Elsevier

Human Pathology

Volume 39, Issue 7, July 2008, Pages 1059-1063
Human Pathology

Original contribution
Frameshift mutation of UVRAG, an autophagy-related gene, in gastric carcinomas with microsatellite instability

https://doi.org/10.1016/j.humpath.2007.11.013Get rights and content

Summary

Alteration of autophagy is involved in tumor development. Beclin1, an important regulator of autophagy, acts as a tumor suppressor. Ultraviolet (UV) radiation resistance–associated gene (UVRAG) binds with Beclin1 and induces autophagy. There is a polyadenine tract in UVRAG gene (A10 in exon 8) that is a target for frameshift mutations in colorectal carcinomas with microsatellite instability (MSI). Functionally, colon cancer cells with the frameshift mutation of UVRAG show reduced autophagy formation and increased tumorigenicity. The aim of this study was to determine whether the frameshift mutations of UVRAG are also present in gastric carcinomas with MSI. For this, we analyzed human UVRAG exon 8 in 45 gastric carcinomas with MSI and 92 gastric carcinomas without MSI by a single-strand conformation polymorphism analysis. Overall, we detected 3 frameshift mutations of UVRAG in the polyadenine tract (3/45; 6.7%), and all of them were found in MSH-high (H) subtypes (3/32; 9.4%). The 3 mutations consisted of 2 c.708_709delA and 1 c.709delA which would result in premature stops of the UVRAG protein synthesis. The present data indicate that frameshift mutations in the polyadenine tract in UVRAG gene are present in gastric carcinomas as well and suggest that the affected gastric cancer cells with the mutations may have a reduced autophagy activity.

Introduction

Autophagy, a cellular homeostatic mechanism responsible for the removal or turnover of cytoplasmic components, induces type II programmed cell death [1], [2], [3]. Compared with apoptosis, data connecting cancer pathogenesis with autophagic cell death are limited, and most of them were related to Beclin1 [4], [5], [6], [7], [8], [9]. Beclin1, a mammalian orthologue of yeast Atg6, plays a crucial role in the vesicle nucleation process of autophagy [4], [5]. In breast cancer cell lines, beclin-1 gene is deleted mono-allelically [6]. Experimentally, Beclin1-deficient mice suffer from a high incidence of tumors, suggesting Beclin1 is a haploinsufficient tumor suppressor gene [8], [9]. However, our recent study revealed that Beclin1 point mutation is rare in common human cancers, including breast, colorectal, gastric, and lung cancers [10], suggesting that there may be another inactivating mechanism of Beclin1-mediated autophagy in cancers.

The ultraviolet (UV) radiation resistance–associated gene (UVRAG) was initially identified as a gene that is responsible for partial complement of UV sensitivity in xeroderma pigmentosum cells [11]. Recently, Liang et al [12] found that UVRAG binds with Beclin1/PI(3)kinase III (PI(3)KC3) complex and induces autophagy. UVRAG-induced activation of autophagy formation suppresses the tumorigenic activity of cancer cells [12]. Also, Bif-1, a Bax activator, interacts with Beclin-1 through UVRAG and regulates autophagy and tumorigenesis [13]. UVRAG may act as a tumor suppressor by activating autophagic cell death and might be inactivated in cancer cells. In exon 8 of UVRAG there is a polyadenine repeat (A10), and an earlier study detected a frameshift mutation in the A10 in 18% (2/11) of microsatellite instability (MSI)–positive colorectal cancers [14]. Because the frameshift mutation would result in the production of truncated UVRAG protein, the autophagy activity of UVRAG would be inactivated in the cancer cells with the frameshift mutation. The aim of this study was to determine whether the UVRAG mutation occurs in gastric cancers as well.

Section snippets

Materials and methods

Methacarn-fixed tissues of 137 gastric adenocarcinomas were used for this study. All of the patients with cancers were Asians (Koreans). Approval for this study was obtained from the Catholic University of Korea, College of Medicine's institutional review board. The gastric carcinomas consisted of 32 MSI-high (MSI-H), 13 MSI-low (MSI-L), and 92 microsatellite-stable (MSS) cancers according to the National Cancer Institute criteria [15]. The gastric carcinomas consisted of 55 diffuse-type, 52

Results

Genomic DNAs isolated from normal and tumor tissues of the 137 gastric carcinomas through the microdissection were analyzed for detection of mutation in UVRAG gene (exon 8) by the PCR-SSCP analysis. The PCR-SSCP analysis identified aberrant bands in 3 (2.2%) of the 137 gastric carcinomas (Fig. 1). DNA from normal tissues from the same patients showed no evidence of the mutation in SSCP, indicating the mutations had risen somatically (Fig. 1A). DNA sequence analysis of the aberrantly migrating

Discussion

Frequent alterations of cell death–related genes and their products in cancers [16], [17], [18], [19] led us to analyze the somatic mutation of UVRAG gene in gastric cancer tissues. Because mononucleotide repeats are frequent targets for somatic mutation in gastric carcinomas with MSI, we focused our analysis within the polyadenine tract of UVRAG gene. Because a previous study showed a moderate frequency (17.1%) of UVRAG exon 8 mutation in colorectal carcinomas with MSI [14], we expected to

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    This work was supported by funding from the Korea Research Foundation made in the program year of 2007 (E00042).

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