PKCδ mediates Nrf2-dependent protection of neuronal cells from NO-induced apoptosis

Quercetin modified electrospun PHBV fibrous scaffold enhances cartilage regeneration

It suggests that the poly (3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) scaffold can be used for cartilage tissue engineering, but PHBV is short of bioactivity that is required for cartilage regeneration. To fabricate a bioactive cartilage tissue engineering scaffold that promotes cartilage regeneration, quercetin (QUE) modified PHBV (PHBV-g-QUE) fibrous scaffolds were prepared by a two-step surface modification method. The PHBV-g-QUE fibrous scaffold facilitates the growth of chondrocytes and maintains chondrocytic phenotype resulting from the upregulation of SOX9, COL II, and ACAN. The PHBV-g-QUE fibrous scaffold inhibited apoptosis of chondrocyte and reduced oxidative stress of chondrocytes by regulating the transcription of related genes. Following PHBV-g-QUE fibrous scaffolds and PHBV fibrous scaffolds with adhered chondrocytes were implanted into nude mice for 4 weeks, it demonstrated that PHBV-g-QUE fibrous scaffolds significantly promoted cartilage regeneration compared with the PHBV fibrous scaffolds. Hence, it suggests that the PHBV-g-QUE fibrous scaffold can be potentially applied in the clinical treatment of cartilage defects in the future.

Bisphenol A and its substitutes regulate human B cell survival via Nrf2 expression

B cells contribute to produce inflammatory cytokines and antibodies, to present autoantigens, and to interact with T cells, which lead to body defense and disease control. Nuclear factor (erythroid-derived 2)-like 2(Nrf2) is responsible for gene expression of antioxidant enzymes to protect cells from oxidative stress by reactive oxygen species(ROS) production. Bisphenol A(BPA) may not be safe due to the effect on body's physiological functions. The chemicals that substitute for BPA may still have similar effects in the body. Tritan™ copolyester is a novel plastic form using BPA substitutes, 1,4-cyclohexanedimethanol(CHDM), dimethyl terephthalate(DMT), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol(TMCD). Isosorbide(ISO) was also used as a substitute for TMCD and DMT. Here, we investigated whether B cell viability is influenced by BPA and its substitutes via Nrf2 induction using WiL2-NS human B lymphoblast cells. When cytotoxicity was measured by using assays with MTT, CellTiter-Glo, trypan blue and propidium iodide, cytotoxicity by BPA was higher than that by substitutes. BPA and its substitutes showed significant cytotoxicity and ROS production, which were attenuated by the treatment with N-acetylcysteine(NAC), a ROS scavenger. In addition, BPA treatment enhanced gene expression of antioxidant enzymes, heme oxygenase(HO)-1, catalase, superoxide dismutase(SOD) 1 and 2. As H₂O₂ treatment induced cell death and Nrf2 amount in WiL2-NS cells, BPA treatment increased Nrf2. Cell death by H₂O₂ was increased in doxycycline-inducible Nrf2-knockdown(KD) cells. In Cytotoxicity by the treatment with BPA or its substitutes was also enhanced in Nrf2-KD cells but that was reduced by Nrf2 overexpression compared to control cells. Taken together, these results implicate that B cell cytotoxicity by substitutes should be lower than BPA and Nrf2 can prevent B cells from BPA- or BPA substitutes-induced cytotoxicity via ROS production. Data suggest that the comprehensive studies or evaluation could be necessary to replace BPA in manufacture by other substitutes.

Antioxidant and antihypertensive responses to oral nitrite involves activation of the Nrf2 pathway

Impaired redox balance contributes to the cardiovascular alterations of hypertension and activation of nuclear factor erythroid 2-related factor 2 (Nrf2) pathway may counteract these alterations. While nitrite recycles back to NO and exerts antioxidant and antihypertensive effects, the mechanisms involved in these responses are not fully understood. We hypothesized that nitrite treatment of two-kidney, one-clip (2K1C) hypertensive rats activates the Nrf2 pathway, promotes the transcription of antioxidant genes, and improves the vascular redox imbalance and dysfunction in this model. Two doses of oral nitrite were studied: 15 mg/kg and the sub-antihypertensive dose of 1 mg/kg. Nitrite 15 mg/kg (but not 1 mg/kg) decreased blood pressure and increased circulating plasma nitrite and nitrate. Both doses blunted hypertension-induced increases in mesenteric artery reactive oxygen species concentrations assessed by DHE technique and restored the impaired mesenteric artery responses to acetylcholine. While 2K1C hypertension decreased nuclear Nrf2 accumulation, both doses of nitrite increased nuclear Nrf2 accumulation and mRNA expression of Nrf2-regulated genes including superoxide dismutase-1 (SOD1), catalase (CAT), glutathione peroxidase (GPX), thioredoxin-1(TRDX-1) and -2 (TRDX-2). To further confirm nitrite-mediated antioxidant effects, we measured vascular SOD and GPX activity and we found that nitrite at 1 or 15 mg/kg increased the activity of both enzymes (P < 0.05). These results suggest that activation of the Nrf2 pathway promotes antioxidant effects of nitrite, which may improve the vascular dysfunction in hypertension, even when nitrite is given at a sub-antihypertensive dose. These findings may have many clinical implications, particularly in the therapy of hypertension and other cardiovascular diseases.

