PTPalpha activates Lyn and Fyn and suppresses Hck to negatively regulate FcepsilonRI-dependent mast cell activation and allergic responses

Mast cell activation via FcεRI involves activation of the Src family kinases (SFKs) Lyn, Fyn, and Hck that positively or, in the case of Lyn, negatively regulate cellular responses. Little is known of upstream activators of these SFKs in FcεRI-dependent signaling. We investigated the role of receptor protein tyrosine phosphatase (PTP)α, a well-known activator of SFKs in diverse signaling systems, FcεRI-mediated mast cell activation, and IgE-dependent allergic responses in mice. PTPα(-/-) bone marrow-derived mast cells hyperdegranulate and exhibit increased cytokine and cysteinyl leukotriene secretion, and PTPα(-/-) mice display enhanced IgE-dependent anaphylaxis. At or proximal to FcεRI, PTPα(-/-) cells have reduced IgE-dependent activation of Lyn and Fyn, as well as reduced FcεRI and SHIP phosphorylation. In contrast, Hck and Syk activation is enhanced. Syk hyperactivation correlated with its increased phosphorylation at positive regulatory sites and defective phosphorylation at a negative regulatory site. Distal to FcεRI, we observed increased activation of PI3K and MAPK pathways. These findings demonstrate that PTPα activates the FcεRI-coupled kinases Lyn and Fyn and suppresses Hck activity. Furthermore, the findings indicate that hyperactivation of PTPα(-/-) mast cells and enhanced IgE-dependent allergic responses of PTPα(-/-) mice are due to the ablated function of PTPα as a critical regulator of Lyn negative signaling.

Protein tyrosine phosphatase-alpha complexes with the IGF-I receptor and undergoes IGF-I-stimulated tyrosine phosphorylation that mediates cell migration

Protein tyrosine phosphatase-alpha (PTPalpha) is a widely expressed receptor-type phosphatase that functions in multiple signaling systems. The actions of PTPalpha can be regulated by its phosphorylation on serine and tyrosine residues, although little is known about the conditions that promote PTPalpha phosphorylation. In this study, we tested the ability of several extracellular factors to stimulate PTPalpha tyrosine phosphorylation. The growth factors IGF-I and acidic FGF induced the highest increase in PTPalpha phosphorylation at tyrosine 789, followed by PMA and lysophosphatidic acid, while EGF had little effect. Further investigation of IGF-I-induced PTPalpha tyrosine phosphorylation demonstrated that this occurs through a novel Src family kinase-independent mechanism that does not require focal adhesion kinase, phosphatidylinositol 3-kinase, or MEK. We also show that PTPalpha physically interacts with the IGF-I receptor. In contrast to IGF-I-induced PTPalpha phosphorylation, this association does not require IGF-I. The interaction of PTPalpha and the IGF-I receptor is independent of PTPalpha catalytic activity, and expression of exogenous PTPalpha does not promote IGF-I receptor tyrosine dephosphorylation, indicating that PTPalpha does not act as an IGF-I receptor phosphatase. However, PTPalpha mediates IGF-I signaling, because IGF-I-stimulated fibroblast migration was reduced by approximately 50% in cells lacking PTPalpha or in cells with mutant PTPalpha lacking the tyrosine 789 phosphorylation site. Our results suggest that PTPalpha tyrosine phosphorylation can occur in response to diverse stimuli and can be mediated by various tyrosine kinases. In the case of IGF-I, we propose that IGF-I-induced tyrosine 789 phosphorylation of PTPalpha, possibly catalyzed by the PTPalpha-associated IGF-I receptor tyrosine kinase, is required for efficient cell migration in response to this growth factor.

Protein-tyrosine phosphatase alpha regulates stem cell factor-dependent c-Kit activation and migration of mast cells

