A Metabolic Immune Checkpoint: Adenosine in Tumor Microenvironment
- Akio Ohta
- Front. Immunol.
We have examined the effects of adenosine receptors and protein kinases A and C in the regulation of erythropoietin (Epo) production using hepatocellular carcinoma (Hep3B) cells in culture and in vivo in normal mice under normoxic and hypoxic conditions. CGS-21680, a selective adenosine A(2A) agonist, significantly increased levels of Epo in normoxic Hep3B cell cultures and in serum of normal mice under both normoxic and hypoxic conditions. CGS-21680 also produced a significant increase in Epo mRNA levels in Hep3B cell cultures. SCH-58261, a selective adenosine A(2A) receptor antagonist, significantly inhibited the increase in medium levels of Epo in Hep3B cell cultures exposed to hypoxia (1% O(2)). Enprofylline, a selective adenosine A(2B) receptor antagonist, significantly inhibited the increase in plasma levels of Epo in normal mice exposed to hypoxia. Chelerythrine chloride, an antagonist of protein kinase C activation, significantly inhibited hypoxia-induced increases in serum levels of Epo in normal mice. A model is presented for adenosine in hypoxic regulation of Epo production that involves kinases A and C and phospholipase A(2) pathways.