Modulation of α-catenin Tyr phosphorylation by SHP2 positively effects cell transformation induced by the constitutively active FGFR3

Abstract

The Src homology 2 phosphotyrosyl phosphatase (SHP2) is a nonreceptor-type phosphatase that acts as a positive transducer of receptor Tyr kinase (RTK) signaling, particularly the Ras-REK and PI3K-Akt pathways. Recently, we have demonstrated that SHP2 is required for cell transformation induced by the constitutively active fibroblast growth factor receptor 3 (K/E-FR3) (Oncogene, 22,(6909)(6910)(6911)(6912)(6913)(6914)(6915)(6916)(6917)(6918). In that study, we had detected a phosphotyrosyl protein of B100 KDa (p100) in cells expressing dominant-negative SHP2 (R/E-SHP2), but its identity and relevance in SHP2-meditaed transformation was not known. Here, we report the identification of p100 as a-catenin, a vinculin-related protein involved in adherens junction-mediated intercellular adhesion. We show that a-catenin becomes Tyr phosphorylated in intercellular adhesion-dependent manner and this event is counteracted by SHP2. Substrate trapping in intact cells and immunocomplex phosphatse assays confirmed that a-catenin is in deed an SHP2 substrate. Tyr phosphorylation of a-catenin enhances its translocation to the plasma membrane and its interaction with bcatenin, leading to enhanced actin polymerization and stabilization of adherens junction-mediated intercellular adhesion, a phenomenon commensurate with loss of the transformation phenotype. Site-directed mutagenesis studies also suggested that Tyr phosphorylation of a-catenin enhances its inhibitory role on cell transformation. Based on our previous work and the current report, we demonstrate that mediation of cell transformation by SHP2 is a complex process that involves modulation of the Ras-ERK and PI3K-Akt signaling pathways, intercellular adhesion, focal adhesion and actin cytoskeletal reorganization. To our knowledge, this is the first report showing regulation of a-catenin function by Tyr phosphorylation and its inhibitory effect on cell transformation.

Inhibition of SHP2 leads to mesenchymal to epithelial transition in breast cancer cells

“…9,12,30 Second, SHP2 promotes cell transformation induced by v-Src and the constitutively active form of FGFR3. [1][2][3] and associated leukemia. 4 And finally, the SHP2 protein is overexpressed in approximately 70% of infiltrating ductal carcinoma of the human breast.…”

“…First, SHP2 is essential for cell transformation induced by v-Src 1 and the constitutively active form of fibroblast growth factor receptor 3 (K650E-FGFR3). 2,3 And second, SHP2 has been implicated in the development of Noonan syndrome and associated leukemia. 4 This was based on the discovery of activating SHP2 mutations, sometimes referred to as leukemogenic SHP2 mutants, in patients with these diseases.…”

Bench to bedside and back again: Molecular mechanisms of α-catenin function and roles in tumorigenesis

“…This latter site can be phosphorylated by Fer, Fyn or cMet and is conserved in all β-catenin homologues that function in cell-cell adhesion [17]. In addition to phosphorylation of β-catenin, a novel phosphorylation site Y148 on α-catenin has been identified that promotes β-catenin binding [63], but the kinase involved has not been determined. Significantly, over-expression of the protein tyrosine phosphatase SHP2, a known oncogene that is mutated and abnormally regulated in several cancers [64], results in decreased binding between α-catenin and β-catenin, perhaps through de-phosphorylation of Y148 [63].…”

“…In addition to phosphorylation of β-catenin, a novel phosphorylation site Y148 on α-catenin has been identified that promotes β-catenin binding [63], but the kinase involved has not been determined. Significantly, over-expression of the protein tyrosine phosphatase SHP2, a known oncogene that is mutated and abnormally regulated in several cancers [64], results in decreased binding between α-catenin and β-catenin, perhaps through de-phosphorylation of Y148 [63]. Additional α-catenin phosphorylation sites S641 [65] and S652/655 [66] have been identified by large scale mass spectrometry studies but their biological significance has not yet been tested.…”

α-catenin phosphorylation promotes intercellular adhesion through a dual-kinase mechanism

“…How cell signaling events enhance or antagonize the mechanosensitivity of a-catenin is unknown. Previous work has indicated that acatenin present within the CCC can undergo phosphorylation (Burks and Agazie, 2006;Chen et al, 2009;Dupre-Crochet et al, 2007;Ji et al, 2009;Stappert and Kemler, 1994), but the identification of key sites and their functional significance has remained largely unexplored. Here, we identify a highly conserved phospho-domain in a-catenin that contributes to intercellular adhesion in mammalian cells and Drosophila through a dual-kinase mechanism.…”