MAPKAPK-3 has a single potential SH3-binding site in the proline-rich amino terminus, a putative ATP-binding site, 2 MAP kinase phosphorylation site motifs, and a putative nuclear localization signal. It shares 72% nucleotide and 75% amino acid identity with MAPKAPK-2. 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.
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