title: Protein phosphatase 2A and neutral sphingomyelinase 2 regulate IRAK-1 protein ubiquitination and degradation in response to interleukin-1beta.
abstract: The IL-1β signaling cascade is initiated by the phosphorylation of IL-1β receptor-associated kinase-1 (IRAK-1), followed by its ubiquitination and degradation. This paper investigates the regulation of IRAK-1 degradation in primary hepatocytes and in HEK cells overexpressing the IL-1β receptor. We provide evidence that protein phosphatase 2A (PP2A) is a negative regulator of the phosphorylation, Lys(48)-linked ubiquitination, and degradation of IRAK-1. PP2A catalytic activity increased within 30 min of stimulation with IL-1β. siRNA against PP2A catalytic subunit (PP2Ac) or treatment with pharmacological inhibitor, okadaic acid, enhanced IRAK-1 Lys(48)-linked ubiquitination and degradation. Direct interaction between PP2Ac and IRAK-1 was observed, suggesting that IRAK-1 might be a PP2A substrate. The mechanisms of PP2A activation by IL-1β involved neutral sphingomyelinase-2 (NSMase-2) and an accumulation of ceramide. Overexpression of NSMase-2 delayed IRAK-1 degradation in a PP2A-dependent manner, whereas NSMase-2 silencing had the opposite effect. The addition of sphingomyelinase, ceramide, or a proteasome inhibitor all led to retention of IRAK-1 at the cell membrane and to increased JNK phosphorylation. This study suggests that NSMase-2- and PP2A-dependent regulation of IRAK-1 degradation is a novel mechanism to fine tune the magnitude of IL-1β response.
authors.affiliation: Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky 40536, USA.
authors.forename: Aneta
authors.initials: A
authors.lastname: Dobierzewska
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Giltiay
authors.forename: Sathish
authors.initials: S
authors.lastname: Sabapathi
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Karakashian
authors.forename: Mariana N
authors.initials: MN
authors.lastname: Nikolova-Karakashian
mesh_terms: D000818:Animals; D020868:Gene Silencing; D057809:HEK293 Cells; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics / Q000378:metabolism*; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism*; D008297:Male; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D013108:Sphingomyelin Phosphodiesterase / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology*
chemical_list: C508585:IL1B protein, human; D053583:Interleukin-1beta; C507768:IRAK1 protein, human; C547807:IRAK1 protein, rat; D053592:Interleukin-1 Receptor-Associated Kinases; D054648:Protein Phosphatase 2; C491484:SMPD3 protein, human; C107180:Smpd3 protein, rat; D013108:Sphingomyelin Phosphodiesterase