The role of glucocorticoid hormones in interleukin-1 signal transduction via the sphingomyelin pathway

Interleukin-1 and glucocorticoid hormones are the key transmitters of interaction between the neuroendocrine and immune systems. To study the molecular mechanisms of immunomodulatory effects of Interleukin-1 and glucocorticoid hormones, a search for changes in activity of neutral sphingomyelinase: the main marker of initiation of Interleukin-1beta signal transduction via the sphingomyelin pathway in target cells, was accomplished. The Interleukin-1beta was found to activate neutral sphingomyelinase both in P2 fraction of murine brain cortex and membranes of immune-competent cells. Experimental modifications of endogenous glucocorticoid level in the mouse blood were for the first time shown to induce changes in neutral sphingomyelinase activity in membranes of the cells of the immune and nervous systems. It appears that the sphingomyelinase pathway of Interleukin-1beta signaling might be a possible target for glucocorticoid hormones' immune-modulating effects.     

Activation of neutral sphingomyelinase by IL-1beta requires the type 1 interleukin 1 receptor

The cytokine interleukin 1beta (IL-1beta) plays an important role in host defence reactions and neuro-immune interactions but it is still not clear which of the two interleukin 1 receptor subtypes is coupled to activation of neutral sphingomyelinase (nSMase) by IL-1beta. To investigate involvement of neutral sphingomyelinase (nSMase) in central IL-1beta effects we used P(2)fractions of brain cerebral cortex from wild-type mice and mice deficient in the type 1 IL-1 receptor. IL-1beta (human, recombinant) was shown to activate, in a dose-dependent manner, nSMase in the P(2)brain fraction of the wild-type mice while in the knock-out mice the stimulatory effect of IL-1beta on nSMase was absent. In the presence of an IL-1 receptor antagonist (IL-1ra), IL-1beta did not activate nSMase either in the cortex of wild-type or knock-out mice. These data suggest that nSMase, a key enzyme of the sphingomyelin signal transduction pathway, might be involved in IL-1beta signalling in the brain and that activation of the enzyme requires the IL-1 receptor type 1.     

Protein phosphatase 2A and neutral sphingomyelinase 2 regulate IRAK-1 protein ubiquitination and degradation in response to interleukin-1beta

The IL-1β signaling cascade is initiated by the phosphorylation of IL-1β receptor-associated kinase-1 (IRAK-1), followed by its ubiquitination and degradation. This paper investigates the regulation of IRAK-1 degradation in primary hepatocytes and in HEK cells overexpressing the IL-1β receptor. We provide evidence that protein phosphatase 2A (PP2A) is a negative regulator of the phosphorylation, Lys(48)-linked ubiquitination, and degradation of IRAK-1. PP2A catalytic activity increased within 30 min of stimulation with IL-1β. siRNA against PP2A catalytic subunit (PP2Ac) or treatment with pharmacological inhibitor, okadaic acid, enhanced IRAK-1 Lys(48)-linked ubiquitination and degradation. Direct interaction between PP2Ac and IRAK-1 was observed, suggesting that IRAK-1 might be a PP2A substrate. The mechanisms of PP2A activation by IL-1β involved neutral sphingomyelinase-2 (NSMase-2) and an accumulation of ceramide. Overexpression of NSMase-2 delayed IRAK-1 degradation in a PP2A-dependent manner, whereas NSMase-2 silencing had the opposite effect. The addition of sphingomyelinase, ceramide, or a proteasome inhibitor all led to retention of IRAK-1 at the cell membrane and to increased JNK phosphorylation. This study suggests that NSMase-2- and PP2A-dependent regulation of IRAK-1 degradation is a novel mechanism to fine tune the magnitude of IL-1β response.     

The role of calcium in signal transduction processes in Sertoli cells

Sertoli cells play a pivotal role in regulation and maintenance of spermatogenesis. They are hormonally regulated predominantly by follicle-stimulating hormone (FSH) and testosterone (T). Although FSH and T have distinct mechanisms of action they act synergistically in promoting spermatogenesis. Stimulation of freshly isolated Sertoli cells with FSH evokes a prompt rise in cytosolic calcium which is quantitatively reproduced by cAMP. The cytosolic calcium response to FSH in Sertoli cells is predominantly attributable to serial signaling after the generation of endogenous cAMP. Calcium homeostasis of Sertoli cells may also be regulated by cAMP-independent metabolism. Vasoactive testicular paracrine hormones such as angiotensin II (AII) and vasopressin acting via inositol triphosphate generation induce cytosolic calcium rise predominantly derived from the thapsigargin-sensitive endoplasmic reticulum. Investigations involving androgens action on cytosolic calcium reveal a common mechanism of action between the peptide and steroid regulators of Sertoli cell function, indicating that cytosolic calcium ions may represent a unifying biochemical mechanism that could explain the synergism of FSH and T. Androgens rapidly and specifically increase cytosolic calcium, consistent with a plasma membrane site of action. This argues for the possible existence of a short term non-genomic signaling pathway in hormonal regulation of Sertoli cell function in addition to the classical longer term, slower genomic response.     

