Activation of Neutral Sphingomyelinase‐2 and Protein Phosphatase 2A by Interleukin‐1B: role in IRAK‐1 degradation and intracellular translocation

Abstract

The objective of this study is to understand the role of Neutral sphingomyelinase‐2 (NSMase‐2) in hepatic response to Interleukin 1β (IL‐1β). The IL‐1β signaling cascade is initiated by rapid phosphorylation of IL‐1β receptor activated kinase‐1 (IRAK‐1) in response to ligand binding. Subsequently, the phoshporylated IRAK‐1 is ubiquitinated and degraded and the rate of its degradation is known to affect the magnitude of IL‐1β response. We show that the activity of protein phosphatase 2A (PP2A) gradually increases in response to IL‐1β stimulation with a maximum effect seen 30 minutes after the stimulation. The PP2A catalytic subunit directly interacts with IRAK‐1, indicating that IRAK‐1 is a novel PP2A substrate. Furthermore, treatment of primary rat hepatocytes or HEK293cells overexpressing the IL‐1β receptor with PP2A inhibitor, okadaic acid, enhances the rate of IL‐1β‐induced IRAK‐1 ubiquitination and degradation.NSMase‐2 mediates the activation of PP2A by IL‐1β. Overexpression of NSMase‐2 enhances PP2A activity and delays IRAK‐1 degradation. In contrast, NSMase‐2 silencing or inhibition by pharmacological inhibitor causes faster IRAK‐1 degradation. NSMase‐2 also plays a role in IRAK‐1 intracellular translocation in response to IL‐1β. These experiment identify NSMase 2‐and PP2A as novel physiological regulators of IRAK‐1 phosphorylation.Supported by NIA RO1 AG026711.