Spleen tyrosine kinase-dependent Nrf2 activation regulates oxidative stress-induced cell death in WiL2-NS human B lymphoblasts

Autoimmune rheumatic lesions are often characterised by the immune cell recruitment including B lymphocytes and the presence of reactive oxygen species (ROS), which increase antioxidant gene transcription via nuclear factor (erythroid-derived 2)-like 2 (Nrf2). Spleen tyrosine kinase (Syk) has a major role in the signal transmission of all haematopoietic lineage cells including B/T cells, mast cells, and macrophages. In this study, we investigated whether B cell survival is regulated by Nrf2 via ROS-mediated Syk activation in WiL2-NS human B lymphoblast cells. When WiL2-NS cells were incubated with 1% foetal bovine serum (FBS), the survival rate and mitochondrial membrane potential (MMP) were reduced. In addition, 1% FBS increased caspase 3 activity, cytochrome C release, nuclear localisation of Nrf2, and ROS production. N-acetylcysteine attenuated ROS production and nuclear translocation of Nrf2. It also inhibited cell death, caspase 3 activation, MMP collapse, and cytochrome C release. Results from the 1% FBS treatment were consistent with those of H₂O₂ treatment. Syk phosphorylation at tyrosine 525/526 was increased by incubation with 1% FBS or treatment with 100 µM H₂O₂. Nuclear translocation of Nrf2 by H₂O₂ was inhibited by treatment with BAY61-3606, a Syk inhibitor. BAY61-3606 also promoted MMP collapse, cytochrome C release, caspase 3 activation, and cell death. Taken together, these results implicate that Syk controls oxidative stress-induced human B cell death via nuclear translocation of Nrf2 and MMP collapse. These results suggest that Syk is a novel regulator of Nrf2 activation.

Differentiating Antiproliferative and Chemopreventive Modes of Activity for Electron-Deficient Aryl Isothiocyanates against Human MCF-7 Cells

The consumption of Brassica vegetables provides beneficial effects through organic isothiocyanates (ITCs), products of the enzymatic hydrolysis of glucosinolate secondary metabolites. The ITC l-sulforaphane (l-SFN) is the principle agent in broccoli that demonstrates several modes of anticancer action. While the anticancer properties of ITCs like l-SFN have been extensively studied and l-SFN has been the subject of multiple human clinical trials, the scope of this work has largely been limited to those derivatives found in nature. Previous studies have demonstrated that structural changes in an ITC can lead to marked differences in a compound's potency to 1) inhibit the growth of cancer cells, and 2) alter cellular transcriptional profiles. This study describes the preparation of a library of non-natural aryl ITCs and the development of a bifurcated screening approach to evaluate the dose- and time-dependence on antiproliferative and chemopreventive properties against human MCF-7 breast cancer cells. Antiproliferative effects were evaluated using a commercial MTS cell viability assay. Chemopreventive properties were evaluated using an antioxidant response element (ARE)-promoted luciferase reporter assay. The results of this study have led to the identification of 1) several key structure-activity relationships and 2) lead ITCs for continued development.

