Aman M J, Lamkin T D, Okada H, Kurosaki T, Ravichandran K S
Beirne Carter Center for Immunology Research and the Department of Microbiology, University of Virginia, Charlottesville, Virginia 22908, USA.
J Biol Chem. 1998 Dec 18;273(51):33922-8. doi: 10.1074/jbc.273.51.33922.
The serine-threonine kinase Akt/PKB is activated downstream of phosphatidylinositol 3-kinase in response to several growth factor stimuli and has been implicated in the promotion of cell survival. Although both phosphatidylinositol 3,4,5-trisphosphate (PIP3) and phosphatidylinositol 3,4-bisphosphate (PI 3,4-P2) have been implicated in the regulation of Akt activity in vitro, the relative roles of these two phospholipids in vivo are not well understood. Co-ligation of the B cell receptor (BCR) and the inhibitory FcgammaRIIB1 on B cells results in the recruitment of the 5'-inositol phosphatase SHIP to the signaling complex. Since SHIP is known to cleave PIP3 to generate PI 3,4-P2 both in vivo and in vitro, and Akt activity has been reported to be regulated by either PIP3 or PI 3,4-P2, we hypothesized that recruitment of SHIP through FcgammaRIIB1 co-cross-linking to the BCR in B cells might regulate Akt activity. The nature of this regulation, positive or negative, might also reveal the relative contribution of PIP3 and PI 3,4-P2 to Akt activation in vivo. Here we report that Akt is activated by stimulation through the BCR in a phosphatidylinositol 3-kinase-dependent manner and that this activation is inhibited by co-cross-linking of the BCR to FcgammaRIIB1. Using mutants of FcgammaRIIB1 and SHIP-deficient B cells, we demonstrate that inhibition of Akt activity is mediated by the immune cell tyrosine-based inhibitory motif within FcgammaRIIB1 as well as SHIP. The SHIP-dependent inhibition of Akt activation also suggests that PIP3 plays a greater role in Akt activation than PI 3,4-P2 in vivo.
丝氨酸 - 苏氨酸激酶Akt/PKB在磷脂酰肌醇3激酶下游被激活，以响应多种生长因子刺激，并与促进细胞存活有关。尽管磷脂酰肌醇3,4,5 - 三磷酸（PIP3）和磷脂酰肌醇3,4 - 二磷酸（PI 3,4 - P2）在体外均与Akt活性的调节有关，但这两种磷脂在体内的相对作用尚不清楚。B细胞上B细胞受体（BCR）与抑制性FcγRIIB1的共连接导致5'-肌醇磷酸酶SHIP募集到信号复合物中。由于已知SHIP在体内和体外均可将PIP3切割生成PI 3,4 - P2，并且据报道Akt活性受PIP3或PI 3,4 - P2调节，我们推测通过FcγRIIB1共交联将SHIP募集到B细胞中的BCR可能调节Akt活性。这种调节的性质，是正向还是负向，也可能揭示PIP3和PI 3,4 - P2在体内对Akt激活的相对贡献。在此我们报道，Akt通过BCR刺激以磷脂酰肌醇3激酶依赖性方式被激活，并且这种激活被BCR与FcγRIIB1的共交联所抑制。使用FcγRIIB1突变体和SHIP缺陷型B细胞，我们证明Akt活性的抑制是由FcγRIIB1内基于免疫细胞酪氨酸的抑制基序以及SHIP介导的。SHIP依赖性对Akt激活的抑制也表明，在体内PIP3在Akt激活中比PI 3,4 - P2发挥更大作用。
