Pei-Ei Wu

Mechanisms of inactivation of E-cadherin in breast carcinoma: modification of the two-hit hypothesis of tumor suppressor gene.

Loss of heterozygosity (LOH) allows the expression of recessive mutation in tumor suppressor genes (TSG). Therefore, on the basis of Knudsons ‘two-hit’ hypothesis for TSG inactivation, the detection of a high LOH frequency in a chromosomal region is considered critical for TSG localization. One of these LOH regions in breast cancer is 16q22.1, which has been suggested to reflect the involvement of E-cadherin (E-cad), a cell–cell adhesion molecule. To confirm the tumorigenic role of E-cad, 81 sporadic invasive ductal carcinomas (IDCs) of the breast were tested for the ‘two hits’ required to inactivate this gene. A high frequency (37.3%) of LOH was detected in 67 informative tumors, but no mutation was found. To examine the possibility that transcriptional mechanisms serve as the second hit in tumors with LOH, specific pathways, including genetic variant and hypermethylation at the promoter region and abnormal expression of positive (WT1) and negative (Snail) transcription factors, were identified. Of these, promoter hypermethylation and increased expression of Snail were found to be common (>35%), and to be strongly associated with reduced/negative E-cad expression (P<0.05). However, unexpectedly, a significantly negative association was found between the existence of LOH and promoter hypermethylation (P<0.05), which contradicts the ‘two-hit’ model. Instead, since they coexisted in a high frequency of tumors, hypermethylation may work in concert with increased Snail to inactivate E-cad expression. Given that E-cad is involved in diverse mechanisms, loss of which is beneficial for tumors to invade but may also trigger apoptosis, this study suggests that maintaining a reversible mechanism, either by controlling the gene at the transcriptional level or by retaining an intact allele subsequent to LOH, might be important for E-cad in IDC and may also be common in TSGs possessing diverse functions. These findings provide clues to explain why certain TSGs identified by LOH cannot fulfil the two-hit hypothesis.

Breast cancer risk associated with genotype polymorphism of the catechol estrogen-metabolizing genes: a multigenic study on cancer susceptibility.

Estrogen has been suggested to trigger breast cancer development via an initiating mechanism involving its metabolite, catechol estrogen (CE). To examine this hypothesis, we carried out a multigenic case‐control study of 469 incident breast cancer patients and 740 healthy controls to define the role of important genes involved in the different metabolic steps that protect against the potentially harmful effects of CE metabolism. We studied the 3 genes involved in CE detoxification by conjugation reactions involving methylation (catechol‐O‐methyltransferase, COMT), sulfation (sulfotransferase 1A1, SULT1A1), or glucuronidation (UDP‐glucuronosyltransferase 1A1, UGT1A1), one (manganese superoxide dismutase, MnSOD) involved in protection against reactive oxidative species‐mediated oxidation during the conversion of CE‐semiquinone (CE‐SQ) to CE‐quinone (CE‐Q), and 2 of the glutathione S‐transferase superfamily, GSTM1 and GSTT1, involved in CE‐Q metabolism. Support for this hypothesis came from the observations that (i) there was a trend toward an increased risk of breast cancer in women harboring a greater number of putative high‐risk genotypes of these genes (p < 0.05); (ii) this association was stronger and more significant in those women who were more susceptible to estrogen [no history of pregnancy or older (≥26 years) at first full‐term pregnancy (FFTP)]; and (iii) the risks associated with having one or more high‐risk genotypes were not the same in women having experienced different menarche‐to‐FFTP intervals, being more significant in women having been exposed to estrogen for a longer period (≥12 years) before FFTP. Furthermore, because CE‐Q can attack DNA, leading to the formation of double‐strand breaks (DSB), we examined whether the relationship between cancer risk and the genotypic polymorphism of CE‐metabolizing genes was modified by the genotypes of DSB repair genes, and found that a joint effect of CE‐metabolizing genes and one of the two DSB repair pathways, the homologous recombination pathway, was significantly associated with breast cancer development. Based on comprehensive CE metabolizing gene profiles, our study provides support to the hypotheses that breast cancer can be initiated by estrogen exposure and that increased estrogen exposure confers a higher risk of breast cancer by causing DSB to DNA.

