Methylation of CpG island promoters in uveal melanoma -- Moulin et al. 92 (2): 281 -- British Journal of Ophthalmology

All DNA samples were obtained from paraffin-embedded formalin-fixed tissue blocks. Conclusions: Promoter methylation of hTERT is a common calamity in uveal melanoma. Hypermethylation of the other genes studied does not seem to be an crucial component in the enlargement of this tumour.

As promoter methylation of APC, RASSF1 and RARB is regularly observed in cutaneous melanoma, these results propose that clashing epigenetic events crop up in the adulthood of cutaneous and uveal melanoma. 1 In spite of brand-new treatment modalities, mortality has not decreased, 2 principally seeing of liver metastases. Although jillion studies obtain addressed the genetic events involved in the boost of uveal melanoma, alone a infrequent get focused on the epigenetic events that may eventualize during tumorigenesis.

CpG islands promoter methylation, associated with transcriptional gene silencing, has emerged as one of the most influential epigenetic alterations in the system of human malignancies.

10 Although cutaneous and uveal melanoma fist accepted morphological features, they differ considerably in their behaviour, metastatic spread and response to chemotherapy. There is increasing evidence that this is related to differences in their molecular phenotype. DNA review has revealed that uveal and cutaneous melanoma cell lines admit disparate expression profiles. 11 BRAF mutations, ofttimes observed in cutaneous melanoma, were not father in uveal melanomas.

We specifically examined solution promoter genes that keep formerly been shown to be methylated in cutaneous melanoma and other cancers. Cases in which there had been preceding irradiation were excluded from the study. Nine uveal melanomas had involvement of the ciliary body. Vascular patterns were assessed as previously described. The interpret adhered to the tenets of the Helsinki Declaration.

After deparaffinisation, selected areas in tumor tissue sections were microdissected, and the DNA extracted as previously described. Table 2 lists conditions and primer sequences. Single-strand conformation dialogue was performed as previously described. Particular probes were developed to detect the amplified DNA.

One probe was designed to hybridise to methylated DNA containing two CG dinucleotides, and the other one contained two TG dinucleotides in plan to recognise the unmethylated DNA. Table 3 describes the conditions of the dot-blot and probe sequences. The results were obtained by comparing the intensity of the spots on both membranes. Methylation patterns of the changed promoter genes were constant by MS-SSCA and MS-DBA.

No methylation was initiate for APC and FHIT. No correlation was established between promoter methylation status and either the histopathological characteristics of the tumours or the date of the patients. DNA methylation resulting in epigenetic silencing of tumour suppressor genes is an alternative mechanism for loss of tumour suppressor gene function. Patterns with selective methylation of specific tumour suppressor gene promoters retain been described in a broad reach of tumours, creating a separate methylation profile distinctive of a specific tumour type.

The anterior studies of the methylation status of the hTERT CpG island had led to a paradox. In natural somatic cells, this CpG island was unmethylated while the gene was transcriptionally silent. However, in most cancer cells, this region was hypermethylated, whereas telomerase activities and hTERT mRNA were unambiguously detected. Likewise, Heine et al 30 showed no correlation between telomerase vitality and morphology or the boost fraction of the tumour. This denouement corroborates previous studies on leading uveal tumours.

8 The discrepancy between these information may be related to the sensitivity of the contradistinct techniques used for methylation analysis. Furthermore, conversation of promoter methylation in cell lines does not necessarily appear as promoter methylation status in influential tumour specimens.

We evaluated in this occasion the promoter methylation status of three genes located on chromosome 3, FHIT, RARB and RASSF1. On the argument of our data, CpG island methylation does not check in to be a bourgeois mechanism involved in the silencing of these genes in uveal melanoma. In conclusion, our scan indicates that epigenetic alterations of the hTERT gene is a eloquent action in uveal melanoma.

Our findings engage in not, however, exclude silencing of these genes by promoter methylation during following tumour progression. They too demonstrate that contrasting epigenetic events arise in the course of cutaneous and uveal melanoma. FOOTNOTES Competing interests: None. CrossRef Medline Jones PA, Baylin SB. Term profiling reveals that methylation of TIMP3 is involved in uveal melanoma development.

CrossRef Medline Maat W, automobile der Velden PA, et al. Epigenetic inactivation of RASSF1a in uveal melanoma. Molecular grouping of cutaneous malignant melanoma by gene vocable profiling. CrossRef Medline Rimoldi D, Salvi S, Liénard D, et al. Curtailment of BRAF mutations in uveal melanoma. Absence of BRAF gene mutations in uveal melanomas in contrast to cutaneous melanomas.