Insulin selectively activates STAT5b, but not STAT5a, via a JAK2-independent signalling pathway in Kym-1 rhabdomyosarcoma cells

AbstractThe STAT multigene family of transcriptional regulators conveys signals from several cytokines and growth factors upon phosphorylation by janus kinases (JAK). Activation of STAT5 is typically mediated by JAK2, but more recent data indicate a direct activation by the insulin receptor kinase. STAT5 exists in two closely homologous isoforms, STAT5a and b. We here describe the selective tyrosine phosphorylation of STAT5b in Kym-1 cells in response to insulin. Blocking insulin signalling by HNMPA-(AM)3, an insulin receptor kinase inhibitor, resulted in the loss of insulin-induced STAT5b tyrosine phosphorylation, whereas the inhibition of JAK2 by the JAK selective inhibitor tyrphostin AG490 had no effect. By contrast, in the same cells, IFNγ-induced STAT5b activation was JAK2-dependent, indicating that this signal pathway is functional in Kym-1 cells. We conclude from this rhabdomyosarcoma model that STAT5b, but not STAT5a is a direct target of the insulin receptor kinase

A TNF Receptor 2 Selective Agonist Rescues Human Neurons from Oxidative Stress-Induced Cell Death

Tumor necrosis factor (TNF) plays a dual role in neurodegenerative diseases. Whereas TNF receptor (TNFR) 1 is predominantly associated with neurodegeneration, TNFR2 is involved in tissue regeneration and neuroprotection. Accordingly, the availability of TNFR2-selective agonists could allow the development of new therapeutic treatments of neurodegenerative diseases. We constructed a soluble, human TNFR2 agonist (TNC-scTNFR2) by genetic fusion of the trimerization domain of tenascin C to a TNFR2-selective single-chain TNF molecule, which is comprised of three TNF domains connected by short peptide linkers. TNC-scTNFR2 specifically activated TNFR2 and possessed membrane-TNF mimetic activity, resulting in TNFR2 signaling complex formation and activation of downstream signaling pathways. Protection from neurodegeneration was assessed using the human dopaminergic neuronal cell line LUHMES. First we show that TNC-scTNFR2 interfered with cell death pathways subsequent to H2O2 exposure. Protection from cell death was dependent on TNFR2 activation of the PI3K-PKB/Akt pathway, evident from restoration of H2O2 sensitivity in the presence of PI3K inhibitor LY294002. Second, in an in vitro model of Parkinson disease, TNC-scTNFR2 rescues neurons after induction of cell death by 6-OHDA. Since TNFR2 is not only promoting anti-apoptotic responses but also plays an important role in tissue regeneration, activation of TNFR2 signaling by TNC-scTNFR2 appears a promising strategy to ameliorate neurodegenerative processes

Regulation of secretory transport by protein kinase D–mediated phosphorylation of the ceramide transfer protein

Protein kinase D (PKD) has been identified as a crucial regulator of secretory transport at the trans-Golgi network (TGN). Recruitment and activation of PKD at the TGN is mediated by the lipid diacylglycerol, a pool of which is generated by sphingomyelin synthase from ceramide and phosphatidylcholine. The nonvesicular transfer of ceramide from the endoplasmic reticulum to the Golgi complex is mediated by the lipid transfer protein CERT (ceramide transport). In this study, we identify CERT as a novel in vivo PKD substrate. Phosphorylation on serine 132 by PKD decreases the affinity of CERT toward its lipid target phosphatidylinositol 4-phosphate at Golgi membranes and reduces ceramide transfer activity, identifying PKD as a regulator of lipid homeostasis. We also show that CERT, in turn, is critical for PKD activation and PKD-dependent protein cargo transport to the plasma membrane. Thus, the interdependence of PKD and CERT is key to the maintenance of Golgi membrane integrity and secretory transport

Structural requirements for localization and activation of protein kinase C μ (PKCμ) at the Golgi compartment

We here describe the structural requirements for Golgi localization and a sequential, localization-dependent activation process of protein kinase C (PKC)μ involving auto- and transphosphorylation. The structural basis for Golgi compartment localization was analyzed by confocal microscopy of HeLa cells expressing various PKCμ–green fluorescent protein fusion proteins costained with the Golgi compartment–specific markers p24 and p230. Deletions of either the NH2-terminal hydrophobic or the cysteine region, but not of the pleckstrin homology or the acidic domain, of PKCμ completely abrogated Golgi localization of PKCμ. As an NH2-terminal PKCμ fragment was colocalized with p24, this region of PKCμ is essential and sufficient to mediate association with Golgi membranes. Fluorescence recovery after photobleaching studies confirmed the constitutive, rapid recruitment of cytosolic PKCμ to, and stable association with, the Golgi compartment independent of activation loop phosphorylation. Kinase activity is not required for Golgi complex targeting, as evident from microscopical and cell fractionation studies with kinase-dead PKCμ found to be exclusively located at intracellular membranes. We propose a sequential activation process of PKCμ, in which Golgi compartment recruitment precedes and is essential for activation loop phoshorylation (serines 738/742) by a transacting kinase, followed by auto- and transphosphorylation of NH2-terminal serine(s) in the regulatory domain. PKCμ activation loop phosphorylation is indispensable for substrate phosphorylation and thus PKCμ function at the Golgi compartment

Continuous infusion of an agonist of the tumor necrosis factor receptor 2 in the spinal cord improves recovery after traumatic contusive injury.

