The protein-tyrosine phosphatase DEP-1 promotes migration and phagocytic activity of microglial cells in part through negative regulation of fyn tyrosine kinase

MicroRNAs dysregulated in multiple sclerosis affect the differentiation of CG-4 cells, an oligodendrocyte progenitor cell line

Introduction

Demyelination is one of the hallmarks of multiple sclerosis (MS). While remyelination occurs during the disease, it is incomplete from the start and strongly decreases with its progression, mainly due to the harm to oligodendrocyte progenitor cells (OPCs), causing irreversible neurological deficits and contributing to neurodegeneration. Therapeutic strategies promoting remyelination are still very preliminary and lacking within the current treatment panel for MS.

Methods

In a previous study, we identified 21 microRNAs dysregulated mostly in the CSF of relapsing and/or remitting MS patients. In this study we transfected the mimics/inhibitors of several of these microRNAs separately in an OPC cell line, called CG-4. We aimed (1) to phenotypically characterize their effect on OPC differentiation and (2) to identify corroborating potential mRNA targets via immunocytochemistry, RT-qPCR analysis, RNA sequencing, and Gene Ontology enrichment analysis.

Results

We observed that the majority of 13 transfected microRNA mimics decreased the differentiation of CG-4 cells. We demonstrate, by RNA sequencing and independent RT-qPCR analyses, that miR-33-3p, miR-34c-5p, and miR-124-5p arrest OPC differentiation at a late progenitor stage and miR-145-5p at a premyelinating stage as evidenced by the downregulation of premyelinating oligodendrocyte (OL) [Tcf7l2, Cnp (except for miR-145-5p)] and mature OL (Plp1, Mbp, and Mobp) markers, whereas only miR-214-3p promotes OPC differentiation. We further propose a comprehensive exploration of their change in cell fate through Gene Ontology enrichment analysis. We finally confirm by RT-qPCR analyses the downregulation of several predicted mRNA targets for each microRNA that possibly support their effect on OPC differentiation by very distinctive mechanisms, of which some are still unexplored in OPC/OL physiology.

Conclusion

miR-33-3p, miR-34c-5p, and miR-124-5p arrest OPC differentiation at a late progenitor stage and miR-145-5p at a premyelinating stage, whereas miR-214-3p promotes the differentiation of CG-4 cells. We propose several potential mRNA targets and hypothetical mechanisms by which each microRNA exerts its effect. We hereby open new perspectives in the research on OPC differentiation and the pathophysiology of demyelination/remyelination, and possibly even in the search for new remyelinating therapeutic strategies in the scope of MS.

FYN: emerging biological roles and potential therapeutic targets in cancer

Src family protein kinases (SFKs) play a key role in cell adhesion, invasion, proliferation, survival, apoptosis, and angiogenesis during tumor development. In humans, SFKs consists of eight family members with similar structure and function. There is a high level of overexpression or hyperactivity of SFKs in tumor, and they play an important role in multiple signaling pathways involved in tumorigenesis. FYN is a member of the SFKs that regulate normal cellular processes. Additionally, FYN is highly expressed in many cancers and promotes cancer growth and metastasis through diverse biological functions such as cell growth, apoptosis, and motility migration, as well as the development of drug resistance in many tumors. Moreover, FYN is involved in the regulation of multiple cancer-related signaling pathways, including interactions with ERK, COX-2, STAT5, MET and AKT. FYN is therefore an attractive therapeutic target for various tumor types, and suppressing FYN can improve the prognosis and prolong the life of patients. The purpose of this review is to provide an overview of FYN's structure, expression, upstream regulators, downstream substrate molecules, and biological functions in tumors.

