title: MYC phosphorylation at novel regulatory regions suppresses transforming activity.
abstract: Despite its central role in human cancer, MYC deregulation is insufficient by itself to transform cells. Because inherent mechanisms of neoplastic control prevent precancerous lesions from becoming fully malignant, identifying transforming alleles of MYC that bypass such controls may provide fundamental insights into tumorigenesis. To date, the only activated allele of MYC known is T58A, the study of which led to identification of the tumor suppressor FBXW7 and its regulator USP28 as a novel therapeutic target. In this study, we screened a panel of MYC phosphorylation mutants for their ability to promote anchorage-independent colony growth of human MCF10A mammary epithelial cells, identifying S71A/S81A and T343A/S344A/S347A/S348A as more potent oncogenic mutants compared with wild-type (WT) MYC. The increased cell-transforming activity of these mutants was confirmed in SH-EP neuroblastoma cells and in three-dimensional MCF10A acini. Mechanistic investigations initiated by a genome-wide mRNA expression analysis of MCF10A acini identified 158 genes regulated by the mutant MYC alleles, compared with only 112 genes regulated by both WT and mutant alleles. Transcriptional gain-of-function was a common feature of the mutant alleles, with many additional genes uniquely dysregulated by individual mutant. Our work identifies novel sites of negative regulation in MYC and thus new sites for its therapeutic attack.
authors.affiliation: Authors' Affiliations: Department of Medical Biophysics, University of Toronto; Ontario Cancer Institute, Campbell Family Institute for Cancer Research, Princess Margaret Cancer Centre; and Ontario Institute for Cancer Research, Toronto, Ontario, Canada.
authors.forename: Amanda R
authors.initials: AR
authors.lastname: Wasylishen
authors.forename: Michelle
authors.initials: M
authors.lastname: Chan-Seng-Yue
authors.forename: Christina
authors.initials: C
authors.lastname: Bros
authors.forename: Dharmendra
authors.initials: D
authors.lastname: Dingar
authors.forename: William B
authors.initials: WB
authors.lastname: Tu
authors.forename: Manpreet
authors.initials: M
authors.lastname: Kalkat
authors.forename: Pak-Kei
authors.initials: PK
authors.lastname: Chan
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Mullen
authors.forename: Ling
authors.initials: L
authors.lastname: Huang
authors.forename: Natalie
authors.initials: N
authors.lastname: Meyer
authors.forename: Brian
authors.initials: B
authors.lastname: Raught
authors.forename: Paul C
authors.initials: PC
authors.lastname: Boutros
authors.forename: Linda Z
authors.initials: LZ
authors.lastname: Penn
mesh_terms: D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D002448:Cell Adhesion; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000473:pathology*; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D003114:Colony-Forming Units Assay; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D042361:Mammary Glands, Human / Q000378:metabolism / Q000473:pathology*; D009154:Mutation / Q000235:genetics*; D009447:Neuroblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D020411:Oligonucleotide Array Sequence Analysis; D010101:Oxygen Consumption; D010766:Phosphorylation; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012045:Regulatory Sequences, Nucleic Acid; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D014408:Biomarkers, Tumor; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger