PTP-PEST targets a novel tyrosine site in p120 catenin to control epithelial cell motility and Rho GTPase activity

Extracellular Matrix Protein-1 as a Mediator of Inflammation-Induced Fibrosis After Myocardial Infarction

Irreversible fibrosis is a hallmark of myocardial infarction (MI) and heart failure. Extracellular matrix protein-1 (ECM-1) is up-regulated in these hearts, localized to fibrotic, inflammatory, and perivascular areas. ECM-1 originates predominantly from fibroblasts, macrophages, and pericytes/vascular cells in uninjured human and mouse hearts, and from M1 and M2 macrophages and myofibroblasts after MI. ECM-1 stimulates fibroblast-to-myofibroblast transition, up-regulates key fibrotic and inflammatory pathways, and inhibits cardiac fibroblast migration. ECM-1 binds HuCFb cell surface receptor LRP1, and LRP1 inhibition blocks ECM-1 from stimulating fibroblast-to-myofibroblast transition, confirming a novel ECM-1-LRP1 fibrotic signaling axis. ECM-1 may represent a novel mechanism facilitating inflammation-fibrosis crosstalk.

Dephosphorylation of Y228 and Y217 and phosphorylation of Y335 in p120 catenin activate convergent extension during zebrafish gastrulation

BACKGROUND

The cadherin-associated protein p120 catenin regulates convergent extension through interactions with cadherin proteins, Cdc42, and Rac1, as we previously showed in zebrafish (Danio rerio). Phosphorylation of p120 catenin changes the nature of its activity in vitro but is virtually unexplored in embryos. We used our previously developed antisense RNA splice-site morpholino targeted to endogenous p120 catenin-δ1 to cause defects in axis elongation probing the functions of three p120 catenin tyrosine-phosphorylation sites in gastrulating zebrafish embryos.

RESULTS

The morpholino-induced defects were rescued by co-injections with mouse p120 catenin-δ1-3A mRNAs mutated at residues Y228 and Y217 to a non-phosphorylatable phenylalanine (F) or mutated at residue Y335 to a phosphomimetic glutamic acid (E). Co-injection of the complementary mutations Y228E, Y217E, or Y335F mRNAs partially rescued embryos whereas dual mutation to Y228E-Y217E blocked rescue. Immunopurification showed Y228F mutant proteins preferentially interacted with Rac1, potentially promoting cell migration. In contrast, the phosphomimetic Y228E preferentially interacted with E-cadherin increasing adhesion. Both Y228F and Y335F strongly bind VAV2.

CONCLUSIONS

p120 catenin serves dual roles during gastrulation of zebrafish. Phosphorylation and dephosphorylation of tyrosine residues Y217, Y228, and Y335 precisely balance cell adhesion and cell migration to facilitate somite compaction and axis elongation.

CD99-PTPN12 Axis Suppresses Actin Cytoskeleton-Mediated Dimerization of Epidermal Growth Factor Receptor

Simple Summary

The epidermal growth factor receptor (EGFR) is activated through growth factor-dependent dimerization accompanied by functional reorganization of the actin cytoskeleton. Lee et al. demonstrate that CD99 activation by agonist ligands inhibits epidermal growth factor (EGF)-induced EGFR dimerization through impairment of cytoskeletal reorganization by protein tyrosine phosphatase non-receptor type 12 (PTPN12)-dependent c-Src/focal adhesion kinase (FAK) inactivation, thereby suppressing breast cancer growth.

Abstract

The epidermal growth factor receptor (EGFR), a member of ErbB receptor tyrosine kinase (RTK) family, is activated through growth factor-induced reorganization of the actin cytoskeleton and subsequent dimerization. We herein explored the molecular mechanism underlying the suppression of ligand-induced EGFR dimerization by CD99 agonists and its relevance to tumor growth in vivo. Epidermal growth factor (EGF) activated the formation of c-Src/focal adhesion kinase (FAK)-mediated intracellular complex and subsequently induced RhoA-and Rac1-mediated actin remodeling, resulting in EGFR dimerization and endocytosis. In contrast, CD99 agonist facilitated FAK dephosphorylation through the HRAS/ERK/PTPN12 signaling pathway, leading to inhibition of actin cytoskeletal reorganization via inactivation of the RhoA and Rac1 signaling pathways. Moreover, CD99 agonist significantly suppressed tumor growth in a BALB/c mouse model injected with MDA-MB-231 human breast cancer cells. Taken together, these results indicate that CD99-derived agonist ligand inhibits epidermal growth factor (EGF)-induced EGFR dimerization through impairment of cytoskeletal reorganization by PTPN12-dependent c-Src/FAK inactivation, thereby suppressing breast cancer growth.