The role of protein-tyrosine phosphatase alpha (PTPalpha) in mast cell function was investigated in tissues and cells from PTPalpha-deficient mice. Bone marrow-derived mast cells (BMMCs) lacking PTPalpha exhibit defective stem cell factor (SCF)-dependent polarization and migration. Investigation of the molecular basis for this reveals that SCF/c-Kit-stimulated activation of the Fyn tyrosine kinase is impaired in PTPalpha(-/-) BMMCs, with a consequent inhibition of site-specific c-Kit phosphorylation at tyrosines 567/569 and 719. Although c-Kit-mediated activation of phosphatidylinositol 3-kinase and Akt is unaffected, profound defects occur in the activation of downstream signaling proteins, including mitogen-activated protein kinases and Rho GTPases. Phosphorylation and interaction of Fyn effectors Gab2 and Shp2, which are linked to Rac/JNK activation in mast cells, are impaired in PTPalpha(-/-) BMMCs. Thus, PTPalpha is required for SCF-induced c-Kit and Fyn activation, and in this way regulates a Fyn-based c-Kit signaling axis (Fyn/Gab2/Shp2/Vav/PAK/Rac/JNK) that mediates mast cell migration. These defective signaling events may underlie the altered tissue-resident mast cell populations found in PTPalpha(-/-) mice.

Involvement of Fyn kinase in Kit and integrin-mediated Rac activation, cytoskeletal reorganization, and chemotaxis of mast cells

Kit receptor and its ligand stem cell factor (SCF) are critical regulators of mast cell production, proliferation, degranulation, and chemotaxis. In this study, we investigated how Fyn kinase regulates chemotaxis of mast cells toward SCF. On beta1-integrin engagement, Fyn-deficient (fyn(-/-)) mast cells displayed a striking defect in cell spreading and lamellipodia formation compared to wild-type mast cells. The hematopoietic-specific Src family kinases (Lyn/Fgr/Hck) were not required for initial SCF-induced cell spreading. Reduced SCF-induced activation of Rac1 and Rac2 GTPases, p38 mitogen-activated protein kinase, and filamentous actin polymerization was observed in fyn(-/-) mast cells compared to wild-type mast cells. Retroviral-mediated expression of Fyn, constitutively active forms of Rac2 or phosphatidylinositol 3-kinase (PI3K) in fyn(-/-) mast cells rescued defects in SCF-induced cell polarization and chemotaxis of Fyn-deficient mast cells. Thus, we conclude that Fyn kinase plays a unique role upstream of PI3K and Rac GTPases to promote the reorganization of the cytoskeleton during mast cell spreading and chemotaxis.

Fyn kinase acts upstream of Shp2 and p38 mitogen-activated protein kinase to promote chemotaxis of mast cells towards stem cell factor

The c-Kit receptor protein-tyrosine kinase plays a critical role in the differentiation, growth and survival of mast cells. Binding of its ligand stem cell factor (SCF), induces c-Kit dimerization, autophosphorylation, and recruitment of signaling proteins. The juxtamembrane sequence of c-Kit contains recruitment sites for the Src family kinases Fyn and Lyn, as well as Shp1 and Shp2 protein-tyrosine phosphatases. To characterize the role of Fyn in c-Kit signaling, we generated bone marrow-derived mast cells (BMMCs) from wild-type and Fyn knock-out mice. In contrast with previous studies of Lyn-deficient BMMCs, SCF treatment of Fyn-deficient BMMCs revealed no overt defects in the overall pattern of tyrosine phosphorylation, phosphatidylinositol 3' kinase recruitment to c-Kit, or phosphorylation of Stat3 transcription factor. However, Fyn-deficient mast cells showed a significant reduction in phosphorylation of Shp2 phosphatase and p38 mitogen-activated protein kinase. Defects in Shp2 and p38 phosphorylation were restored in Fyn-deficient mast cells transduced with a Fyn-expressing retrovirus (Fyn-rescue). Fyn-deficient BMMCs displayed reduced chemotaxis towards SCF, and this defect was corrected in Fyn-rescue cells. This study provides evidence that recruitment of both Shp2 and Fyn to juxtamembrane sites in c-Kit results in Shp2 phosphorylation, downstream signaling to p38 mitogen-activated protein kinase, and enhanced chemotaxis of mast cells.

Fer and Fps/Fes participate in a Lyn-dependent pathway from FcepsilonRI to platelet-endothelial cell adhesion molecule 1 to limit mast cell activation