AimThe activation of the TNFR2 receptor is beneficial in several pathologies of the central nervous system, and this study examines whether it can ameliorate the recovery process following spinal cord injury.MethodsEHD2-sc-mTNFR2 , an agonist specific for TNFR2, was used to treat neurons exposed to high levels of glutamate in vitro. In vivo, it was infused directly to the spinal cord via osmotic pumps immediately after a contusion to the cord at the T9 level. Locomotion behavior was assessed for 6 weeks, and the tissue was analyzed (lesion size, RNA and protein expression, cell death) after injury. Somatosensory evoked potentials were also measured in response to hindlimb stimulation.ResultsThe activation of TNFR2 protected neurons from glutamate-mediated excitotoxicity through the activation of phosphoinositide-3 kinase gamma in vitro and improved the locomotion of animals following spinal cord injury. The extent of the injury was not affected by infusing EHD2-sc-mTNFR2 , but higher levels of neurofilament H and 2', 3'-cyclic-nucleotide 3'-phosphodiesterase were observed 6 weeks after the injury. Finally, the activation of TNFR2 after injury increased the neural response recorded in the cortex following hindlimb stimulation.ConclusionThe activation of TNFR2 in the spinal cord following contusive injury leads to enhanced locomotion and better cortical responses to hindlimb stimulation

The transmembrane form of tumor necrosis factor is the prime activating ligand of the 80 kDa tumor necrosis factor receptor

AbstractThe 60 kDa tumor necrosis factor receptor (TNFR60) is regarded as the major signal transducer of TNF-induced cellular responses, whereas the signal capacity and role of the 80 kDa TNFR (TNFR80) remain largely undefined. We show here that the transmembrane form of TNF is superior to soluble TNF in activating TNFR80 in various systems such as T cell activation, thymocyte proliferation, and granulocyte/macrophage colony-stimulating factor production. Intriguingly, activation of TNFR80 by membrane TNF can lead to qualitatively different TNF responses such as rendering resistant tumor cells sensitive to TNF-mediated cytotoxicity. This study demonstrates that the diversity of TNF effects can be controlled through the differential sensitivity of TNFR80 for the two forms of TNF and suggests an important physiological role for TNFR80 in local inflammatory responses

Essential protective role of tumor necrosis factor receptor 2 in neurodegeneration

Despite the recognized role of tumor necrosis factor (TNF) in inflammation and neuronal degeneration, anti-TNF therapeutics failed to treat neurodegenerative diseases. Animal disease models had revealed the antithetic effects of the two TNF receptors (TNFR) in the central nervous system, whereby TNFR1 has been associated with inflammatory degeneration and TNFR2 with neuroprotection. We here show the therapeutic potential of selective inhibition of TNFR1 and activation of TNFR2 by ATROSAB, a TNFR1-selective antagonistic antibody, and EHD2-scTNFR2, an agonistic TNFR2-selective TNF, respectively, in a mouse model of NMDA-induced acute neurodegeneration. Coadministration of either ATROSAB or EHD2-scTNFR2 into the magnocellular nucleus basalis significantly protected cholinergic neurons and their cortical projections against cell death, and reverted the neurodegeneration-associated memory impairment in a passive avoidance paradigm. Simultaneous blocking of TNFR1 and TNFR2 signaling, however, abrogated the therapeutic effect. Our results uncover an essential role of TNFR2 in neuroprotection. Accordingly, the therapeutic activity of ATROSAB is mediated by shifting the balance of the antithetic activity of endogenous TNF toward TNFR2, which appears essential for neuroprotection. Our data also explain earlier results showing that complete blocking of TNF activity by anti-TNF drugs was detrimental rather than protective and argue for the use of next-generation TNFR-selective TNF therapeutics as an effective approach in treating neurodegenerative diseases.</p

The TNFR1 antagonist Atrosimab reduces neuronal loss, glial activation and memory deficits in an acute mouse model of neurodegeneration

Abstract Tumor necrosis factor alpha (TNF-α) and its key role in modulating immune responses has been widely recognized as a therapeutic target for inflammatory and neurodegenerative diseases. Even though inhibition of TNF-α is beneficial for the treatment of certain inflammatory diseases, total neutralization of TNF-α largely failed in the treatment of neurodegenerative diseases. TNF-α exerts distinct functions depending on interaction with its two TNF receptors, whereby TNF receptor 1 (TNFR1) is associated with neuroinflammation and apoptosis and TNF receptor 2 (TNFR2) with neuroprotection and immune regulation. Here, we investigated the effect of administering the TNFR1-specific antagonist Atrosimab, as strategy to block TNFR1 signaling while maintaining TNFR2 signaling unaltered, in an acute mouse model for neurodegeneration. In this model, a NMDA-induced lesion that mimics various hallmarks of neurodegenerative diseases, such as memory loss and cell death, was created in the nucleus basalis magnocellularis and Atrosimab or control protein was administered centrally. We showed that Atrosimab attenuated cognitive impairments and reduced neuroinflammation and neuronal cell death. Our results demonstrate that Atrosimab is effective in ameliorating disease symptoms in an acute neurodegenerative mouse model. Altogether, our study indicates that Atrosimab may be a promising candidate for the development of a therapeutic strategy for the treatment of neurodegenerative diseases