Chk2-dependent phosphorylation of XRCC1 in the DNA damage response promotes base excision repair

The DNA damage response (DDR) has an essential function in maintaining genomic stability. Ataxia telangiectasia‐mutated (ATM)‐checkpoint kinase 2 (Chk2) and ATM‐ and Rad3‐related (ATR)‐Chk1, triggered, respectively, by DNA double‐strand breaks and blocked replication forks, are two major DDRs processing structurally complicated DNA damage. In contrast, damage repaired by base excision repair (BER) is structurally simple, but whether, and how, the DDR is involved in repairing this damage is unclear. Here, we demonstrated that ATM‐Chk2 was activated in the early response to oxidative and alkylation damage, known to be repaired by BER. Furthermore, Chk2 formed a complex with XRCC1, the BER scaffold protein, and phosphorylated XRCC1 in vivo and in vitro at Thr284. A mutated XRCC1 lacking Thr284 phosphorylation was linked to increased accumulation of unrepaired BER intermediate, reduced DNA repair capacity, and higher sensitivity to alkylation damage. In addition, a phosphorylation‐mimic form of XRCC1 showed increased interaction with glycosylases, but not other BER proteins. Our results are consistent with the phosphorylation of XRCC1 by ATM‐Chk2 facilitating recruitment of downstream BER proteins to the initial damage recognition/excision step to promote BER.

Genetic variants of BLM interact with RAD51 to increase breast cancer susceptibility

The role of the familial breast cancer susceptibility genes, BRCA1 and BRCA2, in the homologous recombination (HR) pathway for DNA double-strand break (DSB) repair suggests that the mechanisms involved in HR and DNA DSB repair are of etiological importance during breast tumorigenesis. Bloom (BLM) helicase directly interacts with RAD51 recombinase, which is involved in regulating HR, and it is thus of particular interest to examine whether this interaction is associated with breast cancer susceptibility. This single-nucleotide polymorphism (SNP)-based case-control study was performed to examine this hypothesis using specimens from 933 patients with breast cancer and 1539 healthy controls. The results showed that one SNP (rs2380165) in BLM and two (rs2412546 and rs4417527) in RAD51 were associated with breast cancer risk. Furthermore, haplotype and diplotype analyses based on combinations of five SNPs in RAD51 revealed a strong association between RAD51 polymorphisms and breast cancer risk (P < 0.05). Support for the interaction between BLM and RAD51 in determining breast cancer risk came from the finding that the association between cancer risk and at-risk genotypes/haplotype pairs of RAD51 was stronger and more significant in women harboring homozygous variant alleles of BLM (P for interaction < 0.05). Interestingly, not only the intronic SNP located within the region encoding the helicase domain of BLM but also those within the RAD51-interaction domain-encoding region showed an interaction with RAD51 polymorphisms in determining breast cancer susceptibility. Our results suggest a contribution of BLM and RAD51 to breast cancer development and provide support for the tumorigenic significance of the functional interaction between these two HR proteins.

The clinical implications of MMP-11 and CK-20 expression in human breast cancer

BACKGROUND Tumor invasiveness and metastasis in cancer progression is manifested by epigenetic abnormality. However, it remains unknown whether transcription regulation of matrix metalloproteinase-11(MMP-11) and cytoskeleton-20 (CK-20) genes for the homoeostasis of epithelial/connective interface that can enhance cell dissemination and invasion may act as alternative mutators to tumor clinicopathology. METHODS Paired cancerous and tumor-adjacent normal tissues from 72 breast cancer patients were assayed for the expression of MMP-11 and CK-20 by using real-time RT-PCR. The expression profiles were evaluated for the association with clinicopathological factors. RESULTS Breast tumor tissues displayed higher expression levels of MMP-11 and CK-20 than those of the adjacent non-cancerous tissues. Overexpression of either MMP-11 or CK-20 correlated with patients having poorly differentiated tumors (P(MMP-11)=0.01 and P(CK-20)=0.05) and lymph node metastasis (LNM) (P(MMP-11)=0.004 and P(CK-20)=0.001). A synergistic effect between MMP-11 and CK-20 on risk elevation was significant in patients with advanced tumor stage (OR=2.03, 95%CI=1.10-3.77) and LNM (OR=2.83, 95%CI=1.20-4.71). Additionally, patients lacking progesterone receptor exhibited high expression of MMP-11 and CK-20. CONCLUSION We demonstrate that MMP-11 and CK-20 are probable prognostic markers whose expression reflects the stages of tumor differentiation and LNM of breast cancer.

