CDK1/FBXW7 Facilitates Degradation and Ubiquitination of MLST8 to Inhibit Progression of Renal Cell Carcinoma
Abstract Background: Recent studies have reported that MLST8 is upregulated in many malignant tumors. Nevertheless, the underlying molecular mechanisms is still unclear. The aim of this work was to investigate how MLST8 contribute to the development and progression of renal cancer (ccRCC).Methods: To identify molecular mediators of the oncogenic tumor function of MLST8, we analyzed a quantitative mass spectrometry by a previous study and checked the amino acid sequence in MLST8. Immunoprecipitation and Western Blotting were used to analyze the interaction between FBXW7 and MLST8. Transwell assays determined cell migration and invasion. In vivo experiments were performed to verify tumor growth. Immunohistochemistry was used to analyze protein levels in patients’ tumor samples. Results: MLST8 is an oncogenic protein in TCGA database and ccRCC clinical specimens. We also ascertain that MLST8 interacts with FBXW7, which was universally regarded as an E3 ubiquitin ligase. MLST8 can be degraded and ubiquitinated by tumor suppressor FBXW7. FBXW7 recognizes a consensus motif (T/S) PXX (S/T/D/E) of MLST8 and triggers MLST8 degradation via the ubiquitin-proteasome pathway. Strikingly, the activated CDK1 kinase engages in the MLST8 phosphorylation required for FBXW7-mediated degradation. In vitro and vivo assay, we further prove that MLST8 is an essential mediator of FBXW7 inactivation-induced tumor growth, migration, and invasion. Furthermore, MLST8 and FBXW7 protein are negatively correlated in human renal cancer specimens. Conclusions: Our findings suggest that MLST8 is a putative oncogene that functions via interaction with FBXW7, and inhibition MLST8 can be a potential future target in ccRCC treatment.