Mismatch Repair Gene Expression Defects Contribute to Microsatellite Instability in Ovarian Carcinoma

Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Holden Comprehensive Cancer Center, University of Iowa Hospitals and Clinics, Iowa City, Iowa, USA.
Cancer (Impact Factor: 4.89). 11/2003; 98(10):2199-206. DOI: 10.1002/cncr.11770
Source: PubMed


hMLH1, the human MutL homologue, has been linked to microsatellite instability (MSI) in gastrointestinal tumors. However, to the authors' knowledge, the role of hMLH1, the other mismatch repair genes (MMR), and MSI in ovarian carcinoma has not been well defined. The purpose of the current study was to determine the relation between MSI of ovarian carcinoma and MMR gene expression, hMLH1 and hMSH2 hypermethylation, and hMLH1 and hMSH2 null mutations.
hMLH1 mRNA was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) and amplification of cDNA using a housekeeping gene (glycerol 3-phosphate dehydrogenase) as a control for mRNA quality and quantity. Methylation-specific PCR (MS-PCR) was used to correlate methylation of the hMLH1 and hMSH2 CpG islands with mRNA expression status. Similar techniques were used to evaluate the concomitant expression of five other MMR: hMSH2, hMSH3, hMSH6, PMS1, and PMS2. Microsatellite instability was studied using the National Cancer Institute consensus markers (D2S123, D5S346, D17S250, BAT25, and BAT26) and NM23 as described previously.
One hundred twenty-five primary tumors were analyzed. High-frequency MSI (MSI-H) was found in 21 tumors (16.8%). hMLH1 mRNA was absent in 10 of these 21 tumors (47.6%). In each case, coordinated hypermethylation of both regions A and C of the promoter was identified. Microsatellite stable and low-frequency MSI tumors all were found to express not only hMLH1 but the other MMR genes as well (P < 0.001). Absence of expression of hMSH2 and the four other MMRs occurred in tumors with absent hMLH1 mRNA expression because of CpG island hypermethylation. No absence of expression of hMSH2, hMSH3, hMSH6, PMS1, or PMS2 was found to occur in tumors expressing hMLH1. None of the 11 MSI-H tumors without promoter hypermethylation demonstrated a null mutation in hMLH1 or hMSH2.
A molecular mechanism to explain > 50% of the MSI-H phenotype in ovarian carcinoma cases was demonstrated. MSI-H may occur because of MMR defects, especially hMLH1 promoter hypermethylation. Additional mechanisms are required to explain the balance between the cases of MSI-H as well as the phenomenon of MSI-L tumors.

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Available from: John P Geisler, Apr 27, 2015
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    • "Promoter hypermethyl ation of the hMLH1 gene has been observed in sporadic microsatellite instability-high (MSI-H) cancers, including colorectal and endometrial cancers [13]. In addition, studies in ovarian cancer have reported a frequency of hMLH1 promoter hypermethy lation that ranged from 6% to 12.5% [11] [12] [14] [15]. More recently, preclinic al data suggested a relationship between hMLH1 deficiency and resistance to cisplatin and carbopla tin [16] [17]. "
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    ABSTRACT: Enhancer of zeste homolog 2 (EZH2) is overexpressed in various malignancies and associated with poor prognosis and drug-resistance. A recent study suggested that there is a link between EZH2 expression and the mediation of gene silencing in association with aberrant DNA methylation. In the present study, we showed an inverse correlation between EZH2 and human mutL homolog 1 gene (hMLH1) expression in 30 epithelial ovarian cancer (EOC) tissues. Moreover, we found that EZH2 downregulation could induce the re-expression of the unmethylated, basally expressed hMLH1 gene without affecting DNA methylation in the hMLH1 promoter. These results suggest that EZH2 can modulate the transcription of basally expressed hMLH1 via a non-DNA-methylation-dependent pathway, but it has no effect on hMLH1 silencing that is mediated by DNA hypermethylation.
    Full-text · Article · Mar 2013 · Biochemical and Biophysical Research Communications
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    • "A correlation between hMLH1 hypermethylation , loss of expression, and microsatellite instability has been demonstrated in colorectal, gastric, endometrial [25] [34] [35] [36], and ovarian cancers [31] [37] [38]. The frequencies of hMLH1 promoter methylation have been reported to range from 9% to 39% [32] [33] [39] [40]. "
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    Full-text · Article · Jan 2010 · International Journal of Molecular Epidemiology and Genetics
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    • "Proportion of MSI in unselected ovarian cancers: a meta-analysis plot. Table 1 Frequency of MSI-H phenotype in unselected ovarian cancers Reference Study location No. markers Sample size No. MSI-H Allen et al., 2000 (21) Buffalo, NY 4 26 1 (4%) Alvi et al., 2001 (22) St. Louis, MO 5 43 3 (7%) Buller et al., 2001 (23) Iowa City, IA 6 116 24 (20%) Codegoni et al., 1999 (24) Milan, Italy 8 31 8 (26%) Dellas et al., 2004 (25) Basel, Switzerland 5 66 20 (30%) Fujita et al., 1995 (36) Osaka, Japan 4 47 8 (17%) Geisler et al., 2003 (10) Iowa City, IA 6 107 21 (20%) Gras et al., 2001 (11) Barcelona, Spain 5 42 2 (5%) Han et al., 1993 (27) Seoul, Korea 4 19 1 (5%) Iwabuchi et al., 1995 (28) New Haven, CT 66 95 6 (6%) King et al., 1995 (29) New Haven, CT and Friedburg, Germany 2 41 7 (17%) Kobayashi et al., 1995 (30) Hokkaido, Japan 5 68 2 (3%) Krajinovic et al., 1998 (31) Montreal, Canada 8 12 2 (17%) Osborne et al., 1994 (32) Cambridge, United Kingdom 9 25 2 (8%) Shih et al., 1998 (33) Queensland, Australia 69 31 0 (0%) Sood et al., 1996 (34) Iowa City, IA 10 68 25 (37%) Sood et al., 2001 (35) Iowa City, IA 14 109 13 (12%) Tangir et al., 1996 (36) Boston, MA 13 31 0 (0%) Table 2 Histologic subtypes of MMR-deficient ovarian cancers "
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    ABSTRACT: A meta-analytic approach was used to estimate the frequency of: (a) microsatellite instability-high (MSI-H) phenotype in unselected ovarian cancers and (b) various histologic subtypes of mismatch repair (MMR)-deficient epithelial ovarian cancers. A systematic search of the Medline electronic database was conducted to identify articles published between January 1, 1966, and December 31, 2007, that examined MMR deficiency in ovarian cancers. Data were extracted on the study population, sample size, MSI-H frequency, and histology of MMR-deficient ovarian tumors. The pooled proportion of MSI-H ovarian cancers was 0.12 [95% confidence interval (CI), 0.08-0.17] from 18 studies with 977 cases. The proportion of histologic subtypes in the pooled analysis from 15 studies with 159 cases was serous at 0.32 (95% CI, 0.20-0.44), mucinous at 0.19 (95% CI, 0.12-0.27), endometrioid at 0.29 (95% CI, 0.22-0.36), clear cell at 0.18 (95% CI, 0.09-0.28), and mixed at 0.24 (95% CI, 0.07-0.47). There was significant heterogeneity between studies. The frequency of the MSI-H phenotype in unselected ovarian cancers approximates 12%. MMR-deficient ovarian cancers also seem to be characterized by an overrepresentation of nonserous histologic subtypes. Knowledge of histologic subtype may aid clinicians in identifying the relatively large proportion of ovarian cancers due to MMR defects; such knowledge has potential implications for medical management.
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