Signal Transduction
Ric-8B Stabilizes the α Subunit of Stimulatory G Protein by Inhibiting Its Ubiquitination*

https://doi.org/10.1074/jbc.M109.063313Get rights and content
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The α subunit of stimulatory G protein (Gαs) activates adenylyl cyclase, which catalyzes cAMP production, and regulates many physiological aspects, such as cardiac regulation and endocrine systems. Ric-8B (resistance to inhibitors of cholinesterase 8B) has been identified as the Gαs-binding protein; however, its role in Gs signaling remains obscure. In this study, we present evidence that Ric-8B specifically and positively regulates Gs signaling by stabilizing the Gαs protein. An in vitro biochemical study suggested that Ric-8B does not possess guanine nucleotide exchange factor activity. However, knockdown of Ric-8B attenuated β-adrenergic agonist-induced cAMP accumulation, indicating that Ric-8B positively regulates Gs signaling. Interestingly, overexpression and knockdown of Ric-8B resulted in an increase and a decrease in the Gαs protein, respectively, without affecting the Gαs mRNA level. We found that the Gαs protein is ubiquitinated and that this ubiquitination is inhibited by Ric-8B. This Ric-8B-mediated inhibition of Gαs ubiquitination requires interaction between Ric-8B and Gαs because Ric-8B splicing variants, which are defective for Gαs binding, failed to inhibit the ubiquitination. Taken together, these results suggest that Ric-8B plays a critical and specific role in the control of Gαs protein levels by modulating Gαs ubiquitination and positively regulates Gs signaling.

G Proteins/Heterotrimeric
Proteases/Ubiquitination
Protein/Stability
Signal Transduction/Adenylate Cyclase
Signal Transduction/Cyclic Nucleotides/Cyclic AMP
Signal T1/G proteins

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*

This work was supported by Grant-in-aid for Scientific Research on Priority Areas 17079006 from the Ministry of Education, Culture, Sports, Science, and Technology.

The on-line version of this article (available at http://www.jbc.org) contains supplemental “Materials and Methods” and Figs. S1–S7.