Protein tyrosine phosphatase SHP2 is involved in Semaphorin 4D-induced axon repulsion

Inner retinal injury in experimental glaucoma is prevented upon AAV mediated Shp2 silencing in a caveolin dependent manner

SH2 domain containing tyrosine phosphatase 2 (Shp2; PTPN11) regulates several intracellular pathways downstream of multiple growth factor receptors. Our studies implicate that Shp2 interacts with Caveolin-1 (Cav-1) protein in retinal ganglion cells (RGCs) and negatively regulates BDNF/TrkB signaling. This study aimed to investigate the mechanisms underlying the protective effects of shp2 silencing in the RGCs in glaucomatous conditions.

Methods: Shp2 was silenced in the Cav-1 deficient mice and the age matched wildtype littermates using adeno-associated viral (AAV) constructs. Shp2 expression modulation was performed in an acute and a chronic mouse model of experimental glaucoma. AAV2 expressing Shp2 eGFP-shRNA under a strong synthetic CAG promoter was administered intravitreally in the animals' eyes. The contralateral eye received AAV-eGFP-scramble-shRNA as control. Animals with Shp2 downregulation were subjected to either microbead injections or acute ocular hypertension experimental paradigm. Changes in inner retinal function were evaluated by measuring positive scotopic threshold response (pSTR) while structural and biochemical alterations were evaluated through H&E staining, western blotting and immunohistochemical analysis of the retinal tissues.

Results: A greater loss of pSTR amplitudes was observed in the WT mice compared to Cav-1^-/- retinas in both the models. Silencing of Shp2 phosphatase imparted protection against inner retinal function loss in chronic glaucoma model in WT mice. The functional rescue also translated to structural preservation of ganglion cell layer in the chronic glaucoma condition in WT mice which was not evident in Cav-1^-/- mice retinas.

Conclusions: This study indicates that protective effects of Shp2 ablation under chronic experimental glaucoma conditions are dependent on Cav-1 in the retina, suggesting in vivo interactions between the two proteins.

Upregulated SHP-2 expression in the epileptogenic zone of temporal lobe epilepsy and various effects of SHP099 treatment on a pilocarpine model

Temporal lobe epilepsy (TLE) is defined as the sporadic occurrence of spontaneous recurrent seizures, and its pathogenesis is complex. SHP-2 (Src homology 2-containing protein tyrosine phosphatase 2) is a widely expressed cytosolic tyrosine phosphatase protein that participates in the regulation of inflammation, angiogenesis, gliosis, neurogenesis and apoptosis, suggesting a potential role of SHP-2 in TLE. Therefore, we investigated the expression patterns of SHP-2 in the epileptogenic brain tissue of intractable TLE patients and the various effects of treatment with the SHP-2-specific inhibitor SHP099 on a pilocarpine model. Western blotting and immunohistochemistry results confirmed that SHP-2 expression was upregulated in the temporal neocortex of patients with TLE. Double-labeling experiments revealed that SHP-2 was highly expressed in neurons, astrocytes, microglia and vascular endothelial cells in the epileptic foci of TLE patients. In the pilocarpine-induced C57BL/6 mouse model, SHP-2 upregulation in the hippocampus began one day after status epilepticus, reached a peak at 21 days and then maintained a significantly high level until day 60. Similarly, we found a remarkable increase in SHP-2 expression at 1, 7, 21 and 60 days post-SE in the temporal neocortex. In addition, we also showed that SHP099 increased reactive gliosis, the release of IL-1β, neuronal apoptosis and neuronal loss, while reduced neurogenesis and albumin leakage. Taken together, the increased expression of SHP-2 in the epileptic zone may be involved in the process of TLE.

Regulation of Brain-Derived Neurotrophic Factor and Growth Factor Signaling Pathways by Tyrosine Phosphatase Shp2 in the Retina: A Brief Review

SH2 domain-containing tyrosine phosphatase-2 (PTPN11 or Shp2) is a ubiquitously expressed protein that plays a key regulatory role in cell proliferation, differentiation and growth factor (GF) signaling. This enzyme is well expressed in various retinal neurons and has emerged as an important player in regulating survival signaling networks in the neuronal tissues. The non-receptor phosphatase can translocate to lipid rafts in the membrane and has been implicated to regulate several signaling modules including PI3K/Akt, JAK-STAT and Mitogen Activated Protein Kinase (MAPK) pathways in a wide range of biochemical processes in healthy and diseased states. This review focuses on the roles of Shp2 phosphatase in regulating brain-derived neurotrophic factor (BDNF) neurotrophin signaling pathways and discusses its cross-talk with various GF and downstream signaling pathways in the retina.

