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The molecular events that lead to the perception of pain are a key research field in medicine and drug discovery. The opioid receptors modulate pain signaling in response to endogenous peptide ligands and opiate drugs such as morphine. The kappa opioid receptor plays a key role in the profound analgesia of opiates and is activated by the endogenous peptide ligand dynorphin, encoded by the prodynorphin gene. Production of prodynorphin is transcriptionally regulated by a downstream regulatory element (DRE) in the prodynorphin gene. A transcription factor called DREAM (DRE antagonistic modulator) binds to the DRE and represses prodynorphin transcription when bound. DREAM binds calcium with 4 EF-hand motifs and the binding of DREAM to DNA is repressed in the presence of calcium. Many transcription factors are regulated by calcium indirectly through calcium sensitive kinases and phosphatases, but DREAM is unique to date in being a transcription factor that directly binds calcium and is regulated by calcium binding. DREAM may also regulate other genes such as c-fos. DREAM is expressed in spinal cord neurons in regions involved in pain signaling. The regulation of prodynorphin expression by DREAM also leads to the hypothesis that DREAM is involved in pain signaling. Transgenic mice lacking the DREAM gene were unusually pain insensitive and had elevated spinal levels of dynorphin and tonic activation of the kappa opioid receptor, supporting this hypothesis. Other functions of DREAM may exist such as regulation of presenilins and potassium channel activity in the heart. DREAM is also known as calsenilin and KChIP3 through its association with these other proteins. These processes were not affected in mice lacking the DREAM gene however. (This definition may be outdated - see the DesignNote.)
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