p38 MAPK Regulates Group IIa Phospholipase A2Expression in Interleukin-1β-stimulated Rat Neonatal Cardiomyocytes

Abstract

Group IIa phospholipase A 2 (GIIa PLA 2 ) is released by some cells in response to interleukin-1␤. The purpose of this study was to determine whether interleukin-1␤ would stimulate the synthesis and release of GIIa PLA 2 from cardiomyocytes, and to define the role of p38 MAPK and cytosolic PLA 2 in the regulation of this process. Whereas GIIa PLA 2 mRNA was not identified in untreated cells, exposure to interleukin-1␤ resulted in the sustained expression of GIIa PLA 2 mRNA. Interleukin-1␤ also stimulated a progressive increase in cellular and extracellular GIIa PLA 2 protein levels and increased extracellular PLA 2 activity 70-fold. In addition, interleukin-1␤ stimulated the p38 MAPK-dependent activation of the downstream MAPK-activated protein kinase, MAPKAP-K2. Treatment with the p38 MAPK inhibitor, SB202190, decreased interleukin-1␤ stimulated MAPKAP-K2 activity, GIIa PLA 2 mRNA expression, GIIa PLA 2 protein synthesis, and the release of extracellular PLA 2 activity. Infection with an adenovirus encoding a constitutively active form of MKK6, MKK6(Glu), which selectively phosphorylates p38 MAPK, induced cellular GIIa PLA 2 protein synthesis and the release of GIIa PLA 2 and increased extracellular PLA 2 activity 3-fold. In contrast, infection with an adenovirus encoding a phosphorylation-resistant MKK6, MKK6(A), did not result in GIIa PLA 2 protein synthesis or release by unstimulated cardiomyocytes. In addition, infection with an adenovirus encoding MKK6(A) abrogated GIIa PLA 2 protein synthesis and release by interleukin-1␤-stimulated cells. These results provide direct evidence that p38 MAPK activation was necessary for interleukin-1␤-induced synthesis and release of GIIa PLA 2 by cardiomyocytes. Interleukin-1␤ (IL-1␤)1 has been implicated in the pathophysiology of a variety of myocardial disease states, including cardiac hypertrophy, congestive heart failure, and ischemiareperfusion injury (1-3). IL-1␤ is thought to participate in the genesis of these cardiac pathologies through the induction of specific genes, such as inducible nitric-oxide synthase, cyclooxygenase-2, matrix metalloproteinase, vascular endothelial growth factor, and ␣B-crystallin (4 -6). As the range of genes that are induced by cardiomyocytes following exposure to IL-1␤ have not been fully defined, the precise mechanisms that lead to the phenotypic changes that follow exposure to IL-1␤ remain incompletely understood.The effects of IL-1␤ in cardiomyocytes are mediated, in part, by stimulation of mitogen-activated protein kinase (MAPK) enzymes. The MAPK enzymes include p38 MAPK, p42/44 MAPK, and JNK. Molecular cloning studies have led to the identification of four distinct p38 MAPK isoforms as follows: p38␣, p38␤2, p38␥, and p38␦ (7). The MAPK enzymes exert distinct biological functions, as p38␣ MAPK promoted apoptosis, whereas p38␤2 MAPK promoted myocardial hypertrophy and cell survival (8, 9). p38 MAPK activity is increased by phosphorylation on a Thr-Gly-Tyr motif by MAPK kinases, including MKK3 and MKK6 (10,11). MKK6 forms a function...

Phosphorylation of HSF1 by MAPK-Activated Protein Kinase 2 on Serine 121, Inhibits Transcriptional Activity and Promotes HSP90 Binding

“…4 MK2 is an inducible kinase activated by p38MAPK and through p38 is regulated by cell stress, lipopolysaccharide, and the cytokines IL1␤ and tumor necrosis factor ␣ (30 -32). MK2 plays an important physiological role in the acute inflammatory response, enhancing the expression of proinflammatory cytokines through mRNA stabilization and increasing expression of inflammatory enzymes including lipoxygenase and phospholipase A (28,(33)(34)(35)(36). Inhibition of HSF1 by MK2, as we suggest here, would be consonant with a role in inflammation, as HSF1 inhibition would relieve the repression on cytokine promoters (3,4,37).…”

Interleukin-1β affects calcium signaling and in vitro cell migration of astrocyte progenitors

“…Under these conditions, the outgrowth index (OI) of CM-treated neurospheres was 7.66±0.94 (N=29 neurospheres), while the OI of control neurospheres was 11.04±0.26 (N=66 neurospheres). To further investigate which of the main inflammatory mediators contained in the conditioned media from activated microglia was mediating the reduced OI, we treated neurospheres with two pro-inflammatory cytokines, IL-1β and TNFα that have been previously reported to be released from activated microglia (Aloisi et al, 1997;Degousee et al, 2001;Meme et al, 2006).…”

“…Microglia and astrocytes are the main sources of pro-inflammatory cytokines in the CNS (Aloisi, 2001;Aloisi et al, 1992;Degousee et al, 2001;Gehrmann et al, 1995;Meme et al, 2007) and some of these inflammatory mediators, such as IL-1β and TNFα, were reported to affect in vitro neural progenitor cell proliferation (Wang et al, 2007;Widera et al, 2006) and migration (Ben-Hur et al, 2003a).…”

c-Jun N-terminal Kinase-mediated Stabilization of Microsomal Prostaglandin E2 Synthase-1 mRNA Regulates Delayed Microsomal Prostaglandin E2 Synthase-1 Expression and Prostaglandin E2 Biosynthesis by Cardiomyocytes

“…In all studies, isolated cells had characteristic features of cardiomyocytes and beat spontaneously. The methodology used for RNA isolation and Northern and immunoblot analysis has been described (12,13). All studies were approved by the Animal Care Committee of the Toronto General Hospital.…”

“…Primary Cell Culture and Experimental Protocol-Rat neonatal cardiomyocytes were isolated from the hearts of 1-to 2-day-old SpragueDawley rats (12). Mouse neonatal cardiomyocytes were isolated from 1-to 2-day-old jnk1 Ϫ/Ϫ , jnk1 ϩ/ϩ , jnk2 Ϫ/Ϫ , jnk2 ϩ/ϩ , Ptges ϩ/ϩ , or Ptges Ϫ/Ϫ mice using identical methodology.…”