Perineural Invasion in Head and Neck Cancer

Perineural invasion (PNI) is a mechanism of tumor dissemination that can provide a challenge to tumor eradication and that is correlated with poor survival. Squamous cell carcinoma, the most common type of head and neck cancer, has a high prevalence of PNI. This review provides an overview of clinical studies on the outcomes and factors associated with PNI in head and neck cancer and on findings on cancer-nerve crosstalk.

Glaucoma Pathogenesis and Neurotrophins: Focus on the Molecular and Genetic Basis for Therapeutic Prospects

BACKGROUND

Retinal ganglion cell (RGC) degeneration is a major feature of glaucoma pathology. Neuroprotective approaches that delay or halt the progression of RGC loss are needed to prevent vision loss which can occur even after conventional medical or surgical treatments to lower intraocular pressure.

OBJECTIVE

The aim of this review was to examine the progress in genetics and cellular mechanisms associated with endoplasmic reticulum (ER) stress, RGC dysfunction and cell death pathways in glaucoma.

MATERIALS AND METHODS

Here, we review the involvement of neurotrophins like brain derived neurotrophic factor (BDNF) and its high affinity receptor tropomyosin receptor kinase (TrkB) in glaucoma. The role of ER stress markers in human and animal retinas in health and disease conditions is also discussed. Further, we analysed the literature highlighting genetic linkage in the context of primary open angle glaucoma and suggested mechanistic insights into potential therapeutic options relevant to glaucoma management.

RESULTS

The literature review of the neurobiology underlying neurotrophin pathways, ER stress and gene associations provide critical insights into association of RGCs death in glaucoma. Alteration in signalling pathway is associated with increased risk of misfolded protein aggregation in ER promoting RGC apoptosis. Several genes that are linked with neurotrophin signalling pathways have been reported to be associated with glaucoma pathology.

CONCLUSION

Understanding genetic heterogeneity and involvement of neurotrophin biology in glaucoma could help to understand the complex pathophysiology of glaucoma. Identification of novel molecular targets will be critical for drug development and provide neuroprotection to the RGCs and optic nerve.

Transmembrane semaphorins: Multimodal signaling cues in development and cancer

Semaphorins constitute a large family of membrane-bound and secreted proteins that provide guidance cues for axon pathfinding and cell migration. Although initially discovered as repelling cues for axons in nervous system, they have been found to regulate cell adhesion and motility, angiogenesis, immune function and tumor progression. Notably, semaphorins are bifunctional cues and for instance can mediate both repulsive and attractive functions in different contexts. While many studies focused so far on the function of secreted family members, class 1 semaphorins in invertebrates and class 4, 5 and 6 in vertebrate species comprise around 14 transmembrane semaphorin molecules with emerging functional relevance. These can signal in juxtacrine, paracrine and autocrine fashion, hence mediating long and short range repulsive and attractive guidance cues which have a profound impact on cellular morphology and functions. Importantly, transmembrane semaphorins are capable of bidirectional signaling, acting both in "forward" mode via plexins (sometimes in association with receptor tyrosine kinases), and in "reverse" manner through their cytoplasmic domains. In this review, we will survey known molecular mechanisms underlying the functions of transmembrane semaphorins in development and cancer.

Plexin B1 inhibits MET through direct association and regulates Shp2 expression in melanocytes

Plexin B1, the receptor for Semaphorin 4D (Sema4D), is expressed by melanocytes in the skin. We recently showed that Sema4D suppresses activation of the hepatocyte growth factor receptor, MET, in melanocytes, and that knockdown of Plexin B1 results in activation of MET. MET signaling mediates proliferation, survival and migration in melanocytes, and its activation is associated with transformation of melanocytes to melanoma. In this report we investigated the mechanism by which Plexin B1 inhibits MET activation. Our results show that Plexin B1 and MET exist as an oligomeric receptor-receptor complex in melanocytes, and that receptor association is increased by Sema4D. MET and Plexin B1 receptor complexes were identified along the cell body of melanocytes, and Sema4D increased receptor association on dendrites, suggesting that Sema4D regulates MET-dependent processes at precise locations on the melanocyte. Despite activation of MET, Plexin B1 knockdowns proliferated slowly and showed increased apoptosis compared with controls. Shp2, a non-receptor protein tyrosine phosphatase, translates growth and survival signals from MET and other receptor tyrosine kinases. Plexin B1 knockdowns had markedly lower levels of Shp2 compared with controls, and Sema4D upregulated Shp2 expression at the protein and message level in normal melanocytes. Functional studies showed that blockade of Shp2 activity abrogated MET-dependent activation of Erk1/Erk2 and Akt in melanocytes. These results suggest a complex role for Sema4D and Plexin B1 in orchestrating signaling from the MET receptor in melanocytes. Because Shp2 is a downstream adaptor protein for multiple receptors, Sema4D may control the effects of several growth factors on melanocytes through regulation of Shp2.

