Rapid endocytosis of interleukin-15 by cerebral endothelia

Reduced Serum Levels of Soluble Interleukin-15 Receptor α in Schizophrenia and Its Relationship to the Excited Phenotype

Our previous studies documented that interleukin-15 receptor α (IL-15Rα) knockout (KO) mice exhibited hyperactivity, memory impairment, and desperate behavior, which are core features of schizophrenia and depression. Due to the overlapping symptomology and pathogenesis observed for schizophrenia and depression, the present study attempted to determine whether IL-15Rα was associated with the risk of schizophrenia or depression. One hundred fifty-six participants, including 63 schizophrenia patients, 29 depressive patients, and 64 age-matched healthy controls, were enrolled in the study. We investigated the circulating levels of soluble IL-15Rα and analyzed potential links between the IL-15Rα levels and clinical symptoms present in schizophrenia or depressive patients. We observed reduced serum IL-15Rα levels in schizophrenia patients, but not depressive patients compared with controls. Moreover, a significant negative association was observed between the circulating IL-15Rα levels and excited phenotypes in the schizophrenia patients. The IL-15Rα KO mice displayed pronounced pre-pulse inhibition impairment, which was a typical symptom of schizophrenia. Interestingly, the IL-15Rα KO mice exhibited a remarkable elevation in the startle amplitude in the startle reflex test compared to wild type mice. These results demonstrated that serum levels of soluble IL-15Rα were reduced in schizophrenia and highlighted the relationship of IL-15Rα and the excited phenotype in schizophrenia patients and mice.

Comparative Analysis of the Secretome and Interactome of Trypanosoma cruzi and Trypanosoma rangeli Reveals Species Specific Immune Response Modulating Proteins

Chagas disease, a zoonosis caused by the flagellate protozoan Trypanosoma cruzi, is a chronic and systemic parasitic infection that affects ~5–7 million people worldwide, mainly in Latin America. Chagas disease is an emerging public health problem due to the lack of vaccines and effective treatments. According to recent studies, several T. cruzi secreted proteins interact with the human host during cell invasion. Moreover, some comparative studies with T. rangeli, which is non-pathogenic in humans, have been performed to identify proteins directly involved in the pathogenesis of the disease. In this study, we present an integrated analysis of canonical putative secreted proteins (PSPs) from both species. Additionally, we propose an interactome with human host and gene family clusters, and a phylogenetic inference of a selected protein. In total, we identified 322 exclusively PSPs in T. cruzi and 202 in T. rangeli. Among the PSPs identified in T. cruzi, we found several trans-sialidases, mucins, MASPs, proteins with phospholipase 2 domains (PLA2-like), and proteins with Hsp70 domains (Hsp70-like) which have been previously characterized and demonstrated to be related to T. cruzi virulence. PSPs found in T. rangeli were related to protozoan metabolism, specifically carboxylases and phosphatases. Furthermore, we also identified PSPs that may interact with the human immune system, including heat shock and MASP proteins, but in a lower number compared to T. cruzi. Interestingly, we describe a hypothetical hybrid interactome of PSPs which reveals that T. cruzi secreted molecules may be down-regulating IL-17 whilst T. rangeli may enhance the production of IL-15. These results will pave the way for a better understanding of the pathophysiology of Chagas disease and may ultimately lead to the identification of molecular targets, such as key PSPs, that could be used to minimize the health outcomes of Chagas disease by modulating the immune response triggered by T. cruzi infection.

Alterations in Cellular Processes Involving Vesicular Trafficking and Implications in Drug Delivery

Endocytosis and vesicular trafficking are cellular processes that regulate numerous functions required to sustain life. From a translational perspective, they offer avenues to improve the access of therapeutic drugs across cellular barriers that separate body compartments and into diseased cells. However, the fact that many factors have the potential to alter these routes, impacting our ability to effectively exploit them, is often overlooked. Altered vesicular transport may arise from the molecular defects underlying the pathological syndrome which we aim to treat, the activity of the drugs being used, or side effects derived from the drug carriers employed. In addition, most cellular models currently available do not properly reflect key physiological parameters of the biological environment in the body, hindering translational progress. This article offers a critical overview of these topics, discussing current achievements, limitations and future perspectives on the use of vesicular transport for drug delivery applications.

Cytokine Receptor Endocytosis: New Kinase Activity-Dependent and -Independent Roles of PI3K

Type I and II cytokine receptors are cell surface sensors that bind cytokines in the extracellular environment and initiate intracellular signaling to control processes such as hematopoiesis, immune function, and cellular growth and development. One key mechanism that regulates signaling from cytokine receptors is through receptor endocytosis. In this mini-review, we describe recent advances in endocytic regulations of cytokine receptors, focusing on new paradigms by which PI3K controls receptor endocytosis through both kinase activity-dependent and -independent mechanisms. These advances underscore the notion that the p85 regulatory subunit of PI3K has functions beyond regulating PI3K kinase activity, and that PI3K plays both positive and negative roles in receptor signaling. On the one hand, the PI3K/Akt pathway controls various aspects downstream of cytokine receptors. On the other hand, it stimulates receptor endocytosis and downregulation, thus contributing to signaling attenuation.

