Interleukin 1 induces new protein formation in isolated rat islets of Langerhans

Abstract

It is hypothesized that interleukin 1 induces toxic free radical formation in pancreatic beta-cells leading to beta-cell degeneration and destruction. Therefore, isolated rat pancreatic islets were examined for interleukin 1 and heat shock induced proteins. After exposure to human interleukin 1\g=b\(0.015 to 10 \g=m\g/l ) or heat (40\s=deg\C) for up to 24 h, islets were labelled with 35S-methionine and solubilized. Islets proteins were analysed by SDS-polyacrylamide gel electrophoresis. By autoradiography it was shown that both interleukin 1 and heat exposure induced the formation of a 70 kD protein. Further, interleukin 1 induced the formation of two proteins of 32 and 80 kD, respectively, which was not seen after heat exposure. Possibly, the 70 kD protein is a member of the heat shock protein 70 family, participating in unspecific cellular defence and maybe free radical scavenging. Other candidates are the superoxide radical scavenging enzyme manganous superoxidedismutase, MHC class II molecules, and heme oxygenase.Interleukin Iß (IL-1) was recently proposed to be the major effector molecule in beta-cell destruc¬ tion in insulin-dependent diabetes mellitus (IDDM) (1,2). In vitro studies had shown that con¬ centrations of human recombinant IL-1 of e.g. 0.2 u.g/1 culture medium (RPMI, glucose concentration 11.1 mmol/1, Ca2+ concentration 0.42 mmol/1) were selectively beta-cell cytotoxic after 6 h of exposure. The toxic effect was evidenced by morphology (3), inhibition of protein synthesis, proinsulin biosyn¬ thesis, and insulin secretion (4), decreased insulin and DNA content (5), and severe reduction in mitochondrial glucose oxidation (6). The alpha form of interleukin 1 reproduced the inhibitory effect of interleukin 1 ß on insulin release from isolated is¬ lets, but at an approximately 10-fold higher molar concentration (7). Because IL-1 was shown to in¬ duce toxic free radicals in other cell types (neutrophils (8) and endothelial cells (9)) it was hypo¬ thesized (1,2) that the IL-1 effects were mediated through induction of free radicals for which betacells are exquisitely sensitive (10).In support of this hypothesis we report that these IL-1-induced metabolic effects are paralleled by the induction of new proteins of approximately 32, 70, and 80 kD in rat islets in culture. Material and MethodsIslets of Langerhans from 5-7 days old Wistar rats were isolated and precultured for 6-8 days as previously de¬ scribed (11). After preculture, islets were placed in groups of 125 islets in RPMI 1640 with 11 mmol/1 glucose and 0.42 mmol/1 Ca2f (Flow Laboratories, Irvine, Scotland) with addition of antibiotics and 0.5% normal human serum. Islets were incubated for 5 or 24 h at either 37°C or 40°C (heat schock) with and without the addition of 0.015 to 10 ug/1 (N = 4-10) of human recombinant IL-lß (Batch B19, Nordisk Gentofte, Denmark. Specific activity 400 WHO LAF U/ng, N-terminus: alanine (No. 117), con¬ tent of endotoxin: 13 pg/ug IL-lß (12)). Culture condi¬ tions were furthermore varied with regard to glucose (3.3 m...

Interleukin 1 inhibits insulin secretion from isolated rat pancreatic islets by a process that requires gene transcription and mRNA translation.

“…While this manuscript was in preparation, Helqvist reported that very long (24 h) exposure of islets to IL 1 induces the synthesis of proteins of 32, 70, and 80 kD (27). These proteins were not identified, but it was suggested that they represent heat shock proteins, SOD, or other proteins involved in the functional response of the islet to oxidative stress and toxic free radical formation (27). It therefore appears that IL 1 exerts time-dependent effects on protein synthesis in islets.…”

Interleukin‐1 induces rapid and transient expression of the c‐fos proto‐oncogene in isolated pancreatic islets and in purified β‐cells

“…It is also possible that c-Fos induces the transcription of specific genes whose products are involved in the reported cytotoxic effects of IL-1 on the B-cell [3][4][5][6]. Recently, Helqvist demonstrated that IL-1 induces the synthesis of several proteins in islets [20]. The identities of these proteins have not yet been determined, but the observation that IL-1 induces new protein synthesis in islets underscores the potential importance of specific gene products as mediators of IL-1 action.…”

“…Little is known about the mechanism of action of IL-1 following binding of the cytokine to its receptor, but the observation that IL-1 and its receptor are translocated to the nucleus in the murine T cell line EL-4 indicates that IL-1 may directly modulate the transcription of specific genes in target cells [19]. Helqvist has demonstrated that IL-1 induces protein synthesis in isolated islets [20], and we have recently demonstrated that inhibition of insulin secretion by IL-1 is prevented by an inhibitor of gene transcription (actinomycin D) [21]. These findings underscore the potential importance of new gene products in the functional effects of IL-1 on the/Y-cell.…”

Insulin-like growth factors prevent cytokine-mediated cell death in isolated islets of Langerhans from pre-diabetic non-obese diabetic mice

“…Human islets may be less sensitive to the detrimental effects of IL-1 (Rabinovitch et al 1990, MandrupPoulsen 1996, and the mechanisms of cell death following cytokine exposure may also involve necrosis (Delaney et al 1996). The initiation of cell damage in rats by IL-1 requires signalling via the high affinity IL-1 receptor, mRNA transcription and de novo protein synthesis, and diminished mitochondrial function (Helqvist et al 1989, Hammonds et al 1990). IL-1-induced damage to cell function and the loss of viability are both linked to the production of free radicals such as nitric oxide (NO), and specific inhibitors of NO formation will maintain cell viability (Stamler et al 1992, Kaneto et al 1995.…”