The Structure, Function and Regulation of Protein Tyrosine Phosphatase Receptor Type J and Its Role in Diseases

Protein tyrosine phosphatase receptor type J (PTPRJ), also known as DEP-1, HPTPη, or CD148, belongs to the R3 subfamily of receptor protein tyrosine phosphatases (RPTPs). It was first identified as an antioncogene due to its protein level being significantly downregulated in most epithelial tumors and cancer cell lines (e.g., colon, lung, thyroid, breast, and pancreas). PTPRJ regulates mouse optic nerve projection by inhibiting the phosphorylation of the erythropoietin-producing hepatocellular carcinoma (Eph) receptor and abelson murine leukemia viral oncogene homolog 1 (c-Abl). PTPRJ is crucial for metabolism. Recent studies have demonstrated that PTPRJ dephosphorylates JAK2 at positions Y813 and Y868 to inhibit leptin signaling. Akt is more phosphorylated at the Ser473 and Thr308 sites in Ptprj^-/- mice, suggesting that PTPRJ may be a novel negative regulator of insulin signaling. PTPRJ also plays an important role in balancing the pro- and anti-osteoclastogenic activity of the M-CSF receptor (M-CSFR), and in maintaining NFATc1 expression during the late stages of osteoclastogenesis to promote bone-resorbing osteoclast (OCL) maturation. Furthermore, multiple receptor tyrosine kinases (RTKs) as substrates of PTPRJ are probably a potential therapeutic target for many types of diseases, such as cancer, neurodegenerative diseases, and metabolic diseases, by inhibiting their phosphorylation activity. In light of the important roles that PTPRJ plays in many diseases, this review summarizes the structural features of the protein, its expression pattern, and the physiological and pathological functions of PTPRJ, to provide new ideas for treating PTPRJ as a potential therapeutic target for related metabolic diseases and cancer.

Src family kinases (SFKs): critical regulators of microglial homeostatic functions and neurodegeneration in Parkinson's and Alzheimer's diseases

c-Src was the first protein kinase to be described as capable of phosphorylating tyrosine residues. Subsequent identification of other tyrosine-phosphorylating protein kinases with a similar structure to c-Src gave rise to the concept of Src family kinases (SFKs). Microglia are the resident innate immune cell population of the CNS. Under physiological conditions, microglia actively participate in brain tissue homeostasis, continuously patrolling the neuronal parenchyma and exerting neuroprotective actions. Activation of pathogen-associated molecular pattern (PAMP) and damage-associated molecular pattern (DAMP) receptors induces microglial proliferation, migration toward pathological foci, phagocytosis, and changes in gene expression, concurrent with the secretion of cytokines, chemokines, and growth factors. A significant body of literature shows that SFK stimulation positively associates with microglial activation and neuropathological conditions, including Alzheimer's and Parkinson's diseases. Here, we review essential microglial homeostatic functions regulated by SFKs, including phagocytosis, environmental sensing, and secretion of inflammatory mediators. In addition, we discuss the potential of SFK modulation for microglial homeostasis in Parkinson's and Alzheimer's diseases.

Protein disulfide isomerase A1‑associated pathways in the development of stratified breast cancer therapies

The oxidoreductase protein disulfide isomerase A1 (PDIA1) functions as a cofactor for many transcription factors including estrogen receptor α (ERα), nuclear factor (NF)-κB, nuclear factor erythroid 2-like 2 (NRF2) and regulates the protein stability of the tumor suppressor p53. Taking this into account we hypothesized that PDIA1, by differentially modulating the gene expression of a diverse subset of genes in the ERα-positive vs. the ERα-negative breast cancer cells, might modify dissimilar pathways in the two types of breast cancer. This hypothesis was investigated using RNA-seq data from PDIA1-silenced MCF-7 (ERα-positive) and MDA-MB-231 (ERα-negative) breast cancer cells treated with either interferon γ (IFN-γ) or etoposide (ETO), and the obtained data were further analyzed using a variety of bioinformatic tools alongside clinical relevance assessment via Kaplan-Meier patient survival curves. The results highlighted the dual role of PDIA1 in suppressing carcinogenesis in the ERα(+) breast cancer patients by negatively regulating the response to reactive oxygen species (ROS) and promoting carcinogenesis by inducing cell cycle progression. In the ERα(−) breast cancer patients, PDIA1 prevented tumor development by modulating NF-κB and p53 activity and cell migration and induced breast cancer progression through control of cytokine signaling and the immune response. The findings reported in this study shed light on the differential pathways regulating carcinogenesis in ERα(+) and ERα(−) breast cancer patients and could help identify therapeutic targets selectively effective in ERα(+) vs. ERα(−) patients.