Nrf2/ARE pathway attenuates oxidative and apoptotic response in human osteoarthritis chondrocytes by activating ERK1/2/ELK1-P70S6K-P90RSK signaling axis

Nrf2, a redox regulated transcription factor, has recently been shown to play a role in cartilage integrity but the mechanism remains largely unknown. Osteoarthritis (OA) is a multifactorial disease in which focal degradation of cartilage occurs. Here, we studied whether Nrf2 exerts chondroprotective effects by suppressing the oxidative stress and apoptosis in IL-1β stimulated human OA chondrocytes. Expression of Nrf2 and its target genes HO-1, NQO1 and SOD2 was significantly high in OA cartilage compared to normal cartilage and was also higher in damaged area compared to smooth area of OA cartilage of the same patient. Human chondrocytes treated with IL-1β resulted in robust Nrf2/ARE reporter activity, which was inhibited by pretreatment with antioxidants indicating that Nrf2 activity was due to IL-1β-induced ROS generation. Ectopic expression of Nrf2 significantly suppressed the IL-1β-induced generation of ROS while Nrf2 knockdown significantly increased the basal as well as IL-1β-induced ROS levels in OA chondrocytes. Further, Nrf2 activation significantly inhibited the IL-1β-induced activation of extrinsic and intrinsic apoptotic pathways as determined by inhibition of DNA fragmentation, activation of Caspase-3,-8,-9, cleavage of PARP, release of cytochrome-c, suppression of mitochondrial dysfunction and mitochondrial ROS production in OA chondrocytes. Nrf2 over-expression in OA chondrocytes increased the expression of anti-apoptotic proteins while pro-apoptotic proteins were suppressed. Importantly, Nrf2 over-expression activated ERK1/2 and its downstream targets-ELK1, P70S6K and P90RSK and suppressed the IL-1β-induced apoptosis whereas inhibition of ERK1/2 activation abrogated the protective effects of Nrf2 in OA chondrocytes. Taken together, our data demonstrate that Nrf2 is a stress response protein in OA chondrocytes with anti-oxidative and anti-apoptotic function and acts via activation of ERK1/2/ELK1-P70S6K-P90RSK signaling axis. These activities of Nrf2 make it a promising candidate for the development of novel therapies for the management of OA.

Effects of mild ozonisation on gene expression and nuclear domains organization in vitro

In the last two decades, the use of ozone (O₃) as a complementary medical approach has progressively been increasing; however, its application is still limited due to the numerous doubts about its possible toxicity, despite the low concentrations used in therapy. For an appropriate and safe clinical application of a potentially toxic agent such as O₃, it is crucial to elucidate the cellular response to its administration. Molecular analyses and transmission electron microscopy were here combined to investigate in vitro the effects of O₃ administration on transcriptional activity and nuclear domains organization of cultured SH-SY5Y neuronal cells; low O₃ concentrations were used as those currently administered in clinical practice. Mild ozonisation did not affect cell proliferation or death, while molecular analyses showed an O₃-induced modulation of some genes involved in the cell response to stress (HMOX1, ERCC4, CDKN1A) and in the transcription machinery (CTDSP1). Ultrastructural cytochemistry after experiments of bromouridine incorporation consistently demonstrated an increased transcriptional rate at both the nucleoplasmic (mRNA) and the nucleolar (rRNA) level. No ultrastructural alteration of nuclear domains was observed. Our molecular, ultrastructural and cytochemical data demonstrate that a mild toxic stimulus such as mild ozonisation stimulate cell protective pathways and nuclear transcription, without altering cell viability. This could possibly account for the positive effects observed in ozone-treated patients.

Antioxidant tert-butylhydroquinone ameliorates arsenic-induced intracellular damages and apoptosis through induction of Nrf2-dependent antioxidant responses as well as stabilization of anti-apoptotic factor Bcl-2 in human keratinocytes

Human skin is a known target site of inorganic arsenic with effects ranging from hyperkeratosis to dermal malignancies. Tert-butylhydroquinone (tBHQ), approved food-grade phenolic antioxidant, is demonstrated to induce remarkable antioxidant activity in a variety of cells and tissues. The present study aimed at the protective effects of tBHQ on arsenic-induced cytotoxicity and apoptosis in human keratinocytes. Our results demonstrated that tBHQ antagonized arsenic-induced decrease of cell viability, generation of reactive oxygen species (ROS) and lipid peroxidation, as well as reduction of antioxidative enzymes superoxide dismutase (SOD) and catalase (CAT) activities. We also found that tBHQ relieved the G2/M phase arrest by arsenic exposure, which was associated with altering the expression of cell cycle regulators cyclin D1 and CDK4. tBHQ treatment further reduced the numbers of arsenic-induced mitochondrial-mediated apoptotic cells, which occurred concomitantly with the effective recovery of mitochondrial membrane potential (ΔΨm) depolarization, the release of cytochrome c releasing from the mitochondrial as well as the survival signal related factor caspase 3 activation. Our experiments then confirmed that tBHQ activated nuclear factor E2-related factor 2 (NRF2) pathway by increasing NRF2 protein in both nucleus and cytoplasm and upregulating NRF2 downstream targets

