Omar Y Mian1, Mohamed H Khattab2, Mohammad Hedayati1, Jonathan Coulter1, Budri Abubaker-Sharif1,2, Julie M Schwaninger3, Ravi K Veeraswamy4, James D Brooks5, Lisa Hopkins6, Debika Biswal Shinohara7, Brian Cornblatt8, William G Nelson7, Srinivasan Yegnasubramanian2,7, Theodore L DeWeese1,2,7. 1. Department of Radiation Oncology and Molecular Radiation Sciences, Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins Hospital, Baltimore, Maryland. 2. School of Medicine, Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins Hospital, Baltimore, Maryland. 3. National Institute of Allergies and Infectious Diseases/NIH, Bethesda, Maryland. 4. Department of Vascular Surgery, Emory University, Atlanta, Georgia. 5. Department of Urology, Stanford University, Palo Alto, California. 6. St. Peters University Hospital Breast Center in New Brunswick, New Jersey. 7. Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins Hospital, Baltimore, Maryland. 8. Nuramax Laboratories, Edgewood, Maryland.
Abstract
BACKGROUND: Epigenetic silencing of glutathione S-transferase π (GSTP1) is a hallmark of transformation from normal prostatic epithelium to adenocarcinoma of the prostate. The functional significance of this loss is incompletely understood. The present study explores the effects of restored GSTP1 expression on glutathione levels, accumulation of oxidative DNA damage, and prostate cancer cell survival following oxidative stress induced by protracted, low dose rate ionizing radiation (LDR). METHODS: GSTP1 protein expression was stably restored in LNCaP prostate cancer cells. The effect of GSTP1 restoration on protracted LDR-induced oxidative DNA damage was measured by GC-MS quantitation of modified bases. Reduced and oxidized glutathione levels were measured in control and GSTP1 expressing populations. Clonogenic survival studies of GSTP1- transfected LNCaP cells after exposure to protracted LDR were performed. Global gene expression profiling and pathway analysis were performed. RESULTS: GSTP1 expressing cells accumulated less oxidized DNA base damage and exhibited decreased survival compared to control LNCaP-Neo cells following oxidative injury induced by protracted LDR. Restoration of GSTP1 expression resulted in changes in modified glutathione levels that correlated with GSTP1 protein levels in response to protracted LDR-induced oxidative stress. Survival differences were not attributable to depletion of cellular glutathione stores. Gene expression profiling and pathway analysis following GSTP1 restoration suggests this protein plays a key role in regulating prostate cancer cell survival. CONCLUSIONS: The ubiquitous epigenetic silencing of GSTP1 in prostate cancer results in enhanced survival and accumulation of potentially promutagenic DNA adducts following exposure of cells to protracted oxidative injury suggesting a protective, anti-neoplastic function of GSTP1. The present work provides mechanistic backing to the tumor suppressor function of GSTP1 and its role in prostate carcinogenesis.
BACKGROUND: Epigenetic silencing of glutathione S-transferase π (GSTP1) is a hallmark of transformation from normal prostatic epithelium to adenocarcinoma of the prostate. The functional significance of this loss is incompletely understood. The present study explores the effects of restored GSTP1 expression on glutathione levels, accumulation of oxidative DNA damage, and prostate cancer cell survival following oxidative stress induced by protracted, low dose rate ionizing radiation (LDR). METHODS:GSTP1 protein expression was stably restored in LNCaPprostate cancer cells. The effect of GSTP1 restoration on protracted LDR-induced oxidative DNA damage was measured by GC-MS quantitation of modified bases. Reduced and oxidized glutathione levels were measured in control and GSTP1 expressing populations. Clonogenic survival studies of GSTP1- transfected LNCaP cells after exposure to protracted LDR were performed. Global gene expression profiling and pathway analysis were performed. RESULTS:GSTP1 expressing cells accumulated less oxidized DNA base damage and exhibited decreased survival compared to control LNCaP-Neo cells following oxidative injury induced by protracted LDR. Restoration of GSTP1 expression resulted in changes in modified glutathione levels that correlated with GSTP1 protein levels in response to protracted LDR-induced oxidative stress. Survival differences were not attributable to depletion of cellular glutathione stores. Gene expression profiling and pathway analysis following GSTP1 restoration suggests this protein plays a key role in regulating prostate cancer cell survival. CONCLUSIONS: The ubiquitous epigenetic silencing of GSTP1 in prostate cancer results in enhanced survival and accumulation of potentially promutagenic DNA adducts following exposure of cells to protracted oxidative injury suggesting a protective, anti-neoplastic function of GSTP1. The present work provides mechanistic backing to the tumor suppressor function of GSTP1 and its role in prostate carcinogenesis.
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