細胞の「ショートサーキット」を追う(Chasing Down a Cellular ‘Short Circuit’)

2024-06-04 カリフォルニア大学サンディエゴ校(UCSD)

Growth factors trigger G proteins (in green) to disengage from GPCRs and change localization within cells. At right: A ribbon diagram of the G protein structure shows the position of all phosphoevents the “buzzer” site in red. Photo credit: UC San Diego Health Sciences

<関連情報>

• https://today.ucsd.edu/story/chasing-down-a-cellular-short-circuit
• https://www.science.org/doi/10.1126/scisignal.ade8041

成長因子に依存したGαiのリン酸化がGタンパク質共役型受容体による正常シグナル伝達を形成する Growth factor–dependent phosphorylation of Gαi shapes canonical signaling by G protein–coupled receptors

SUCHISMITA ROY, SAPTARSHI SINHA, ANANTA JAMES SILAS, MAJID GHASSEMIAN, […], AND PRADIPTA GHOSH
Science Signaling  Published:4 Jun 2024
DOI:https://doi.org/10.1126/scisignal.ade8041

Editor’s summary

In addition to being activated by GPCRs, heterotrimeric G proteins can be transactivated by receptor tyrosine kinases, including epidermal growth factor receptor (EGFR). Roy et al. investigated mechanisms of cross-talk between the GPCR CXCR4 and EGFR. Mass spectrometry analysis identified Gα_i residues that were phosphorylated in response to EGF. Studies of Gα_i proteins mutated at these sites showed that Gα_i phosphorylation prevented it from subsequently coupling to CXCR4, in one case because of the cytosolic mislocalization of Gα_i. Together, these findings suggest that cross-talk between growth factor receptors and GPCRs may be mediated at the level of Gα_i phosphorylation. —John F. Foley

Abstract

A long-standing question in the field of signal transduction is how distinct signaling pathways interact with each other to control cell behavior. Growth factor receptors and G protein–coupled receptors (GPCRs) are the two major signaling hubs in eukaryotes. Given that the mechanisms by which they signal independently have been extensively characterized, we investigated how they may cross-talk with each other. Using linear ion trap mass spectrometry and cell-based biophysical, biochemical, and phenotypic assays, we found at least three distinct ways in which epidermal growth factor affected canonical G protein signaling by the G_i-coupled GPCR CXCR4 through the phosphorylation of Gα_i. Phosphomimicking mutations in two residues in the α_E helix of Gα_i (tyrosine-154/tyrosine-155) suppressed agonist-induced Gα_i activation while promoting constitutive Gβγ signaling. Phosphomimicking mutations in the P loop (serine-44, serine-47, and threonine-48) suppressed G_i activation entirely, thus completely segregating growth factor and GPCR pathways. As expected, most of the phosphorylation events appeared to affect intrinsic properties of Gα_i proteins, including conformational stability, nucleotide binding, and the ability to associate with and to release Gβγ. However, one phosphomimicking mutation, targeting the carboxyl-terminal residue tyrosine-320, promoted mislocalization of Gα_i from the plasma membrane, a previously uncharacterized mechanism of suppressing GPCR signaling through G protein subcellular compartmentalization. Together, these findings elucidate not only how growth factor and chemokine signals cross-talk through the phosphorylation-dependent modulation of Gα_i but also how such cross-talk may generate signal diversity.