Activation of protein kinase A-independent pathways by G _s α in  Drosophila

Abstract

One of the best-described transmembrane signal transduction mechanisms is based on receptor activation of the ␣ subunit of the heterotrimeric G protein G s , leading to stimulation of adenylyl cyclase and the production of cAMP. Intracellular cAMP is then thought to mediate its effects largely, if not entirely, by activation of protein kinase A and the subsequent phosphorylation of substrates which in turn control diverse cellular phenomena. In this report we demonstrate, by two different methods, that reduction or elimination of protein kinase A activity had no effect on phenotypes generated by activation of G s ␣ pathways in Drosophila wing epithelial cells. These genetic studies show that the G s ␣ pathway mediates its primary effects by a novel pathway in differentiating wing epithelial cells. This novel pathway may in part be responsible for some of the complex, cell-specific responses observed following activation of this pathway in different cell types.

Activation of the cAMP/PKA signaling pathway is required for post-ecdysial cell death in wing epidermal cells ofDrosophila melanogaster

“…Our gain-of-function analyses, using constitutively activated Gsα, and loss-of-function analyses, using a dgs mutation, indicate that the activity of Gsα is sufficient and necessary for the death of wing epidermal cells. Consistent with this, endogenous Gsα is expressed in the basal and trans-alar membranes of the wing epithelium of pharate adults (Wolfgang et al, 1996). Cellular effects of cAMP are usually mediated by PKA (for reviews, see Gottesman, 1980;Francis and Corbin, 1994), and this holds true in the case of cell death in the wing epidermis.…”

“…To test this in intact flies, we manipulated adenylyl cyclase activity by overexpressing a constitutively active Gsα subunit (Gsα*), generated by substitution of leucine 215 by glutamine 215 (Quan et al, 1991;Wolfgang et al, 1996). Expression of Gsα* results in receptor-independent activation of the α subunit, and thus activates an endogenous adenylyl cyclase (Quan et al, 1991;Chyb et al, 1999).…”

“…The same en-Gal4 line was used to express the following constructs: UAS-GsαWT and UAS-Gsα* (Drosophila wild-type Gsα subunit and constitutively active Gsα subunit, respectively) (Wolfgang et al, 1996); UAS-mC* (constitutively active form of mouse PKA catalytic subunit mC*) (Li et al, 1995); UAS-R* (dominant-negative form of the regulatory subunit of PKA) (Li et al, 1995); or UAS-p35 (anti-apoptotic protein) (Zhou et al, 1997), using the Gal4/UAS expression system (Brand and Perrimon, 1993).…”

Activation of Cyclic AMP-Dependent Kinase Is Required but May Not Be Sufficient To Mimic Cyclic AMP-Dependent DNA Synthesis and Thyroglobulin Expression in Dog Thyroid Cells

“…A putative involvement of a cAMPregulated protein other than PKA in the mitogenic cAMP pathway has not been proposed previously. It has been recently demonstrated that Drosophila strains that are deficient for PKA activity still exhibit constitutively activating Gs␣ protein effects, which also suggests that cAMP was responsible for PKA-independent effects (50). The existence of cAMP-gated channels in olfactory receptor cells and in hippocampal neurons has been described (4,7,16).…”

Transgenic Drosophila expressing human amyloid precursor protein show γ-secretase activity and a blistered-wing phenotype

“…However, other pathways have to be considered. For example, expression of a mutant form of a G protein involved in cAMP signaling results in a comparable phenotype (37). Similarly, the blistered gene, encoding a protein related to human serum-response factor (38), represents an additional candidate for a pathway in which APP might be involved.…”