FBXW8-dependent degradation of MRFAP1 in anaphase controls mitotic cell death.

Mof4 family associated protein 1 (MRFAP1) is a 14 kDa nuclear protein, which involves in maintaining normal histone modification levels by negatively regulating recruitment of the NuA4 (nucleosome acetyltransferase of H4) histone acetyltransferase complex to chromatin. MRFAP1 has been identified as one of the most up-regulated proteins after NEDD8 (neural precursor cell expressed developmentally down-regulated 8) inhibition in multiple human cell lines. However, the biological function of MRFAP1 and the E3 ligase that targets MRFAP1 for destruction remain mysterious. Here we show, by using an immunoprecipitation-based proteomics screen, that MRFAP1 is an interactor of the F-box protein FBXW8. MRFAP1 is degraded by means of the ubiquitin ligase Cul7/FBXW8 during mitotic anaphase-telophase transition and accumulated in mitotic metaphase. Overexpression of FBXW8 increased the polyubiquitination and decreased the stability of MRFAP1, whereas knockdown of FBXW8 prolonged the half-life of MRFAP1. Moreover, forced expression of MRFAP1 in HeLa cells caused growth retardation and genomic instability, leading to severe mitotic cell death. Thus, Cul7/FBXW8-mediated destruction of MRFAP1 is a regulatory component monitoring the anaphase-telophase transition and preventing genomic instability.

Anticancer effects of celecoxib through inhibiton of STAT3 phosphorylation and AKT phosphorylation in nasopharyngeal carcinoma cell lines.

Previously, we showed that treatment with celecoxib obviously inhibited proliferation of nasopharyngeal carcinoma (NPC) cell lines in a dose-dependent manner. However, the underlying molecular mechanisms of its anticancer effect on NPC have not been fully clarified. The present in vitro study was performed to investigate the mechanisms involved in the anticancer effect of celecoxib in NPC. NPC cell line HONE1 was treated with celecoxib at varying concentrations. The antiproliferation effect of celecoxib on the HONE1 cell line was assessed with methyl thiazolyl tetrazolium (MTT) assay. Western blot analysis of signal transducer and activator of transcription 3 (STAT3), phosphorylated STAT3(Y705) (pSTAT3(Y705)), Survivin, Mcl-1, Bcl-2 and Cyclin D1 was carried out at various concentration of celecoxib for 48 h in HONE1 cell line. Western blot analysis of Protein Kinase B (AKT), phosphorylated AKT (pAKT) was performed at increasing doses of celecoxib for 48 h in HNE1, CNE1-LMP1 and HONE1 cells. The results showed that celecoxib inhibited proliferation of HONE1 cell line in a dose-dependent manner. Celecoxib inhibited the activation of STAT3 phosphorylation in HONE1 cells and the downstream genes of STAT3 (Survivin, Mcl-1, Bcl-2 and Cyclin D1) were downregulated after treatment with celecoxib. Furthermore, celecoxib could inhibit AKT phosphorylation in HNE1, CNE1-LMP1 and HONE1 cell lines. These data suggested that celecoxib was a promising agent for the chemoprevention and treatment of NPC.