title: Downregulation of Cdc6 and pre-replication complexes in response to methionine stress in breast cancer cells.
abstract: Methionine and homocysteine are metabolites in the transmethylation pathway leading to synthesis of the methyl-donor S-adenosylmethionine (SAM). Most cancer cells stop proliferating during methionine stress conditions, when methionine is replaced in the growth media by its immediate metabolic precursor homocysteine (Met-Hcy+). Non-transformed cells proliferate in Met-Hcy+ media, making the methionine metabolic requirement of cancer cells an attractive target for therapy, yet there is relatively little known about the molecular mechanisms governing the methionine stress response in cancer cells. To study this phenomenon in breast cancer cells, we selected methionine-independent-resistant cell lines derived from MDAMB468 breast cancer cells. Resistant cells grew normally in Met-Hcy+ media, whereas their parental MDAMB468 cells rapidly arrest in the G 1 phase. Remarkably, supplementing Met-Hcy+ growth media with S-adenosylmethionine suppressed the cell proliferation defects, indicating that methionine stress is a consequence of SAM limitation rather than low amino acid concentrations. Accordingly, mTORC1 activity, the primary effector responding to amino acid limitation, remained high. However, we found that levels of the replication factor Cdc6 decreased and pre-replication complexes were destabilized in methionine-stressed MDAMB468 but not resistant cells. Our study characterizes metabolite requirements and cell cycle responses that occur during methionine stress in breast cancer cells and helps explain the metabolic uniqueness of cancer cells.
authors.affiliation: Department of Biological Chemistry, College of Medicine, University of California Irvine, Irvine, CA USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Booher
authors.forename: Da-Wei
authors.initials: DW
authors.lastname: Lin
authors.forename: Stacey L
authors.initials: SL
authors.lastname: Borrego
authors.forename: Peter
authors.initials: P
authors.lastname: Kaiser
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002843:Chromatin / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects*; D005260:Female; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D006710:Homocysteine / Q000494:pharmacology; D006801:Humans; D061986:MCF-7 Cells; D000076222:Mechanistic Target of Rapamycin Complex 1; D008715:Methionine / Q000494:pharmacology*; D046912:Multiprotein Complexes; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
chemical_list: C103706:CDC6 protein, human; D018797:Cell Cycle Proteins; D002843:Chromatin; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D011506:Proteins; D006710:Homocysteine; D012436:S-Adenosylmethionine; D008715:Methionine; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D051357:Cyclin-Dependent Kinase 2