SAPK/Erk kinase (SEK1), also known as MEK4 or MKK4 or Jun kinase kinase (JNKK), activates the MAP kinase homologues SAPK and JNK in response to various cellular stresses and inflammatory cytokines . Activation of SEK1 occurs through MEKK phosphorylation of serine and threonine residues at positions 257 and 261, respectively. Like MEK, SEK is a dual-specificity protein kinase that phosphorylates SAPK/JNK at a conserved T*PY* site in its activation loop . Phosphorylation by Akt at Ser80 inhibits SEK1 and suppresses stress-activated signal transduction .
