IL-10 Inhibits Apoptosis of Promyeloid Cells by Activating Insulin Receptor Substrate-2 and Phosphatidylinositol 3′-Kinase1

IL-10 is well known to be a potent inhibitor of the synthesis of proinflammatory cytokines, but noninflammatory hemopoietic cells also express IL-10Rs. Here we show that IL-10 directly affects progenitor myeloid cells by protecting them from death following the removal of growth factors. Murine factor-dependent cell progenitors cultured in the absence of growth factors were 43 ± 1% apoptotic after 12 h. Addition of IL-10 at a concentration as low as 100 pg/ml significantly reduced the apoptotic population to 32 ± 3%. At 10 ng/ml, IL-10 caused a 4-fold reduction in the apoptotic population (11 ± 1%). The anti-apoptotic activity of IL-10 was significantly inhibited with a neutralizing IL-10R Ab. Factor-dependent cell progenitor promyeloid cells expressed functional IL-10Rs, as assessed by precipitation of a 110-kDa protein with an Ab to the IL-10R and by the ability of IL-10 to activate Jak1 and Tyk2 and to phosphorylate tyrosine 705 on Stat-3. IL-10 increased tyrosyl phosphorylation of insulin receptor substrate-2 and stimulated the enzymatic activity of both phosphatidylinositol 3′-kinase and Akt. The anti-apoptotic activity of IL-10 was blocked by inhibition of phosphatidylinositol 3′-kinase. Wortmannin and LY294002 also totally inhibited activation of extracellular signal-related kinase (ERK)1/2 by IL-10. Direct inhibition of ERK1/2 with the mitogen-activated protein kinase/ERK kinase inhibitor PD98059 partially, but significantly, impaired the anti-apoptotic activity of IL-10. These data establish that activation of the IL-10R promotes survival of progenitor myeloid cells. This survival-promoting activity is totally due to IL-10 stimulating the insulin receptor substrate-2/PI 3-kinase/Akt pathway, which increases the anti-apoptotic activity of ERK1/2.