Valeria Mancino

Instability of GGL domain-containing RGS proteins in mice lacking the G protein β-subunit Gβ5

RGS (regulator of G protein signaling) proteins containing the G protein γ-like (GGL) domain (RGS6, RGS7, RGS9, and RGS11) interact with the fifth member of the G protein β-subunit family, Gβ5. This interaction is necessary for the stability of both the RGS protein and for Gβ5. Consistent with this notion, we have found that elevation of RGS9-1 mRNA levels by transgene expression does not increase RGS9-1 protein level in the retina, suggesting that Gβ5 levels may be limiting. To examine further the interactions of Gβ5 and the GGL domain-containing RGS proteins, we inactivated the Gβ5 gene. We found that the levels of GGL domain-containing RGS proteins in retinas and in striatum are eliminated or reduced drastically, whereas the levels of Gγ2 and RGS4 proteins remain normal in the absence of Gβ5. The homozygous Gβ5 knockout (Gβ5–/–) mice derived from heterozygous knockout mating are runty and exhibit a high preweaning mortality rate. We concluded that complex formation between GGL domain-containing RGS proteins and the Gβ5 protein is necessary to maintain their mutual stability in vivo. Furthermore, in the absence of Gβ5 and all four RGS proteins that form protein complexes with Gβ5, the animals that survive into adulthood are viable and have no gross defects in brain or retinal morphology.

Interaction of Gα12 with Gα13 and Gαq signaling pathways

The G12 subfamily of heterotrimeric G-proteins consists of two members, G12 and G13. Gene-targeting studies have revealed a role for G13 in blood vessel development. Mice lacking the α subunit of G13 die around embryonic day 10 as the result of an angiogenic defect. On the other hand, the physiological role of G12 is still unclear. To address this issue, we generated Gα12-deficient mice. In contrast to the Gα13-deficient mice, Gα12-deficient mice are viable, fertile, and do not show apparent abnormalities. However, Gα12 does not seem to be entirely redundant, because in the offspring generated from Gα12± Gα13± intercrosses, at least one intact Gα12 allele is required for the survival of animals with only one Gα13 allele. In addition, Gα12 and Gα13 showed a difference in mediating cell migratory response to lysophosphatidic acid in embryonic fibroblast cells. Furthermore, mice lacking both Gα12 and Gαq die in utero at about embryonic day 13. These data indicate that the Gα12-mediated signaling pathway functionally interacts not only with the Gα13- but also with the Gαq/11-mediated signaling systems.

Gq Signaling Is Required for Allergen-Induced Pulmonary Eosinophilia

The complexity and magnitude of interactions leading to the selective infiltration of eosinophils in response to inhaled allergens are formidable obstacles to a larger understanding of the pulmonary pathology associated with allergic asthma. This study uses knockout mice to demonstrate a novel function for the heterotrimeric G protein, Gq, in the regulation of pulmonary eosinophil recruitment. In the absence of Gq signaling, eosinophils failed to accumulate in the lungs following allergen challenge. These studies demonstrate that the inhibition of eosinophil accumulation in the airways is attributed to the failure of hemopoietically derived cells to elaborate GM-CSF in the airways. The data suggest that activation of a Gq-coupled receptor(s) on resident leukocytes in the lung elicits expression of GM-CSF, which, in turn, is required for allergen-induced pulmonary eosinophilia, identifying a novel pathway of eosinophil-associated effector functions leading to pulmonary pathology in diseases such as asthma.

Interaction of G 12 with G 13 and G q signaling pathways

The G12 subfamily of heterotrimeric G-proteins consists of two members, G12 and G13. Gene-targeting studies have revealed a role for G13 in blood vessel development. Mice lacking the α subunit of G13 die around embryonic day 10 as the result of an angiogenic defect. On the other hand, the physiological role of G12 is still unclear. To address this issue, we generated Gα12-deficient mice. In contrast to the Gα13-deficient mice, Gα12-deficient mice are viable, fertile, and do not show apparent abnormalities. However, Gα12 does not seem to be entirely redundant, because in the offspring generated from Gα12± Gα13± intercrosses, at least one intact Gα12 allele is required for the survival of animals with only one Gα13 allele. In addition, Gα12 and Gα13 showed a difference in mediating cell migratory response to lysophosphatidic acid in embryonic fibroblast cells. Furthermore, mice lacking both Gα12 and Gαq die in utero at about embryonic day 13. These data indicate that the Gα12-mediated signaling pathway functionally interacts not only with the Gα13- but also with the Gαq/11-mediated signaling systems.

Gq signaling is required for allergen-induced pulmonary eosinophilia in the mouse

The complexity and magnitude of interactions leading to the selective infiltration of eosinophils in response to inhaled allergens are formidable obstacles to a larger understanding of the pulmonary pathology associated with allergic asthma. This study uses knockout mice to demonstrate a novel function for the heterotrimeric G protein, G(q), in the regulation of pulmonary eosinophil recruitment. In the absence of G(q) signaling, eosinophils failed to accumulate in the lungs following allergen challenge. These studies demonstrate that the inhibition of eosinophil accumulation in the airways is attributed to the failure of hemopoietically derived cells to elaborate GM-CSF in the airways. The data suggest that activation of a G(q)-coupled receptor(s) on resident leukocytes in the lung elicits expression of GM-CSF, which, in turn, is required for allergen-induced pulmonary eosinophilia, identifying a novel pathway of eosinophil-associated effector functions leading to pulmonary pathology in diseases such as asthma.