Il-1β Transduces Different Signals than IL-1α Leading to Class II Antigen Expression on β-Insulinoma Rin-5AH Cells through Specific Receptors

Abstract

Like most cytokines, IL-1 transduces its signals for growth, differentiation and diverse cellular functions after binding to specific receptors on the cell surface. Up to now two IL-1 receptors have been reported, type I which induces signal transduction and type II which binds IL-1 but does not transduce signalling. By using the rat insulinoma RIN-5AH cell line that expresses both types of receptor mRNA, and computer-assisted binding analysis, we show that interleukin-1β (IL-1β) binds to a single class of high affinity receptors with a K_d of 155 pmol/l. The average number of receptors on adherent cell layer is calculated to be 7300 per cell. ¹²⁵I-IL-1β binding can be competed out by unlabelled IL-1β. ¹²⁵I-IL-1α binding can be also obtained and is subject to competition by cold IL-1α. Its saturation curve, however, varies within experiments due to differential receptor up-regulation. These results have also been confirmed by FACS analysis using specific antibodies to type I and II IL-1 receptors, where type I receptor antibody binds strongly to RIN-5AH cells, and type II receptor antibody shows weak staining, also due to inadequate receptor up-regulation.

In order to determine whether functional signal transduction occurs via the receptors detected, it is shown that IL-1β is able to induce MHC class II antigen expression on the surface of the RIN cells, whereas IL-1α is unable to do so, indicating different signal reception by the cells. IL-1β-induced class II upregulation shows moderate signs of p21ras or/and PKC dependency, whereas IL-1α strongly activates both pathways that probably regulate different functions. Finally, both IL-1α and β induce nitric oxide (NO) production in a time-dependent fashion which appears to be unrelated to the signals and pathways described, but may be involved in the onset of autoimmune type 1 diabetes.