title: p21 modulates threshold of apoptosis induced by DNA-damage and growth factor withdrawal in prostate cancer cells.
abstract: Current therapy for advanced prostate cancer is largely based on androgen deprivation and is mostly palliative because all patients eventually relapse with androgen-independent disease. Doxorubicin (Dx), an anthracycline used commonly as a chemotherapeutic agent in relapsed prostate cancer, is a strong inducer of p53 expression and p21(CIP1/WAF1) (p21) transactivation. Previous reports suggest that p21 may have a role in the modulation to chemotherapy-induced apoptosis, prostate cancer progression and androgen regulation. In order to investigate if p21 has a pro-survival role in the response of prostate cancer cells to cellular stress, we exposed two androgen-regulated human prostate cancer cell lines (MDA PCa 2b and LNCaP) to Dx and growth factor withdrawal. We then studied expression of p53 and p21, cell-cycle kinetics and apoptosis. We have found that p53 protein accumulated in a dose- and time-dependent manner after Dx treatment, while p21 expression increased over time with low but decreased with high Dx doses. Apoptosis occurred in parallel with p21 down-modulation. Dx treatment of p53 knockout cells demonstrated that p21 induction was strictly p53 dependent. Reduction of p21 levels in prostate cancer cells with an antisense p21 adenovirus resulted in sensitization to Dx and accelerated onset of apoptosis in response to growth factor withdrawal. The evidence presented here also suggests that caspase activation mediates the apoptosis in this system and supports that p21 may modulate the threshold of apoptosis in prostate cancer. These observations may thus provide implications onto the integration of chemotherapy and androgen ablation.
authors.affiliation: Department of Genitourinary Medical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Luis A
authors.initials: LA
authors.lastname: Martinez
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.forename: Elba S
authors.initials: ES
authors.lastname: Vazquez
authors.forename: María del Carmen
authors.initials: Mdel C
authors.lastname: Rodriguez-Vargas
authors.forename: Matilde
authors.initials: M
authors.lastname: Olive
authors.forename: Jer-Tsong
authors.initials: JT
authors.lastname: Hsieh
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Logothetis
authors.forename: Nora M
authors.initials: NM
authors.lastname: Navone
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D002453:Cell Cycle; D002470:Cell Survival; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism / Q000502:physiology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004249:DNA Damage; D004317:Doxorubicin / Q000494:pharmacology; D006133:Growth Substances / Q000378:metabolism*; D006801:Humans; D008297:Male; D009376:Neoplasms, Hormone-Dependent / Q000378:metabolism / Q000473:pathology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000473:pathology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D015853:Cysteine Proteinase Inhibitors; D006133:Growth Substances; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D004317:Doxorubicin; D011065:Poly(ADP-ribose) Polymerases