Plexin-B1 and semaphorin 4D cooperate to promote perineural invasion in a RhoA/ROK-dependent manner

Perineural invasion (PNI) is a tropism of tumor cells for nerve bundles located in the surrounding stroma. It is a pathological feature observed in certain tumors, referred to as neurotropic malignancies, that severely limits the ability to establish local control of disease and results in pain, recurrent growth, and distant metastases. Despite the importance of PNI as a prognostic indicator, its biological mechanisms are poorly understood. The semaphorins and their receptors, the plexins, compose a family of proteins originally shown to be important in nerve cell adhesion, axon migration, and proper central nervous system development. Emerging evidence has demonstrated that these factors are expressed in tissues outside of the nervous system and represent a widespread signal transduction system that is involved in the regulation of motility and adhesion in different cell types. We believe that the plexins and semaphorins, which are strongly expressed in both axons and many carcinomas, play a role in PNI. In this study, we show that plexin-B1 is overexpressed in tissues and cell lines from neurotropic malignancies and is attracted to nerves that express its ligand, semaphorin 4D, in a Rho/Rho kinase-dependent manner. We also demonstrate that nerves are attracted to tumors through this same system of proteins, suggesting that both plexin-B1 and semaphorin 4D are important in the promotion of PNI.

Hippocampal SH2-containing protein-tyrosine phosphatases are involved in extinction of contextual fear

Contextual fear memory is attenuated by re-exposure of animals to a context alone without pairing it with an unconditioned stimulus, and this phenomenon is referred to as fear extinction. In this study we demonstrated that stereotaxic injection of an inhibitor of Src homology 2-containing protein-tyrosine phosphatases 1 and 2 (SHP1/2), NSC87877, into the hippocampus significantly suppressed extinction of contextual fear in the mouse. Intra-hippocampal injection of NSC87877, however, had no effect on the initial memory formation in contextual fear conditioning. These findings suggest that SHP1/2 activity in the hippocampus is involved in the control of contextual fear extinction.

Inhibition of cellular Shp2 activity by a methyl ester analog of SPI-112

The protein tyrosine phosphatase (PTP) Shp2 (PTPN11) is an attractive target for anticancer drug discovery because it mediates growth factor signaling and its gain-of-function mutants are causally linked to leukemias. We previously synthesized SPI-112 from a lead compound of Shp2 inhibitor, NSC-117199. In this study, we demonstrated that SPI-112 bound to Shp2 by surface plasmon resonance (SPR) and displayed competitive inhibitor kinetics to Shp2. Like some other compounds in the PTP inhibitor discovery efforts, SPI-112 was not cell permeable, precluding its use in biological studies. To overcome the cell permeation issue, we prepared a methyl ester SPI-112 analog (SPI-112Me) that is predicted to be hydrolyzed to SPI-112 upon entry into cells. Fluorescence uptake assay and confocal imaging suggested that SPI-112Me was taken up by cells. Incubation of cells with SPI-112Me inhibited epidermal growth factor (EGF)-stimulated Shp2 PTP activity and Shp2-mediated paxillin dephosphorylation, Erk1/2 activation, and cell migration. SPI-112Me treatment also inhibited Erk1/2 activation by a Gab1-Shp2 chimera. Treatment of Shp2(E76K) mutant-transformed TF-1 myeloid cells with SPI-112Me resulted in inhibition of Shp2(E76K)-dependent cell survival, which is associated with inhibition of Shp2(E76K) PTP activity, Shp2(E76K)-induced Erk1/2 activation, and Bcl-XL expression. Furthermore, SPI-112Me enhanced interferon-gamma (IFN-gamma)-stimulated STAT1 tyrosine phosphorylation, ISRE-luciferase reporter activity, p21 expression, and the anti-proliferative effect. Thus, the SPI-112 methyl ester analog was able to inhibit cellular Shp2 PTP activity.