Signaling by Small GTPases at Cell-Cell Junctions: Protein Interactions Building Control and Networks

A number of interesting reports highlight the intricate network of signaling proteins that coordinate formation and maintenance of cell-cell contacts. We have much yet to learn about how the in vitro binding data is translated into protein association inside the cells and whether such interaction modulates the signaling properties of the protein. What emerges from recent studies is the importance to carefully consider small GTPase activation in the context of where its activation occurs, which upstream regulators are involved in the activation/inactivation cycle and the GTPase interacting partners that determine the intracellular niche and extent of signaling. Data discussed here unravel unparalleled cooperation and coordination of functions among GTPases and their regulators in supporting strong adhesion between cells.

Expression, purification and characterization of a catalytic domain of human protein tyrosine phosphatase non-receptor 12 (PTPN12) in Escherichia coli with FKBP-type PPIase as a chaperon

Protein tyrosine phosphatase non-receptor type 12 (PTPN12), also known as PTP-PEST, was broadly expressed in hemopoietic cells. Recent research has shown that this enzyme is involved in tumorigenesis, as well as in tumor progression and transfer, as it can suppress multiple oncogenic tyrosine kinases. However, the difficulty of soluble expression of PTP-PEST in prokaryotic cells has resulted in great limitations in investigating its structure and functions. In this study, we successfully carried out soluble expression of the catalytic domain of PTP-PEST (ΔPTP-PEST) in Escherichia coli and performed an enzymatic characterization and kinetics. To confirm expression efficiency, we also induced the expression of the chaperon, FKBP_C. FKBP_C expression indicated efficacious prokaryotic expression of ΔPTP-PEST. In conclusion, our work yielded a practical expression system and two-step chromatography purification method that may serve as a valuable tool for the structural and functional analysis of proteins that are difficult to express in the soluble form in prokaryotic cells.

Defining functional interactions during biogenesis of epithelial junctions

In spite of extensive recent progress, a comprehensive understanding of how actin cytoskeleton remodelling supports stable junctions remains to be established. Here we design a platform that integrates actin functions with optimized phenotypic clustering and identify new cytoskeletal proteins, their functional hierarchy and pathways that modulate E-cadherin adhesion. Depletion of EEF1A, an actin bundling protein, increases E-cadherin levels at junctions without a corresponding reinforcement of cell–cell contacts. This unexpected result reflects a more dynamic and mobile junctional actin in EEF1A-depleted cells. A partner for EEF1A in cadherin contact maintenance is the formin DIAPH2, which interacts with EEF1A. In contrast, depletion of either the endocytic regulator TRIP10 or the Rho GTPase activator VAV2 reduces E-cadherin levels at junctions. TRIP10 binds to and requires VAV2 function for its junctional localization. Overall, we present new conceptual insights on junction stabilization, which integrate known and novel pathways with impact for epithelial morphogenesis, homeostasis and diseases.

Formation and reinforcement of E-cadherin-mediated adhesion depends on intracellular trafficking and interactions with the actin cytoskeleton, but how these are coordinated is not known. Here the authors conduct a focused phenotypic screen to identify new pathways regulating cell–cell junction homeostasis.

