Abstract
Transaldolase (TAL) is a key enzyme of the reversible nonoxidative branch of the pentose phosphate pathway (PPP) that is responsible for the generation of NADPH to maintain glutathione at a reduced state (GSH) and, thus, to protect cellular integrity from reactive oxygen intermediates (ROIs). Formation of ROIs have been implicated in certain types of apoptotic cell death. To evaluate the role of TAL in this process, Jurkat human T cells were permanently transfected with TAL expression vectors oriented in the sense or antisense direction. Overexpression of TAL resulted in a decrease in glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities and NADPH and GSH levels and rendered these cells highly susceptible to apoptosis induced by serum deprivation, hydrogen peroxide, nitric oxide, tumor necrosis factor-alpha, and anti-Fas monoclonal antibody. In addition, reduced levels of TAL resulted in increased glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities and increased GSH levels with inhibition of apoptosis in all five model systems. The effect of TAL expression on susceptibility to apoptosis through regulating the PPP and GSH production is consistent with an involvement of ROIs in each pathway tested. Production of ROIs in Fas-mediated cell death was further substantiated by measurement of intracellular ROI production with oxidation-sensitive fluorescent probes, by the protective effects of GSH precursor, N-acetyl cysteine, free radical spin traps 5,5-dimethyl-1-pyrroline-1-oxide and 3,3,5,5-tetramethyl-1-pyrroline-1-oxide, the antioxidants desferrioxamine, nordihydroguaiaretic acid, and Amytal, and by the enhancing effects of GSH depletion with buthionine sulfoximine. The results provide definitive evidence that TAL has a role in regulating the balance between the two branches of PPP and its overall output as measured by GSH production and thus influences sensitivity to cell death signals.
Highlights
Apoptosis is a fundamental form of programmed cell death that is indispensable for normal development and maintenance of homeostasis within multicellular organisms [1]
Overexpression of TAL in Jurkat human leukemic T cells was accompanied by a decrease in G6PD and 6PGD activities, a concomitant depletion in NADPH and GSH levels, and increased sensitivity to apoptosis provoked by serum deprivation, H2O2, nitric oxide (NO), tumor necrosis factor-␣ (TNF), and anti-Fas monoclonal antibody
The phosphate pathway (PPP) fulfills two essential functions consisting of the formation of pentose phosphates for synthesis of nucleotides, RNA, and DNA and the generation of NADPH for biosynthetic reactions and to maintain glutathione at a reduced state, protecting sulfhydryl groups and cellular integrity from oxygen radicals
Summary
Apoptosis is a fundamental form of programmed cell death that is indispensable for normal development and maintenance of homeostasis within multicellular organisms [1]. Apoptosis and bcl-2 protection were demonstrated in very low oxygen pressure, suggesting that ROI may not be an absolute requirement for programmed cell death [10]. A normal reducing atmosphere, required for cellular integrity, is provided by reduced GSH, which protects cells from damage by ROIs [11]. Overexpression of TAL in Jurkat human leukemic T cells was accompanied by a decrease in G6PD and 6PGD activities, a concomitant depletion in NADPH and GSH levels, and increased sensitivity to apoptosis provoked by serum deprivation, H2O2, nitric oxide (NO), TNF, and anti-Fas monoclonal antibody. Susceptibility to apoptosis could be regulated by TAL through control of the balance between the two branches of the PPP and its overall output as measured by NADPH and GSH production
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
