Cyclic Nucleotides Suppress Tumor Necrosis Factor α-Mediated Apoptosis by Inhibiting Caspase Activation and Cytochrome cRelease in Primary Hepatocytes via a Mechanism Independent of Akt Activation

ArticleinJournal of Biological Chemistry 275(17):13026-34 · May 2000with3 Reads
DOI: 10.1074/jbc.275.17.13026 · Source: PubMed
Abstract
Cyclic nucleotides have been previously shown to modulate cell death processes in many cell types; however, the mechanisms by which cyclic nucleotides regulate apoptosis are unclear. In this study, we demonstrated that cAMP as well as cGMP analogs suppressed tumor necrosis factor alpha (TNFalpha) plus actinomycin D (ActD)-induced apoptosis in a dose-dependent manner in cultured primary hepatocytes. Furthermore, forskolin, which increases intracellular cAMP levels, also effectively suppressed TNFalpha+ActD-induced apoptosis. Activation of multiple caspases was suppressed in cells exposed to TNFalpha+ActD in the presence of cAMP or cGMP analogs. TNFalpha+ActD-induced cytochrome c release from mitochondria was also inhibited by cAMP or cGMP, reinforcing our conclusion that cyclic nucleotides interfere with the early signaling events of TNFalpha-mediated apoptosis. We evaluated the possibility that cAMP and cGMP inhibit apoptosis by activating the serine/threonine kinase Akt, which is known to promote cell survival. Both cAMP- and cGMP-elevating agents led to marked increases in Akt activation that was inhibited by the phosphatidylinositol 3'-kinase inhibitors, LY294002 and wortmannin. However, complete inhibition of cyclic nucleotide-induced Akt activation had little effect on cyclic nucleotide-mediated cell survival, indicating the existence of other survival pathways. Interestingly, the specific inhibitor of protein kinase A (PKA), KT5720, blocked cGMP-mediated protection but only partially prevented the anti-apoptotic effect of cAMP, indicating that both PKA-dependent and -independent mechanisms are involved in cAMP-mediated suppression of apoptosis signaling. Our data suggest that multiple survival signaling pathways coexist in cells and that cyclic nucleotides delay apoptosis by interfering with apoptosis signaling by both PKA-dependent and -independent mechanisms.
    • "PDE4B, plays an essential role in LPS-induced TLR4 signaling and inflammatory cytokine expression by monocytes/ macrophages (Jin and Conti, 2002; Jin et al., 2005; Gobejishvili et al., 2011). In cholestatic liver injury, besides downregulating systemic and hepatic inflammatory cytokines, increases in cAMP have been shown to protect hepatocytes from apoptosis due to several related stimuli, including bile acids, LPS, Fas, and TNF-a (Fladmark et al., 1997; Li et al., 2000; Webster et al., 2002; Cullen et al., 2004; Reinehr and Haussinger, 2004). Work done with PDE inhibitors has demonstrated their beneficial effect in experimental liver injury (Fischer et al., 1993; Gantner et al., 1997; Windmeier and Gressner, 1997; Taguchi et al., 1999; Xiang et al., 1999; Matsuhashi et al., 2005; Tukov et al., 2007), but there have been no studies examining the causal role of PDEs in the pathogenesis of liver fibrosis. "
    [Show abstract] [Hide abstract] ABSTRACT: Anti-inflammatory and anti-fibrotic effects of the broad spectrum PDE inhibitor Pentoxifylline have suggested an important role for cyclic nucleotides in the pathogenesis of hepatic fibrosis; however studies examining the role of specific PDEs are lacking. Endotoxemia and Toll-like receptor 4 (TLR4) mediated inflammatory and pro-fibrotic signaling play a major role in the development of hepatic fibrosis. Since cAMPspecific PDE4 critically regulates LPS-TLR4 induced inflammatory cytokine expression, its pathogenic role in bile duct ligation induced hepatic injury and fibrogenesis in Sprague Dawley rats was examined. Initiation of cholestatic liver injury and fibrosis was accompanied by a significant induction of PDE4A, B and D expression and activity. Treatment with the PDE4-specific inhibitor, rolipram, significantly decreased liver PDE4 activity, hepatic inflammatory and pro-fibrotic cytokine expression, injury and fibrosis. At the cellular level, in relevance to endotoxemia and inflammatory cytokine production, PDE4B was observed to play a major regulatory role in the LPS-inducible TNF production by isolated Kupffer cells. Moreover, PDE4 expression was also involved in the in vitro activation and transdifferentiation of isolated hepatic stellate cells (HSCs). Particularly, PDE4A, B and D up-regulation preceded induction of the HSC activation marker α-SMA. In vitro treatment of HSCs with rolipram effectively attenuated α-SMA, collagen expression and accompanying morphological changes. Overall, these data strongly suggest that up-regulation of PDE4 expression during cholestatic liver injury plays a potential pathogenic role in the development of inflammation, injury and fibrosis.