SdrG gene activated joint surface membrane protein PTPRJ to induce periprosthetic joint infection after total hip arthroplasty

WHAT IS KNOWN AND OBJECTIVE

Up to now, no study focused on the role of SdrG in PJI after THA. To explore the mechanism of periprosthetic joint infection (PJI) after total hip arthroplasty (THA).

METHODS

Joint fluid and blood were collected from patients with PJI after THA, aseptic loosening of the joints or bacterial infection after traumatic fractures of the extremities alone. The expression of SdrG in the 3 groups was determined by agarose gel electrophoresis. The expression of protein tyrosine phosphatase receptor J (PTPRJ) was measured by immunohistochemistry method. The platelet adhesion rate was determined by biochemical analysis. The content of D-dimer, CRP and ESR in blood was determined by latex agglutination method. Multiple linear correlation analysis was used to analyse the correlation between PJI and the expression of PTPRJ protein, platelet adhesion rate, D-dimer content, CRP and ESR.

RESULTS AND DISCUSSION

The expression of SdrG and PTPRJ in PJI group was markedly increased compared to the other 2 groups. The platelet adhesion rate in PJI group was markedly larger compared to aseptic loosening and simple wound infection group, and the rate in simple wound infection group was larger than aseptic loosening group. The level of D-dimer, CRP and ESR in PJI group was higher than that of the other groups. The expression of PTPRJ protein, D-dimer content, CRP and ESR was all closely related to PJI, while platelet adhesion rate had no correlation with PJI.

WHAT IS NEW AND CONCLUSION

SDRG gene around joint prosthesis was over-expressed, which activated joint surface membrane protein PTPRJ and then induced platelet aggregation to reduce joint function.

PI3Kγ Mediates Microglial Proliferation and Cell Viability via ROS

(1) Background: Rapid microglial proliferation contributes to the complex responses of the innate immune system in the brain to various neuroinflammatory stimuli. Here, we investigated the regulatory function of phosphoinositide 3-kinase γ (PI3Kγ) and reactive oxygen species (ROS) for rapid proliferation of murine microglia induced by LPS and ATP. (2) Methods: PI3Kγ knockout mice (PI3Kγ KO), mice expressing catalytically inactive PI3Kγ (PI3Kγ KD) and wild-type mice were assessed for microglial proliferation using an in vivo wound healing assay. Additionally, primary microglia derived from newborn wild-type, PI3Kγ KO and PI3Kγ KD mice were used to analyze PI3Kγ effects on proliferation and cell viability, senescence and cellular and mitochondrial ROS production; the consequences of ROS production for proliferation and cell viability after LPS or ATP stimulation were studied using genetic and pharmacologic approaches. (3) Results: Mice with a loss of lipid kinase activity showed impaired proliferation of microglia. The prerequisite of induced microglial proliferation and cell viability appeared to be PI3Kγ-mediated induction of ROS production. (4) Conclusions: The lipid kinase activity of PI3Kγ plays a crucial role for microglial proliferation and cell viability after acute inflammatory activation.

