Fyn Mediates Leptin Actions in the Thymus of Rodents

BACKGROUND:Several effects of leptin in the immune system rely on its capacity to modulate cytokine expression and apoptosis in the thymus. Surprisingly, some of these effects are dependent on signal transduction through the IRS1/PI3-kinase, but not on the activation of JAK2. Since all the well known effects of leptin in different cell types and tissues seem to be dependent on JAK2 activation, we hypothesized that, at least for the control of thymic function, another, unknown kinase could mediate the transduction of the leptin signal from the ObR towards the IRS1/PI3-kinase signaling cascade. METHODOLOGY/PRINCIPAL FINDINGS:Here, by employing immunoblot, real-time PCR and flow citometry we show that the tyrosine kinase, Fyn, is constitutively associated with the ObR in thymic cells. Following a leptin stimulus, Fyn undergoes an activating tyrosine phosphorylation and a transient association with IRS1. All these effects are independent of JAK2 activation and, upon Fyn inhibition, the signal transduction towards IRS1/PI3-kinase is abolished. In addition, the inhibition of Fyn significantly modifies the effects of leptin on thymic cytokine expression. CONCLUSION/SIGNIFICANCE:Therefore, in the thymus, Fyn acts as a tyrosine kinase that transduces the leptin signal independently of JAK2 activation, and mediates some of the immunomodulatory effects of leptin in this tissue

Initiation of T cell signaling by CD45 segregation at 'close contacts'.

It has been proposed that the local segregation of kinases and the tyrosine phosphatase CD45 underpins T cell antigen receptor (TCR) triggering, but how such segregation occurs and whether it can initiate signaling is unclear. Using structural and biophysical analysis, we show that the extracellular region of CD45 is rigid and extends beyond the distance spanned by TCR-ligand complexes, implying that sites of TCR-ligand engagement would sterically exclude CD45. We also show that the formation of 'close contacts', new structures characterized by spontaneous CD45 and kinase segregation at the submicron-scale, initiates signaling even when TCR ligands are absent. Our work reveals the structural basis for, and the potent signaling effects of, local CD45 and kinase segregation. TCR ligands have the potential to heighten signaling simply by holding receptors in close contacts.The authors thank R.A. Cornall, M.L. Dustin and P.A. van der Merwe for comments on the manuscript and S. Ikemizu for useful discussions about the structure. We also thank W. Lu and T. Walter for technical support with protein expression and crystallization, the staff at Diamond Light Source beamlines I02, I03 and I04-1 (proposal mx10627) and European Synchrotron Radiation Facility beamlines ID23EH1 and ID23EH2 for assistance at the synchrotrons, G. Sutton for assistance with MALS experiments, and M. Fritzsche for advice on the calcium analysis. This work was funded by the Wellcome Trust (098274/Z/12/Z to S.J.D.; 090532/Z/09/Z to R.J.C.G.; 090708/Z/09/Z to D.K.), the UK Medical Research Council (G0700232 to A.R.A.), the Royal Society (UF120277 to S.F.L.) and Cancer Research UK (C20724/A14414 to C.S.; C375/A10976 to E.Y.J.). The Oxford Division of Structural Biology is part of the Wellcome Trust Centre for Human Genetics, Wellcome Trust Core Award Grant Number 090532/Z/09/Z. We acknowledge financial support from Instruct, an ESFRI Landmark Project. The OPIC electron microscopy facility was funded by a Wellcome Trust JIF award (060208/Z/00/Z).This is the author accepted manuscript. The final version is available from Nature Publishing Group via https://doi.org/10.1038/ni.339

Tyrosine kinase inhibitors: potential use and safety considerations in HIV-1 infection

INTRODUCTION: Infection caused by HIV-1 is nowadays a chronic disease due to a highly efficient antiretroviral treatment that is nevertheless, unable to eliminate the virus from the organism. New strategies are necessary in order to impede the formation of the viral reservoirs, responsible for the failure of the antiretroviral treatment to cure the infection. Areas covered: The purpose of this review is to discuss the possibility of using tyrosine kinase inhibitors (TKIs) for the treatment of HIV-1 infection. These inhibitors are successfully used in patients with distinct cancers such as chronic myeloid leukemia. The most relevant papers have been selected and commented. Expert opinion: The family of TKIs are directed against the activation of tyrosine kinases from the Src family. Some of these kinases are essential for the activation of CD4 + T cells, the major target of HIV-1. During acute or primary infection the CD4 + T cells are massively activated, which is mostly responsible for the generation of the reservoirs, the spread of the infection and the destruction of activated CD4 + T cells, infected or not. Consequently, we discuss the possibility of using TKIs as adjuvant of the antiretroviral treatment against HIV-1 infection mostly, but not exclusively, during the acute/recent phase.This work was supported by the Spanish Ministry of Economy and Competitiveness (SAF2013-44677-R, SAF2016-78480-R); the Instituto de Salud Carlos III (INT15/00168, ISCIII-FIS PI16CIII/00034); the Spanish AIDS Research Network RD12/0036/0004, RD16CIII/0002/0001-ISCIII-FEDER and the grant RD12/0036/0004; Bristol-Myers Squibb partially financed our study (grant BMS AI471-041). J Ambrosioni developed this work in the frame of a ‘Juan de la Cierva 2012ʹ postdoctoral program, Spanish Ministry of Economy and Competitiveness, Spain. JMM received a personal intensification research grant INT15/00168 in 2016 from Instituto de Salud Carlos III, Madrid, Spain. The European Regional Development Fund (ERDF) ‘A way to build Europe’ also provided funding.S