Downregulation of Cdc6 and pre-replication complexes in response to methionine stress in breast cancer cells

Cell Cycle. 2012 Dec 1;11(23):4414-23. doi: 10.4161/cc.22767. Epub 2012 Nov 16.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Cell Cycle Proteins / metabolism*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Chromatin / metabolism
  • Cyclin-Dependent Kinase 2 / metabolism
  • Down-Regulation / drug effects*
  • Female
  • G1 Phase Cell Cycle Checkpoints / drug effects
  • Homocysteine / pharmacology
  • Humans
  • MCF-7 Cells
  • Mechanistic Target of Rapamycin Complex 1
  • Methionine / pharmacology*
  • Multiprotein Complexes
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Proteins / antagonists & inhibitors
  • Proteins / metabolism
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / metabolism
  • S-Adenosylmethionine / pharmacology
  • TOR Serine-Threonine Kinases


  • CDC6 protein, human
  • Cell Cycle Proteins
  • Chromatin
  • Multiprotein Complexes
  • Nuclear Proteins
  • Proteins
  • Homocysteine
  • S-Adenosylmethionine
  • Methionine
  • TOR Serine-Threonine Kinases
  • Mechanistic Target of Rapamycin Complex 1
  • Proto-Oncogene Proteins c-akt
  • Cyclin-Dependent Kinase 2