Figure 5.

An intact purine synthesis pathway is necessary for MICA induction. A, DON, an inhibitor of proximal de novo purine synthesis, prevents GIME. B, azaserine, a second de novo pathway inhibitor, also blocks GIME. C, azaserine, DON, and the GLUT transporter inhibitor phloretin each prevent GIME in HEK-293T cells. D, HAT-selected HEK-293T cells produce purine nucleotides exclusively through the salvage pathway. Azaserine is unable to prevent GIME in HAT-selected cells, showing that inhibition of GIME by azaserine depends on its action in inhibiting de novo purine synthesis. DON, like phloretin, appears to have additional off-target actions. E, the salvage pathway substrate hypoxanthine rescues MICA expression in azaserine-treated cells in 25 mm glucose. F, similarly, AICA-Rs also rescues MICA expression in azaserine-treated cells. G, AICA-Rs, which can be converted to AICA-Rt by adenosine kinase, is sufficient to induce MICA expression even in conditions of low glucose. Error bars, 95% confidence interval.