Roles of human epidermal growth factor receptor 2, c-jun NH2-terminal kinase, phosphoinositide 3-kinase, and p70 S6 kinase pathways in regulation of cyclin G2 expression in human breast cancer cells.

The CCNG2 gene that encodes the unconventional cyclin G2 was one of the few genes up-regulated on anti-human epidermal growth factor receptor 2 (HER2) antibody-mediated inhibition of HER2 signaling. The purpose of this study was to explore how HER2 signaling modulates cyclin G2 expression and the effect of elevated cyclin G2 on breast cancer cell growth. Treatment of breast cancer cells that overexpress HER2 (BT474, SKBr3, and MDAMB453) with the anti-HER2 antibody trastuzumab or its precursor 4D5 markedly up-regulated cyclin G2 mRNA in vitro and in vivo, as shown by real-time PCR. Immunoblot and immunofluorescence analysis with specific antibodies against cyclin G2 showed that anti-HER2 antibody significantly increased cyclin G2 protein expression and translocated the protein to the nucleus. Trastuzumab was not able to induce cyclin G2 expression in cells weakly expressing HER2 (MCF7) or in cells that had developed resistance to trastuzumab. Enforced expression of HER2 in T47D and MDAMB435 breast cancer cells reduced cyclin G2 levels. Collectively, these data suggest that HER2-mediated signaling negatively regulates cyclin G2 expression. Inhibition of phosphoinositide 3-kinase (LY294002), c-jun NH(2)-terminal kinase (SP600125), and mammalian target of rapamycin (mTOR)/p70 S6 kinase (p70S6K; rapamycin) increased cyclin G2 expression. In contrast, treatment with inhibitors of p38 mitogen-activated protein kinase (SB203580), mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2 (U0126), or phospholipase Cgamma (U73122) did not affect cyclin G2 expression. Anti-HER2 antibody in combination with LY294002, rapamycin, or SP600125 induced greater cyclin G2 expression than either agent alone. Ectopic expression of cyclin G2 inhibited cyclin-dependent kinase 2 activity, Rb phosphorylation, cell cycle progression, and cellular proliferation without affecting p27(Kip1) expression. Thus, cyclin G2 expression is modulated by HER2 signaling through multiple pathways including phosphoinositide 3-kinase, c-jun NH(2)-terminal kinase, and mTOR signaling. The negative effects of cyclin G2 on cell cycle and cell proliferation, which occur without altering p27(Kip1) levels, may contribute to the ability of trastuzumab to inhibit breast cancer cell growth.
AuthorsXiao-Feng Le, Aruni S Arachchige-Don, Weiqun Mao, Mary C Horne, Robert C Bast Jr
JournalMolecular cancer therapeutics (Mol Cancer Ther) Vol. 6 Issue 11 Pg. 2843-57 (Nov 2007) ISSN: 1535-7163 [Print] United States
PMID18025271 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, U.S. Gov't, Non-P.H.S.)
Chemical References
  • Antibodies, Monoclonal
  • CCNG2 protein, human
  • Cyclin G2
  • Cyclins
  • Enzyme Inhibitors
  • Retinoblastoma Protein
  • Protein Kinases
  • Phosphatidylinositol 3-Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • ERBB2 protein, human
  • Receptor, ErbB-2
  • Ribosomal Protein S6 Kinases, 70-kDa
  • Cyclin-Dependent Kinase 2
  • Extracellular Signal-Regulated MAP Kinases
  • JNK Mitogen-Activated Protein Kinases
  • p38 Mitogen-Activated Protein Kinases
  • Phospholipase C gamma
  • Animals
  • Antibodies, Monoclonal (pharmacology)
  • Breast Neoplasms (enzymology, genetics, pathology)
  • Cell Cycle (drug effects)
  • Cell Line, Tumor
  • Cell Nucleus (drug effects, pathology)
  • Cell Proliferation (drug effects)
  • Cyclin G2
  • Cyclin-Dependent Kinase 2 (metabolism)
  • Cyclins (genetics)
  • Enzyme Inhibitors (pharmacology)
  • Extracellular Signal-Regulated MAP Kinases (antagonists & inhibitors)
  • Female
  • Gene Expression Regulation, Neoplastic (drug effects)
  • Humans
  • JNK Mitogen-Activated Protein Kinases (antagonists & inhibitors, metabolism)
  • Mice
  • Phosphatidylinositol 3-Kinases (antagonists & inhibitors, metabolism)
  • Phospholipase C gamma (antagonists & inhibitors)
  • Phosphorylation (drug effects)
  • Protein Kinases (metabolism)
  • Protein Transport (drug effects)
  • Receptor, ErbB-2 (metabolism)
  • Retinoblastoma Protein (metabolism)
  • Ribosomal Protein S6 Kinases, 70-kDa (metabolism)
  • TOR Serine-Threonine Kinases
  • p38 Mitogen-Activated Protein Kinases (antagonists & inhibitors)

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