Elevated extracellular inorganic phosphate inhibits ecto-phosphatase activity in breast cancer cells: Regulation by hydrogen peroxide.

For cells to obtain inorganic phosphate, ectoenzymes in the plasma membrane, which contain a catalytic site facing the extracellular environment, hydrolyze phosphorylated molecules. In this study, we show that increased Pi levels in the extracellular environment promote a decrease in ecto-phosphatase activity, which is associated with Pi-induced oxidative stress. High levels of Pi inhibit ecto-phosphatase because Pi generates H 2 O 2 . Ecto-phosphatase activity is inhibited by H 2 O 2 , and this inhibition is selective for phospho-tyrosine hydrolysis. Additionally, it is shown that the mechanism of inhibition of ecto-phosphatase activity involves lipid peroxidation. In addition, the inhibition of ecto-phosphatase activity by H 2 O 2 is irreversible. These findings have new implications for understanding ecto-phosphatase regulation in the tumor microenvironment. H 2 O 2 stimulated by high Pi inhibits ecto-phosphatase activity to prevent excessive accumulation of extracellular Pi, functioning as a regulatory mechanism of Pi variations in the tumor microenvironment.