Modulation of 5-HT(1A) receptor-mediated Ca(2+) responses by co-expression with various recombinant G(alpha) proteins in CHO-K1 cells

The ability of the human 5-HT(1A) receptor to activate different recombinant G(alpha) proteins was investigated in CHO-K1 cells by monitoring 5-HT ligand-mediated Ca(2+) responses upon co-expression with either G(alphaq), G(alpha15) or chimeric G(alphaq/i3) proteins. Each G(alpha) protein yielded a typical 5-HT-dependent Ca(2+) response with different kinetic parameters both for the onset-time of maximal Ca(2+) response (21 to 30 s) and time-dependent attenuation (43 to 73% of residual activity at 1 min upon peak Ca(2+) response). Pertussis toxin-treatment fully abolished the Ca(2+) responses mediated by both the endogenous G(i/o) and the chimeric-PTX-sensitive G(alphaq/i3) proteins. In contrast, Ca(2+) responses driven by recombinant G(alphaq) and G(alpha15) proteins were decreased by PTX, respectively by 52% and 35%, corresponding to the level of endogenous G protein activation. The pharmacology of the 5-HT ligand-mediated Ca(2+) responses was highly affected by both the presence and nature of the co-expressed G(alpha) protein. This influence was more pronounced for the partial agonists L 694247, 8-OH-DPAT, flesinoxan and buspirone in contrast to ipsapirone. The G(alpha) protein rank order for apparent increase of ligands' intrinsic activity was: G(alphaq) <G(alphaq/i3) <G(alpha15) protein. Each of the 5-HT-mediated Ca(2+) responses could be antagonised by WAY 100635, buspirone and methiothepin regardless of the absence or presence of a G(alphaq), G(alphaq/i3) or G(alpha15) protein. In conclusion, these data reinforce that depending on the presence and nature of the G(alpha) protein environment, 5-HT(1A) ligands may display a large spectrum of activities.

The Arabidopsis cupin domain protein AtPirin1 interacts with the G protein alpha-subunit GPA1 and regulates seed germination and early seedling development

Heterotrimeric G proteins are implicated in diverse signaling processes in plants, but the molecular mechanisms of their function are largely unknown. Finding G protein effectors and regulatory proteins can help in understanding the roles of these signal transduction proteins in plants. A yeast two-hybrid screen was performed to search for proteins that interact with Arabidopsis G protein alpha-subunit (GPA1). One of the identified GPA1-interacting proteins is the cupin-domain protein AtPirin1. Pirin is a recently defined protein found because of its ability to interact with a CCAAT box binding transcription factor. The GPA1-AtPirin1 interaction was confirmed in an in vitro binding assay. We characterized two atpirin1 T-DNA insertional mutants and established that they display a set of phenotypes similar to those of gpa1 mutants, including reduced germination levels in the absence of stratification and an abscisic acid-imposed delay in germination and early seedling development. These data indicate that AtPirin1 likely functions immediately downstream of GPA1 in regulating seed germination and early seedling development.

The G-protein alpha-subunit GasC plays a major role in germination in the dimorphic fungus Penicillium marneffei

The opportunistic human pathogen Penicillium marneffei exhibits a temperature-dependent dimorphic switch. At 25 degrees, multinucleate, septate hyphae that can undergo differentiation to produce asexual spores (conidia) are produced. At 37 degrees hyphae undergo arthroconidiation to produce uninucleate yeast cells that divide by fission. This work describes the cloning of the P. marneffei gasC gene encoding a G-protein alpha-subunit that shows high homology to members of the class III fungal Galpha-subunits. Characterization of a DeltagasC mutant and strains carrying a dominant-activating gasC(G45R) or a dominant-interfering gasC(G207R) allele show that GasC is a crucial regulator of germination. A DeltagasC mutant is severely delayed in germination, whereas strains carrying a dominant-activating gasC(G45R) allele show a significantly accelerated germination rate. Additionally, GasC signaling positively affects the production of the red pigment by P. marneffei at 25 degrees and negatively affects the onset of conidiation and the conidial yield, showing that GasC function overlaps with functions of the previously described Galpha-subunit GasA. In contrast to the S. cerevisiae ortholog Gpa2, our data indicate that GasC is not involved in carbon or nitrogen source sensing and plays no major role in either hyphal or yeast growth or in the switch between these two forms.

Administration of antisense oligonucleotides to Galpha(Q/11) reduces the severity of murine lupus

Our principle hypothesis is that the hypothalamic hormone, gonadotropin-releasing hormone (GnRH), is an immunostimulatory hormone and plays a pivotal role in the gender differences in immunity and/or autoimmunity. As a general rule, females display heightened immune responses and heightened endocrinological responsiveness to GnRH compared to males. We have previously demonstrated that GnRH receptor antagonists are effective in ameliorating murine lupus and that GnRH receptor agonists exacerbate murine lupus. GnRH exerts its actions via stimulatory G proteins, specifically via Galpha(s) and the homologous G proteins Galpha(q) and Galpha(11) (referred to together as Galpha(q/11)). We have previously demonstrated that females express higher levels of Galpha(q/11) mRNA and protein compared to males. We hypothesized that antisense inhibition of these specific G proteins would lead to a reduction in inflammatory cytokines and to an amelioration of disease in a mouse model of lupus. We randomized gonadectomized female (NZB x NZW) F1 hybrid mice to treatment with antisense oligonucleotides to Galpha(q/11) or to missense oligonucleotides. Administration of antisense oligonucleotides to Galpha(q/11) led to significant reductions in autoantibody levels, serum IgG levels, hematuria, and proteinuria compared to missense oligos. A trend toward prolonged survival was also noted. In vitro co-culture experiments demonstrated that antisense to Galpha(q/11) significantly inhibited IL-6 production compared to control.

[Gene families of G protein subunits]

G proteins are heterotrimers composed of alpha, beta, and gamma subunits. So far 16 alpha, 6 beta, and 12 gamma subunit genes have been described in mammals. G protein subunit gene families are comparatively conservative and primitive, with all of which exon-intron junctions conform to the GT-AG rule except for one alternative splice site at 5'-end of exon 4 in Gnas which uses GT-TG junction. In the coding regions, exon-intron structures and intron positions among each of the subunit gene families are comparatively conserved. Most of the G protein genes have some characteristics of housekeeping genes. Analysis of distribution of G protein subunit genes in mammalian genomes reveals a tendency of clustering, with five pairs of the alpha subunit genes arranging as tandem duos.

[Effects of hypothyroidism on Goalpha gene expression in hippocampus and dentate gyrus during early development of rat brain]

AIM

To study the expression of Goalpha mRNA in hippocampus and dentate gyrus of 7-day rats with hypothyroidism.

METHODS

We use wistar rat model of hypothyroidism and non-radioactive in situ hybridization technique to observe the changs of Goalpha mRNA levels in hippocampus and dentate gyrus of 7-day rats with or without hypothyroidism.

RESULTS

Perinatal hypothyroidism can increase Goalpha mRNA levels in all areas of hippocampus and dentate gyrus of 7-day rats.

CONCLUSION

Thyroid hormone can down-regulate Goalpha gene transcription in hippocampus and dentate gyrus during the early development of rat brain.