Genetic and epigenetic silencing of the beclin 1gene in sporadic breast tumors

Abstract

BackgroundBeclin 1, an important autophagy-related protein in human cells, is involved in cell death and cell survival. Beclin 1 mapped to human chromosome 17q21. It is widely expressed in normal mammary epithelial cells. Although down-regulated expression with mono-allelic deletions of beclin 1 gene was frequently observed in breast tumors, whether there was other regulatory mechanism of beclin 1 was to be investigated. We studied the expression of beclin 1 and explored the possible regulatory mechanisms on its expression in breast tumors.Methods20 pairs of tumors and adjacent normal tissues from patients with sporadic breast invasive ductal cancer (IDCs) were collected. The mRNA expression of beclin 1 was detected by real-time quantitative RT-PCR. Loss of heterozygosity (LOH) was determined by real-time quantitative PCR and microsatellite methods. The protein expression of beclin 1, p53, BRCA1 and BRCA2 was assessed by immunohistochemistry. CpG islands in 5' genomic region of beclin 1 gene were identified using MethylPrimer Program. Sodium bisulfite sequencing was used in examining the methylation status of each CpG island.ResultsDecreased beclin 1 mRNA expression was detected in 70% of the breast tumors, and the protein levels were co-related to the mRNA levels. Expression of beclin 1 mRNA was demonstrated to be much higher in the BRCA1 positive tumors than that in the BRCA1 negative ones. Loss of heterozygosity was detected in more than 45% of the breast tumors, and a dense cluster of CpG islands was found from the 5' end to the intron 2 of the beclin 1 gene. Methylation analysis showed that the promoter and the intron 2 of beclin 1 were aberrantly methylated in the tumors with decreased expression.ConclusionsThese data indicated that LOH and aberrant DNA methylation might be the possible reasons of the decreased expression of beclin 1 in the breast tumors. The findings here shed some new light on the regulatory mechanisms of beclin 1 in breast cancer.

Autophagy as a mediator of chemotherapy-induced cell death in cancer

“…Both genetic and epigenetic silencing of the Beclin-1 gene has been shown in human breast tumors [21]. Combined decreased expression of Beclin-1 and LC-3 is also observed in human glioblastomas [22].…”

Beclin1: A role in membrane dynamics and beyond

“…2A). 76 Beclin 1 protein levels are also controlled by calpain-mediated degradation and caspase-dependent cleavage (Fig. 2C).…”

“…Additionally, a dense cluster of CpG islands is found between the 5′ end and intron 2 of the BECN1 gene. 76 Hypermethylation of this cluster in some sporadic breast tumors results in decreased expression of Beclin 1 ( Fig. 2A).…”

“…46 Allelic deletion of BECN1 is frequently found in carcinoma cell lines, and Beclin 1 expression is reduced in breast, ovarian and brain tumors. 44,76,78,114 In addition, Beclin 1 expression in the human breast carcinoma cell line MCF-7 inhibits in vitro clonigenicity and tumorigenesis in nude mice. 16 Moreover, Beclin 1 +/− mice have a high incidence of spontaneous tumors, including lymphoma and liver and lung cancer.…”

Autophagy: for better or for worse

“…CpG hypermethylation Breast cancer [216] Loss-of-heterozygosity Breast cancer [216] Missense mutations Gastric cancer [217] Colorectal cancer Breast cancer…”