Identification of Novel Candidate Genes for Early-Onset Colorectal Cancer Susceptibility

Approximately 25-30% of colorectal cancer (CRC) cases are expected to result from a genetic predisposition, but in only 5-10% of these cases highly penetrant germline mutations are found. The remaining CRC heritability is still unexplained, and may be caused by a hitherto-undefined set of rare variants with a moderately penetrant risk. Here we aimed to identify novel risk factors for early-onset CRC using whole-exome sequencing, which was performed on a cohort of CRC individuals (n = 55) with a disease onset before 45 years of age. We searched for genes that were recurrently affected by rare variants (minor allele frequency ≤ 0.001) with potentially damaging effects and, subsequently, re-sequenced the candidate genes in a replication cohort of 174 early-onset or familial CRC individuals. Two functionally relevant genes with low frequency variants with potentially damaging effects, PTPN12 and LRP6, were found in at least three individuals. The protein tyrosine phosphatase PTP-PEST, encoded by PTPN12, is a regulator of cell motility and LRP6 is a component of the WNT-FZD-LRP5-LRP6 complex that triggers WNT signaling. All variants in LRP6 were identified in individuals with an extremely early-onset of the disease (≤30 years of age), and two of the three variants showed increased WNT signaling activity in vitro. In conclusion, we present PTPN12 and LRP6 as novel candidates contributing to the heterogeneous susceptibility to CRC.

Phosphorylation and isoform use in p120-catenin during development and tumorigenesis

P120-catenin is essential to vertebrate development, modulating cadherin and small-GTPase functions, and growing evidence points also to roles in the nucleus. A complexity in addressing p120-catenin's functions is its many isoforms, including optional splicing events, alternative points of translational initiation, and secondary modifications. In this review, we focus upon how choices in the initiation of protein translation, or the earlier splicing of the RNA transcript, relates to primary sequences that harbor established or putative regulatory phosphorylation sites. While certain p120 phosphorylation events arise via known kinases/phosphatases and have defined outcomes, in most cases the functional consequences are still to be established. In this review, we provide examples of p120-isoforms as they relate to phosphorylation events, and thereby to isoform dependent protein-protein associations and downstream functions. We also provide a view of upstream pathways that determine p120's phosphorylation state, and that have an impact upon development and disease. Because other members of the p120 subfamily undergo similar processing and phosphorylation, as well as related catenins of the plakophilin subfamily, what is learned regarding p120 will by extension have wide relevance in vertebrates.

Alterations of the apical junctional complex and actin cytoskeleton and their role in colorectal cancer progression

Colorectal cancer represents the fourth highest mortality rate among cancer types worldwide. An understanding of the molecular mechanisms that regulate their progression can prevents or reduces mortality due to this disease. Epithelial cells present an apical junctional complex connected to the actin cytoskeleton, which maintains the dynamic properties of this complex, tissue architecture and cell homeostasis. Several studies have indicated that apical junctional complex alterations and actin cytoskeleton disorganization play a critical role in epithelial cancer progression. However, few studies have examined the existence of an interrelation between these 2 components, particularly in colorectal cancer. This review discusses the recent progress toward elucidating the role of alterations of apical junctional complex constituents and of modifications of actin cytoskeleton organization and discusses how these events are interlinked to modulate cellular responses related to colorectal cancer progression toward successful metastasis.

Protein tyrosine phosphatase-PEST and β8 integrin regulate spatiotemporal patterns of RhoGDI1 activation in migrating cells

Directional cell motility is essential for normal development and physiology, although how motile cells spatiotemporally activate signaling events remains largely unknown. Here, we have characterized an adhesion and signaling unit comprised of protein tyrosine phosphatase (PTP)-PEST and the extracellular matrix (ECM) adhesion receptor β8 integrin that plays essential roles in directional cell motility. β8 integrin and PTP-PEST form protein complexes at the leading edge of migrating cells and balance patterns of Rac1 and Cdc42 signaling by controlling the subcellular localization and phosphorylation status of Rho GDP dissociation inhibitor 1 (RhoGDI1). Translocation of Src-phosphorylated RhoGDI1 to the cell's leading edge promotes local activation of Rac1 and Cdc42, whereas dephosphorylation of RhoGDI1 by integrin-bound PTP-PEST promotes RhoGDI1 release from the membrane and sequestration of inactive Rac1/Cdc42 in the cytoplasm. Collectively, these data reveal a finely tuned regulatory mechanism for controlling signaling events at the leading edge of directionally migrating cells.