxidant capacity by co-expressing high levels of wild-type human Cu/Zn superoxide dismutase 1 (SOD1) was beneficial. However, no improvement in motor performance or life expectancy was observed. Although we would argue that positive outcomes in mice carry far greater weight than negative outcomes, we suggest that caution may be warranted in testing Celecoxib in HD patients. The positive outcomes achieved by CoQ10 therapy and environmental stimuli point toward two potentially therapeutic approaches that should be readily accessible to HD patients and at-risk family members.

Coenzyme Q10 and remacemide hydrochloride ameliorate motor deficits in a Huntington's disease transgenic mouse model

Huntington's disease (HD) is a progressive inherited neurodegenerative disorder, for which there is no effective therapy. The CARE-HD study, recently published, evaluated the ability of a combination of coenzyme Q10 (CoQ10) and remacemide hydrochloride (R) to ameliorate symptoms, which might arise from glutamate-mediated excitotoxicity and abnormalities in mitochondrial energy production. In this study, we examined the efficacy of CoQ10/R therapy on ameliorating the motor dysfunction and premature death of HD-N171-82Q transgenic mice. Motor performance, measured on the Rotarod, was specifically but transiently improved beginning 3 weeks after initiating the CoQ10/R therapy. Survival, however was not prolonged. Our findings suggest that further study of CoQ10/R in mouse models is warranted to investigate whether this therapeutic approach can ameliorate the symptoms of HD in early stages of the disease.

Distinct behavioral and neuropathological abnormalities in transgenic mouse models of HD and DRPLA

Huntington's disease (HD) and Dentatorubral and pallidoluysian atrophy (DRPLA) are autosomal dominant, neurodegenerative disorders caused by the expansion of polyglutamine tracts in their respective proteins, huntingtin and atrophin-1. We have previously generated mouse models of these disorders, using transgenes expressed via the prion protein promoter. Here, we report the first direct comparison of abnormalities in these models. The HD mice show abbreviated lifespans (4-6 months), hypoactivity, and mild impairment of motor skills. The DRPLA mice show severe tremors, are hyperactive, and are profoundly uncoordinated. Neuropathological analyses reveal that the distribution of diffuse nuclear immunolabeling and neuronal intranuclear inclusions (NII's), in the CNS of both models, was remarkably similar. Cytoplasmic aggregates of huntingtin were the major distinguishing neuropathological feature of the HD mice; mutant atrophin-1 accumulated/aggregated only in the nucleus. We suggest that the distinct behavioral and neuropathological phenotypes in these mice reflect differences in the way these mutant proteins perturb neuronal function.

Histidine kinase activity of the ETR1 ethylene receptor from Arabidopsis

ETR1 represents a prototypical ethylene receptor. Homologues of ETR1 have been identified in Arabidopsis as well as in other plant species, indicating that ethylene perception involves a family of receptors and that the mechanism of ethylene perception is conserved in plants. The amino-terminal half of ETR1 contains a hydrophobic domain responsible for ethylene binding and membrane localization. The carboxyl-terminal half of the polypeptide contains domains with homology to histidine kinases and response regulators, signaling motifs originally identified in bacteria. The putative histidine kinase domain of ETR1 was expressed in yeast as a fusion protein with glutathione S-transferase and affinity purified. Autophosphorylation of the purified fusion protein was observed on incubation with radiolabeled ATP. The incorporated phosphate was resistant to treatment with 3 M NaOH, but was sensitive to 1 M HCl, consistent with phosphorylation of histidine. Autophosphorylation was abolished by mutations that eliminated either the presumptive site of phosphorylation (His-353) or putative catalytic residues within the kinase domain. Truncations were used to delineate the region required for histidine kinase activity. An examination of cation requirements indicated that ETR1 requires Mn2+ for autophosphorylation. These results demonstrate that higher plants contain proteins with histidine kinase activity. Furthermore, these results indicate that aspects of ethylene signaling may be regulated by changes in histidine kinase activity of the receptor.