白细胞介素1细胞信号转导机制研究现状

白细胞介素１是多种炎症增殖性疾病中炎症介导作用极强的细胞因子这一,对其细胞信号转导机制的研究令人瞩目。白细胞介素１与其特异受体结合后,通过某些调节蛋白作用,激活胞膜上或胞浆内的多种磷脂酶,产生多种信使类物质。此外,近年来还发现白细胞介素１可激活多种蛋白激酶和转录调节因子。不同传导途径的细胞信号与白细胞介素１导致的炎症效应密度切相关。     

The role of phosphatases in signal transduction

The importance of phosphatases in regulating the phosphorylation of proteins involved in cell signaling has been demonstrated by four recent discoveries. First, a new family of receptor-like transmembrane phosphotyrosine phosphatases, highly conserved throughout evolution, was shown to be distributed in a wide variety of tissues. Extensive heterogeneity in the extracellular regions of these molecules points to the existence of a wide diversity of ligands. These ligands are thought to mediate transduction of signals to the cell interior by means of the phosphatase activity occurring within the cytoplasmic domains of the receptor-like transmembrane phosphotyrosine phosphatases. Second, cell-permeable tumor promoters, such as okadaic acid, were shown to be potent phosphatase inhibitors that have multiple effects on signaling pathways. Third, the subunits of the type 2A phosphatase were found to associate with transforming antigens encoded by DNA tumor viruses, indicating a role for phosphatases in mediating abnormal proliferative events. Fourth, several cell-cycle mutants were found to encode phosphatases. This review focuses on the significance of the transmembrane phosphotyrosine phosphatases and on the possible ways in which intracellular phosphatases function in signaling pathways.     

胚胎植入中白细胞介素-1的信号转导及其生理作用

本文论述了白细胞介素－１（ＩＬ－１）的信号转导通路及其在胚胎植入中的调节作用。指出：植入过程中,ＩＬ－１起着十分重要的作用,但并非唯一的重要因子,成功的胚胎植入需要多种细胞因子的协同作用。     

Fas-mediated apoptosis and sphingomyelinase signal transduction: the role of ceramide as a second messenger for apoptosis

In this article, we review the role of sphingomyelinases and ceramide in the Fas-mediated apoptosis signal transduction cascade. Several stimuli, including ligation of Fas, have been shown to enhance either neutral and/or acidic sphingomyelinase activity and increase ceramide content in intact cells or cell membrane preparations. Ceramide seems to have different functions, including induction of apoptosis, growth arrest, and/or differentiation, depending on cell type or location of sphingomyelin hydrolysis within the cell. Several putative targets for ceramide activity, including a kinase and a phosphatase, have also been identified. While ceramide and acidic sphingomyelinase activity appear to be involved in apoptotic signalling for Fas and other members of the tumour necrosis factor receptor family, it is clear that other signals and mechanisms are necessary for Fas-mediated apoptosis.     

The role of mitochondria in the oncogenic signal transduction

Mitochondria are intracellular organelles thought to have evolved from an alphaproteobacterium engulfed by the ancestor of the eukaryotic cell, an archeon, two billion years ago. Although mitochondria are frequently recognised as the “power plant” of the cell, the function of these organelles go beyond the simple generation of ATP. In fact, mounting evidence suggests that mitochondria are involved in several cellular processes, from regulation of cell death to signal transduction. Given this important role in cell physiology, mitochondrial dysfunction has been frequently associated with human diseases including cancer. Importantly, recent evidence suggests that mitochondrial function is directly regulated by oncogenes and tumour suppressors. However, the consequences of deregulation of mitochondrial function in tumour formation are still unclear. In this review, I propose that mitochondria play a pivotal role in shaping the oncogenic signalling cascade and that mitochondrial dysfunction, in some circumstances, is a required step for cancer transformation.     

The role of calcium in follicle-stimulating hormone signal transduction in Sertoli cells.

