Genetic or epigenetic silencing of low density lipoprotein receptor‐related protein 1B expression in oral squamous cell carcinoma

Abstract

Previously, we have reported frequent silencing of the expression of LRP1B by genetic and epigenetic mechanisms in esophageal squamous cell carcinoma. As the same events might be involved in the development/progression of OSCC, we examined intragenic homozygous deletions, expression levels, and methylation status in the CpG island of this gene. Homozygous deletion was detected in only 1 of 18 (5.6%) OSCC lines, whereas the expression of LRP1B mRNA was silenced in 8 of 17 (47.1%) OSCC lines without homozygous deletion. An inverse correlation between mRNA expression and methylation status of the LRP1B CpG island was clearly observed in OSCC lines, and LRP1B mRNA expression was restored by treatment with 5-aza-dCyd. Frequent methylation of the LRP1B promoter was also observed in primary OSCC. Taken O ral cancer, predominantly OSCC, is the most common head and neck neoplasm, affecting >400 000 people worldwide every year.(1,2) Despite advances in surgical techniques, chemotherapy, and radiation, 50% of patients die of the disease or complications from it within 5 years.(3) Moreover, OSCC has a severe impact on quality of life through impairments of swallowing and speaking or esthetic disorders. Despite recent progress in the diagnosis and therapeutic methods for OSCC, the prognosis has not improved, reflecting the ineffectiveness of current treatment regimens.(4) An improved understanding of the molecular pathogenesis of OSCC is urgently needed to identify new targets and strategies for effective therapy.(5,6) However, the molecular mechanisms of the progression of OSCC are still unknown.The carcinogenesis of OSCC is thought to be a multistep phenomenon in which a variety of genetic alterations can be segregated into early to late stages.(7) Recently, in addition, evidence has emerged that epigenetic mechanisms, such as altered DNA methylation patterns, play a significant role in the silencing of tumor suppressor genes and contribute to malignant transformation during carcinogenesis.(8) Although several genes, for example, p14, p15, p16, RASSF1A, VHL, hMLH1, and MGMT, have been reported to be silenced by aberrant DNA methylation, (9)(10)(11)(12)(13)(14)(15)(16) some of them were infrequently methylated in OSCC compared with other tumors. In order to create the b.est possible panel of markers for the prediction of outcome, sensitivity to chemotherapy and radiation, and disease status OSCC, more candidates for tumor-suppressor genes targeted by promoter methylation will no doubt be tested in this disease. (16) Recently, we have reported frequent inactivation of the LRP1B (2q22.1) through intragenic homozygous deletion or promoter hypermethylation in ESCC. (17) In the study reported here, homozygous deletion of LRP1B was observed in only 1 of 18 OSCC cell lines, whereas silencing of the expression of LRP1B mRNA through methylation of the promoter was observed in 8 of 18 OSCC cell lines, suggesting that LRP1B is mainly inactivated through an epigenetic mechanism in OSCC. Frequent hypermethylation of the LRP1B promote...

High-Resolution Genomic Copy Number Profiling of Glioblastoma Multiforme by Single Nucleotide Polymorphism DNA Microarray

“…LRP1B has been classified as a tumor suppressor gene and is frequently mutated in GBM (42)(43)(44)(45)(46)(47). We discovered a novel internal deletion of LRP1B in the U118 GBM cell line and four GBM samples.…”

“…Other studies have suggested that LRP1B may be a tumor suppressor gene that is deleted or abnormal in several other tumor types, as well as GBM (42)(43)(44)(45)(46)(47). In addition, LRP1B is deleted or epigenetically silenced in oral urothelial, esophageal, and non-small-cell lung cancers; taken together, LRP1B behaves as a tumor suppressor gene that is frequently mutated in several solid tumors, including GBM (42)(43)(44)(45)(46)(47). Our data suggest that LRP1B acts as a tumor suppressor gene in glioma cells and is aberrant in GBM.…”

Aberrant methylation impairs low density lipoprotein receptor‐related protein 1B tumor suppressor function in gastric cancer

“…Previous studies have found homozygous deletions of LRP1B exons 1, 5, 7, and 10 in other cancers (Liu et al, 2000a;Sonoda et al, 2004;Nakagawa et al, 2006). To investigate whether homozygous deletion of these LRP1B exons is common in gastric cancer, we used quantitative real-time genomic PCR to detect homozygous deletions in proximal exons (1, 5, 7, and 10) and distal exons (85 and 88) in gastric cancer cell lines, normal stomach tissue and 74 paired tumor/ adjacent normal tissue.…”

“…One of our candidate genes LRP1B, ranked number four among the 107 differential hypermethylated genes (P < 0.001, Supporting Information Fig. S1) has previously been shown to be genetically or epigenetically silenced in cancers (Sonoda et al, 2004;Nakagawa et al, 2006). To analyze whether LRP1B is indeed differentially methylated in gastric cancer, we performed LRP1B bisulfite sequencing using gastric cancer cell lines and normal stomach tissue.…”

“…Homozygous deletions within this gene have been reported in nonsmall cell lung cancer cell line (NSCLC) (Liu et al, 2000a,b), urothelial cancer (Langbein et al, 2002), liver cancer (Pineau et al, 2003), and glioblastoma (Roversi et al, 2006). In addition, recent studies have shown that LRP1B expression can be down-regulated by DNA methylation in esophageal squamous carcinoma (ESC) (Sonoda et al, 2004), oral squamous carcinoma (OSC) (Nakagawa et al, 2006), acute lymphoblastic leukemia (ALL) (Taylor et al, 2007), and small B cell-lymphoma (Rahmatpanah et al, 2006). These findings prompted us to investigate whether DNA methylation might play an important role in the inactivation of the LRP1B gene, and whether this could be pathogenetically important in gastric cancer.…”