Genetic susceptibility to the development and progression of breast cancer associated with polymorphism of cell cycle and ubiquitin ligase genes.

Tumor levels of the cell cycle regulators cyclin E and p27 correlate strongly with survival in breast cancer patients and are specifically regulated by the ubiquitin ligases hCDC4 and SKP2. This study was to explore whether genetic susceptibility to breast cancer is associated with polymorphism of these genes and whether gene-gene and gene-risk factor [i.e. full-term pregnancy (FTP)] interactions are important in determining cancer risk. A two-stage case-control study based on single-nucleotide polymorphisms was performed. The first study (560 cases and 1122 controls) was to define the contribution of cell cycle and ubiquitin ligase genes to cancer susceptibility. The second study (926 cases and 923 controls) was to confirm the association identified in the first stage and to map the variant alleles. Increased breast cancer risk was associated with both polymorphism of hCDC4 and a joint effect of cyclin E and hCDC4. These associations were more significant in nulliparous women, and cancer risk associated with a lower number of FTPs was only seen in women with a higher number of high-risk genotypes, providing support for an effect of gene-risk factor interaction in determining susceptibility. Sequence variants of intron 2 in hCDC4 were found to be the most significant polymorphism and high-stage estrogen receptor (ER)-negative patients carrying the homozygous variant genotype manifested significantly poorer survival. This study concludes that polymorphism of hCDC4 is a risk factor for breast cancer development by interacting with either cyclin E or FTP and may also prove useful in predicting progression of patients with high-stage and ER-negative breast cancers.

Genetic polymorphisms in oestrogen receptor-binding sites affect clinical outcomes in patients with prostate cancer receiving androgen-deprivation therapy

Abstract.  Huang C‐N, Huang S‐P, Pao J‐B, Hour T‐C, Chang T‐Y, Lan Y‐H, Lu T‐L, Lee H‐Z, Juang S‐H, Wu P‐P, Huang C‐Y, Hsieh C‐J, Bao B‐Y (Kaohsiung Medical University Hospital, Kaohsiung; Kaohsiung Medical University, Kaohsiung; Taipei City Hospital, Taipei; Kaohsiung Medical University, Kaohsiung; China Medical University, Taichung; National Taiwan University Hospital; Oriental Institute of Technology; National Taiwan University, Taipei; China Medical University Hospital, Taichung, Taiwan). Genetic polymorphisms in oestrogen receptor‐binding sites affect clinical outcomes in patients with prostate cancer receiving androgen‐deprivation therapy. J Intern Med 2012; 271: 499–509.

A novel estrogen receptor-microRNA 190a-PAR-1-pathway regulates breast cancer progression, a finding initially suggested by genome-wide analysis of loci associated with lymph-node metastasis