Sertoli cells are hormonally regulated by follicle-stimulating hormone (FSH) acting upon a G-protein-linked cell surface FSH receptor. FSH increases intracellular cyclic AMP but the involvement of other signal transduction mechanisms including intracellular calcium in FSH action are not proven. Using freshly isolated rat Sertoli cells we measured cytosolic free ionized calcium levels by dual-wavelength fluorescence spectrophotometry using the calcium-sensitive fluorescent dye Fura2-AM. The cytosolic calcium concentration in unstimulated Sertoli cells was 89 +/- 2 nM (n = 151 experiments) and was markedly increased by either calcium channel ionophores (ionomycin, Bay K8644) or plasma membrane depolarization consistent with the presence of voltage-sensitive and -independent calcium channel in Sertoli cell membranes. Ovine FSH stimulated a specific, sensitive (ED50, 5.0 ng of S-16/ml), and dose-dependent (maximal at 20 ng/ml) rise in cytosolic calcium commencing within 60 s to reach levels of 192 +/- 31 nM after 180 s and lasting for at least 10 min. The effect of FSH was replicated by forskolin, cholera toxin, and dibutyryl cyclic AMP, suggesting that cyclic AMP may mediate the FSH-induced rise in cytosolic calcium. The FSH-induced rise in cytosolic calcium required extracellular calcium and was abolished by calcium channel blockers specific for dihydropyridine (verapamil, nicardipine), nonvoltage-gated (ruthenium red) or all calcium channels (cobalt). Thus FSH action on Sertoli cells involves a specific, rapid, and sustained increase in cytosolic calcium which requires extracellular calcium and involves both dihydropyridine-sensitive, voltage-gated calcium channels and voltage-independent, receptor-gated calcium channels in the plasma membranes of rat Sertoli cells. The replication by cyclic AMP of the effects of FSH suggests that calcium may be a signal-amplification or -modulating mechanism rather than an alternate primary signal transduction system for FSH in Sertoli cells.     

Sphingosine 1-phosphate signal transduction in muscle cells

Sphingosine 1-phosphate (S1P) is a powerful bioactive sphingolipid recently recognized to act as extracellular ligand for various subtypes of G protein-coupled receptors belonging to the S1P family. In our study, focused on mouse skeletal muscle cells, we showed that S1P activated enzymes crucial for membrane signal transduction, such as phospholipase D (PLD) and protein kinase C; it promoted also a significant increase of cytosolic Ca2+ via ligation to S1P2 and S1P3 receptor subtypes. Interestingly, myogenic differentiation was found to be accompanied by a profound variation of S1P receptor expression levels and the progressive uncoupling of S1P from PLD activation, suggesting that this signaling pathway is exclusively required for S1P action on proliferating cells.     

Tubulin polymerization modulates interleukin-2 receptor signal transduction in human T cells

Few data exist on the modulation of cytokine receptor signaling by the actin or tubulin cytoskeleton. Therefore, we studied interleukin-2 receptor (IL-2R) signaling in phytohemagglutinine (PHA)-pretreated human T cells in the context of alterations in the cytoskeletal system induced by cytochalasin D (CyD), jasplaklinolide (Jas), taxol (Tax), or colchicine (Col). We found that changes in cytoskeletal tubulin polymerization altered the strength of several IL-2-triggered signals. Moreover, Tax-induced tubulin hyperpolymerization augmented the surface expression of the IL-2R ss -chain and enhanced the association of the IL-2R beta -chain with cytoskeletal tubulin. The IL-2R beta-chain, in turn, was constitutively associated with tubulin and, more weakly, actin. To exclude the possibility that these associations are artifacts caused by PHA, we confirmed them in T cells from TCR-transgenic DO 11.10 mice stimulated with their nominal antigen. We conclude that altered polymerization of cytoskeletal components, especially tubulin, is accompanied by modulation of IL-2 signaling at the receptor level.     

Intracellular signal transduction for interleukin-1 beta-induced endothelin production in human umbilical vein endothelial cells.

The authors investigated the intracellular signal transduction for interleukin (IL)-1 beta-induced endothelin (ET) production by endothelial cells from cultured human umbilical vein (HUVEC). Cultured HUVEC released immunoreactive (iR)-ET into the media in a time-dependent manner and a significant increase of iR-ET production was observed by the addition of IL-1 beta. The stimulating effect of IL-1 beta on iR-ET production was respectively inhibited by protein kinase C (C kinase) inhibitor (H-7), Ca-calmodulin inhibitor (W-7), cyclic AMP-dependent protein kinase (A kinase) inhibitor (H-8) and tyrosine kinase inhibitor (genistain) in a dose-dependent fashion. The data suggested that intracellular signal transduction for IL-1 beta-induced iR-ET production were via such pathways as C kinase, A kinase, Ca-calmodulin and tyrosine kinase in combination or independently, though possible mediation by other pathways cannot be ruled out.