TY - JOUR
T1 - FcγRIIb modulation of surface immunoglobulin-induced Akt activation in murine B cells
AU - Jacob, Anand
AU - Cooney, Damon
AU - Tridandapani, Susheela
AU - Kelley, Todd
AU - Coggeshall, K. Mark
PY - 1999/5/7
Y1 - 1999/5/7
N2 - We examined activation of the serine/threonine kinase Akt in the murine B cell line A20. Akt is activated in a phosphoinositide 3-kinase (PtdIns 3- kinase)-dependent manner upon stimulation of the antigen receptor, surface immunoglobulin (sIg). In contrast, Akt induction is reduced upon co- clustering of sIg with the B cell IgG receptor, FcγRIIb. Co-clustering of sIg-FcγRIIb transmits a dominant negative signal and is associated with reduced accumulation of the PtdIns 3-kinase product phosphatidylinositol 3,4,5-trisphosphate (PtdIns 3,4,5-P3), known to be a potent activator of Akt. PtdIns 3-kinase is activated to the same extent with and without FcγRIIb co-ligation, indicating conditions supporting the generation of PtdIns 3,4,5-P3. We hypothesized that the decreased Akt activity arises from the consumption of PtdIns 3,4,5-P3 by the inositol-5-phosphatase Src homology 2-containing inositol 5-phosphatase (SHIP), which has been shown by us to be tyrosine-phosphorylated and associated with FcγRIIb when the latter is co-ligated. In direct support of this hypothesis, we report here that Akt induction is greatly reduced in fibroblasts expressing catalytically active but not inactive SHIP. Likewise, the reduction in Akt activity upon sIg- FcγRIIb co-clustering is absent from avian B cells lacking expression of SHIP. These findings indicate that SHIP acts as a negative regulator of Akt activation.
AB - We examined activation of the serine/threonine kinase Akt in the murine B cell line A20. Akt is activated in a phosphoinositide 3-kinase (PtdIns 3- kinase)-dependent manner upon stimulation of the antigen receptor, surface immunoglobulin (sIg). In contrast, Akt induction is reduced upon co- clustering of sIg with the B cell IgG receptor, FcγRIIb. Co-clustering of sIg-FcγRIIb transmits a dominant negative signal and is associated with reduced accumulation of the PtdIns 3-kinase product phosphatidylinositol 3,4,5-trisphosphate (PtdIns 3,4,5-P3), known to be a potent activator of Akt. PtdIns 3-kinase is activated to the same extent with and without FcγRIIb co-ligation, indicating conditions supporting the generation of PtdIns 3,4,5-P3. We hypothesized that the decreased Akt activity arises from the consumption of PtdIns 3,4,5-P3 by the inositol-5-phosphatase Src homology 2-containing inositol 5-phosphatase (SHIP), which has been shown by us to be tyrosine-phosphorylated and associated with FcγRIIb when the latter is co-ligated. In direct support of this hypothesis, we report here that Akt induction is greatly reduced in fibroblasts expressing catalytically active but not inactive SHIP. Likewise, the reduction in Akt activity upon sIg- FcγRIIb co-clustering is absent from avian B cells lacking expression of SHIP. These findings indicate that SHIP acts as a negative regulator of Akt activation.
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U2 - 10.1074/jbc.274.19.13704
DO - 10.1074/jbc.274.19.13704
M3 - Article
C2 - 10224144
AN - SCOPUS:0033531796
SN - 0021-9258
VL - 274
SP - 13704
EP - 13710
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 19
ER -