Characterization of low molecular weight protein tyrosine phosphatases of Entamoeba histolytica

Entamoeba histolytica is an intestinal protozoan parasite of humans and is endemic in developing countries. E. histolytica has two low molecular weight protein tyrosine phosphatase (LMW-PTP) genes, EhLMW-PTP1 and EhLMW-PTP2, which are expressed in cultured trophozoites, clinical isolates, and cysts. The amino acid sequences of proteins EhLMW-PTP1 and EhLMW-PTP2 showed only one amino acid difference between them at position A85V, respectively. Both genes are expressed in cultured trophozoites, mainly EhLMW-PTP2, and in trophozoites recovered from amoebic liver abscess, the expression of EhLMW-PTP1 is downregulated. We cloned the two genes and purified the corresponding recombinant (rEhLMW-PTPs) proteins. Antibodies anti-rEhLMW-PTP2 showed that during red blood cells uptake by E. histolytica, the EhLMW-PTPs were found in the phagocytic cups based on analysis of fluorescence signals. On the other hand, rEhLMW-PTPs showed an optimum phosphatase activity at pH 6.0 with p-nitrophenyl phosphate as the substrate. They dephosphorylate phosphotyrosine and 3-O-methylfluorescein phosphate, but not phosphoserine or phosphothreonine, and the enzymatic activity is inhibited by orthovanadate. rEhLMW-PTP1 and rEhLMW-PTP2 exhibited optimum temperatures of activities at 60 °C and 58 °C, respectively, with high thermal stability at 50 °C. Also, the rEhLMW-PTPs showed high specific activities and specific km value with pNPP or OMFP as the substrates at the physiological temperature (37 °C).

Impact of ambient temperature on inflammation-induced encephalopathy in endotoxemic mice-role of phosphoinositide 3-kinase gamma

BACKGROUND

Sepsis-associated encephalopathy (SAE) is an early and frequent event of infection-induced systemic inflammatory response syndrome. Phosphoinositide 3-kinase γ (PI3Kγ) is linked to neuroinflammation and inflammation-related microglial activity. In homeotherms, variations in ambient temperature (Ta) outside the thermoneutral zone lead to thermoregulatory responses, mainly driven by a gradually increasing sympathetic activity, and may affect disease severity. We hypothesized that thermoregulatory response to hypothermia (reduced Ta) aggravates SAE in PI3Kγ-dependent manner.

METHODS

Experiments were performed in wild-type, PI3Kγ knockout, and PI3Kγ kinase-dead mice, which were kept at neutral (30 ± 0.5 °C) or moderately lowered (26 ± 0.5 °C) Ta. Mice were exposed to lipopolysaccharide (LPS, 10 μg/g, from Escherichia coli serotype 055:B5, single intraperitoneal injection)-evoked systemic inflammatory response (SIR) and monitored 24 h for thermoregulatory response and blood-brain barrier integrity. Primary microglial cells and brain tissue derived from treated mice were analyzed for inflammatory responses and related cell functions. Comparisons between groups were made with one-way or two-way analysis of variance, as appropriate. Post hoc comparisons were made with the Holm-Sidak test or t tests with Bonferroni's correction for adjustments of multiple comparisons. Data not following normal distribution was tested with Kruskal-Wallis test followed by Dunn's multiple comparisons test.

RESULTS

We show that a moderate reduction of ambient temperature triggers enhanced hypothermia of mice undergoing LPS-induced systemic inflammation by aggravated SAE. PI3Kγ deficiency enhances blood-brain barrier injury and upregulation of matrix metalloproteinases (MMPs) as well as an impaired microglial phagocytic activity.

CONCLUSIONS

Thermoregulatory adaptation in response to ambient temperatures below the thermoneutral range exacerbates LPS-induced blood-brain barrier injury and neuroinflammation. PI3Kγ serves a protective role in suppressing release of MMPs, maintaining microglial motility and reinforcing phagocytosis leading to improved brain tissue integrity. Thus, preclinical research targeting severe brain inflammation responses is seriously biased when basic physiological prerequisites of mammal species such as preferred ambient temperature are ignored.

