1. ¹Free Radical and Radiation Biology Program – ESR Facility, University of Iowa, Iowa City, IA 52242-1101, USA
2. ²Department of Radiation Oncology, University of Iowa, Iowa City, IA 52242-1101, USA
3. ³Holden Comprehensive Cancer Center, University of Iowa, Iowa City, IA 52242-1101, USA

Correspondence: GR Buettner, Free Radical and Radiation Biology, EMRB 68, The University of Iowa, Iowa City, IA 52242-1101, USA. E-mail: garry-buettner@uiowa.edu

Received 21 January 2004; Revised 26 August 2004; Accepted 26 August 2004; Published online 15 November 2004.

Abstract

This study investigates the role of the antioxidant enzyme manganese superoxide dismutase (MnSOD) in androgen-independent human prostate cancer (PC-3) cells' growth rate in vitro and in vivo. MnSOD levels were found to be lower in parental PC-3 cells compared to nonmalignant, immortalized human prostate epithelial cells (P69SV40T). To unravel the role of MnSOD in the prostate cancer phenotype, PC-3 cells were stably transfected with MnSOD cDNA plasmid. The MnSOD protein and activity levels in clones overexpressing MnSOD were increased seven- to eightfold. These cell lines showed elongated cell doubling time, reduced anchorage-independent growth in soft agar compared to parental PC-3 (Wt) cells, and reduced growth rate of PC-3 tumor xenografts in athymic nude mice. Flow cytometric studies showed an increase in membrane potential in the MnSOD-overexpressing clone (Mn32) compared to Wt and Neo cells. Also, production of extracellular H₂O₂ was increased in the MnSOD-overexpressing clones. As determined by DNA cell cycle analysis, the proportion of cells in G₁ phase was enhanced by MnSOD overexpression. Therefore, MnSOD not only regulates cell survival but also affects PC-3 cell proliferation by retarding G₁ to S transition. Our results are consistent with MnSOD being a tumor suppressor gene in human prostate cancer.