Promoter Hypermethylation of the RB1 Gene in Glioblastomas

Abstract

SUMMARY:Loss of expression of the retinoblastoma gene (RB1) has been shown to occur in up to 25% of glioblastomas (WHO Grade IV). To elucidate the underlying mechanism, we assessed RB1 promoter hypermethylation using methylation-specific polymerase chain reaction and RB1 expression by immunohistochemistry in 35 primary (de novo) glioblastomas and in 21 secondary glioblastomas that had progressed from low-grade diffuse astrocytoma (WHO Grade II) or anaplastic astrocytoma (WHO Grade III). Promoter hypermethylation was significantly more frequent in secondary (9 of 21, 43%) than in primary glioblastomas (5 of 35, 14%; p ϭ 0.0258). There was a clear correlation between loss of RB1 expression and promoter hypermethylation. In the majority of glioblastomas with loss of RB1 expression, there was promoter hypermethylation (11 of 13, 85%), whereas 93% of tumors with RB1 expression had a normal RB1 gene status (p Ͻ 0.0001). In three glioblastomas, areas with and without RB1 expression were microdissected; promoter hypermethylation was detected only in areas lacking RB1 expression. In patients with multiple biopsies, methylation of the RB1 promoter was not detectable in the less malignant precursor lesions, ie, low-grade diffuse and anaplastic astrocytoma. These results indicate that promoter hypermethylation is a late event during astrocytoma progression and is the major mechanism underlying loss of RB1 expression in glioblastomas. (Lab Invest 2001, 81:77-82).

Frequent LOH on 22q12.3 and TIMP-3 inactivation occur in the progression to secondary glioblastomas

“…26 Sodium bisulfite modification was Novel tumor suppressor loci on 22q12.3 in secondary glioblastoma M Nakamura et al performed using a CpGenomet DNA Modification Kit (Intergen, Oxford, UK) according to the manufacturer's protocol with minor modifications. 8,27,28 The primer sequences, with methylated and unmethylated PCR and MSP conditions, have been previously reported. 29 Amplified products were electrophoresed on 2% agarose gels and visualized by ethidium bromide staining.…”

“…1 Recent genetic analyses have shown that these glioblastoma subtypes develop through different genetic pathways; 2-4 primary glioblastomas occur in older patients characterized by EGFR amplification/overexpression, PTEN mutation, homozygous p16 INK4a deletion, and loss of heterozygosity (LOH) throughout chromosome 10, 3,5,6 while secondary glioblastomas develop in younger patients and typically show frequent p53 mutations, LOH preferentially on chromosomes 10q and 19q, 3,[5][6][7] and promoter methylation of the RB1 gene. 8 LOH on 22q seems to be of interest, since this allelic loss is a common event in gliomas, occurring with a frequency varying between 11 and 39%. Interestingly, 22q LOH appears to be uncommon in low-grade astrocytomas, but is more frequently detected in anaplastic astrocytomas and glioblastomas.…”

Alterations of the RB1 gene in dedifferentiated liposarcoma

“…Experimental data have shown that in vitro methylation of the RB1 promoter region reduced pRB expression. 28 Unilateral retinoblastoma and some brain tumors show loss of pRB expression which is associated with aberrant methylation of the CpG island within the RB1 promoter region; [29][30][31] however, the methylation status of the RB1 gene in soft-tissue sarcoma has not been described. RB1 promoter hypermethylation was detected in four out of 27 (14.8%) dedifferentiated components, whereas no hypermethylation was detected in any of the well-differentiated components.…”

Hormony tarczycy w ośrodkowym układzie nerwowym (OUN) i ich wpływ na nowotworzenie, zwłaszcza na rozwój i przebieg glioblastoma multiforme — hipoteza badawcza

“…/RB1 jest ważny dla procesu proliferacji, ponieważ białko RB1 podobnie jak białko TP53 reguluje cykl komórkowy, kontrolując przejście z fazy G1 do fazy S. Zaburzenia tego szlaku występują zarówno w pierwotnym, jak i we wtórnym GBM [77,78] i polegają na delecji P16…”