Molecular Mechanism for SHP2 in Promoting HER2-induced Signaling and Transformation

Xiangdong Zhou,Yehenew M Agazie

doi:10.1074/jbc.m900020200

Abstract

The Src homology phosphotyrosyl phosphatase 2 (SHP2) plays a positive role in HER2-induced signaling and transformation, but its mechanism of action is poorly understood. Given the significance of HER2 in breast cancer, defining a mechanism for SHP2 in the HER2 signaling pathway is of paramount importance. In the current report we show that SHP2 positively modulates the Ras-extracellular signal-regulated kinase 1 and 2 and the phospoinositide-3-kinase-Akt pathways downstream of HER2 by increasing the half-life the activated form of Ras. This is accomplished by dephosphorylating an autophosphorylation site on HER2 that serves as a docking platform for the SH2 domains of the Ras GTPase-activating protein (RasGAP). The net effect is an increase in the intensity and duration of GTP-Ras levels with the overall impact of enhanced HER2 signaling and cell transformation. In conformity to these findings, the HER2 mutant that lacks the SHP2 target site exhibits an enhanced signaling and cell transformation potential. Therefore, SHP2 promotes HER2-induced signaling and transformation at least in part by dephosphorylating a negative regulatory autophosphorylation site. These results suggest that SHP2 might serve as a therapeutic target against breast cancer and other cancers characterized by HER2 overexpression.

Highlights

20) has led to the conclusion that disregulation of Src homology phosphotyrosyl phosphatase 2 (SHP2) is responsible for these disease states
We have further shown that SHP2 dephosphorylates an autophosphorylation site on HER2 that serves as a docking site for the Src homology 2 (SH2) domains of the Ras GTPase-activating protein (RasGAP), the down-regulator of Ras
The anti-HER2, the anti-PTP1D (SHP2), and the anti-Ras monoclonal antibodies were purchased from Pharmingen, the anti-␤-actin and the anti-FLAGtag monoclonal antibodies were from Sigma, the anti-EGFR antibody was a kind gift from Dr Mike Hayman (Stony Brook University), and the anti-phospho-ERK1/2 and the anti-phospho-Akt antibodies were from Cell Signaling

Summary

Introduction

20) has led to the conclusion that disregulation of SHP2 is responsible for these disease states. The phosphotyrosyl phosphatase (PTP) domain in the C-terminal region is responsible for dephosphorylation of target substrates [13, 22]. In the closed conformation the N-SH2 domain interacts with the PTP domain, physically impeding the activity of the enzyme. Interaction between specific residues on the N-SH2 and the PTP domains mediates the closed conformation. Mutation of these residues leads to a constitutively active SHP2, and the occurrence of such mutations in humans causes the development of Noonan syndrome and associated leukemia (16 –18). We have shown that inhibition of SHP2 in the HER2-positive breast cancer cell lines abolishes mitogenic and cell survival signaling and reverses transformation, leading to differentiation of malignant cells into a normal breast epithelial phenotype [27]. This effect of SHP2 increases the intensity and duration of GTP-Ras levels with the overall impact of enhanced HER2 signaling and cell transformation

Methods

Results

Conclusion