Cooperative Activation of PI3K by Ras and Rho Family Small GTPases

Abstract

Summary Phosphoinositide 3-kinases (PI3Ks) and Ras and Rho family small GTPases are key regulators of cell polarization, motility, and chemotaxis.They influence each other's activities by direct and indirect feedback processes that are only partially understood. Here, we show that 21 small GTPase homologs activate PI3K. Using a microscopy-based binding assay, we show that K-Ras, H-Ras, and five homologous Ras family small GTPases function upstream of PI3K by directly binding the PI3K catalytic subunit, p110. In contrast, several Rho family small GTPases activated PI3K by an indirect cooperative positive feedback that required a combination of Rac, CDC42, and RhoG small GTPase activities. Thus, a distributed network of Ras and Rho family small GTPases induces and reinforces PI3K activity, explaining past challenges to elucidate the specific relevance of different small GTPases in regulating PI3K and controlling cell polarization and chemotaxis.

Light-inducible receptor tyrosine kinases that regulate neurotrophin signalling

“…In addition, light stimulation promoted plasma membrane localization of the pleckstrin homology domain of mCherrytagged AKT1 (mCh-PH AKT1 ) ( Supplementary Fig. 2a), indicating PI3K/Akt signalling activation 18 , and resulted in an increase in R-GECO1 signal, demonstrating [Ca 2 þ ] i elevation ( Supplementary Fig. 2b).…”

“…mCherry-PH AKT1 has been described previously 18 and the R-GECO1 expression vector (CMV-R-GECO1) is available from Addgene (plasmid 32444). mCherry-LifeAct was constructed by replacing GFP from GFP-LifeAct 25 to mCherry by using NheI and BsrGI restriction sites.…”

Truncating PREX2 mutations activate its GEF activity and alter gene expression regulation in NRAS-mutant melanoma

“…We hypothesized that the increased GEF activity of PREX2 mutants and resulting activation of Rac1 contributes to this activation of Akt based on several reports that have shown Rac1 can activate PI3K/Akt signaling by directly binding to PI3K (29)(30)(31). To test this hypothesis in our model system, we expressed a constitutively active Rac1 construct, Q61L, in primary melanocytes.…”

PLEKHG3 enhances polarized cell migration by activating actin filaments at the cell front

“…Several studies have shown that F-actin generates positive feedback for the activation of PI3K, Ras-related C3 botulinum toxin (Rac), and/or cell division control protein 42 (Cdc42) (4)(5)(6). The feedback activation of PI3K is, in turn, regulated by multiple Rho family small GTPases via coupled positive feedback loops (7) in which the existing filaments generate new free barbed ends, and new F-actin filaments grow on the free ends (8). In fibroblasts, T cells, and macrophages, cell polarity and chemotaxis are abrogated when Rac or Cdc42 is inhibited (9,10).…”