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Sonic Hedgehog-induced proliferation requires specific G? inhibitory proteins.

ABSTRACT: Proliferation of cerebellar granular neuronal precursors (CGNPs) is mediated by Sonic Hedgehog (Shh), which activates the Patched and Smoothened (Smo) receptor complex. Although its protein sequence suggests that Smo is a G protein coupled receptor (GPCR), the evidence that this receptor utilizes heterotrimeric G proteins as downstream effectors is controversial. In Drosophila, G?(i) is required for Hedgehog (Hh) activity, but the involvement of heterotrimeric G proteins in vertebrate Shh signaling has not yet been established. Here, we show that Shh-induced proliferation of rat CGNPs is enhanced strongly by the expression of the active forms of G?(i/o) proteins (G?(i1), G?(i2), G?(i3), and G?(o)) but not by members of another class (G?(12)) of heterotrimeric G proteins. Additionally, the mRNAs of these different G?(i) members display specific expression patterns in the developing cerebellum; only G?(i2) and G?(i3) are substantially expressed in the outer external granular layer, where CGNPs proliferate. Consistent with this, Shh-induced proliferation of CGNPs is reduced significantly by knockdowns of G?(i2) and G?(i3) but not by silencing of other members of the G?(i/o) class. Finally, our results demonstrate that G?(i2) and G?(i3) locate to the primary cilium when expressed in CGNP cultures. In summary, we conclude that the proliferative effects of Shh on CGNPs are mediated by the combined activity of G?(i2) and G?(i3) proteins.

SUBMITTER: Barzi M

PROVIDER: S-EPMC3048693 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature

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Sonic Hedgehog-induced proliferation requires specific Gα inhibitory proteins.

Barzi Mercedes M Kostrz Dorota D Menendez Anghara A Pons Sebastian S

The Journal of biological chemistry 20110105 10

Proliferation of cerebellar granular neuronal precursors (CGNPs) is mediated by Sonic Hedgehog (Shh), which activates the Patched and Smoothened (Smo) receptor complex. Although its protein sequence suggests that Smo is a G protein coupled receptor (GPCR), the evidence that this receptor utilizes heterotrimeric G proteins as downstream effectors is controversial. In Drosophila, Gα(i) is required for Hedgehog (Hh) activity, but the involvement of heterotrimeric G proteins in vertebrate Shh signal ...[more]

PMID: 21209076

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Project description:The intraflagellar transport (IFT) machinery is essential for cilia assembly, maintenance, and trans-localization of signaling proteins. The IFT machinery consists of two large multiprotein complexes, one of which is the IFT-B. TTC30A and TTC30B are integral components of this complex and were previously shown to have redundant functions in the context of IFT, preventing the disruption of IFT-B and, thus, having a severe ciliogenesis defect upon loss of one paralog. In this study, we re-analyzed the paralog-specific protein complexes and discovered a potential involvement of TTC30A or TTC30B in ciliary signaling. Specifically, we investigated a TTC30A-specific interaction with protein kinase A catalytic subunit α, a negative regulator of Sonic hedgehog (Shh) signaling. Defects in this ciliary signaling pathway are often correlated to synpolydactyly, which, intriguingly, is also linked to a rare TTC30 variant. For an in-depth analysis of this unique interaction and the influence on Shh, TTC30A or B single- and double-knockout hTERT-RPE1 were employed, as well as rescue cells harboring wildtype TTC30 or the corresponding mutation. We could show that mutant TTC30A inhibits the ciliary localization of Smoothened. This observed effect is independent of Patched1 but associated with a distinct phosphorylated PKA substrate accumulation upon treatment with forskolin. This rather prominent phenotype was attenuated in mutant TTC30B. Mass spectrometry analysis of wildtype versus mutated TTC30A or TTC30B uncovered differences in protein complex patterns and identified an impaired TTC30A-IFT57 interaction as the possible link leading to synpolydactyly. We could observe no impact on cilia assembly, leading to the hypothesis that a slight decrease in IFT-B binding can be compensated, but mild phenotypes, like synpolydactyly, can be induced by subtle signaling changes. Our systematic approach revealed the paralog-specific influence of TTC30A KO and mutated TTC30A on the activity of PRKACA and the uptake of Smoothened into the cilium, resulting in a downregulation of Shh. This downregulation, combined with interactome alterations, suggests a potential mechanism of how mutant TTC30A is linked to synpolydactyly.

Project description:Cilia assembly, maintenance and the localization of signal-transduction proteins necessitate a functioning intraflagellar transport (IFT). The IFT machinery moves cargo along a microtubule scaffold from the proximal to the distal end of the cilium. This anterograde transport is facilitated by a large multiprotein complex IFT-B, which consists of 16 proteins in total and recruits motor protein Kinesin-2 for active movement. TTC30A and TTC30B are integral components of this complex and were shown before to have redundant function in context of IFT. One paralogue could compensate the loss of the other, preventing the disruption of IFT-B and thus a severe ciliogenesis defect with no formation of the cilium. Affinity-based protein complex analysis of endogenously tagged cells, generated via CRISPR/Cas9 system as described before, revealed paralogue specific protein interactors proposing the involvement of TTC30A or TTC30B in other ciliary functions, particularly Sonic hedgehog signaling (Shh). Defects in this ciliary signaling pathway are often correlated to synpolydactyly, which intriguingly is also linked to a rare TTC30 variant. In this study we focus on the so far unknown interaction of TTC30A with protein kinase A catalytic subunit α PRKACA, which is a negative regulator of Shh pathway. For an in-depth analysis of this unique interaction and the influence on Shh, we used previously, via the CRISPR/Cas9 system, generated TTC30A or B single- and double-knockout hTERT-RPE1 cells as well as rescue cells harboring the TTC30 mutation. Our systematic approach revealed the paralogue specific influence of TTC30A KO and mutated TTC30A on the activity of PRKACA as well as the uptake of Smoothened into the cilium resulting in a downregulation of Sonic hedgehog signaling. Affinity-based protein complex analysis of wildtype versus mutated TTC30A or TTC30B uncovered differences in interaction pattern. These interactome alterations combined with Shh downregulation suggest a possible mechanism of how mutant TTC30A and respectively TTC30A KO are linked to synpolydactyly.

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Sonic Hedgehog-induced proliferation requires specific G? inhibitory proteins.

Publications

Sonic Hedgehog-induced proliferation requires specific Gα inhibitory proteins.

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