title: Repression of microRNA-768-3p by MEK/ERK signalling contributes to enhanced mRNA translation in human melanoma.
abstract: Increased global protein synthesis and selective translation of mRNAs encoding proteins contributing to malignancy is common in cancer cells. This is often associated with elevated expression of eukaryotic translation initiation factor 4 (eIF4E), the rate-limiting factor of cap-dependent translation initiation. We report here that in human melanoma downregulation of miR-768-3p as a result of activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway has an important role in the upregulation of eIF4E and enhancement in protein synthesis. Melanoma cells displayed increased nascent protein production and elevated eIF4E expression, which was associated with the downregulation of miR-768-3p that was predicted to target the 3'-untranslated region of the eIF4E mRNA. Overexpression of miR-768-3p led to the downregulation of the endogenous eIF4E protein, reduction in nascent protein synthesis and inhibition of cell survival and proliferation. These effects were efficiently reversed when eIF4E was co-overexpressed in melanoma cells. On the other hand, introduction of anti-miR-768-3p into melanocytes upregulated endogenous eIF4E protein expression and increased global protein synthesis. Downregulation of miR-768-3p appeared to be mediated by activation of the MEK/ERK pathway, in that treatment of BRAF(V600E) melanoma cells with the mutant BRAF inhibitor PLX4720 or exposure of either BRAF(V600E) or wild-type BRAF melanoma cells to the MEK inhibitor U0126 resulted in the upregulation of miR-768-3p and inhibition of nascent protein synthesis. This inhibition was partially blocked in cells cointroduced with anti-miR-768-3p. Significantly, miR-768-3p was similarly downregulated, which was inversely associated with the expression levels of eIF4E in fresh melanoma isolates. Taken together, these results identify downregulation of miR-768-3p and subsequent upregulation of eIF4E as an important mechanism in addition to phosphorylation of eIF4E responsible for MEK/ERK-mediated enhancement of protein synthesis in melanoma.
authors.affiliation: 1] Priority Research Centre for Cancer Research, University of Newcastle, Callaghan, NSW, Australia [2] School of Medicine and Public Health, University of Newcastle, Callaghan, NSW, Australia.
authors.forename: C C
authors.initials: CC
authors.lastname: Jiang
authors.affiliation: 1] Priority Research Centre for Cancer Research, University of Newcastle, Callaghan, NSW, Australia [2] Oncology and Immunology Unit, Calvary Mater Newcastle Hospital, Waratah, NSW, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Croft
authors.affiliation: 1] Priority Research Centre for Cancer Research, University of Newcastle, Callaghan, NSW, Australia [2] School of Medicine and Public Health, University of Newcastle, Callaghan, NSW, Australia.
authors.forename: H-Y
authors.initials: HY
authors.lastname: Tseng
authors.affiliation: Department of Molecular Biology, Shanxi Cancer Hospital and Institute, Taiyuan, Shanxi, People's Republic of China.
authors.forename: S T
authors.initials: ST
authors.lastname: Guo
authors.affiliation: Kolling Institute for Medical Research, University of Sydney, St Leonards, NSW, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Jin
authors.affiliation: Kolling Institute for Medical Research, University of Sydney, St Leonards, NSW, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Hersey
authors.affiliation: 1] Priority Research Centre for Cancer Research, University of Newcastle, Callaghan, NSW, Australia [2] School of Medicine and Public Health, University of Newcastle, Callaghan, NSW, Australia [3] Department of Molecular Biology, Shanxi Cancer Hospital and Institute, Taiyuan, Shanxi, People's Republic of China.
authors.forename: X D
authors.initials: XD
authors.lastname: Zhang
mesh_terms: D045744:Cell Line, Tumor; D015536:Down-Regulation; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System; D008545:Melanoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D035683:MicroRNAs / Q000235:genetics*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D015398:Signal Transduction; D015854:Up-Regulation
chemical_list: D039561:Eukaryotic Initiation Factor-4E; C000589673:MIRN768 microRNA, human; D035683:MicroRNAs; D012333:RNA, Messenger