Abstract.
Background: The molecular mechanisms
controlling initiation and progression of medulloblastomas are largely unclear.
Changes in DNA methylation of promoter regions have been shown to disturb the
expression of growth regulatory genes. Patients and Methods:
We evaluated DNA methylation patterns in 17 medulloblastomas, 5 stPNETs
and 5 medulloblastoma cell lines using Restriction Landmark Genomic Scanning
(RLGS), a method displaying up to 2.000 potential gene loci in a single gene.
To test whether previously characterized tumor suppressor genes are affected by
hypermethylation we performed MS-PCR for p15INK4B , p16INK4A , VHL, TP53 and
E-cadherin . Results: The
analysis of RLGS profiles from tumors revealed an abundance of hypermethylation
in primary tumors and cell lines. Extrapolated to the human genome with its
∼ 36,000 genes a total of 420 loci become hypermethylated in the
tumor genomes. The previously characterized medulloblastoma breakpoint cluster
in 17p11.2 appears to be a hotspot for aberrant methylation. Cox regression
analysis of survival data identified seven CpG islands for which
hypermethylation is suggestive of a poor prognosis. MS-PCR analysis of known
genes demonstrated hypermethylation of p16INK4A
in a limited number of tumors. The
pattern of DNA hypermethylation was similar in medulloblastomas and stPNETs.
However, some CpG islands were shown to be specific for a tumor type, while
others were shared targets. Conclusions:
Hypermethylation is a common abnormality in primary medulloblastomas and
supratentorial PNETs. Several hundreds of CpG islands are potential targets for
methylation in medulloblastomas including the breakpoint cluster in 17p11.2.
The methylation status of certain gene sequences appears to be associated with
the clinical outcome. Promoter hypermethylation has an outstanding potential as
a marker for the identification of novel tumor suppressors as well as
diagnostic and therapeutic targets in medulloblastomas.
Hintergrund: Die zu einem Medulloblastom
führenden molekularen Mechanismen sind weitgehend unklar.
Veränderungen des normalen Methylierungsmusters regulatorischer
Promoterregionen ist ein Mechanismus, der, ohne die Basenpaarsequenz der DNA zu
verändern, Tumor-Suppressor-Gene inaktivieren kann. Patienten und Methoden: Wir untersuchten die Bedeutung von
DNA-Methylierung in 17 Medulloblastomen und 5 stPNETs mittels einer
Screening-Methode, dem Restriction Landmark Genomic Scanning (RLGS). RLGS kann
in einem einzelnen Gen bis zu 2.000 Genloci auflösen. Vormals
charakterisierte Zielgene für aberrante Methylierung in Tumoren
Erwachsener (p15INK4B
, p16INK4A
, VHL ,
TP53 und E-cadherin ) wurden
durch Methylierungsspezifische PCR (MS-PCR) analysiert. Ergebnisse: Auf die ca. 36 000 Gene des menschlichen
Genoms hochgerechnet fanden sich in Medulloblastomen bis zu 420
hypermethylierte Loci. Mehrere von diesen konnten dem Medulloblastombruchpunkt
auf 17p11.2 zugeordnet werden. Regressionsanalysen deuten darauf hin, dass die
Hypermethylierung von sieben der untersuchten Genloci mit einer
ungünstigen Prognose einhergeht. MS-PCR Analysen zeigten nur bei wenigen
Medulloblastomen Hypermethylierung des Gens p16INK4A
. Es fanden sich CpG islands, die
bevorzugt in Medulloblastomen oder stPNETs hypermethyliert waren.
Schlussfolgerung: Hypermethylierung tritt in
Medulloblastomen und anderen PNETs des ZNS häufig auf. Mehrere hundert CpG
islands sind von Hypermethylierung in Medulloblastomen betroffen, so auch der
chromosomale Bruchpunkt auf Chromosom 17p11.2. Der Methylierungsstatus
bestimmter Loci ist mit der klinischen Prognose assoziiert.
Methylierungsanalysen können sowohl prognostische Marker aufdecken als
auch neue therapeutische Zielgene offenlegen.
Key words
Medulloblastoma - primitive neuroectodermal tumor - hypermethylation - prognosis
Schlüsselwörter
Medulloblastom - primitive neuroectodermale Tumoren - Hypermethylierung - Prognose
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Dr. Michael C. Frühwald M. D., Ph. D.
Westfälische Wilhelms-Universität
Münster Klinik und Poliklinik für
Kinderheilkunde Pädiatrische Hämatologie/Onkologie
Albert-Schweitzer-Straße 33
48149 Münster
Telefon: Tel. (02 51) 83-4 77 42
Fax: Fax (02 51) 83-4 78 28
eMail: E-mail: fruhwald@uni-muenster.de