title: Anti-HER2 antibody trastuzumab inhibits CDK2-mediated NPAT and histone H4 expression via the PI3K pathway.
abstract: The anti-HER2 antibody trastuzumab (Herceptin) has been used to treat patients with breast cancers that overexpress HER2. We have demonstrated that p27(Kip1) upregulation is one of the key events that cause G(1) arrest upon trastuzumab treatment. Here, we have examined the effect of trastuzumab on expression of CDK2, Rb, E2F, NPAT and histone H4 in breast cancer cells that overexpress HER2. Trastuzumab treatment dramatically inhibited the kinase activity and expression of CDK2, whereas the kinase activity and expression of CDK4 were not affected. Unlike the p27(Kip1) upregulation that occurs primarily through post-translational mechanisms, CDK2 was downregulated primarily at a transcriptional level as shown by Northern blotting and real-time RT-PCR analyses. With a decrease in CDK2 activity, trastuzumab decreased the kinase activity of cyclin E but had little effect on cyclin E protein level. Overexpression of wild-type cyclin E or its lower molecular weight forms did not influence the response to trastuzumab. Levels and activities of CDK6, cyclin A, and cyclin D1 were all suppressed by trastuzumab. As a result, trastuzumab inhibited Rb phosphorylation that associates with CDK2, cyclin E, CDK6, cyclin A, or cyclin D1. As predicted from these changes, trastuzumab decreased the DNA-binding activity of E2F, decreased the level of NPAT protein, and decreased the level of histone H4 mRNA. Blockade of the PI3K pathway with LY294002 produced similar effects to trastuzumab treatment on expression of each of these genes. Taken together, treatment of breast cancer cells that overexpress HER2 with the anti-HER2 antibody trastuzumab inhibits CDK2, Rb phosphorylation, E2F activity, NPAT, and histone H4 via PI3K signaling that are needed for both DNA and histone synthesis during progression from G(1) phase to S phase of the cell cycle.
authors.affiliation: Department of Experimental Therapeutics, University of Texas MD Anderson Cancer Center, Houston, Texas 77030-4009, USA.
authors.forename: Xiao-Feng
authors.initials: XF
authors.lastname: Le
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bedrosian
authors.forename: Weiqun
authors.initials: W
authors.lastname: Mao
authors.forename: Mollianne
authors.initials: M
authors.lastname: Murray
authors.forename: Zhen
authors.initials: Z
authors.lastname: Lu
authors.forename: Khandan
authors.initials: K
authors.lastname: Keyomarsi
authors.forename: Mong-Hong
authors.initials: MH
authors.lastname: Lee
authors.forename: Jiyong
authors.initials: J
authors.lastname: Zhao
authors.forename: Robert C
authors.initials: RC
authors.lastname: Bast
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics; D018797:Cell Cycle Proteins / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism; D004273:DNA, Neoplasm / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D009687:Nuclear Proteins / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000378:metabolism; D000068878:Trastuzumab; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D004273:DNA, Neoplasm; D050687:E2F1 Transcription Factor; D006657:Histones; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010768:Phosphoserine; D010769:Phosphothreonine; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D016160:Retinoblastoma Protein; D000068878:Trastuzumab; C101693:NPAT protein, human