Regulation of receptor tyrosine kinase signaling by protein tyrosine phosphatase-1B.
ABSTRACT Receptor tyrosine kinases (RTKs) are key regulators of cellular homeostasis. Based on in vitro and ex vivo studies, protein tyrosine phosphatase-1B (PTP1B) was implicated in the regulation of several RTKs, yet mice lacking PTP1B show defects mainly in insulin and leptin receptor signaling. To address this apparent paradox, we studied RTK signaling in primary and immortalized fibroblasts from PTP1B(-/-) mice. After growth factor treatment, cells lacking PTP1B exhibit increased and sustained phosphorylation of the epidermal growth factor receptor (EGFR) and the platelet-derived growth factor receptor (PDGFR). However, Erk activation is enhanced only slightly, and there is no increase in Akt activation in PTP1B-deficient cells. Our results show that PTP1B does play a role in regulating EGFR and PDGFR phosphorylation but that other signaling mechanisms can largely compensate for PTP1B deficiency. In-gel phosphatase experiments suggest that other PTPs may help to regulate the EGFR and PDGFR in PTP1B(-/-) fibroblasts. This and other compensatory mechanisms prevent widespread, uncontrolled activation of RTKs in the absence of PTP1B and probably explain the relatively mild effects of PTP1B deletion in mice.
Article: Regulation of signaling at regions of cell-cell contact by endoplasmic reticulum-bound protein-tyrosine phosphatase 1B.[show abstract] [hide abstract]
ABSTRACT: Protein-tyrosine phosphatase 1B (PTP1B) is a ubiquitously expressed PTP that is anchored to the endoplasmic reticulum (ER). PTP1B dephosphorylates activated receptor tyrosine kinases after endocytosis, as they transit past the ER. However, PTP1B also can access some plasma membrane (PM)-bound substrates at points of cell-cell contact. To explore how PTP1B interacts with such substrates, we utilized quantitative cellular imaging approaches and mathematical modeling of protein mobility. We find that the ER network comes in close proximity to the PM at apparently specialized regions of cell-cell contact, enabling PTP1B to engage substrate(s) at these sites. Studies using PTP1B mutants show that the ER anchor plays an important role in restricting its interactions with PM substrates mainly to regions of cell-cell contact. In addition, treatment with PTP1B inhibitor leads to increased tyrosine phosphorylation of EphA2, a PTP1B substrate, specifically at regions of cell-cell contact. Collectively, our results identify PM-proximal sub-regions of the ER as important sites of cellular signaling regulation by PTP1B.PLoS ONE 01/2012; 7(5):e36633. · 4.09 Impact Factor
Article: Protein tyrosine phosphatase 1B deficiency potentiates PERK/eIF2α signaling in brown adipocytes.[show abstract] [hide abstract]
ABSTRACT: Protein-tyrosine phosphatase 1B (PTP1B) is a physiological regulator of glucose homeostasis and body mass, and has been implicated in endoplasmic reticulum (ER) stress. Herein, we assess the role of PTP1B in ER stress in brown adipocytes, which are key regulators of thermogenesis and metabolic response. To determine the role of PTP1B in ER stress, we utilized brown adipose tissue (BAT) from mice with adipose-specific PTP1B deletion, and brown adipocytes deficient in PTP1B and reconstituted with PTP1B wild type (WT) or the substrate-trapping PTP1B D181A (D/A) mutant. PTP1B deficiency led to upregulation of PERK-eIF2α phosphorylation and IRE1α-XBP1 sub-arms of the unfolded protein response. In addition, PTP1B deficiency sensitized differentiated brown adipocytes to chemical-induced ER stress. Moreover, PERK activation and tyrosine phosphorylation were increased in BAT and adipocytes lacking PTP1B. Increased PERK activity resulted in the induction of eIF2α phosphorylation at Ser51 and better translatability of ATF4 mRNA in response to ER stress. At the molecular level, we demonstrate direct interaction between PTP1B and PERK and identify PERK Tyr615 as a mediator of this association. Collectively, the data demonstrate that PTP1B is a physiologically-relevant modulator of ER stress in brown adipocytes and that PTP1B deficiency modulates PERK-eIF2α phosphorylation and protein synthesis.PLoS ONE 01/2012; 7(4):e34412. · 4.09 Impact Factor
[show abstract] [hide abstract]
ABSTRACT: Liver regeneration (LR) is a compensatory growth that occurs in response to resection or injury of the liver aimed at restoring the liver mass and maintaining body homeostasis. The activation of intracellular signaling pathways due to extracellular stimuli mainly reflects a highly coordinated spatial and temporal organization of phosphotyrosine-based signals generated by the concerted action of three basic functional modules, namely protein tyrosine kinases, protein tyrosine phosphatases, and the Src homology 2 (SH2) domain. In this review, we have selected a set of signaling proteins downstream of activated cytokine and growth factor receptors that highlight the multifaceted aspects of tyrosine phosphorylation with their impact on the course of LR. Besides being a process of remarkable biological interest, LR has recently emerged as a model for dissecting molecular mechanisms underlying diverse pathophysiological states, offering new perspectives in primarily, but not only, managing life-threatening liver diseases.International Union of Biochemistry and Molecular Biology Life 12/2011; 64(1):27-35. · 3.51 Impact Factor