Mast cells express the high affinity IgE receptor FcepsilonRI, which upon aggregation by multivalent antigens elicits signals that cause rapid changes within the mast cell and in the surrounding tissue. We previously showed that FcepsilonRI aggregation caused a rapid increase in phosphorylation of both Fer and Fps/Fes kinases in bone marrow-derived mast cells. In this study, we report that FcepsilonRI aggregation leads to increased Fer/Fps kinase activities and that Fer phosphorylation downstream of FcepsilonRI is independent of Syk, Fyn, and Gab2 but requires Lyn. Activated Fer/Fps readily phosphorylate the C terminus of platelet-endothelial cell adhesion molecule 1 (Pecam-1) on immunoreceptor tyrosine-based inhibitory motifs (ITIMs) and a non-ITIM residue (Tyr(700)) in vitro and in transfected cells. Mast cells devoid of Fer/Fps kinase activities display a reduction in FcepsilonRI aggregation-induced tyrosine phosphorylation of Pecam-1, with no defects in recruitment of Shp1/Shp2 phosphatases observed. Lyn-deficient mast cells display a dramatic reduction in Pecam-1 phosphorylation at Tyr(685) and a complete loss of Shp2 recruitment, suggesting a role as an initiator kinase for Pecam-1. Consistent with previous studies of Pecam-1-deficient mast cells, we observe an exaggerated degranulation response in mast cells lacking Fer/Fps kinases at low antigen dosages. Thus, Lyn and Fer/Fps kinases cooperate to phosphorylate Pecam-1 and activate Shp1/Shp2 phosphatases that function in part to limit mast cell activation.

Effects of chlorpyrifos on reproductive performances of guppy (Poecilia reticulata)

Guppy (Poecilia reticulata) was selected to investigate the effects of chlorpyrifos on reproductive performances. Male and female guppy with proven fertility were selected from our own colony and the groups of fish (n=72/group) were exposed to pre-determined chlorpyrifos concentrations (0.002 microg/l, 2 microg/l) based on the 96-h LC50 for guppy. Mating behavior of males was recorded on the 2nd day of exposure. Offspring were counted and survival recorded on the 14th day. Gonopodial thrusts (8/15 min) in 0.002 microg/l and (4/15 min) in 2 microg/l were significantly different from the control group (11/15 min). Similarly, live birth reduced significantly to 8/female in 2 microg/l compared to 27/female in the control group. Survival of offspring after 14 days was reduced to 47% in the 2 microg/l group compared to 94% of survival in the control. Our findings demonstrate that low soluble concentrations of chlorpyrifos affect mating behavior, number of offspring and offspring survival of guppy.

Low concentrations of lorsban in water result in far reaching behavioral and histological effects in early life stages in guppy

Chlorpyrifos (O,O-diethyl-O (3,5,6-trichlor-2-pyridyl) phosphorothioate) is a broad-spectrum organophosphate compound. A number of previous work of different countries, institutes, and individuals have confirmed that chlorpyrifos is very highly toxic to freshwater fish and to aquatic invertebrates. The acute toxicity and subacute toxic effects on different concentrations of chlorpyrifos in guppy were investigated in the current study. Twelve guppy juveniles (x 6) were exposed to a range of chlorpyrifos concentrations and 96 h. There was one control group. Subacute exposures were predetermined based on 96-h LC50 values. Fish were exposed to three concentrations 0.5, 1, and 2.0 microg/L chlorpyrifos (Lorsban) for 14 consecutive days. Numbers of live and dead juveniles, signs of paralysis, and deformations were monitored every 24 h. The acute toxicity results revealed that even low concentrations of Lorsban were toxic to guppy juveniles, and with toxicity being evident from 7.17 microg/L LC50 for 96 h at 26 +/- 1 degree C. Low concentrations of Lorsban were also responsible for changes in swimming behavior. Malformations were common to all treated groups but increased in the highest exposure group. Gill histology revealed several pathological changes, including loss and shortening of secondary lamellae. Collectively, the present study reveals that low concentrations of chlorpyrifos can be highly detrimental to guppy in the early life stages, with clear evidence of behavioral, morphologic, and histologic effects. The present findings warrant further studies.

Sperm maturation in vitro: co-culture of spermatozoa and epididymal epithelium

Sperm maturation involves an intimate interaction between spermatozoa and the epididymal epithelium. Aspects of this relationship can be examined by co-incubating epididymal spermatozoa with epididymal epithelium in vitro. Plaques of epididymal epithelium from a variety of species (for example rodents, dogs, humans) can be maintained in culture medium supplemented with growth factors and androgens. When co-incubated with these epithelial cultures, immature epididymal spermatozoa undergo maturation changes that lead to the acquisition of progressive motility, zona binding and, in some instances, fertilizing capacity in vitro. The use of such co-culture techniques for the understanding of sperm maturation in vitro and in vivo is reviewed with reference to recent experiments.