CD148 Serves as a Prognostic Marker of Gastric Cancer and Hinders Tumor Progression by Dephosphorylating EGFR

CD148 is a member of the receptor-type protein tyrosine phosphatase family encoded by the PTPRJ gene and has controversial impacts on cancers. In this study, we investigated the clinical significance of CD148 in gastric cancer and the possible mechanisms. Suppressed CD148 expression indicated adverse pathological features and poor outcomes in gastric cancer patients. CD148 overexpression impeded tumor proliferation, motility, and invasiveness, while CD148 knock-down or knockout promoted the ability of gastric cancer cells to grow and metastasize in vitro and in vivo. Mechanistically, CD148 negatively regulated EGFR phosphorylation of multiple tyrosine residues, including Y1173, Y1068, and Y1092, and remarkably inhibited downstream PI3K/AKT and MEK/ERK pathways. In silico analysis revealed that gene deletions or missense/truncated mutations of PTPRJ gene rarely occurred in gastric cancers. Instead, a 3' UTR-specific methylation might regulate CD148 expression, and the potential regulators were TET2 and TET3. Collectively, our results suggest that CD148 is a convincing prognostic marker as well as a potential therapeutic target for gastric cancer.

Loss of PTPRJ/DEP-1 enhances NF2/Merlin-dependent meningioma development

INTRODUCTION

Meningiomas are common tumors in adults, which develop from the meningeal coverings of the brain and spinal cord. Loss-of-function mutations or deletion of the NF2 gene, resulting in loss of the encoded Merlin protein, lead to Neurofibromatosis type 2 (NF2), but also cause the formation of sporadic meningiomas. It was shown that inactivation of Nf2 in mice caused meningioma formation. Another meningioma tumor-suppressor candidate is the receptor-like density-enhanced phosphatase-1 (DEP-1), encoded by PTPRJ. Loss of DEP-1 enhances meningioma cell motility in vitro and invasive growth in an orthotopic xenograft model. Ptprj-deficient mice develop normally and do not show spontaneous tumorigenesis. Another genetic lesion may be required to interact with DEP-1 loss in meningioma genesis.

METHODS

In the present study we investigated in vitro and in vivo whether the losses of DEP-1 and Merlin/NF2 may have a combined effect.

RESULTS

Human meningioma cells deficient for DEP-1, Merlin/NF2 or both showed no statistically significant changes in cell proliferation, while DEP-1 or DEP1/NF2 deficiency led to moderately increased colony size in clonogenicity assays. In addition, the loss of any of the two genes was sufficient to induce a significant reduction of cell size (p < .05) and profound morphological changes. Most important, in Ptprj knockout mice Cre/lox mediated meningeal Nf2 knockout elicited a four-fold increased rate of meningioma formation within one year compared with mice with Ptprj wild type alleles (25% vs 6% tumor incidence).

CONCLUSIONS

Our data suggest that loss of DEP-1 and Merlin/NF2 synergize during meningioma genesis.

Memory-Like Inflammatory Responses of Microglia to Rising Doses of LPS: Key Role of PI3Kγ

Trained immunity and immune tolerance have been identified as long-term response patterns of the innate immune system. The causes of these opposing reactions remain elusive. Here, we report about differential inflammatory responses of microglial cells derived from neonatal mouse brain to increasing doses of the endotoxin LPS. Prolonged priming with ultra-low LPS doses provokes trained immunity, i.e., increased production of pro-inflammatory mediators in comparison to the unprimed control. In contrast, priming with high doses of LPS induces immune tolerance, implying decreased production of inflammatory mediators and pronounced release of anti-inflammatory cytokines. Investigation of the signaling processes and cell functions involved in these memory-like immune responses reveals the essential role of phosphoinositide 3-kinase γ (PI3Kγ), one of the phosphoinositide 3-kinase species highly expressed in innate immune cells. Together, our data suggest profound influence of preceding contacts with pathogens on the immune response of microglia. The impact of these interactions—trained immunity or immune tolerance—appears to be shaped by pathogen dose.