TNF stimulates nuclear export and secretion of IL-15 by acting on CRM1 and ARF6

Interleukin (IL)-15 is a ubiquitously expressed cytokine that in the basal state is mainly localized intracellularly, including the nucleus. Unexpectedly, tumor necrosis factor-α (TNF) time-dependently induced nuclear export of IL-15Rα and IL15. This process was inhibited by leptomycine B (LMB), a specific inhibitor of nuclear export receptor chromosomal region maintenance 1 (CRM1). In the presence of TNF, LMB co-treatment led to accumulation of both IL-15Rα and IL-15 in the nucleus of HeLa cells, suggesting that CRM1 facilitates nuclear export and that TNF enhances CRM1 activity. Once in the cytoplasm, IL-15 showed partial co-localization with late endosomes but very little with other organelles tested 4 h after TNF treatment. IL-15Rα showed co-localization with both early and late endosomes, and to a lesser extent with endoplasmic reticulum and Golgi. This indicates different kinetics and possibly different trafficking routes of IL-15 from its specific receptor. The TNF-induced secretion of IL-15 was attenuated by pretreatment of cells by brefeldin A that inhibits ER-to-Golgi transport, or by use of domain negative ADP-ribosylation factor 6 (ARF6) that interferes with exocytotic sorting. We conclude that TNF abolishes nuclear localization of IL-15 and IL-15Rα by acting on CRM1, and it facilitates exocytosis of IL-15 with the involvement of ARF6.

Interleukin-15 plays a central role in human kidney physiology and cancer through the γc signaling pathway

The ability of Interleukin-15 (IL-15) to activate many immune antitumor mechanisms renders the cytokine a good candidate for the therapy of solid tumors, particularly renal cell carcinoma. Although IL-15 is being currently used in clinical trials, the function of the cytokine on kidney's components has not been extensively studied; we thus investigated the role of IL-15 on normal and tumor renal epithelial cells. Herein, we analyzed the expression and the biological functions of IL-15 in normal renal proximal tubuli (RPTEC) and in their neoplastic counterparts, the renal clear cell carcinomas (RCC). This study shows that RPTEC express a functional heterotrimeric IL-15Rαβγc complex whose stimulation with physiologic concentrations of rhIL-15 is sufficient to inhibit epithelial mesenchymal transition (EMT) commitment preserving E-cadherin expression. Indeed, IL-15 is not only a survival factor for epithelial cells, but it can also preserve the renal epithelial phenotype through the γc-signaling pathway, demonstrating that the cytokine possess a wide range of action in epithelial homeostasis. In contrast, in RCC in vitro and in vivo studies reveal a defect in the expression of γc-receptor and JAK3 associated kinase, which strongly impacts IL-15 signaling. Indeed, in the absence of the γc/JAK3 couple we demonstrate the assembly of an unprecedented functional high affinity IL-15Rαβ heterodimer, that in response to physiologic concentrations of IL-15, triggers an unbalanced signal causing the down-regulation of the tumor suppressor gene E-cadherin, favoring RCC EMT process. Remarkably, the rescue of IL-15/γc-dependent signaling (STAT5), by co-transfecting γc and JAK3 in RCC, inhibits EMT reversion. In conclusion, these data highlight the central role of IL-15 and γc-receptor signaling in renal homeostasis through the control of E-cadherin expression and preservation of epithelial phenotype both in RPTEC (up-regulation) and RCC (down-regulation).

NFĸB is an unexpected major mediator of interleukin-15 signaling in cerebral endothelia

Interleukin (IL)-15 and its receptors are induced by tumor necrosis factor α (TNF) in the cerebral endothelial cells composing the blood-brain barrier, but it is not yet clear how IL-15 modulates endothelial function. Contrary to the known induction of JAK/STAT3 signaling, here we found that nuclear factor (NF)- κB is mainly responsible for IL-15 actions on primary brain microvessel endothelial cells and cerebral endothelial cell lines. IL-15-induced transactivation of an NFκB luciferase reporter resulted in phosphorylation and degradation of the inhibitory subunit IκB that was followed by phosphorylation and nuclear translocation of the p65 subunit of NFκB. An IκB kinase inhibitor Bay 11-7082 only partially inhibited IL-15-induced NFκB luciferase activity. The effect of IL-15 was mediated by its specific receptor IL-15Rα, since endothelia from IL-15Rα knockout mice showed delayed nuclear translocation of p65, whereas those from knockout mice lacking a co-receptor IL-2Rγ did not show such changes. At the mRNA level, IL-15 and TNF showed similar effects in decreasing the tight junction protein claudin-2 and increasing the p65 subunit of NFκB but exerted different regulation on caveolin-1 and vimentin. Taken together, NFκB is a major signal transducer by which IL-15 affects cellular permeability, endocytosis, and intracellular trafficking at the level of the blood-brain barrier.

Early gene response of human brain microvascular endothelial cells to Listeria monocytogenes infection

The gene expression of human brain microvascular endothelial cells (HBMEC) in response to 4 h of infection by Listeria monocytogenes was analyzed. Four hours after infection, the expression of 456 genes of HBMEC had changed (p < 0.05). We noted that many active genes were involved in the formyl-methionyl-leucyl-phenylalanine pathway in infected HBMEC. In the upregulated genes, mRNA levels of interleukin-8 and interleukin-15 in infected cells increased according to microarray and real-time reverse transcription - PCR analyses. Since both cytokines are regarded as potent chemotactic factors, the results suggest that HBMEC are capable of recruiting cells of innate and adaptive immune responses during early L. monocytogenes infection.