TY - JOUR
T1 - Anti-HER2 antibody trastuzumab inhibits CDK2-mediated NPAT and histone H4 expression via the PI3K pathway
AU - Le, Xiao Feng
AU - Bedrosian, Isabelle
AU - Mao, Weiqun
AU - Murray, Mollianne
AU - Lu, Zhen
AU - Keyomarsi, Khandan
AU - Lee, Mong Hong
AU - Zhao, Jiyong
AU - Bast, Robert C.
PY - 2006/8/1
Y1 - 2006/8/1
N2 - The anti-HER2 antibody trastuzumab (Herceptin®) has been used to treat patients with breast cancers that overexpress HER2. We have demonstrated that p27Kip1 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 p27Kip1 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 G1 phase to S phase of the cell cycle.
AB - The anti-HER2 antibody trastuzumab (Herceptin®) has been used to treat patients with breast cancers that overexpress HER2. We have demonstrated that p27Kip1 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 p27Kip1 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 G1 phase to S phase of the cell cycle.
KW - CDK2
KW - Cell cycle
KW - Her2/c-neu
KW - Histone
KW - NPAT
KW - Trastuzumab
UR - http://www.scopus.com/inward/record.url?scp=33747868707&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33747868707&partnerID=8YFLogxK
U2 - 10.4161/cc.5.15.3007
DO - 10.4161/cc.5.15.3007
M3 - Article
C2 - 16861913
AN - SCOPUS:33747868707
SN - 1538-4101
VL - 5
SP - 1654
EP - 1661
JO - Cell Cycle
JF - Cell Cycle
IS - 15
ER -