Fcepsilon RI control of Ras via inositol (1,4,5) trisphosphate 3-kinase and inositol tetrakisphosphate.
The inositol (1,4,5) trisphosphate 3-kinase (ITP3K) phosphorylates Ins (1,4,5) P3 to produce Ins (1,3,4,5) P4. The ITP3K substrate, InsP3, and its product, InsP4, both have the potential to regulate mast cell function. Here, we explore the effects of dominant inhibition of ITP3K upon secretory responses and Ras GTPase activation following antigenic cross-linking of the mast cell immunoreceptor, FcvarepsilonRI. Inhibition of ITP3K potentiates both calcium release from intracellular stores and calcium-dependent secretory responses in mast cells. Moreover, mast cells with dominantly inhibited ITP3K display constitutive activation of Ras and certain Ras effector pathways. We propose three mechanisms by which ITP3K inhibition could influence Ras activation. The protection of InsP3 that results from ITP3K inhibition may lead to enhanced activation of calcium-sensitive Ras-GAPs or -GRFs. Similarly, the deficit in InsP4 may change the behavior of the InsP4 receptor, the GAP1(IP4BP). Our data are inconsistent with calcium-sensitive Ras-GAP activation being the primary consequence of ITP3K inhibition in mast cells. Rather, we observe potentiation of Ras responses in mast cells transfected with dominant negative GAP1(IP4BP). Moreover, shRNA-mediated knockdown of GAP1(IP4BP) potentiates FcvarepsilonRI-mediated Ras activation, indicating that this InsP4-binding GAP protein may be used by the FcvarepsilonRI immunoreceptor to regulate Ras.
Stokes
Alexander J
AJ
Laboratory of Cell Biology and Immunology, Center for Biomedical Research at the Queen's Medical Center, Honolulu, HI, USA.
Shimoda
Lori M N
LM
Lee
Jae Wook
JW
Rillero
Cora
C
Chang
Young-Tae
YT
Turner
Helen
H
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D008407:Mast Cells / Q000166:cytology / Q000378:metabolism; D015394:Molecular Structure; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D017455:Receptors, IgE / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
D007295:Inositol Phosphates; D018160:Receptors, Cytoplasmic and Nuclear; D017455:Receptors, IgE; D011993:Recombinant Fusion Proteins; C061107:inositol-1,3,4,5-tetrakisphosphate receptor; C081655:inositol-1,3,4,5-tetrakisphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins; D002118:Calcium