Regulation of 5-HT1A repressor human Freud-1CC2D1A by calciumcalmodulin sensitive phosphorylation

Abstract

Altered regulation of the serotonin system is implicated in depression and anxiety. The 5-hydroxytryptamine 1A (5-HT1A) receptor is a major regulator of the serotonin system. We have previously identified a calcium-regulated transcription factor, Freud-1, which represses 5-HT1A receptor expression in neurons. Analysis of human Freud-1 amino acid sequence revealed the presence of two putative calcium calmodulin kinase (CaMK) phosphorylation sites. We demonstrate the ability of Freud-1 to be phosphorylated by CaMKII in vitro. Mutations of Freud-1 phosphorylation sites reduced CaMKII mediated phosphorylation. Furthermore, CaMKII phosphorylation inhibited binding of Freud-1 to the 5-HT1A promoter elements in vitro. In cells, CaMKIV induced phosphorylation of Freud-1 and prevented Freud-1 induced repressor activity. Freud-1 mutants prevented the inhibitory effect of CaMKIV on Freud-1 mediated repression of 5-HT1A receptor gene. Together these results implicate phosphorylation of Freud-1 by CaMK, in calcium-dependent regulation of 5-HT1A receptor expression, could participate in antidepressant actions to restore 5-HT1A receptor levels.