Coligation of the Fc receptor on B cells, Fc gamma RIIB1, with the B cell antigen receptor (BCR) leads to abortive BCR signaling. Here it was shown that the Fc gamma RIIB1 recruits the phosphotyrosine phosphatase PTP1C after BCR coligation. This association is mediated by the binding of a 13-amino acid tyrosine-phosphorylated sequence to the carboxyl-terminal Src homology 2 domain of PTP1C and activates PTP1C. Inhibitory signaling and PTP1C recruitment are dependent on the presence of the tyrosine within the 13-amino acid sequence. Inhibitory signaling mediated by Fc gamma RIIB1 is deficient in motheaten mice which do not express functional PTP1C. Thus, PTP1C is an effector of BCR-Fc gamma RIIB1 negative signal cooperativity.

Recent evidence shows the involvement of reactive oxygen species (ROS) in the mitogenic cascade initiated by the tyrosine kinase receptors of several growth factor peptides. We have asked whether also the vascular endothelial growth factor (VEGF) utilizes ROS as messenger intermediates downstream of the VEGF receptor-2 (VEGFR-2)/KDR receptor given that the proliferation of endothelial cells during neoangiogenesis is physiologically regulated by oxygen and likely by its derivative species. In porcine aortic endothelial cells stably expressing human KDR, receptor activation by VEGF is followed by a rapid increase in the intracellular generation of hydrogen peroxide as revealed by the peroxidesensitive probe dichlorofluorescein diacetate. Genetic and pharmacological studies suggest that such oxidant burst requires as upstream events the activation of phosphatidylinositol 3-kinase and the small GTPase Rac-1 and is likely initiated by lipoxygenases. Interestingly, ROS generation in response to VEGF is not blocked but rather potentiated by endothelial nitricoxide synthase inhibitors diphenyleneiodonium and N G methyl-L-arginine, ruling out the possibility of nitric oxide being the oxidant species here detected in VEGFstimulated cells. Inhibition of KDR-dependent generation of ROS attenuates early signaling events including receptor autophosphorylation and binding to a phospholipase C-␥-glutathione S-transferase fusion protein. Moreover, catalase, the lipoxygenase inhibitor nordihydroguaiaretic acid, the synthetic ROS scavenger EUK-134, and phosphatidylinositol 3-kinase inhibitor wortmannin all reduce ERK phosphorylation in response to VEGF, and antioxidants prevent VEGF-dependent mitogenesis. Finally, cell culture and stimulation in a nearly anoxic environment mimic the effect of ROS scavenger on receptor and ERK phosphorylation, reinforcing the idea that ROS are necessary components of the mitogenic signaling cascade initiated by KDR. These data identify ROS as a new class of intracellular angiogenic mediators and may represent a potential premise for new antioxidant-based antiangiogenic therapies.

Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.

According to a "canonical" view, reactive oxygen species (ROS) positively contribute, in different ways, to carcinogenesis and to malignant progression of tumor cells: they drive genomic damage and genetic instability, transduce, as signaling intermediates, mitogenic and survival inputs by growth factor receptors and adhesion molecules, promote cell motility and shape the tumor microenvironment by inducing inflammation/repair and angiogenesis. Chemopreventive and tumor-inhibitory effects of endogenous, diet-derived or supplemented antioxidants largely support this notion. However, emerging lines of evidence indicates that tumor cells also need to defend themselves from oxidative damage in order to survive and successfully spread at distance. This "heresy" has recently received important impulse from studies on the role of antioxidant capacity in cancer stem cells self-renewal and resistance to therapy; additionally, the transforming activity of some oncogenes has been unexpectedly linked to their capacity to maintain elevated intracellular levels of reduced glutathione (GSH), the principal redox buffer. These studies underline the importance of cellular antioxidant capacity in metastasis, as the result of a complex cell program involving enhanced motility and a profound change in energy metabolism. The glycolytic switch (Warburg effect) observed in malignant tissues is triggered by mitochondrial oxidative damage and/or activation of redox-sensitive transcription factors, and results in an increase of cell resistance to oxidants. On the other hand, cytoskeleton rearrangement underlying cell motile and tumor-aggressive behavior use ROS as intermediates and are therefore facilitated by oxidative stress. Along this line of speculation, we suggest that metastasis represents an integrated strategy for cancer cells to avoid oxidative damage and escape excess ROS in the primary tumor site, explaning why redox signaling pathways are often up-regulated in malignancy and metastasis.

Signal transduction by reactive oxygen species (ROS; “redox signaling”) has recently come into focus in cellular biology studies. The signaling properties of ROS are largely due to the reversible oxidation of redox-sensitive target proteins, and especially of protein tyrosine phosphatases, whose activity is dependent on the redox state of a low pKa active site cysteine. A variety of mitogenic signals, including those released by receptor tyrosine kinase (RTKs) ligands and oncogenic H-Ras, involve as a critical downstream event the intracellular generation of ROS. Signaling by integrins is also essential for the growth of most cell types and is constantly integrated with growth factor signaling. We provide here evidence that intracellular ROS are generated after integrin engagement and that these oxidant intermediates are necessary for integrin signaling during fibroblast adhesion and spreading. Moreover, we propose a synergistic action of integrins and RTKs for redox signaling. Integrin-induced ROS are required to oxidize/inhibit the low molecular weight phosphotyrosine phosphatase, thereby preventing the enzyme from dephosphorylating and inactivating FAK. Accordingly, FAK phosphorylation and other downstream events, including MAPK phosphorylation, Src phosphorylation, focal adhesion formation, and cell spreading, are all significantly attenuated by inhibition of redox signaling. Hence, we have outlined a redox circuitry whereby, upon cell adhesion, oxidative inhibition of a protein tyrosine phosphatase promotes the phosphorylation/activation and the downstream signaling of FAK and, as a final event, cell adhesion and spreading onto fibronectin.

