Transducin γ-Subunit Sets Expression Levels of α- and β-Subunits and Is Crucial for Rod Viability

Abstract

Transducin is a prototypic heterotrimeric G-protein mediating visual signaling in vertebrate photoreceptor cells. Despite its central role in phototransduction, little is known about the mechanisms that regulate its expression and maintain approximately stoichiometric levels of the ␣-and ␤␥-subunits. Here we demonstrate that the knock-out of transducin ␥-subunit leads to a major downregulation of both ␣-and ␤-subunit proteins, despite nearly normal levels of the corresponding transcripts, and fairly rapid photoreceptor degeneration. Significant fractions of the remaining ␣-and ␤-subunits were mislocalized from the light-sensitive outer segment compartment of the rod. Yet, the tiny amount of the ␣-subunit present in the outer segments of knock-out rods was sufficient to support light signaling, although with a markedly reduced sensitivity. These data indicate that the ␥-subunit controls the expression level of the entire transducin heterotrimer and that heterotrimer formation is essential for normal transducin localization. They further suggest that the production of transducin ␤-subunit without its constitutive ␥-subunit partner sufficiently stresses the cellular biosynthetic and/or chaperone machinery to induce cell death.

Proteasome overload is a common stress factor in multiple forms of inherited retinal degeneration

“…Previous work by us and others (10,11) showed that Gγ 1 knockout results in progressive photoreceptor loss. Even before degeneration begins, affected rods sustain a >90% loss of other transducin subunits: Gα t and Gβ 1 .…”

“…The Gγ 1 knockout and Gβ 1 heterozygous mice were licensed from Deltagen and the former was characterized previously (10). Details on other animal strains, antibodies, immunoblotting, histological techniques, and immunohistochemical procedures are available in SI Materials and Methods.…”

“…Even before degeneration begins, affected rods sustain a >90% loss of other transducin subunits: Gα t and Gβ 1 . This led us to hypothesize that Gγ 1 −/− rods degenerate as a result of ongoing cellular stress caused by their inability to form normal transducin heterotrimer and/or the requirement to proteolyze Gβ 1 and Gα t instead of transporting them to the outer segment (10). Previously, we attempted to ameliorate this stress by knocking out Gα t in addition to Gγ 1 ; however, rods of these double knockout mice degenerated at the same rate as in Gγ 1 −/− mice (10).…”

Pivotal Role of Extended Linker 2 in the Activation of Gα by G Protein-coupled Receptor

“…We should note that previous studies with rhodopsin and transducin had indicated that high concentrations of rhodopsin might activate transducin in the absence of G␤␥, and that G␤ 1 or G␥ 1 knock-out mice still had some light response (35)(36)(37)(38)(39)(40). Thus, GPCRs possess the ability to catalyze the nucleotide exchange on G␣ subunits.…”

Time and space model of urban pollution migration: Economy-energy-environment nexus network

“…where S þ ðFÞ is the number of all positive relations, and S À ðFÞ is all negative relations in matrix U(F) [61]. Thus, J(F) characterizes the ratio between the number of all positive and all negative relations.…”