PARENT SESSION
3:45 PM to 5:15 PM
Tuesday, April 23, 2002
Mini-Symposium 12
Cell Cycle and Apoptosis
Room: Nevada 4-5
, Co-Chair: Muschel, Ruth¹; Haimovitz-Friedman, Adriana²¹University of Pennsylvania, Philadelphia, PA²Memorial Sloan-Kettering Cancer Center, New York, NY

(MS12-8) The regulation of Cyclin E and apoptosis in response to genotoxic stress.

DuPree, Erica^*,1,2, Mazumder, Suparna², Gong, Bendi², Buchsbaum, Jeffrey³, Almasan, Alexandru^2,3, ¹ Department of Chemistry, Cleveland, Ohio² Department of Cancer Biology, Cleveland, Ohio³ Department of Radiation Oncology, Cleveland, Ohio

ABSTRACT-
Progression through the eukaryotic cell cycle is regulated by the expression of several growth regulatory proteins. The cyclin-dependent kinase 2 (CDK2) controls the progression of the cells through the G1 phase into and through the DNA synthesis (S) phase of the cell division cycle. CDK2 activity is dependent on its association with its catalytic partners, Cyclins E1, A, and E2, a newly identified CDK2-binding protein whose function is yet unknown. Altered expression of the proteins which control these key regulatory pathways of the G1/S phase progression is characteristic to most human cancers. Genotoxic stressors, such as ionizing radiation (IR), have the ability to affect cell cycle regulation and also induce programmed cell death, or apoptosis. We have recently focused on the regulation of the G1/S phase of the cell cycle in the IR-response of prostate cancer cells. A global survey of IR-induced gene expression using Affymetrix oligonucleotide arrays in LNCaP-C4-2 (C4-2) cells grown in cell culture has revealed a decrease in the expression levels of Cyclin E2. Immunoprecipitations (IPs) showed that Cyclin E2 protein expression exhibited a significant time-dependent decrease following irradiation, but this was not seen with Cyclins E1 or A. There was also a similar decrease in E2F-1, a transcriptional factor, providing evidence, along with the RNA data, that Cyclin E2 is regulated at transcriptional level. Kinase assays were also carried out in C4-2 cells subjected to IP followed by sequential immunodepletion for Cyclins E1, E2, and A. To investigate post-transcriptional regulation, we have examined a putative upstream regulator, the CDC25A phosphatase. IPs were carried out using anti-CDC25A followed by Western blotting with anti-CDC25A and then with anti-Cyclin E2 antibodies. Both proteins showed similar time-dependent changes, indicating a post-transcriptional regulation of Cyclin E2. The impact of Cyclin E2 and other CDK2-associated cyclins on the cell cycle and survival of these cells following IR is under investigation. We have located Cyclin E2 to a region of chromosome 8, among the most commonly altered in prostate carcinoma. This work identifies Cyclin E2 as a cyclin specifically regulated by radiation treatment with a potential role in prostate cancer.

KEYWORDS: cyclin e2, ionizing radiation, prostate cancer