Epigenetic inactivation of DLC-1 in supratentorial primitive neuroectodermal tumor.
Supratentorial primitive neuroectodermal tumors (SPNETs) and medulloblastomas (MBs) are histologically similar intracranial tumors found in different anatomic locations of the brain. Our group has previously demonstrated that loss of chromosome 8p is a frequent event in MBs. The aim of this study was to evaluate whether DLC-1, a newly identified tumor-suppressor gene on chromosome 8p22, is involved in the tumorigenesis of MBs and the histologically similar SPNETs. We first assessed for alterations of gene expression in microdissected tumors and detected lack of DLC-1 transcript in 1 of 9 MBs (case M44) and 1 of 3 SPNETs (case M1). Neither somatic base substitutions nor homozygous deletion were found in tumors without DLC-1 transcript. We then explored the possibility of hypermethylation of the CpG island in DLC-1 as the mechanism of suppressed expression. Methylation-specific polymerase chain reaction revealed promotor hypermethylation of DLC-1 in M1 but not in M44. Bisulfite sequencing further verified a densely methylated pattern of 35 CpG sites studied in M1 that were not found in normal brain, indicating that inactivation of DLC-1 by hypermethylation is involved in SPNET. Based on this finding, we examined an additional 20 MBs, 8 SPNETs, and 4 MB and 2 SPNET cell lines for hypermethylation of the CpG island of DLC-1, finding that none of these samples exhibited DLC-1 methylation. In conclusion, our results demonstrate that transcriptional silencing of DLC-1 through promoter hypermethylation may contribute to tumorigenesis in a subset of SPNETs, and that loss of DLC-1 expression in MBs may be related to mechanisms other than promoter hypermethylation, genomic deletion, and mutation.
Pang
Jesse Chung-Sean
JC
Department of Anatomical and Cellular Pathology, Prince of Wales Hospital, The Chinese University of Hong Kong, People's Republic of China.
Chang
Qing
Q
Chung
Yuk Fei
YF
Teo
Jennifer Gek Choo
JG
Poon
Wai Sang
WS
Zhou
Liang-Fu
LF
Kong
Xiangyin
X
Ng
Ho-Keung
HK
D000293:Adolescent; D000328:Adult; D001483:Base Sequence; D045744:Cell Line, Tumor; D002528:Cerebellar Neoplasms / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D002898:Chromosomes, Human, Pair 8 / Q000235:genetics; D018899:CpG Islands; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D020690:GTPase-Activating Proteins; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D007223:Infant; D007834:Lasers; D019656:Loss of Heterozygosity; D008297:Male; D008527:Medulloblastoma / Q000235:genetics; D042282:Microdissection; D008969:Molecular Sequence Data; D018242:Neuroectodermal Tumors, Primitive / Q000235:genetics*; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015173:Supratentorial Neoplasms / Q000235:genetics*; D025521:Tumor Suppressor Proteins / Q000235:genetics*
C112352:DLC1 protein, human; D020690:GTPase-Activating Proteins; D025521:Tumor Suppressor Proteins