Release of Inorganic Phosphate into the Tumor Environment: Possible Roles of Ecto- Nucleotidases and Ecto-Phosphatases

Abstract

Inorganic phosphate (Pi) is essential for several biochemical reaction. Serum Pi is maintained at relatively narrow range concentrations, between 0.7 and 1.55mM. Tumor microenvironment presents a high Pi concentration (1.8±0.2mM Pi) and this could be associated wi the rapid growth in the “Growth Rate Hypothesis”. Several studies have identified high expression of Pi transporters in various tumor tissues. Similarly, ecto-enzymes (like ecto-nucleotidases or ecto- phosphates) act by dephosphorylating phospho-substrates in the extracellular environment, and its high expression has been observed in various types of cancer. Little is known about the function of these ecto-enzymes on Pi releasing and accumulation in the tumor environment. Therefore, the purpose of this study is to correlate a possible contribution of the Pi release in the tumor microenvironment by ecto-nucleotidases and ecto-phosphatases, concomitant to the regulation of Pi extracellular pool by specific Pi transporters, associating it to the tumorigenesis.