Transcriptional Regulatory Mechanisms of Freud-1, a Novel Mental Retardation Gene

CaMKIV-Mediated Phosphorylation Inactivates Freud-1/CC2D1A Repression for Calcium-Dependent 5-HT1A Receptor Gene Induction

“…The S644D/T780D mutant, meant to be a phosphomimic, also bound to complexes 1, 2 and 3. However, unlike the other mutants, the S644D/T780D mutant showed reduced binding to phosphatidyl inositol poly-phosphorylated forms [ 30 ], suggesting a partial impairment of the Freud-1 function in this mutant. These results indicate that the Freud-1 phospho-site mutants retain binding to the DRE, but that the mutation of the T780 site alters the complex formed.…”

“…However, the mutation of the S644 or T780 sites to alanine or aspartate did not prevent Freud-1-DRE binding in vitro or the Freud-1-mediated repression in cells, indicating that these phosphorylation-resistant mutants remain functional. By contrast, unlike the alanine mutants, the S644D/T780D did show reduced binding to phosphatidyl inositol poly-phosphates, suggesting a partial impairment of this mutant [ 30 ]. Importantly, these mutants retained repressor function but prevented the inactivation of Freud-1 by CaMKIV, indicating the role of Ser644 and Thr780 phosphorylation in the CaMKIV-induced inactivation of Freud-1 repressor activity.…”

“…The ability of Freud-1 S644 and T780 mutants to bind and repress at the 5-HT1A DRE suggests that these mutations do not impair the recruitment of key regulators, but it is possible that the mutations may shift the HDAC dependence of the Freud-1 repressor function. In addition to interacting with transcriptional regulators, Freud-1 also interacts with a variety of phosphatidyl inositol 3′-phosphate lipids [ 30 ] and cytoplasmic proteins including PDK1-Akt scaffolding, endocytotic CHMP-4B/4C and centrosome cohesin proteins [ 3 ]. However, since nuclear-localized CaMKIV blocked the Freud-1 repressor function while CaMKIIα did not, this indicates that nuclear rather than cytoplasmic phosphorylation may be critical.…”