Expression of the Receptor Protein-tyrosine Phosphatase, PTPμ, Restores E-cadherin-dependent Adhesion in Human Prostate Carcinoma Cells

Abstract

Normal prostate expresses the receptor protein-tyrosine phosphatase, PTP, whereas LNCaP prostate carcinoma cells do not. PTP has been shown previously to interact with the E-cadherin complex. LNCaP cells express normal levels of E-cadherin and catenins but do not mediate either PTP-or E-cadherin-dependent adhesion. Re-expression of PTP restored cell adhesion to PTP and to E-cadherin. A mutant form of PTP that is catalytically inactive was re-expressed, and it also restored adhesion to PTP and to E-cadherin. Expression of PTP-extra (which lacks most of the cytoplasmic domain) induced adhesion to PTP but not to E-cadherin, demonstrating a requirement for the presence of the intracellular domains of PTP to restore E-cadherinmediated adhesion. We previously observed a direct interaction between the intracellular domain of PTP and RACK1, a receptor for activated protein kinase C (PKC). We demonstrate that RACK1 binds to both the catalytically active and inactive mutant form of PTP. In addition, we determined that RACK1 binds to the PKC␦ isoform in LNCaP cells. We tested whether PKC could be playing a role in the ability of PTP to restore E-cadherin-dependent adhesion. Activation of PKC reversed the adhesion of PTPWT-expressing cells to E-cadherin, whereas treatment of parental LNCaP cells with a PKC␦-specific inhibitor induced adhesion to E-cadherin. Together, these studies suggest that PTP regulates the PKC pathway to restore E-cadherin-dependent adhesion via its interaction with RACK1.A diverse set of cellular behaviors including growth, differentiation, adhesion, and migration are regulated by protein tyrosine phosphorylation. Protein tyrosine kinases and proteintyrosine phosphatases (PTPs) 1 regulate intracellular phosphotyrosine levels. A subfamily of receptor-like PTPs (RPTPs) has extracellular segments containing adhesion molecule-like domains and intracellular segments that possess tyrosine phosphatase activity (1, 2). This structural arrangement suggests that RPTPs directly send signals in response to cell adhesion. The receptor protein-tyrosine phosphatase PTP is a member of the Ig superfamily of adhesion molecules. The extracellular segment of PTP contains a MAM ( (Meprin/A5/PTP ) domain, an Ig domain, and four fibronectin type III repeats (3). Expression of PTP induces aggregation of non-adherent cells (4, 5) through a homophilic binding site that resides within the Ig domain (6). The MAM domain plays a role in cell-cell aggregation by determining the specificity of the adhesive interaction (7). PTP contains a single membrane-spanning region with two cytoplasmic PTP domains. Only the membrane proximal PTP domain has catalytic activity (8). The role of the membrane distal PTP domain is not known, but this domain has been implicated in directing protein-protein interactions in other RPTPs (reviewed in Ref.2). The intracellular juxtamembrane domain of PTP contains a region that is homologous to the conserved intracellular domain of the cadherins (9

Protein tyrosine phosphatase receptor-like genes are frequently hypermethylated in sporadic colorectal cancer

“…The increased expression of PTPRM in normal cell and low-grade astrocytomas compared to high grade glioblastomas, along with the results of in vivo experiments, also confirmed that loss of this protein promotes tumor cell migration and propagation (17). The lack of expression of PTPRM in prostate cancer cells connected with the lack of PTPRM-mediated adhesion also suggests a role of PTPRM as a tumor suppressor gene (16). AlthoughtAlthough these autorsauthors have not mentioned about PTPs in theirtop "top ranking lists" of genes with aberrant methylation, the available raw data shows differences in PTPs methylation accordingas compared to healthy tissue (19,20).…”

“…shown to be expressed in neurons, glia, epithelia and prostate (16,17,18). PTPRM plays a crucial role in EGFR signaling -reduced expression of PTPRM increases the EGFR specific phosphorylation of tyrosine residue, thus causing phospholipase C-gamma (PLC)γ1 activation and cell migration (18).…”

Rack1 promotes epithelial cell–cell adhesion by regulating E-cadherin endocytosis

“…Perhaps Rack1 inhibits other tyrosine kinases from phosphorylating the E-cadherin/catenin complex and/or recruits tyrosine phosphatases to dephosphorylate the complex. Thus, we examined Rack1's influence on protein tyrosine phosphatase m (PTPm), a tyrosine phosphatase that is known to associate with the E-cadherin/ catenin complex (Brady-Kalnay et al, 1995 and with Rack1 (Mourton et al, 2001;Hellberg et al, 2002;Chattopadhyay et al, 2003). We did not observe changes in PTPm expression or in the association of PTPm with E-cadherin in cells overexpressing Rack1 (data not shown).…”

RACK1 Is an Insulin-like Growth Factor 1 (IGF-1) Receptor-interacting Protein That Can Regulate IGF-1-mediated Akt Activation and Protection from Cell Death

“…However, it is possible that other RACK1-interacting proteins are also involved in regulating Akt activity. For example the regulatory phosphatase PTP interacts with RACK1 and was found to be active in regulating focal adhesions via PKC␦ (47,49). It will be necessary to do a complete analysis of RACK1-associated proteins in response to IGF-1 or insulin stimulation of cells to get a comprehensive picture of how RACK1 regulates signaling from these receptors.…”