G Proteins in Signal Transduction

Birnbaumer, Lutz; Birnbaumer, Mariel

doi:10.1002/9783527615490.ch4

Cited by 33 publications

(24 citation statements)

References 187 publications

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“…2 The plasmid CDM8-XLN1a contains the XL-exon spliced to exon 2, exon 3, and exon N1 (8) and encodes a C-terminaltruncated version of the XL␣s protein because of the presence of the stop codon-containing exon N1 (Fig. 1A).…”

Section: Methodsmentioning

confidence: 99%

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Characterization of the Extra-large G Protein α-Subunit XLαs

Pasolli

Klemke

Kehlenbach

et al. 2000

Journal of Biological Chemistry

109

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Our group previously described a new type of G protein, the 78-kDa XLalphas (extra large alphas) (Kehlenbach, R. H., Matthey, J., and Huttner, W. B. (1994) Nature 372, 804-809 and (1995) Nature 375, 253). Upon subcellular fractionation, XLalphas labeled by ADP-ribosylation with cholera toxin was previously mainly detected in the bottom fractions of a velocity sucrose gradient that contained trans-Golgi network and was differentially distributed to Galphas, which also peaked in the top fractions containing plasma membrane. Here, we investigate, using a new antibody specific for the XL domain, the tissue distribution and subcellular localization of XLalphas and novel splice variants referred to as XLN1. Upon immunoblotting and immunofluorescence analysis of various adult rat tissues, XLalphas and XLN1 were found to be enriched in neuroendocrine tissues, with a particularly high level of expression in the pituitary. By both immunofluorescence and immunogold electron microscopy, endogenous as well as transfected XLalphas and XLN1 were found to be predominantly associated with the plasma membrane, with only little immunoreactivity on internal, perinuclear membranes. Upon subcellular fractionation, immunoreactive XLalphas behaved similarly to Galphas but was differentially distributed to ADP-ribosylated XLalphas. Moreover, the bottom fractions of the velocity sucrose gradient were found to contain not only trans-Golgi network membranes but also certain subdomains of the plasma membrane, which reconciles the present with the previous observations. To further investigate the molecular basis of the association of XLalphas with the plasma membrane, chimeric proteins consisting of the XL domain or portions thereof fused to green fluorescent protein were analyzed by fluorescence and subcellular fractionation. In both neuroendocrine and non-neuroendocrine cells, a fusion protein containing the entire XL domain, in contrast to one containing only the proline-rich and cysteine-rich regions, was exclusively localized at the plasma membrane. We conclude that the physiological role of XLalphas is at the plasma membrane, where it presumably is involved in signal transduction processes characteristic of neuroendocrine cells.

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Section: Methodsmentioning

confidence: 99%

“…Heterotrimeric G proteins, which consist of an ␣-subunit and a ␤␥ complex, transduce extracellular signals detected by heptahelical receptors to intracellular effectors (1)(2)(3)(4)(5). Our laboratory previously identified a new type of G protein, XL␣s (extra large ␣s), that is characterized by a bipartite structure (6).…”

mentioning

confidence: 99%

Characterization of the Extra-large G Protein α-Subunit XLαs

Pasolli

Klemke

Kehlenbach

et al. 2000

Journal of Biological Chemistry

109

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“…G␣ 12 and G␣ 13 exhibit 67% amino acid identity with each other, but only 35-44% of amino acid identity to ␣ subunits of other classes, such as G q, G i , and G s (57). Furthermore, whereas members of the G␣ q family of G proteins activate phosphatidylinositol-specific phospholipases, the G␣ s family stimulate adenylyl cyclases, and G␣ i inhibits adenylyl cyclases and activate certain phosphodiesterases and promote the opening of several ion channels (58 -60), members of the G␣ 12 family of GTPases appear not to affect any of these second messenger-generating systems (60). In this regard, the finding that concertina (cta), a Drosophila gene involved in embryogenesis (41), and that G␣ 12 and G␣ 13 can behave as remarkably potent oncogenes (29,42), provided early indications that this G protein class might be involved in growth regulation, albeit through poorly defined mechanisms.…”

Section: A Dh and Ph Deletion Mutant Of Pdz-rhogef Prevents Signalingmentioning

confidence: 99%

A Novel PDZ Domain Containing Guanine Nucleotide Exchange Factor Links Heterotrimeric G Proteins to Rho

