MAPKAPK-3 also known as MAPKAP kinase 3, 3PK, MK3 is a member of the Ser/Thr protein kinase family. MAPKAPK-3 has been shown to be activated by growth inducers and stress stimulation of cells. In vitro studies have demonstrated that Erk, p38 MAP kinase, and Jun amino-terminal kinase are able to phosphorylate and activate MAPKAPK-3, which suggested a role for this kinase as an integrative element of signaling in both mitogen and stress responses. MAPKAPK-3 was reported to interact with, phosphorylate, and repress the activity of E47, which is a basic helix-loop-helix transcription factor involved in the regulation of tissue-specific gene expression and cell differentiation. MAPKAPK-3 may also support luteal maturation through the phosphorylation and activation of the nuclear transcription factor CREB.