No abstract

SummaryThe association of PTPIC deficiency with the multiplicity of lymphoid cell abnormalities manifested by motheaten (me) and viable motheaten (me 9 mice suggests a pivotal role for this tyrosine phosphatase in the regulation of lymphocyte differentiation and function. To delineate the relevance of PTP1C to T cell physiology, we have examined me and me ~ T cells with regards to their capacity to transduce activating signals through the T cell antigen receptor (TCR). Although thymocyte maturation appeared normal in the mutant mice, both thymocytes and peripheral T cells from these animals exhibited proliferative responses to TCR stimulation that were markedly increased relative to those elicited in normal cells. Compared to normal thymocytes, PTP1C-deficient thymocytes also showed increased constitutive tyrosine phosphorylation of the TCR complex and enhanced and prolonged TCR-induced tyrosine phosphorylation of the TCR-~ and CD3-e, as well as a number of cytosolic proteins, most notably a 38-kD phosphoprotein found to associate with the Grb2 adaptor SH2 domain in activated thymocytes. These latter phosphoproteins also associated with the Vav guanine nucleotide exchange factor upon TCR ligation, and were dephosphorylated by recombinant PTP1C in vitro. In conjunction with the finding of PTP1C-TCR association in unstimulated normal thymocytes, these results reveal the capacity of PTP1C to interact with and likely dephosphorylate resting and activated TCR complex components, as well as more distal signaling effectors that are normally recruited to the Vav and Grb2 SH2 domains after TCR stimulation. These data therefore strongly implicate PTP1C in the downregnlation of TCR signaling capacity and, taken together with the aberrant prolongation of TCR-induced, mitogen-associated kinase (MAPK) activation observed in PTP1C-deficient thymocytes, these findings suggest that the inhibitory influence of PTP1C on TCR signal relay is realized through its effects on both the TCR complex and downstream signaling elements that couple the activated antigen receptor to the Ras/MAPK response pathway.T he intracellular events linking TCR engagement to a physiologic response involve a multiplicity of molecular interactions, the specificity and sequelae of which depend on the cell's developmental stage and exposure to costimulatory signals. Although the precise amalgam of molecular events that translate TCR engagement to specific types of cell behavior remain unclear, a wealth of information has accrued with respect to the general molecular strategies used to couple the stimulated TCR to the nucleus. As for other growth receptors, the downstream propagation of activation signals from the TCR is known to be critically dependent on tyrosine phosphorylation, both TCR components and numerous cytosolic signaling effectors becoming rapidly phosphorylated after TCR stimulation (1). In contrast to many growth factors, however, the signaling elements within the TCR complex lack intrinsic enzymatic activity, and their tyrosine phosphorylation...

Calorie restriction delays brain senescence and prevents neurodegeneration, but critical regulators of these beneficial responses other than the NAD + -dependent histone deacetylase Sirtuin-1 (Sirt-1) are unknown. We report that effects of calorie restriction on neuronal plasticity, memory and social behavior are abolished in mice lacking cAMP responsive-element binding (CREB)-1 in the forebrain. Moreover, CREB deficiency drastically reduces the expression of Sirt-1 and the induction of genes relevant to neuronal metabolism and survival in the cortex and hippocampus of dietaryrestricted animals. Biochemical studies reveal a complex interplay between CREB and Sirt-1: CREB directly regulates the transcription of the sirtuin in neuronal cells by binding to Sirt-1 chromatin; Sirt-1, in turn, is recruited by CREB to DNA and promotes CREB-dependent expression of target gene peroxisome proliferator-activated receptor-γ coactivator-1α and neuronal NO Synthase. Accordingly, expression of these CREB targets is markedly reduced in the brain of Sirt KO mice that are, like CREB-deficient mice, poorly responsive to calorie restriction. Thus, the above circuitry, modulated by nutrient availability, links energy metabolism with neurotrophin signaling, participates in brain adaptation to nutrient restriction, and is potentially relevant to accelerated brain aging by overnutrition and diabetes. P rogressive decline of cognitive functions and an increased risk of developing neurodegenerative disorders, such as Alzheimer's and Parkinson diseases, are severe and debilitating consequences on brain senescence. A moderate reduction of food intake (calorie restriction, CR) delays aging and improves resistance to disease in a fashion that is evolutionarily conserved from yeast to primates and humans (1), and these beneficial effects include in mammals the prevention of age-associated cognitive impairment and neurodegeneration (2). Conversely, obesity and type 2 diabetes increase the risk of developing Alzheimer's disease (AD) (3), and reduced insulin signaling in the brain may contribute to neurodegeneration (4). Elucidation of the molecular mechanisms whereby nutritional/metabolic cues impinge on neuronal survival and health may be an avenue to new pharmacological strategies that exploit nutrient-sensitive protective circuitries to prevent the catastrophic impact of aging and dysmetabolism on the brain.Most of the current molecular knowledge on the beneficial effects of CR involves Sirtuins, the mammalian homologs of the yeast Silent Information Regulator (Sir2.1) NAD + -dependent histone deacetylase (5, 6). This class of enzymes plays an evolutionarily conserved role in promoting genomic stability, cell survival, and stress resistance in response to limited nutrient availability. Such action results in extended longevity in lower organisms, and prevents in mammals a variety of age-associated pathologic changes from cardiovascular disease and diabetes, to cancer, to neurologic disorders. In particular, neuronal Sirt-1 has been shown to ...