title: MBP-1 is efficiently encoded by an alternative transcript of the ENO1 gene but post-translationally regulated by proteasome-dependent protein turnover.
abstract: The c-myc promoter-binding protein-1 (MBP-1) is a transcriptional suppressor of tumorigenesis and thought to be the product of alternative translation initiation of the α-enolase (ENO1) transcript. In the present study, we cloned a 2552-bp novel cDNA with a putative coding sequence of MBP-1 and functionally examined its ability to encode the MBP-1 protein. Similarly to ENO1, the obtained MBP-1 was widely and differentially expressed in a variety of normal tissues and cancer cells. Experiments using MBP-1 promoter-driven luciferase reporter assays, biochemical cell fractionation followed by RT-PCR detection of the cytoplasmic mRNA, and transcription/translation-coupled reactions, consistently demonstrated that this novel transcript was alternatively transcribed from intron III of the ENO1 gene and was feasible for MBP-1 production. Hypoxia treatments significantly increased the transcriptional activation of the MBP-1 gene. Blocking the proteasomal degradation by MG132 stabilized the MBP-1 protein in cells. Compared with the translation efficiency for production of the MBP-1 protein, the MBP-1 transcript was 17.8 times more efficient than the ENO1 transcript. Thus, we suggest that this newly discovered transcript is a genuine template for the protein synthesis of MBP-1 in cells, and optimal expression of this gene in tumors may lead to effective clinical therapies for cancers.
authors.affiliation: National Institute of Cancer Research, National Health Research Institutes, Tainan, Taiwan.
authors.forename: Jrhau
authors.initials: J
authors.lastname: Lung
authors.forename: Ko-Jiunn
authors.initials: KJ
authors.lastname: Liu
authors.forename: Jang-Yang
authors.initials: JY
authors.lastname: Chang
authors.forename: Sy-Jye
authors.initials: SJ
authors.lastname: Leu
authors.forename: Neng-Yao
authors.initials: NY
authors.lastname: Shih
mesh_terms: D014408:Biomarkers, Tumor / Q000235:genetics*; D001980:Bronchi / Q000166:cytology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D000860:Hypoxia; D007438:Introns; D010751:Phosphopyruvate Hydratase / Q000235:genetics*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins / Q000235:genetics*
chemical_list: D014408:Biomarkers, Tumor; C088830:DENND4A protein, human; D004268:DNA-Binding Proteins; D011506:Proteins; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; D046988:Proteasome Endopeptidase Complex; C095157:ENO1 protein, human; D010751:Phosphopyruvate Hydratase