NAD(P)H

quinine oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1). More interestingly, arsenic-induced decrease of anti-apoptotic factor B-cell lymphoma-2 (Bcl-2) and increase of pro-apoptotic factor Bcl-2-associated X protein (Bax) could all be reversed by tBHQ pretreatment. These results suggested together that tBHQ could ameliorate arsenic-induced cytotoxicity and apoptosis, which might be linked with the induction of Nrf2-dependent antioxidant responses as well as stabilization of anti-apoptotic factor Bcl-2 in human keratinocytes.

Laquinimod reduces neuroaxonal injury through inhibiting microglial activation

OBJECTIVE

Laquinimod is an emerging oral medication for multiple sclerosis (MS) that reduces brain atrophy and progression of disability in two Phase III clinical trials. The mechanism of these effects is unclear. Persistent activation of microglia occurs in MS and contributes to injury. Thus, we investigated whether laquinimod alters properties of microglia in culture and in experimental autoimmune encephalomyelitis (EAE), and whether this reduces neurodegeneration.

METHODS

Microglia were cultured from human brains. EAE was induced in mice.

RESULTS

The activation of human microglia increased levels of several pro- and anti-inflammatory cytokines and these elevations were attenuated by pretreatment with laquinimod. Laquinimod prevented the decline in activated microglia of miR124a, a microRNA implicated in maintaining microglia quiescence, and reduced the activity of several signaling pathways (Jun-N-terminal kinase, ribosomal S6 kinase, and AKT/protein kinase B) in activated microglia. In EAE, axonal injury correlated with accumulation of microglia/macrophages in the spinal cord. EAE mice treated with laquinimod before onset of clinical signs subsequently had reduced microglia/macrophage density and axonal injury. Remarkably, when laquinimod treatment was initiated well into the disease course, the progressive demyelination, and axonal loss was halted. Besides inflammatory molecules associated with microglia, the level of inducible nitric oxide (NO) synthase capable of producing free radical toxicity was attenuated by laquinimod in EAE mice. Finally, in coculture where microglia activation caused neuronal death, laquinimod decreased NO levels, and neurotoxicity.

INTERPRETATION

Laquinimod is a novel inhibitor of microglial activation that lowers microglia-induced neuronal death in culture and axonal injury/loss in EAE.

Nitric oxide sets off an antioxidant response in adrenal cells: involvement of sGC and Nrf2 in HO-1 induction

Induction of microsomal heme oxygenase 1 (HO-1) activity is considered a cytoprotective mechanism in different cell types. In adrenal cells, HO-1 induction by ACTH exerts a modulatory effect on steroid production as well. As nitric oxide (NO) has been also regarded as an autocrine/paracrine modulator of adrenal steroidogenesis we sought to study the effects of NO on the induction of HO-1 and the mechanism involved. We hereby analyzed the time and dose-dependent effect of a NO-donor (DETA/NO) on HO-1 induction in a murine adrenocortical cell line. We showed that this effect is mainly exerted at a transcriptional level as it is inhibited by actinomycin D and HO-1 mRNA degradation rates were not affected by DETA/NO treatment. HO-1 induction by NO does not appear to involve the generation of oxidative stress as it was not affected by antioxidant treatment. We also demonstrated that NO-treatment results in the nuclear translocation of the nuclear factor-erythroid 2-related factor (Nrf2), an effect that is attenuated by transfecting the cells with a dominant negative isoform of Nrf2. We finally show that the effects of the NO-donor are reproduced by a permeable analog of cGMP and that a soluble guanylate cyclase specific inhibitor blocked both the induction of HO-1 by NO and the nuclear translocation of Nrf2.

Protein kinase C δ (PKCδ) splice variants modulate apoptosis pathway in 3T3L1 cells during adipogenesis: identification of PKCδII inhibitor

Increased food intake and lack of physical activity results in excess energy stored in adipocytes, and this imbalance contributes to obesity. New adipocytes are required for storage of energy in the white adipose tissue. This process of adipogenesis is widely studied in differentiating 3T3L1 preadipocytes in vitro. We have identified a key signaling kinase, protein kinase C delta (PKCδ), whose alternative splice variant expression is modulated during adipogenesis. We demonstrate that PKCδII splice variant promotes survival in differentiating 3T3L1 cells through the Bcl2 pathway. Here we demonstrate that resveratrol, a naturally occurring polyphenol, increases apoptosis and inhibits adipogenesis along with disruption of PKCδ alternative splicing during 3T3L1 differentiation. Importantly, we have identified a PKCδII splice variant inhibitor. This inhibitor may be a valuable tool with therapeutic implications in obesity.

