Inhibition of Mitogen-Activated Kinase Kinase Kinase 3 Activity through Phosphorylation by the Serum- and Glucocorticoid-Induced Kinase 1

Abstract

The mitogen-activated protein kinase kinase kinase 3 (MEKK3) is a member of the MAP kinase family whose cellular activity is elevated in response to growth factors, oxidative stress, and hyperosmolar conditions. MEKK3 regulates MKK3 and MKK5/6/7. MEKK3 is involved distinctively in the signal pathway for blocking cell proliferation and cell cycle progression, contradictory to the biological responses commonly associated with other members of MEKKs. Based information concerning the substrate specificity of serum- and glucocorticoid-induced kinase 1 (SGK1), R-x-R-x-x-(S/T)-phi, where phi indicates a hydrophobic amino acid, two putative phosphorylation sites (Ser(166) and Ser(337)) were found in MEKK3. It was shown that the recombinant MEKK3 protein and fluorescein-labeled MEKK3 peptides (FITC-(159)epRsRhlSVi(168) and FITC-(330)dpRgRlpSAd(339)) are phosphorylated by SGK1 in vitro. It was also observed that the intrinsic kinase activity of MEKK3 on Ser(189) of MKK3 (equivalent to Ser(207) of MKK6) decreased along with phosphorylation of Ser(166) and Ser(337) in MEKK3 in vitro and in vivo. Therefore, it is suggested that SGK1 inhibits MEKK3-MKK3/6 signal transduction by phosphorylation of MEKK3.

Regulation Fe65 localization to the nucleus by SGK1 phosphorylation of its Ser566 residue

“…The identification and characterization of SGK1 substrates may provide clues to our understanding of how SGK1 contributes to cell survival and death (3,4,8,10,11,18). We demonstrated that Fe65 is a SGK1 substrate that contains the consensus motif RxRxxS/Tφ: where φ is a hydrophobic amino acid, which subsequently demonstrated that phosphorylation of Fe65 by SGK1 controls its subcellular localization (Figs.…”

“…After electrophoresis, the gel was photographed on a transilluminator. The optical density of the phosphorylated product was measured by densitometry (10,22).…”

“…SGK1 has been identified as a protein that was designed to promote cell survival, it has the same function as Akt kinase (7)(8)(9). We found that SGK1 plays a role in the phosphorylation of MEKK3 and, thus, inhibits its kinase activity (10). The consensus SGK1 substrate site has been described by the structural formula R-X-R-X-X-(S/T)-φ, where φ is any hydrophobic amino acid.…”

IL-6 activates serum and glucocorticoid kinase via p38α mitogen-activated protein kinase pathway

“…Recently, the mitogen-activated protein kinase kinase kinase 3 (MEKK3) has been shown to be a target substrate for SGK (7). MEKK3 lies upstream of mitogen-activated protein kinase kinase (MKK) 3 and 6, which are activators of p38 MAPK signaling.…”

Hypotonic activation of volume-sensitive outwardly rectifying chloride channels in cultured PASMCs is modulated by SGK

“…SGK mediates cell cycle progression (8,11) and transmembrane ion and metabolite transport (30). SGK is involved in osmotic cell adaptation via regulation of epithelial Na ϩ channels in kidney-collecting duct (A6) cells (49).…”