MAPK-activated Protein Kinase-2 (MK2)-mediated Formation and Phosphorylation-regulated Dissociation of the Signal Complex Consisting of p38, MK2, Akt, and Hsp27

Abstract

The p38 MAPK and heat shock protein 27 (hsp27) form a signaling complex with serine/threonine kinase Akt and MAPK-activated protein kinase-2 (MK2), which plays an important role in controlling stress-induced apoptosis and reorganizing actin cytoskeleton. However, regulation of the complex is poorly understood. In this study, the interaction between p38 and hsp27 was visualized in single living L929 cells using fluorescence resonance energy transfer technology, while their association with Akt was examined by immunoprecipitation analysis. Under normal growth conditions, p38 kinase constitutively interacts with hsp27. When cells were exposed to H 2 O 2 or stimulated by arachidonic acid, this interaction was disrupted. However, inhibition of the activation of p38 and Akt by selective inhibitors or overexpression of the kinase-dead mutant of p38 diminished such effects. Furthermore, mutation of phosphorylation sites of hsp27 renders the interaction resistant to H 2 O 2 and arachidonic acid. It was interesting to find that the interaction disappeared in the cells from MK2-knock-out mice or the cells treated with lemptomycin B that blocks export of MK2 from nucleus to cytosol. However, MK2 is not required for the association of hsp27 with Akt. This study suggests that MK2 mediates the incorporation of p38 into the pre-existing complex of hsp27 with Akt. Phosphorylation of hsp27 finally breaks the signaling complex.

Arachidonic Acid Stimulates Cell Adhesion through a Novel p38 MAPK-RhoA Signaling Pathway That Involves Heat Shock Protein 27

“…The data suggest that phospho-HSP27 is the critical species involved in the complex, but we cannot rule out that p38 activation modulates the activity of another factor that serves to facilitate formation of an HSP27⅐p115 complex. The presence of HSP27 is consistent with and complementary to other findings that suggest HSP27 can serve a scaffolding function for various kinase complexes (75,76). Thus, our data are compatible with a model (Fig.…”

Characterization of hsp27 kinases activated by elevated aortic pressure in heart

“…Of the kinases shown to catalyze the phosphorylation of hsp27, PKC is lipid-dependent and the experiments conducted herein were performed without lipid and in the presence of EGTA plus a peptide inhibitor of PKA (PKI, 1 μM); hence, these kinases would not be active. PKB forms a complex with [50] and phosphorylates hsp27 [41,42]. However, activated PKB requires higher [NaCl] to elute from Mono Q than observed for the hsp27 kinase activities reported herein.…”

Hsp27 Regulates Akt Activation and Polymorphonuclear Leukocyte Apoptosis by Scaffolding MK2 to Akt Signal Complex

“…These studies indicated the importance of Akt/Hsp27 interaction to Akt activation and PMN survival. Recently Zheng et al (30) demonstrated that MK2 was required for p38 MAPK/ Hsp27 interaction. However, MK2 was not required for association of Hsp27 with Akt.…”