DNA Methylation Profiles of MGMT, DAPK1, hMLH1, CDH1, SHP1, and HIC1 in B-Cell Lymphomas

BACKGROUND: This study was designed to examine the prevalence of aberrant promoter methylation in a selected panel of genes potentially involved in lymphoid tumors. METHODS: The promoter hypermethylation status of MGMT, DAPK1, hMLH1, CDH1, SHP1, and HIC1 was measured by methylation-specific PCR for 82 cases of B-cell lymphoma. Immunohistochemical staining using MGMT and SHP1 antibodies was conducted on 43 out of 82 cases. RESULTS: The number of MGMT aberrant methylations was lower in diffuse large B-cell lymphoma (DLBCL) than in other malignant lymphomas. The methylation of DAPK1 was frequently detected in follicular lymphoma (FL), marginal zone B-cell lymphoma (MZL) and DLBCL. With one exception, methylation of hMLH1 was not observed in B-cell lymphomas. The methylation frequency of CDH1, and HIC1 was similar in B-cell lymphomas. However, the methylation of SHP1 gene was more frequently observed in cases of FL, DLBCL, and MZL than in chronic lymphocytic lymphoma. MGMT and SHP1 promoter methylation were inversely correlated with the protein expression observed upon immunohistochemical staining. CONCLUSIONS: Aberrant promoter methylation of multiple genes occurs with variable frequency throughout the B-cell lymphomas, and methylation of hMLH1 is rarely observed in B-cell lymphomas.

Claudin-7 is Highly Expressed in Chromophobe Renal Cell Carcinoma and Renal Oncocytoma

Claudin-7 has recently been suggested to be a distal nephron marker. We tested the possibility that expression of claudin-7 could be used as a marker of renal tumors originating from the distal nephron. We examined the immunohistochemical expression of claudin-7 and parvalbumin in 239 renal tumors, including 179 clear cell renal cell carcinoma (RCC)s, 29 papillary RCCs, 20 chromophobe RCCs, and 11 renal oncocytomas. In addition, the methylation specific-PCR (MSP) of claudin-7 was performed. Claudin-7 and parvalbumin immunostains were positive in 3.4%, 7.8% of clear cell RCCs, 34.5%, 31.0% of papillary RCCs, 95.0%, 80.0% of chromophobe RCCs, and 72.7%, 81.8% of renal oncocytomas, respectively. The sensitivity and specificity of claudin-7 in diagnosing chromophobe RCC among subtypes of RCC were 95.0% and 92.3%. Those of parvalbumin were 80.0% and 88.9%. The expression pattern of claudin-7 was mostly diffuse in chromophobe RCC and was either focal or diffuse in oncocytoma. All of the cases examined in the MSP revealed the presence of unmethylated promoter of claudin-7 without regard to claudin-7 immunoreactivity. Hypermethylation of the promoter might not be the underlying mechanism for loss of its expression in RCC. Claudin-7 can be used as a useful diagnostic marker in diagnosing chromophobe RCC and oncocytoma.