PT  - JOURNAL ARTICLE
AU  - Orr, Michael S.
AU  - Watson, Nicole C.
AU  - Sundaram, Sujatha
AU  - Randolph, Joyce K.
AU  - Jain, Pramod T.
AU  - Gewirtz, David A.
TI  - Ionizing Radiation and Teniposide Increase p21<sup>waf1/cip1</sup> and Promote Rb Dephosphorylation but Fail to Suppress E2F Activity in MCF-7 Breast Tumor Cells
AID  - 10.1124/mol.52.3.373
DP  - 1997 Sep 01
TA  - Molecular Pharmacology
PG  - 373--379
VI  - 52
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/52/3/373.short
4100  - http://molpharm.aspetjournals.org/content/52/3/373.full
SO  - Mol Pharmacol1997 Sep 01; 52
AB  - Ionizing radiation and the topoisomerase II inhibitor, teniposide (VM-26) both increase levels of the cyclin dependent kinase inhibitor, p21waf1/cip1 and promote dephosphorylation of the retinoblastoma tumor suppressor protein, Rb, in MCF-7 breast tumor cells, perturbations associated with suppression of the activity of the transcription factor, E2F. However, studies using an E2F binding site-luciferase reporter plasmid transfected into MCF-7 cells failed to demonstrate a reduction in E2F activity in response to VM-26 or to ionizing radiation. In contrast, E2F activity (both basal and E1A stimulated) could be suppressed by transfection with a plasmid expressing Rb, indicating that the capacity of E2F to bind to Rb and to be inactivated by Rb is functionally intact in MCF-7 cells. These findings in MCF-7 breast tumor cells suggest that E2F activity may not be directly susceptible to modulation by endogenous p21waf1/cip1 and Rb.