To identify microRNAs that are important in regulating breast cancer progression, the present study used data for the 199 961 single-nucleotide polymorphisms (SNPs) in 837 breast cancer patients genotyped in a recent genome-wide association study to identify loci associated with lymph node metastasis (LNM). SNPs tagging the 15q22.2 locus showed a significant association with LNM and miR-190a was found to be the only microRNA in this region. The role of miR-190a in LNM was supported by the findings that increased miR-190a expression inhibited cell migration and invasiveness and that the target of miR-190a was protease-activated-receptor 1 (PAR-1), which is a metastasis promoting protein in several cancers. In addition, the promoter region of miR-190a was defined and found to contain half of an estrogen response element, suggesting that miR-190a is regulated by estrogen receptor (ER) signaling. This was confirmed by the findings that miR-190a expression was activated by 17β-estradiol and that ERα bound directly to this promoter. The importance of this ERα-miR190a-PAR-1 link in breast tumorigenesis is suggested by the findings of (i) an association between genetic polymorphism of the miR-190a-containing region and LNM that is modified by SNPs of PAR-1 and is particularly significant in ERα-positive patients and (ii) a combined effect of ERα and miR-190a expression on tumor grade/cancer stage. More importantly, the level of miR-190a expression in primary breast carcinomas correlated with overall survival. These findings suggest a novel pathway in which ERα signaling regulates miR-190a expression, causing inhibition of PAR-1 expression, correlated with inhibition of cancer metastasis.

Genetic variation in the genome-wide predicted estrogen response element-related sequences is associated with breast cancer development

IntroductionEstrogen forms a complex with the estrogen receptor (ER) that binds to estrogen response elements (EREs) in the promoter region of estrogen-responsive genes, regulates their transcription, and consequently mediates physiological or tumorigenic effects. Thus, sequence variants in EREs have the potential to affect the estrogen-ER-ERE interaction. In this study, we examined the hypothesis that genetic variations of EREs are associated with breast cancer development.MethodsThis case-control study involved 815 patients of Asian descent with incident breast cancer and 821 healthy female controls. A total of 13,737 ERE sites in the whole genome predicted by a genome-wide computational algorithm were blasted with single-nucleotide polymorphism (SNP) sequences. Twenty-one SNPs located within 2,000 bp upstream or within introns 1 and 2 of putative genes and with a minor allele frequency greater than 5% were identified and genotyped. Frequencies of SNPs were compared between cases and controls to identify SNPs associated with cancer susceptibility.ResultsA significant combined effect of rs12539530, an ERE SNP in intron 2 of NRCAM which codes for a cell adhesion molecule, and SNPs of ESR1, the gene coding for ER, on breast cancer risk was found. Interestingly, this combined effect was more significant in women who had experienced a longer period of lifetime estrogen exposure, supporting a hormonal etiology of this SNP in breast tumorigenesis.ConclusionsOur findings provide support for a role of genetic variation in ERE-ESR1 in determining susceptibility of breast cancer development.

Diverse Associations between ESR1 Polymorphism and Breast Cancer Development and Progression

Purpose: To test the hypothesis that polymorphisms of ESR1, the gene encoding estrogen receptor α (ERα), are associated with susceptibility, clinical phenotype, and progression of breast cancer. Patients and Methods: A case-control study was done on 940 patients with incident breast cancer and 1,547 healthy female controls. Fifteen single-nucleotide polymorphisms (SNP) selected from chr6:152,170,379-152,466,100 (exons 1–8 of the ESR1 gene, excluding flanking sequences), reflecting major polymorphisms of this gene, were genotyped. Frequencies of SNPs were compared between cases and controls to identify SNPs associated with cancer susceptibility and between cases with different clinical phenotypes to determine the role of ESR1 polymorphism in cancer progression. Results: SNPs located in one cluster in intron 1 and one haplotype, based on these SNPs, showed a significant association with breast cancer susceptibility. The tumorigenic contribution of these intron 1 SNPs was more obvious in combination with reproductive risk factors (P for interaction <0.05). One of these intron 1 SNPs was also significantly associated with low ERα expression in tumors. Interestingly, the same intron 1 SNPs showed a correlation with worse clinical phenotypes, including poor differentiation of tumor cells and a late stage. These intron 1 SNPs also showed a significant association with the 5-year breast cancer–specific survival rate of patients, but had opposite effects in ERα-negative and ERα-positive early-stage patients. Conclusions: Our findings provide support for diverse roles of ESR1 polymorphism in determining susceptibility in different stages of breast cancer. The differences between the important ESR1 SNPs identified in Chinese women in this study and those identified in studies on Western women with breast cancer suggest different roles of ERα in these two populations. Clin Cancer Res; 16(13); 3473–84. ©2010 AACR.