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Activation of the Gi protein-RHOA axis by non-canonical Hedgehog signaling is independent of primary cilia.

ABSTRACT: Primary cilia are solitary organelles that emanate from the plasma membrane during growth arrest in almost all mammalian cells. The canonical Hedgehog (HH) pathway requires trafficking of the G protein-coupled receptor SMOOTHENED (SMO) and the GLI transcription factors to the primary cilium upon binding of a HH ligand to PATCHED1. However, it is unknown if activation of the small GTPase RHOA by SMO coupling to heterotrimeric Gi proteins, a form of non-canonical HH signaling, requires localization of SMO in the primary cilium. In this study, we compared RHOA and Gi protein stimulation by activation of SMO or sphingosine 1-phosphate receptor (S1P) receptors in WT and KIF3A-deficient mouse embryonic fibroblasts that lack primary cilia. We found that activation of SMO in response to Sonic HH (SHH) or purmorphamine (PUR), a small molecule agonist of SMO, stimulates Gi proteins and RHOA independently of the presence of primary cilia, similar to the effects of S1P. However, while S1P induced a fast activation of AKT that is sensitive to the Gi inhibitor pertussis toxin, HH pathway activators did not significantly activate AKT, suggesting that RHOA activation is not downstream of AKT. Our findings demonstrate that early events in some forms of non-canonical HH signaling occur in extraciliary membranes, which might be particularly relevant for actively-cycling cells, for some cancers characterized by loss of primary cilia, and in ciliopathies.

SUBMITTER: Ho Wei L

PROVIDER: S-EPMC6110505 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Activation of the Gi protein-RHOA axis by non-canonical Hedgehog signaling is independent of primary cilia.

Ho Wei Lan L Arastoo Mohammad M Georgiou Ioanna I Manning David R DR Riobo-Del Galdo Natalia A NA

PloS one 20180827 8

Primary cilia are solitary organelles that emanate from the plasma membrane during growth arrest in almost all mammalian cells. The canonical Hedgehog (HH) pathway requires trafficking of the G protein-coupled receptor SMOOTHENED (SMO) and the GLI transcription factors to the primary cilium upon binding of a HH ligand to PATCHED1. However, it is unknown if activation of the small GTPase RHOA by SMO coupling to heterotrimeric Gi proteins, a form of non-canonical HH signaling, requires localizatio ...[more]

PMID: 30148884

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Project description:Background:Primary cilia are small non-motile microtubule and cell membrane protrusions expressed on most vertebrate cells, including cortical and hippocampal neurons. These small organelles serve as sensory structures sampling the extracellular environment and reprogramming the transcriptional machinery in response to environmental change. Primary cilia are decorated with a variety of receptor proteins and are necessary for specific signaling cascades such as the Sonic hedgehog (Shh) pathway. Disrupting cilia structure or function results in a spectrum of diseases collectively referred to as ciliopathies. Common to human ciliopathies is cognitive impairment, a symptom also observed in Alzheimer's disease (AD). One hallmark of AD is accumulation of senile plaques composed of neurotoxic Amyloid-? (A?) peptide. The A? peptide is generated by the proteolytic cleavage of the amyloid precursor protein (APP). We set out to determine if A? affects primary cilia structure and the Shh signaling cascade. Methods:We utilized in vitro cell-based assays in combination with fluorescent confocal microscopy to address our study goals. Shh signaling and cilia structure was studied using two different cell lines, mouse NIH3T3 and human HeLa cells. To investigate how A? levels affect Shh signaling and cilia structure in these cells, we utilized naturally secreted A? as well as synthetic A?. Effects on Shh signaling were assessed by luciferase activity while cilia structure was analyzed by fluorescent microscopy. Results:Here, we report that APP localizes to primary cilia and A? treatment results in distorted primary cilia structure. In addition, we demonstrate that A? treatment interrupts canonical Shh signal transduction. Conclusions:Overall, our study illustrates that A? can alter primary cilia structure suggesting that elevated A? levels, like those observed in AD patients, could have similar effects on neuronal primary cilia in the brain. Additionally, our study suggests that A? impairs the Shh signaling pathway. Together our findings shed light on two novel targets for future AD therapeutics.

Dataset Information

Activation of the Gi protein-RHOA axis by non-canonical Hedgehog signaling is independent of primary cilia.

Publications

Activation of the Gi protein-RHOA axis by non-canonical Hedgehog signaling is independent of primary cilia.

Similar Datasets

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