Scaffolding protein Gab2 mediates fibroblast transformation by the SEA tyrosine kinase

Abstract

Transformation of fibroblasts by V-SEA involves activation of the ERK and phosphatidylinositol 3-kinase (PI3K) pathways. Effector proteins that are key mediators of the ERK and PI3K pathways, namely Grb2, the tyrosine phosphatase, SHP2 and PI3K, interact with the two phosphotyrosines found in the bidentate motif in the carboxy-terminal region of V-SEA. Genetic analysis demonstrated that while Y557 was a primary binding site and thus activator of the PI3K-Akt pathway, Y564 also contributed to the activation of this pathway. Y564 was located within a Grb2-binding motif, this raised the possibility that a protein that associated with Grb2 might be important for this PI3K activation. The scaffolding proteins Gab1 and/or Gab2 were candidates for this role. In this report, we demonstrate that V-SEA preferentially interacts with Gab2. Furthermore by using Gab2 null fibroblasts, we demonstrate that Gab2 is essential for fibroblast transformation by V-SEA. Using mutant forms of Gab2, we show that activation of the PI3K-Akt pathway via Gab2 is required for V-SEA-induced transformation. However, efficient fibroblast transformation also requires the SHP2 interaction site on Gab2.

Focal amplification and oncogene dependency of GAB2 in breast cancer

“…GRB2-associated binding protein 2 (GAB2) is a scaffolding adapter protein that amplifies signaling from cytoplasmic and receptor tyrosine kinases by recruiting (with GRB2) signaling molecules such as SHP2 and the p85 subunit of phosphatidylinositol 3-kinase (PI3K) (Gu and Neel, 2003;Sarmay et al, 2006). GAB2 has been shown to be required for v-SEA and BCR/ABL-mediated transformation (Sattler et al, 2002;Ischenko et al, 2003). Although mainly studied in immune cells, GAB2 was recently found overexpressed in a subset of breast cancer cell lines (mainly estrogen receptor positive), in which it was phosphorylated in response to growth factor-receptor tyrosine kinase (including ErbB family) stimulation, and induced by estrogens (Daly et al, 2002).…”

Gab2 and Src co-operate in human mammary epithelial cells to promote growth factor independence and disruption of acinar morphogenesis

“…Gab2 transforms fibroblasts when relieved from Akt-mediated negative feedback (Lynch and Daly, 2002) and is essential for the transforming activity of oncogenes such as v-Sea (Ischenko et al, 2003), Bcr-Abl (Sattler et al, 2002) and Shp2 E76K, a Shp2 hyperactive mutant (Mohi et al, 2005). It is also overexpressed in breast cancer cell lines and primary breast cancers BentiresAlj et al, 2006;Brummer et al, 2006) and supporting a functional role for Gab2 in the development and/or progression of this disease, Gab2 overexpression increases proliferation and promotes EGF-independence of MCF-10A immortalized mammary epithelial cells in three-dimensional culture (Bentires-Alj et al, 2006;Brummer et al, 2006).…”

Uncoupling Ligand-dependent and -independent Mechanisms for Mitogen-activated Protein Kinase Activation by the Murine Ron Receptor Tyrosine Kinase

“…Gab1 contains a number of potential phosphorylation sites, coupling Met to downstream signaling pathways through interaction with various adaptor proteins, including Grb2, p85, Shp2, and CRKL, to mediate biological responses (20,21). RTKs can also recruit the Gab family of scaffolding proteins through the unique C-terminal SH3 domain of the Grb2 adap-tor protein (22), and the recruitment of Gab2 to murine Ron (STK) and chicken SEA is required for transformation by these receptors (23). 3 Binding of Grb2 to the docking site tyrosines of the Met/Ron family of RTKs plays a critical role in the induction of cellular transformation by these receptors (24 -26).…”