Optic nerve as a source of activated retinal microglia post-injury

Using mice expressing green fluorescent protein (GFP) from a transgenic CD11c promoter we found that a controlled optic nerve crush (ONC) injury attracted GFP^hi retinal myeloid cells to the dying retinal ganglion cells and their axons. However, the origin of these retinal myeloid cells was uncertain. In this study we use transgenic mice in conjunction with ONC, partial and full optic nerve transection (ONT), and parabiosis to determine the origin of injury induced retinal myeloid cells. Analysis of parabiotic mice and fate mapping showed that responding retinal myeloid cells were not derived from circulating macrophages and that GFP^hi myeloid cells could be derived from GFP^lo microglia. Comparison of optic nerve to retina following an ONC showed a much greater concentration of GFP^hi cells and GFP^lo microglia in the optic nerve. Optic nerve injury also induced Ki67⁺ cells in the optic nerve but not in the retina. Comparison of the retinal myeloid cell response after full versus partial ONT revealed fewer GFP^hi cells and GFP^lo microglia in the retina following a full ONT despite it being a more severe injury, suggesting that full transection of the optic nerve can block the migration of responding myeloid cells to the retina. Our results suggest that the optic nerve can be a reservoir for activated microglia and other retinal myeloid cells in the retina following optic nerve injury.

Suppression of protein tyrosine phosphatase N23 predisposes to breast tumorigenesis via activation of FYN kinase

Zhang et al. identified PTPN23 as a suppressor of cell motility and invasion in mammary epithelial and breast cancer cells. They validated the underlying mechanism of PTPN23 function in breast tumorigenesis as that of a key phosphatase that normally suppresses the activity of FYN in two different models.

Disruption of the balanced modulation of reversible tyrosine phosphorylation has been implicated in the etiology of various human cancers, including breast cancer. Protein Tyrosine Phosphatase N23 (PTPN23) resides in chromosomal region 3p21.3, which is hemizygously or homozygously lost in some breast cancer patients. In a loss-of-function PTPome screen, our laboratory identified PTPN23 as a suppressor of cell motility and invasion in mammary epithelial and breast cancer cells. Now, our TCGA (The Cancer Genome Atlas) database analyses illustrate a correlation between low PTPN23 expression and poor survival in breast cancers of various subtypes. Therefore, we investigated the tumor-suppressive function of PTPN23 in an orthotopic transplantation mouse model. Suppression of PTPN23 in Comma 1Dβ cells induced breast tumors within 56 wk. In PTPN23-depleted tumors, we detected hyperphosphorylation of the autophosphorylation site tyrosine in the SRC family kinase (SFK) FYN as well as Tyr142 in β-catenin. We validated the underlying mechanism of PTPN23 function in breast tumorigenesis as that of a key phosphatase that normally suppresses the activity of FYN in two different models. We demonstrated that tumor outgrowth from PTPN23-deficient BT474 cells was suppressed in a xenograft model in vivo upon treatment with AZD0530, an SFK inhibitor. Furthermore, double knockout of FYN and PTPN23 via CRISPR/CAS9 also attenuated tumor outgrowth from PTPN23 knockout Cal51 cells. Overall, this mechanistic analysis of the tumor-suppressive function of PTPN23 in breast cancer supports the identification of FYN as a therapeutic target for breast tumors with heterozygous or homozygous loss of PTPN23.

Stepping out of the shadows: Oncogenic and tumor-promoting protein tyrosine phosphatases

Protein tyrosine phosphorylation is critical for proper function of cells and organisms. Phosphorylation is regulated by the concerted but generically opposing activities of tyrosine kinases (PTKs) and tyrosine phosphatases (PTPs), which ensure its proper regulation, reversibility, and ability to respond to changing physiological situations. Historically, PTKs have been associated mainly with oncogenic and pro-tumorigenic activities, leading to the generalization that protein dephosphorylation is anti-oncogenic and hence that PTPs are tumor-suppressors. In many cases PTPs do suppress tumorigenesis. However, a growing body of evidence indicates that PTPs act as dominant oncogenes and drive cell transformation in a number of contexts, while in others PTPs support transformation that is driven by other oncogenes. This review summarizes the known transforming and tumor-promoting activities of the classical, tyrosine specific PTPs and highlights their potential as drug targets for cancer therapy.