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PKB-mediated negative feedback tightly regulates mitogenic signalling via Gab2
Danielle K Lynch1, Roger J Daly
1Cancer Research Program, Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010, Australia.
The EMBO Journal
|January 10, 2002
Summary
Protein kinase B (PKB) negatively regulates Gab2 signaling by phosphorylating it. Mutating this site enhances growth factor signaling and transforms cells, establishing Gab2 as a proto-oncogene.
Area of Science:
- Cellular signaling
- Molecular biology
- Oncogenesis
Background:
- Gab2 is a docking protein involved in growth factor signaling.
- PI3-kinase-dependent pathways regulate Gab2 activity.
- Protein kinase B (PKB) is implicated in negative regulation of Gab2.
Purpose of the Study:
- To investigate the role of PKB in regulating Gab2 tyrosine phosphorylation.
- To determine the functional consequences of inhibiting PKB-mediated phosphorylation of Gab2.
- To establish Gab2 as a proto-oncogene.
Main Methods:
- Heregulin (HRG) stimulation
- Wortmannin pretreatment
- Site-directed mutagenesis (S159A Gab2)
- Immunoprecipitation and Western blotting
- Fibroblast transformation assays
Main Results:
- PKB phosphorylates Gab2 at Ser159, inhibiting its tyrosine phosphorylation.
- S159A Gab2 mutation enhanced HRG-induced tyrosine phosphorylation of Gab2, Shc, and ErbB2.
- S159A Gab2 amplified ErbB2 signaling, ERK, and PKB pathways.
- S159A Gab2 exhibited potent transforming activity in fibroblasts.
Conclusions:
- Gab2 is negatively regulated by PKB-mediated phosphorylation at Ser159.
- Disruption of this negative regulation enhances growth factor signaling and promotes cellular transformation.
- Gab2 functions as a proto-oncogene, tightly regulated by PKB.