The methylation status of FBXW7 beta-form correlates with histological subtype in human thymoma.

FBXW7 is reported to be a tumor suppressor gene, and the functional inactivation of FBXW7 has been reported in various human tumors. In this study, we investigated the FBXW7 gene in human thymoma; although no mutations were evident, a significantly high frequency of methylation in the FBXW7 beta-form promoter was observed in types B1 or higher (P=0.014). We propose a novel mechanism for the pathogenesis of thymoma by FBXW7 beta-form and hypothesize that expressional suppression plays an important role in the malignant potential of thymoma.

Promoter hypermethylation is not the major mechanism for inactivation of the FBXW7 beta-form in human gliomas.

FBXW7 has been reported to be a candidate tumor suppressor gene on 4q31. Three isoforms (alpha-form, beta-form, and gamma-form) of FBXW7 are produced from mRNAs with distinct 5' exons. Our previous study identified the specific suppression of the mRNA expression of the FBXW7 beta-form in human gliomas. Because this form is the major FBXW7 isoform in the human brain, we elucidated the silencing mechanisms for the FBXW7 beta-form in gliomas. No genetic alterations were found in the whole FBXW7 gene including putative promoter region of the beta-form. Treatments with 5-azacytidine and trichostatin A did not induce re-expression. A sodium bisulfite-modification assay indicated that CpG sequences in the promoter of FBXW7 beta-form were not methylated in glioma cells. Meanwhile we searched for the expression of FBXW7 and the sodium bisulfite sequences in normal human peripheral blood cells, and we surprisingly found that the mRNA expression of the FBXW7 beta-form was highly suppressed and the CpG sequences in the promoter region of the FBXW7 beta-form were heavily methylated. Our data suggest that the inactivation of the FBXW7 beta-form plays an important role in the pathogenesis of gliomas and that an unknown mechanism(s) other than mutation and methylation is the major cause of the suppression of the FBXW7 beta-form in gliomas.

siRNA targeting against EGFR, a promising candidate for a novel therapeutic application to lung adenocarcinoma.

OBJECTIVE: To understand the molecular pathogenesis of lung cancer and to establish a novel therapeutic application, we examined the genetic alterations in lung cancer, and studied the effects of gefitinib and siRNA-mediated knockdown of EGFR on lung cancer. METHODS: We analyzed mutations in EGFR, KRAS, TP53, and ERBB2 in 198 surgically resected lung cancer specimens. We then analyzed the effects of gefitinib and siRNA treatment on lung adenocarcinoma cell lines. RESULTS: Mutations in EGFR were found only in adenocarcinoma (35 of 106 adenocarcinoma), mainly in females (73%). Mutually exclusive mutations of EGFR and KRAS genes were observed. Mutations of EGFR were well associated with a positive response to gefitinib. Cells with EGFR mutations were very sensitive to gefitinib as well as siRNA-mediated knockdown of EGFR, those with KRAS mutations responded poorly, and those without mutations of KRAS and EGFR showed moderate responses to both treatments. CONCLUSIONS: Our present results imply that (1) mutation analyses of EGFR and KRAS provide valuable information about whether or not to apply treatments targeting against EGFR and the selection of dosage for such treatments, and (2) siRNA-mediated knockdown is effective in lung adenocarcinomas with EGFR mutation, probably in those with resistance to gefitinib by acquired mutation in EGFR.

The FBXW7 beta-form is suppressed in human glioma cells.

FBXW7 (F-box and WD40 domain protein 7) is an F-box protein with 7 tandem WDs (tryptophan-aspartic acid) that functions as a phosphoepitope-specific substrate recognition component of SCF (Skp1-Cul1-F-box protein) ubiquitin ligases and catalyzes the ubiquitination of proteins promoting cell proliferation, such as CCNE1, MYC, AURKA, NOTCH1, and JUN, which are frequently activated in a wide range of human cancers. FBXW7 is a candidate tumor suppressor, and mutations have been reported in some human tumors. In this study, we analyzed 84 human tumor cell lines in search for genetic alterations of FBXW7, as well as mRNA and protein expressional changes, and compared them with expression levels of the CCNE1, MYC, and AURKA proteins. We found a novel nonsense mutation in a colon cancer cell line SCC and confirmed the missense mutations in SKOV3, an ovarian cancer cell line, and LoVo, a colon cancer cell line. Moreover, suppressed expression of FBXW7 accompanied by activation of the target proteins were observed in ovarian, colon, endometrial, gastric, and prostate cancers. It is notable that highly suppressed mRNA expression of the FBXW7 beta-form was found in all the human glioma cell lines analyzed; enhanced expressions of CCNE1, MYC, and AURKA were observed in these cells. Our present results imply that FBXW7 plays a pivotal role in many tissues by controlling the amount of cell cycle promoter proteins and that dysfunction of this protein is one of the essential steps in carcinogenesis in multiple organs.