Hyperactive Variants of p38α Induce, whereas Hyperactive Variants of p38γ Suppress, Activating Protein 1-mediated Transcription

Abstract

The p38 family of kinases is a subgroup of the mitogen-activated protein kinase family. It is composed of four isoforms and is involved in critical biological processes as well as in inflammatory diseases. The exact unique role of each p38 isoform in these processes is not understood well. To approach this question we have been developing intrinsically active variants of p38s. Recently we described a series of mutants of the human p38␣, which were spontaneously active as recombinant proteins purified from Escherichia coli cells. We show here that some of these mutants are spontaneously active in several mammalian cells in culture. The spontaneous activity of some mutants is higher than the activity of the fully activated wild type counterpart. We further produced mutants of the other p38 isoforms and found that p38␤ D176A , p38␥ D179A , p38␦ D176A , and p38␦ F324S are spontaneously active in vivo. The active mutants are also spontaneously phosphorylated. To test whether the mutants actually fulfill downstream duties of p38 proteins, we tested their effect on activating protein 1(AP-1)-mediated transcription. Active mutants of p38␣ induced AP-1-driven reporter genes, as well as the c-jun and c-fos promoters. An active variant of p38␥ suppressed AP-1-mediated transcription. When active variants of p38␣ and p38␥ were co-expressed, AP-1 activity was not induced, showing that p38␥ is dominant over p38␣ with respect to AP-1 activation. Thus, intrinsically active variants that are spontaneously active in vivo have been obtained for all p38 isoforms. These variants have disclosed different effects of each isoform on AP-1 activity.

Induction of p38δ Expression Plays an Essential Role in Oncogenic ras-Induced Senescence

“…We utilized an intrinsically active mutant (F324S) of p38␦ that had acquired spontaneous protein kinase activity in vitro and in vivo, while preserving the substrate and inhibitor specificities of the wild-type protein (35,36). The wild type and the constitutively active F324S mutant of p38␦ were transduced into BJ cells via retrovirus.…”

Effect of pressure overload-induced hypertrophy on the expression and localization of p38 MAP kinase isoforms in the mouse heart

“…Although p38γ was previously reported to be exclusively cytosolic in neonatal rat ventricular myocytes [3], in the present study, p38γ immunoreactivity accumulated in the nuclei during chronic pressure overload. Nuclear substrates for p38γ identified to date include transcription factors such as ATF2, AP-1, Elk-1, MEF2A, p53, SAP1 and SAP2 [40][41][42]. MEF2 transcription factors are involved in the regulation of inducible gene expression during hypertrophy and MEF2 activity is increased during pressure or volume overload [43].…”

Tuning of Protein Kinase Circuitry by p38α Is Vital for Epithelial Tissue Homeostasis

“…Plasmid DNA and siRNA Transfection-Plasmid vectors expressing TAK1 and the constitutively active p38␣ variant (p38␣ CA ), p38␣ D176A/F327S, were described previously (32,33). Control siRNA was an siRNA negative control duplex with medium GC content (Invitrogen).…”