Promoter hypermethylation of FBXO32, a novel TGF-β/SMAD4 target gene and tumor suppressor, is associated with poor prognosis in human ovarian cancer

Abstract

Resistance to TGF-b is frequently observed in ovarian cancer, and disrupted TGF-b/SMAD4 signaling results in the aberrant expression of downstream target genes in the disease. Our previous study showed that ADAM19, a SMAD4 target gene, is downregulated through epigenetic mechanisms in ovarian cancer with aberrant TGF-b/SMAD4 signaling. In this study, we investigated the mechanism of downregulation of FBXO32, another SMAD4 target gene, and the clinical significance of the loss of FBXO32 expression in ovarian cancer. Expression of FBXO32 was observed in the normal ovarian surface epithelium, but not in ovarian cancer cell lines. FBXO32 methylation was observed in ovarian cancer cell lines displaying constitutive TGF-b/SMAD4 signaling, and epigenetic drug treatment restored FBXO32 expression in ovarian cancer cell lines regardless of FBXO32 methylation status, suggesting that epigenetic regulation of this gene in ovarian cancer may be a common event. In advanced-stage ovarian tumors, a significant (29.3%; Po0.05) methylation frequency of FBXO32 was observed and the association between FBXO32 methylation and shorter progression-free survival was significant, as determined by both Kaplan-Meier analysis (Po0.05) and multivariate Cox regression analysis (hazard ratio: 1.003, Po0.05). Reexpression of FBXO32 markedly reduced proliferation of a platinum-resistant ovarian cancer cell line both in vitro and in vivo, due to increased apoptosis of the cells, and resensitized ovarian cancer cells to cisplatin. In conclusion, the novel tumor suppressor FBXO32 is epigenetically silenced in ovarian cancer cell lines with disrupted TGFb/SMAD4 signaling, and FBXO32 methylation status predicts survival in patients with ovarian cancer. Ovarian cancer is the fifth leading cause of death in women and the most deadly of gynecological malignancies. 1 The lifetime risk of ovarian cancer in women is B1.5%. 2 As ovarian cancer has few symptoms early in its course, the majority of patients are diagnosed with advanced-stage disease. Despite advances in chemotherapy, the poor prognosis for patients with ovarian cancer is reflected in the o20% 5-year survival rate after initial diagnosis for patients with stage III and IV disease, whereas survival of patients with stage I or II disease is 480% for the same period. 3 Current

FBXO32 Targets c-Myc for Proteasomal Degradation and Inhibits c-Myc Activity

“…Moreover, patients with higher FBXO32 promoter methylation tend to have shorter progression-free survival. This suggests a tumor-suppressive role of FBXO32 (9). In addition, the FBXO32 expression is also decreased in esophageal squamous cell carcinoma (10).…”

“…The expression level of FBXO32 is closely correlated with the methylation status of the FBXO32 promoter in ovarian cancer cell lines (9). Restoration of FBXO32 in ovarian cancer cells inhibits colony formation in vitro and xenograft tumor growth in athymic nude mice.…”

A Sequence Polymorphism in miR-608 Predicts Recurrence after Radiotherapy for Nasopharyngeal Carcinoma

“…Interestingly, Tan and colleagues also showed that FBXO32 was transcriptionally silenced by epigenetic mechanisms in cancer cells (48). Furthermore, Chou and colleagues found that FBXO32 might be a novel tumor suppressor gene that was associated with poor prognosis in human ovarian cancer (50). Our reporter gene assays suggested that the rs4919510C allele affected FBXO32 expression by inhibiting the binding of miR-608 in nasopharyngeal carcinoma cell lines, and these results are consistent with previous findings on the contributions of FBXO32 to tumor suppression.…”

Integration and bioinformatics analysis of DNA-methylated genes associated with drug resistance in ovarian cancer

“…As shown in Table IV (10,11,14,16,(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(29)(30)(31)(32)(33)(34)(35)(36)38,39,(41)(42)(43)(44)(45)(47)(48)(49)(50)(51)(52), we observed that a considerable number of DNA methylated genes, including MLH1, FBXO32, PROM1, RASSF1, PTEN, SFRP, TUBB3, L1TD1 and CLDN4, were associated with the invasion of ovarian cancer. Each gene was hypermethylated, resulting in the silencing of gene expression in ovarian cancer and drug-resistant tissue or cells and ultimately regulating tumour invasion.…”