    Full-text · Article · Jul 2013
    • "In the presence of redox stress, iNOS production may create oxidizing species that potentiate cell death. However, when proapoptotic signals are delivered in the absence of redox stress, iNOS production may facilitate the S-nitrosation of caspases and production of cGMP, both of which have been shown to inhibit apoptosis4041424344 . Understanding how iNOS confers resistance to IFN-γmediated apoptosis in hepatocytes under various physiological and pathological conditions may provide a basis for developing new strategies to treat hepatocellular carcinoma. "
    [Show abstract] [Hide abstract] ABSTRACT: Interferon (IFN)-γ is a cytokine known for its immunomodulatory and anti-proliferative action. In the liver, IFN-γ can induce hepatocyte apoptosis or inhibit hepatocyte cell cycle progression. This article reviews recent mechanistic reports that describe how IFN-γ may direct the fate of hepatocytes either towards apoptosis or a cell cycle arrest. This review also describes a probable role for IFN-γ in modulating hepatocyte fate during liver regeneration, transplantation, hepatitis, fibrosis and hepatocellular carcinoma, and highlights promising areas of research that may lead to the development of IFN-γ as a therapy to enhance recovery from liver disease.
    Full-text · Article · Feb 2011
    • "ERK1/2 is a classical member of the MAPK family. ERK1/2 activation pathway, like p38 MAPK, is considered as a potential target for cancer therapeutics due to its regulatory effect in cellular proliferation [170]. ERK activation-induced cellular responses are brought about by the phosphorylation of membrane proteins (including Syk, CD120a), nuclear substrates [including NF-AT, Elk-1, c-Fos (protein which is the product of the c-fos gene), c-Myc and STAT3], cytoskeletal proteins and MAPK-activated protein kinases [158,171]. "
    [Show abstract] [Hide abstract] ABSTRACT: TNFα (tumour necrosis factor α) is an extensively studied pleiotropic cytokine associated with the pathogenesis of a variety of inflammatory diseases. It elicits a wide spectrum of cellular responses which mediates and regulates inflammation, immune response, cell survival, proliferation and apoptosis. TNFα initiates its responses by binding to its receptors. TNFα-induced effector responses are mediated by the actions and interactions among the various intracellular signalling mediators in the cell. TNFα induces both survival and apoptotic signal in a TRADD (TNF receptor-associated DD)-dependent and -independent way. The signals are further transduced via a variety of signalling mediators, including caspases, MAPKs (mitogen-activated protein kinases), phospholipid mediators and miRNA/miR (microRNA), whose roles in specific functional responses is not fully understood. Elucidating the complexity and cross talks among signalling mediators involved in the TNFα-mediated responses will certainly aid in the identification of molecular targets, which can potentially lead to the development of novel therapeutics to treat TNFα-associated disorders and in dampening inflammation.
    Article · Oct 2010
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