Fukuhara

Murga²,

Zohar

et al. 1999

Journal of Biological Chemistry

364

380

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Small GTP-binding proteins of the Rho family play a critical role in signal transduction. However, there is still very limited information on how they are activated by cell surface receptors. Here, we used a consensus sequence for Dbl domains of Rho guanine nucleotide exchange factors (GEFs) to search DNA data bases, and identified a novel human GEF for Rho-related GTPases harboring structural features indicative of its possible regulatory mechanism(s). This protein contained a tandem DH/PH domain closely related to those of Rho-specific GEFs, a PDZ domain, a proline-rich domain, and an area of homology to Lsc, p115-RhoGEF, and a Drosophila RhoGEF that was termed Lsc-homology (LH) domain. This novel molecule, designated PDZ-RhoGEF, activated biological and biochemical pathways specific for Rho, and activation of these pathways required an intact DH and PH domain. However, the PDZ domain was dispensable for these functions, and mutants lacking the LH domain were more active, suggesting a negative regulatory role for the LH domain. A search for additional molecules exhibiting an LH domain revealed a limited homology with the catalytic region of a newly identified GTPase-activating protein for heterotrimeric G proteins, RGS14. This prompted us to investigate whether PDZ-RhoGEF could interact with representative members of each G protein family. We found that PDZ-Rho-GEF was able to form, in vivo, stable complexes with two members of the G␣ 12 family, G␣ 12 and G␣ 13 , and that this interaction was mediated by the LH domain. Furthermore, we obtained evidence to suggest that PDZ-Rho-GEF mediates the activation of Rho by G␣ 12 and G␣ 13 . Together, these findings suggest the existence of a novel mechanism whereby the large family of cell surface receptors that transmit signals through heterotrimeric G proteins activate Rho-dependent pathways: by stimulating the activity of members of the G␣ 12 family which, in turn, activate an exchange factor acting on Rho.

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“…Four classes of G protein ␣ subunits-G␣s, G␣i, G␣q, and G␣12 (1)-are involved in signal transduction of various hormones, neurotransmitters, and many other biologically active molecules such as lysophosphatidic acid (LPA) and thrombin (2)(3)(4). The G␣s subunits and G␣i subunits regulate adenyl cyclase activities, and the G␣q subunits regulate phospholipase C activities (5,6).…”

mentioning

confidence: 99%

Guanine nucleotide exchange factor GEF115 specifically mediates activation of Rho and serum response factor by the G protein α subunit Gα13

Mao

Yuan

Xie

et al. 1998

Proc. Natl. Acad. Sci. U.S.A.

115

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Signal transduction pathways that mediate activation of serum response factor (SRF) by heterotrimeric G protein ␣ subunits were characterized in transfection systems. G␣q, G␣12, and G␣13, but not G␣i, activate SRF through RhoA. When G␣q, ␣12, or ␣13 were coexpressed with a Rho-specific guanine nucleotide exchange factor GEF115, G␣13, but not G␣q or G␣12, showed synergistic activation of SRF with GEF115. The synergy between G␣13 and GEF115 depends on the N-terminal part of GEF115, and there was no synergistic effect between G␣13 and another Rho-specific exchange factor Lbc. In addition, the Dbl-homology (DH)-domain-deletion mutant of GEF115 inhibited G␣13-and G␣12-induced, but not GEF115 itself-or G␣q-induced, SRF activation. The DH-domain-deletion mutant also suppressed thrombin-and lysophosphatidic acid-induced SRF activation in NIH 3T3 cells, probably by inhibition of G␣12͞13. The N-terminal part of GEF115 contains a sequence motif that is homologous to the regulator of G protein signaling (RGS) domain of RGS12. RGS12 can inhibit both G␣12 and G␣13. Thus, the inhibition of G␣12͞13 by the DH-deletion mutant may be due to the RGS activity of the mutant. The synergism between G␣13 and GEF115 indicates that GEF115 mediates G␣13-induced activation of Rho and SRF.Four classes of G protein ␣ subunits-G␣s, G␣i, G␣q, and G␣12 (1)-are involved in signal transduction of various hormones, neurotransmitters, and many other biologically active molecules such as lysophosphatidic acid (LPA) and thrombin (2-4). The G␣s subunits and G␣i subunits regulate adenyl cyclase activities, and the G␣q subunits regulate phospholipase C activities (5, 6). However, the direct effectors for the G␣12 class of G proteins, which includes G␣12 and G␣13 (7), remains to be elucidated. Activated forms of G␣12 and G␣13 were shown to induce transformation phenotypes when transfected into fibroblasts, suggesting that they are involved in regulation of cell growth (8-10). In addition, G␣12 and G␣13 were shown to induce formation of stress fibers in fibroblast cells and apoptosis through the small G protein RhoA (11,12). This observation was supported by the report that G␣12 activated serum response factor (SRF) through RhoA (13). Moreover, a study using mice that lack G␣13 indicates that G␣13 is involved in the function of endothelial cells because mice lacking G␣13 are embryonic lethal apparently due to the failure to develop vasculature (14). In this study, thrombinmediated chemotaxis of fibroblasts lacking G␣13 was blocked, indicating that the thrombin receptor couples to G␣13. This is consistent with the observation that thrombin could stimulate the binding of a photoaffinity GTP analog to G␣13 (15).In this report, we describe the involvement of a Rho-specific guanine nucleotide exchange factor, GEF115 (16), in G␣13-but not G␣12-or G␣q-mediated SRF activation. We found that the N-terminal portion of GEF115, which contains a region homologous to the regulator of G protein signaling (RGS) domain of the RGS12 protein, is required for mediatin...

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G Proteins in Signal Transduction

Cited by 33 publications

References 187 publications

Characterization of the Extra-large G Protein α-Subunit XLαs

Characterization of the Extra-large G Protein α-Subunit XLαs

A Novel PDZ Domain Containing Guanine Nucleotide Exchange Factor Links Heterotrimeric G Proteins to Rho

Guanine nucleotide exchange factor GEF115 specifically mediates activation of Rho and serum response factor by the G protein α subunit Gα13

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