Nrf2 as a converging node for cellular signaling pathways of gasotransmitters

Gasotransmitters is a family of endogenous molecules of gases or gaseous signaling molecules. To date, nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H(2)S) have been found to be important gasotransmitters in humans. Three gasotransmitters at high concentrations have been confirmed to be detrimental to human health, while evidence shows they at low concentrations may confer protective effects. There are important interactions among three gasotransmitters. Recent evidence reveals that these gasotransmitters may converge at Nrf2, an important transcription factor able to induce the expressions of some critical antioxidant enzymes, which may attribute to the protective effects of these gasotransmitters. Thus, we hypothesize that Nrf2 serves as a converging node for cellular signaling pathways of gasotransmitters, which adds evidence on the interactions among them.

Insulin promotes neuronal survival via the alternatively spliced protein kinase CδII isoform

Insulin signaling pathways in the brain regulate food uptake and memory and learning. Insulin and protein kinase C (PKC) pathways are integrated and function closely together. PKC activation in the brain is essential for learning and neuronal repair. Intranasal delivery of insulin to the central nervous system (CNS) has been shown to improve memory, reduce cerebral atrophy, and reverse neurodegeneration. However, the neuronal molecular mechanisms of these effects have not been studied in depth. PKCδ plays a central role in cell survival. Its splice variants, PKCδI and PKCδII, are switches that determine cell survival and fate. PKCδI promotes apoptosis, whereas PKCδII promotes survival. Here, we demonstrate that insulin promotes alternative splicing of PKCδII isoform in HT22 cells. The expression of PKCδI splice variant remains unchanged. Insulin increases PKCδII alternative splicing via the PI3K pathway. We further demonstrate that Akt kinase mediates phosphorylation of the splicing factor SC35 to promote PKCδII alternative splicing. Using overexpression and knockdown assays, we demonstrate that insulin increases expression of Bcl2 and bcl-xL via PKCδII. We demonstrate increased cell proliferation and increased BrdU incorporation in insulin-treated cells as well as in HT22 cells overexpressing PKCδII. Finally, we demonstrate in vivo that intranasal insulin promotes cognitive function in mice with concomitant increases in PKCδII expression in the hippocampus. This is the first report of insulin, generally considered a growth or metabolic hormone, regulating the alternative isoform expression of a key signaling kinase in neuronal cells such that it results in increased neuronal survival.

Analysis of Nrf2-mediated transcriptional induction of antioxidant response in early embryos

Nrf2 is a transcription factor that regulates the induction of an expansive set of antioxidant proteins that act in synergy to remove reactive oxygen species (ROS). We have recently discovered that Nrf2 signaling is involved in the induction of antioxidant response in ethanol-exposed embryos. We have also demonstrated that chemically induced transcriptional activation of Nrf2 and subsequent induction of a broad spectrum of antioxidant proteins can act as an endogenous protective system against ethanol-induced oxidative stress and apoptosis in early mouse embryos. This chapter describes the methods used to analyze Nrf2-mediated transcriptional induction of antioxidant response in mouse embryos. Data which have been generated by using these methods have also been included to provide examples of their usefulness in evaluating Nrf2-mediated antioxidant response in early embryos.

