A Dominant Role for p53-Dependent Cellular Senescence in Radiosensitization of Human Prostate Cancer Cells

Abstract

ACKnoWLeDgeMenTSSupported in part by grants from the NIH (R01098195 to J.A.M.) and the Brody Brothers Foundation Endowment (#997729 to J.A.M. and D.M.T.). ReportA Dominant Role for p53-Dependent Cellular Senescence in Radiosensitization of Human Prostate Cancer Cells ABSTrACT Because p53 inactivation may limit the effectiveness of radiation therapy for localized prostate cancer, it is important to understand how this gene regulates clonogenic survival after an exposure to ionizing radiation. Here, we show that premature cellular senescence is the principal mode of cell death accounting for the radiosensitivity of human prostate cancer cell lines retaining p53 function. Alternative stress response pathways controlled by this tumor suppressor, including cell cycle arrest, DNA damage repair, mitotic catastrophe and apoptosis, contributed significantly less to radiation-induced clonogenic death. Using a dominant negative C-terminal fragment of p53, we present the first evidence that a complete loss of endogenous p53 function is sufficient to limit the irradiation-induced senescence and clonogenic death of prostate cancer cells. Conversely, inheritance of wild-type p53 by prostate cancer cells lacking a functional allele of this gene (i.e., DU145) significantly increases clonogenic death through p53-dependent cellular senescence and apoptotic pathways. Our data provide evidence that mutations of even one p53 allele may be sufficient to alter their clonogenic fate. In addition, they support the idea that the p53 pathway can be used as a specific target for enhancing the radiosensitivity of prostate cancer cells. Activation of p53 by the drug nutlin-3 is shown to be an effective radiosensitizer of prostate cancer cells retaining functional alleles of p53 and this effect was entirely attributable to an increased induction of p53-dependent cellular senescence.

Suppression of PTEN function increases breast cancer chemotherapeutic drug resistance while conferring sensitivity to mTOR inhibitors

“…When certain cells are treated with chemotherapeutic drugs, they undergo cellular senescence and express senescence-associated (SA) b-galactosidase (SA-b-gal; Lehmann et al, 2007). The effects of the PTEN mutants on the induction of cellular senescence after doxorubicin treatment were examined (Figure 3b).…”

“…A total of 5 Â 10 5 MCF-7 cells were plated into six-well cell culture plates (BD Biosciences, Mountainview, CA, USA) 1 day prior to transfection and subsequently transfected with the various plasmid DNAs as described (Davis et al, 2003;Lehmann et al, 2007). The nomenclature of the transfected cells is MCF/followed by the name of the introduced plasmid DNA.…”

“…Clonogenic assays MCF-7 cells were collected and seeded in six-well cell culture plates at densities of 1000 and 2000 cells per well (three wells at each density) as described (Lehmann et al, 2007).…”

“…Cellular senescence assay Senescent cells were identified by an SA-b-gal assay as described (Lehmann et al, 2007).…”

p53 expression controls prostate cancer sensitivity to chemotherapy and the MDM2 inhibitor Nutlin-3

“…46 We now wanted to examine the effects of p53 functionality in prostate cancer in response to chemotherapeutic drug treatment. In the following study, we were able to demonstrate that the functional status of the p53 protein is important in determining the chemotherapeutic response of prostate cancer cells, sensitivity to the small-molecule MDM2 inhibitor Nutlin-3 and the capability of these cancer cells to form colonies in soft agar.…”