Abstract
OBJECTIVES: Selenium (Se) is a non-metallic, essential trace element for many organisms, including humans. Se may have potential in cancer prevention, as evidenced by multiple animal and human epidemiological studies. Selenium-binding protein 1 (SBP1) is a highly-conserved protein that covalently binds Se. Prostate cells exhibit cytoplasmic and nuclear SBP1 localization. Reduced levels of nuclear SBP1 were previously shown to be associated with a higher tumor grade and a greater likelihood of prostate cancer recurrence following prostatectomy. The Krebs cycle of the normal prostate is inhibited in favor of the production of citrate energy, therefore distinguishing the energy metabolism of the normal prostate from that of other organs. This inhibition is generally relieved during cancer progression. The objective of this study was to investigate a contribution of SBP1 in this process of metabolic shift. METHODS: Human PC-3 prostate cancer cells that express very low levels of SBP1 were engineered to express the native, nuclear-targeted, or nuclear-excluded SBP1 by transfection of constitutive- or inducible-SBP1 expression constructs. Oxidative phosphorylation (OXPHOS) was examined by quantifying the oxygen consumption rate (OCR) using a Seahorse XF analyzer (Agilent, Inc.). Western blotting with SBP1 and phospho-AMPK specific antibodies was employed to interrogate the activation of AMP-activated protein kinase (AMPK), a key regulator of energy homeostasis. RESULTS: Overexpressing SBP1 in PC-3 cells increased the activating phosphorylation of AMPK at Thr172 by approximately 70%. In addition, overexpressing the native, nuclear-targeted or nuclear-excluded SBP1 significantly reduced OCR and mitochondrial ATP synthesis, as measures of mitochondrial respiration (32–43% reduction in basal respiration and 40–55% reduction in maximal respiration). These changes in energy metabolism occurred without affecting cellular proliferation. CONCLUSIONS: These results indicate that the loss of SBP1 during prostate cancer development may contribute to disease progression by facilitating the transition to an energy metabolism that favors increased energy production as well as the building blocks required to sustain tumor growth and survival. FUNDING SOURCES: National Institute of Health.