Nitric oxide activates Nrf2 through S-nitrosylation of Keap1 in PC12 cells

Nitric oxide (NO) exerts bifunctional effects on cell survival. While a high concentration of NO is cytotoxic, a relatively low concentration of NO promotes cytoprotection and cell survival. However, the molecular mechanism underlying the cytoprotective effect of NO remains poorly understood. One of the transcription factors that confer cellular protection against oxidative stress is NF-E2-related factor 2 (Nrf2), which is sequestered in the cytoplasm by forming an inactive complex with Klech-like ECH-associated protein 1 (Keap1). Previous studies suggested that various stimuli could induce the dissociation of Nrf2 from Keap1 in cytosol and/or promote its nuclear translocation by activating several upstream kinases. NO-mediated thiol modification in Keap1 has also been proposed as a possible mechanism of Nrf2 activation. Since NO can modify the function or activity of target proteins through S-nitrosylation of cysteine, we attempted to investigate whether the cytoprotective effect of NO is mediated through Nrf2 activation by directly modifying cysteine residues of Keap1. Our present study reveals that treatment of rat pheochromocytoma (PC12) cells with an NO donor S-nitroso-N-acetylpenicillamine (SNAP) induced nuclear translocation and DNA binding of Nrf2. Under the same experimental conditions, there was NO-mediated S-nitrosylation of Keap1 observed, which coincided with the Nrf2 activation. Moreover, SNAP treatment caused phosphorylation of Nrf2, and pharmacological inhibition of protein kinase C (PKC) abolished the phosphorylation and nuclear localization of Nrf2. In conclusion, NO can activate Nrf2 by S-nitrosylation of Keap1 and alternatively by PKC-catalyzed phosphorylation of Nrf2 in PC12 cells.

Stabilization of Nrf2 protein by D3T provides protection against ethanol-induced apoptosis in PC12 cells

Previous studies have demonstrated that maternal ethanol exposure induces a moderate increase in Nrf2 protein expression in mouse embryos. Pretreatment with the Nrf2 inducer, 3H-1, 2-dithiole-3-thione (D3T), significantly increases the Nrf2 protein levels and prevents apoptosis in ethanol-exposed embryos. The present study, using PC12 cells, was designed to determine whether increased Nrf2 stability is a mechanism by which D3T enhances Nrf2 activation and subsequent antioxidant protection. Ethanol and D3T treatment resulted in a significant accumulation of Nrf2 protein in PC 12 cells. CHX chase analysis has shown that ethanol treatment delayed the degradation of Nrf2 protein in PC12 cells. A significantly greater decrease in Nrf2 protein degradation was observed in the cells treated with D3T alone or with both ethanol and D3T. In addition, D3T treatment significantly reduced ethanol-induced apoptosis. These results demonstrate that the stabilization of Nrf2 protein by D3T confers protection against ethanol-induced apoptosis.

Induction of the Nrf2-driven antioxidant response by tert-butylhydroquinone prevents ethanol-induced apoptosis in cranial neural crest cells

Previous studies have shown that ethanol exposure causes apoptosis in cranial neural crest cells (NCCs), an ethanol-sensitive cell population implicated in Fetal Alcohol Spectrum Disorders (FASD). Additionally, induction of endogenous antioxidants through activation of nuclear factor-erythroid 2-related factor 2 (Nrf2) has been shown to prevent oxidative stress and apoptosis in ethanol-exposed mouse embryos. The objective of this study was to test whether tert-butylhydroquinone (tBHQ), an Nrf2 inducer, can protect NCCs against ethanol-induced apoptosis. Ethanol exposure was shown to cause a moderate increase in the protein expression of Nrf2 and its downstream antioxidants in the NCCs. Treatment of NCCs with tBHQ alone significantly increased the protein expression of Nrf2 and its downstream antioxidants and also significantly increased the activities of the antioxidant enzymes. In NCCs exposed to ethanol, the tBHQ-mediated antioxidant response prevented oxidative stress and apoptosis. These results clearly demonstrate that the activation of Nrf2 signaling confers protection against ethanol-induced apoptosis in NCCs.

Distinct PTPmu-associated signaling molecules differentially regulate neurite outgrowth on E-, N-, and R-cadherin

Classical cadherins play distinct roles in axon growth and guidance in the visual system, however, the signaling pathways they activate remain unclear. Growth cones on each cadherin substrate have a unique morphology suggesting that distinct signals are activated by neurite outgrowth on E-, N-, and R-cadherin. We previously demonstrated that receptor protein tyrosine phosphatase-mu (PTPmu) is required for E- and N-cadherin-dependent neurite outgrowth. In this manuscript, we demonstrate that PTPmu regulates R-cadherin-mediated neurite outgrowth. Furthermore, we evaluated whether known PTPmu-associated signaling proteins, Rac1, Cdc42, IQGAP1 and PKCdelta, regulate neurite outgrowth mediated by these cadherins. While Rac1 activity is required for neurite outgrowth on all three cadherins Cdc42/IQGAP1 are required only for N- and R-cadherin-mediated neurite outgrowth. In addition, we determined that PKC activity is required for E- and R-cadherin-mediated, but not N-cadherin-mediated neurite outgrowth. In summary, distinct PTPmicro-associated signaling proteins are required to promote neurite outgrowth on cadherins.