Abstract #LB-12: SHP-2 is a potential therapeutic target for EGFRvIII-transformed human GBMs
Authors: Yi Zhan, Donald O'Rourke
Journal: Cancer Research (2009)

AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

SHP-2 (also termed PTP1D, PTP2C, PTPL1, SHPTP3 and Syp) is a ubiquitously expressed 68kDa non-transmembrane protein tyrosine phosphatase (PTP) and positively regulates mitogenic signals in receptor tyrosine kinase pathways. In response to stimulation of growth factors, SHP-2 is recruited to their receptors to transduce signals. Oncogenic EGFRvIII is a naturally occurring oncoprotein and is expressed in about 40-50% of human glioblastomas, particular those that arise de novo. This mutated oncoprotein is expressed on the cell surface and constitutively phosphorylated in the absence of EGF. Targeting EGFRvIII for cancer therapy by using monoclonal antibodies or kinase inhibitors is under investigation. However, the intracellular signals activated by oncogenic EGFRvIII are poorly understood. To understand the molecular mechanisms by which this oncoprotein alters transforming phenotypes, and since our previous work indicated that SHP-2 protein tyrosine phosphatase activity modulated EGFRvIII activation and downstream signaling, we examined whether SHP-2 plays a role in EGFRvIII-induced oncogenesis. Ectopic expression of a phosphatase-inactive form of SHP-2, SHP-2 C459S, but not its wild-type SHP-2 or either of two SH2 domain mutants, abrogated transformation of EGFRvIII-expressing U87MG cells in soft agar and in nude mice. Furthermore, shp2 +/- and -/- mouse embryonic fibroblasts (MEFs) could not be transformed by EGFRvIII while shp2 +/+ MEFs displayed a fully transformed phenotype upon introduction of EGFRvIII, again indicating a requirement for functional SHP-2 in EGFRvIII transformation. EGFRvIII expression recruited SHP-2 to the receptor complex and increased endogenous SHP-2 PTPase activity and SHP-2 phosphorylation at Tyr542 in U87MG.EGFRvIII cells. Phosphorylated SHP-2 Tyr542 accumulated in the cellular membrane in parental and EGFRvIII-expressing cells, but only localized to the perinuclear region in EGFRvIII-containing cells by immunofluorescence staining (IF). Activated SHP-2 interacted with focal adhesion kinase (FAK) to further transduce signals and induce a more transformed phenotype . Inhibition of SHP-2 expression by Shp-2 siRNA inhibited cell growth, transformation and altered morphology of EGFRvIII transformed PTEN-deficient U87MG.EGFRvIII and PTEN-intact LN229.EGFRvIII cells. Moreover, the SHP-2 PTPase activity inhibitor NSC-87877 inhibited endogenous SHP-2 activity, Erk phosphorylation and transformation in both GBM cell lines. These data indicate that SHP-2, in particular its PTPase activity, plays a critical role in EGFRvIII-mediated transformation. These data also provide further support that SHP-2 may be a downstream factor of PTEN in human GBMs. Therefore, use of shp-2 siRNAs or SHP-2 inhibitors may represent a potential therapeutic approach for the treatment of human GBMs, in particular primary GBMs that express the EGFRvIII oncoprotein. 

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr LB-12.