The G protein Gα12 stimulates Bruton's tyrosine kinase and a rasGAP through a conserved PH/BM domain

Abstract

Heterotrimeric guanine-nucleotide-binding proteins (G proteins) are signal transducers that relay messages from many receptors on the cell surface to modulate various cellular processes. The direct downstream effectors of G proteins consist of the signalling molecules that are activated by their physical interactions with a G alpha or Gbetagamma subunit. Effectors that interact directly with G alpha12 G proteins have yet to be identified. Here we show that G alpha12 binds directly to, and stimulates the activity of, Bruton's tyrosine kinase (Btk) and a Ras GTPase-activating protein, Gap1m, in vitro and in vivo. G alpha12 interacts with a conserved domain, composed of the pleckstrin-homology domain and the adjacent Btk motif, that is present in both Btk and Gap1m. Our results are, to our knowledge, the first to identify direct effectors for G alpha12 and to show that there is a direct link between heterotrimeric and monomeric G proteins.

Cyclic AMP activates Ras

“…In addition to bifunctional RGS proteins that function both as terminators of serpentine receptor signaling and RhoGEFs (reviewed in Hall, 1998), G protein a subunits have been reported to interact directly with a variety of GAPs for small G proteins. Ga12 binds directly to Gap1 m , a RasGAP (Jiang et al, 1998). Although this interaction resulted in increased GAP activity, interactions between unactivated Gao and a novel Rap1GAP resulted in increased Rap1 activity (Jordan et al, 1991).…”

Up-regulation of ras-GAP genes is reversed by a MEK inhibitor and doxorubicin in v-Ki-ras-transformed NIH/3T3 fibroblasts

“…Though roles of GAP1 are not completely clear, its distinct perinuclear localization [18] leads us to expect that GAP1 m might be involved in the transcriptional process. Physiologically, GAP1 has the G protein (Gα12)- [19] and inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P 4 )-binding sites [20], and activates inositol tetrakisphosphate (IP 4 )-gated Ca 2+ influx [21]. The same line of evidence is provided by us that bradykinin and Ins(1,3,4,5)P 4 induce continuous Ca 2+ influx in oncogenic ras-transformed NIH/3T3 fibroblast DT cells [22], predicting the up-regulated GAP1 function [23,24].…”

Signaling network of the Btk family kinases

“…The PH-TH domain of Btk has been shown to bind to bg, Gaq and Ga12 subunit of heterotrimeric G-proteins (LanghansRajasekaran et al, 1995;Bence et al, 1997;Touhara et al, 1994;Tsukada et al, 1994) and the association results in elevation of kinase activity (Jiang et al, 1998;Langhans-Rajasekaran et al, 1995;Ma and Huang, 1998). In addition, Tec and Bmx/Etk are also regulated by Ga12/13.…”

“…Figure 3 summarizes some of the signals emanating from Btk family of kinases. The most well-studied downstream signal is perhaps the PLCg2 and PKCbI, with concomitant induction of sustained calcium in¯ux (Scharenberg and Kinet, 1998) and eventual MAPK/JNK activation (Jiang et al, 1998;Kawakami et al, 1997Kawakami et al, , 1998Schae er et al, 1999). The interaction with vav can potentially activate the rac/cdc42/Rho pathways which also lead to JNK and p38MAPK activation, and SRF activation (Mao et al, 1998).…”