1 Introduction Tumor necrosis factor (TNF) is a pleiotropic cytokine involved in a broad spectrum of inlammatory and immune responses, including cell diferentiation, cell survival and death (1). TNF exerts these biological efects by engaging two distinct cell surface receptors, the 55-kD TNF receptor type 1 (TNFR1) and the 75-kD TNF receptor type 2 (TNFR2). TNFR1 is rather constitutively expressed on nearly all cell types, whereas expression of TNFR2 is strongly modulated by a number of stimulatory agents and is mainly found in endothelial and immune system cells (2,3). Both TNF receptors (TNFRs) have the ability to mediate cell death via various mechanisms (4). Kupfer cells (KC), the resident liver macrophages, are critically involved in the pathogenesis of hepatic diseases by acting as antigen presenting cells and producing a large number of regulatory mediators (5). hey are the major source of TNFα in liver, a cytokine that can func- tion not only as a paracrine factor, but also as an auto- stimulator of KC (6). Octreotide, a potent somatostatin analogue, has been used in the treatment of several neuroendocrine and gastrointestinal diseases (7). Octreotide binds mainly to somatostatin receptors (ssts) sst 2 and sst 5 and with less ainity to sst 3 and has a signiicantly greater half time in biological luids compared to somatostatin, making it a useful therapeutic and research tool (8). In addition to its antiproliferative, antisecretory and antiangiogenic properties (9), it was also shown to regulate immune responses, including functions of monocytes and mac- rophages (10). RESEARCH ARTICLE TNF receptors in Kupfer cells Maria Georgiadou 1 , George Notas 1,2 , Costas Xidakis 1 , Ioannis Drygiannakis 1 , Ourania Sfakianaki 1 , Stefanos Klironomos 1 , Vassilis Valatas 1 , and Elias Kouroumalis 1 1 Liver Research Laboratory, University of Crete, Faculty of Medicine, Heraklion, Crete, Greece, and 2 Laboratory of Experimental Endocrinology, University of Crete, Faculty of Medicine, Heraklion, Crete, Greece Abstract Introduction: Somatostatin is a mediator of immune functions and has been used as an antineoplastic agent in animal models and human neoplasias. We have demonstrated that Octreotide inhibits only LPS induced secretion of proinlammatory cytokines including TNFa by Kupfer cells (KC). We, therefore, tested the hypothesis that somatostatin modulates the expression of tumor necrosis factor alpha (TNFα) receptors and apoptosis of KC. Methods: Rat KC were isolated by centrifugal elutriation. TNFR1 and TNFR2 expression was studied by RT-PCR, quantitative PCR, Western Blot and immunoluorescence before and after Octreotide pre-incubation. Apoptosis was assessed by quantitative measurement of cytoplasmic histone-associated DNA fragments. TNFa mRNA expression was assessed by semiquantitative PCR and TNFa was measured in cell supernatants by ELISA. Results: TNFR1 and TNFR2 mRNA are constitutively expressed in KC. Octreotide incubation increased both receptors expression with a peak at 6 h and return to basal levels at 24 h. TNFR1 was mostly inluenced. However, only increase in TNFR2 protein was identiied, whereas a band at 90 kD was present instead of a band at 55 kD as expected for TNFR1. TNFα mRNA expression was inhibited by Octreotide and a signiicant inhibition was observed at 48 h. TNF had no efect on KC apoptosis, whereas Octreotide signiicantly increased their apoptosis, and this efect was not inluenced by co-incubation with TNFa. Conclusion: TNFR1 and TNFR2 are constitutively expressed in KC and their expression is strongly increased by somatostatin. Moreover, somatostatin increases KC apoptosis. These indings may in part explain the antineoplasmatic efect of somatostatin. Address for Correspondence: Prof. E.A. Kouroumalis, Professor of Gastroenterology, Head-Department of Gastroenterology, University Hospital, P.O. Box 1351, Heraklion, GR-71100, Crete, Greece. Tel.: +30 2810 392356; Fax: +30 2810 542085. E-mail: kouroum@med.uoc.gr (Received 25 February 2011; revised 26 April 2011; accepted 04 May 2011) Journal of Receptors and Signal Transduction, 2011, 1–8, Early Online © 2011 Informa Healthcare USA, Inc. ISSN 1079-9893 print/ISSN 1532-4281 online DOI: 10.3109/10799893.2011.586354 Journal of Receptors and Signal Transduction Downloaded from informahealthcare.com by University of Crete on 06/22/11 For personal use only.