FBXO31 determines poor prognosis in esophageal squamous cell carcinoma

Cyclin D1 plays important roles in esophageal squamous cell carcinoma (ESCC) cases by amplification of the 11q13.3 locus. FBXO31 is a subunit of the SCF ubiquitin ligase, which targets cyclin D1 for degradation. In this study, we clarified the clinical significance of FBXO31 and characterized the association between cyclin D1 and FBXO31 in ESCC cases. Total RNA was extracted from tumor tissues obtained from 68 ESCC patients who underwent surgical resection. FBXO31 expression levels were determined by quantitative RT-PCR, and both FBXO31 and cyclin D1 protein expression and localization were evaluated by immunohistochemistry (IHC). Furthermore, using CGH and gene expression array data of another subset, we validated the association between cyclin D1 genomic amplification and FBXO31 expression levels. Higher FBXO31 expression levels significantly correlated with depth of tumor invasion and clinical stage (P<0.05). In addition, the FBXO31 high expression group showed a significantly poorer prognosis than the low expression group (P<0.001). Multivariate analysis indicated that FBXO31 expression was an independent prognostic factor [relative risk (RR): 1.79, confidence interval (CI): 1.14-3.01, P=0.01]. Using IHC, concordant expression was observed between cyclin D1 and FBXO31 in the nucleus and cytoplasm, respectively. CGH array indicated that cases having cyclin D1 with increased copy number were significantly associated with elevated FBXO31 expression levels (P<0.05). FBXO31 could be a novel and robust prognostic marker for ESCC.