Rac1-stimulated macropinocytosis enhances Gßγ activation of PI3Kß.
Biochem J
; 474(23): 3903-3914, 2017 11 16.
Article
in En
| MEDLINE
| ID: mdl-29046393
ABSTRACT
Phosphoinositide 3-kinases (PI 3-kinases) are regulated by a diverse range of upstream activators, including receptor tyrosine kinases (RTKs), G-protein-coupled receptors (GPCRs), and small GTPases from the Ras, Rho and Rab families. For the Class IA PI 3-kinase PI3Kß, two mechanisms for GPCR-mediated regulation have been described direct binding of Gßγ subunits to the C2-helical domain linker of p110ß, and Dock180/Elmo1-mediated activation of Rac1, which binds to the Ras-Binding Domain of p110ß. We now show that the integration of these dual pathways is unexpectedly complex. In breast cancer cells, expression of constitutively activated Rac1 (CA-Rac1) along with either GPCR stimulation or expression of Gßγ led to an additive PI3Kß-dependent activation of Akt. Whereas CA-Rac1-mediated activation of Akt was blocked in cells expressing a mutated PI3Kß that cannot bind Gßγ, Gßγ and GPCR-mediated activation of Akt was preserved when Rac1 binding to PI3Kß was blocked. Surprisingly, PI3Kß-dependent CA-Rac1 signaling to Akt was still seen in cells expressing a mutant p110ß that cannot bind Rac1. Instead of directly binding to PI3Kß, CA-Rac1 acts by enhancing Gßγ coupling to PI3Kß, as CA-Rac1-mediated Akt activation was blocked by inhibitors of Gßγ. Cells expressing CA-Rac1 exhibited a robust induction of macropinocytosis, and inhibitors of macropinocytosis blocked the activation of Akt by CA-Rac1 or lysophosphatidic acid. Our data suggest that Rac1 can potentiate the activation of PI3Kß by GPCRs through an indirect mechanism, by driving the formation of macropinosomes that serve as signaling platforms for Gßγ coupling to PI3Kß.
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Pinocytosis
/
Signal Transduction
/
Rac1 GTP-Binding Protein
/
GTP-Binding Protein beta Subunits
/
GTP-Binding Protein gamma Subunits
/
Class Ia Phosphatidylinositol 3-Kinase
Limits:
Humans
Language:
En
Journal:
Biochem J
Year:
2017
Document type:
Article
Affiliation country:
United States