Molecular mechanisms associated with chromosomal and microsatellite instability in sporadic glioblastoma multiforme.
OBJECTIVE
Two chromosomal instability (CIN) pathways are described in glioblastoma multiforme (GBM), type 1 and type 2, which can be observed in up to 70% of the cases. Microsatellite instability (MSI) plays a pathogenic role in sporadic cancers such as colon, gastric and endometrial carcinomas with deficient mismatch repair (MMR). We aimed to perform a comprehensive analysis of the relationship between CIN and MSI mechanisms in sporadic glioblastomas.


METHODS
129 GBMs were examined (109 newly diagnosed and 20 relapses) investigating MSI, immunohistochemical expression of MMR proteins as well as sequencing and promoter methylation of hMLH1. We characterized the molecular changes frequently correlated with CIN in MSI+ GBMs and compared them with 26 microsatellite-stable tumors.


RESULTS
Low-level MSI was observed in 11 of 129 (8.5%) cases and was higher in relapses than in primary GBMs (25 vs. 5.5%, p = 0.027). High-level MSI was not found in any case. A deficient expression of MLH1 and PMS2 without hMLH1 inactivation was observed only in one giant cell GBM. 55% of the MSI+ GBMs showed a profile which did not correspond to one of the known CIN pathways. An inverse association was observed between MSI and mutations of both p53 and PTEN.


CONCLUSIONS
Our data suggest that CIN and MSI contribute to the genomic instability in GBMs via independent pathways. Since MSI was significantly more frequent in relapses, it might play a role in the malignant progression of GBM.
Martinez
Ramon
R
Department of Neurosurgery, Institute of Pathology of the University of Dresden, Dresden, Germany. voelter.martinez@t-online.de
Schackert
Hans-K
HK
Plaschke
Jens
J
Baretton
Gustavo
G
Appelt
Hella
H
Schackert
Gabriele
G
D000293:Adolescent; D000328:Adult; D020137:Base Pair Mismatch; D019175:DNA Methylation; D005260:Female; D042822:Genomic Instability; D005909:Glioblastoma / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D019656:Loss of Heterozygosity; D008297:Male; D018895:Microsatellite Repeats; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000235:genetics; D051059:PTEN Phosphohydrolase; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics; D011401:Promoter Regions, Genetic; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics
D009363:Neoplasm Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human