Phosphorylation by CaMKIV regulates the transcriptional repressor activity and half-life of REST/NRSF

Repressor Element-1 (RE1)-Silencing Transcription Factor (REST) homeostatically regulates neural activity by repressing a large cluster of neural genes. However, whether REST can be regulated by calcium(2+) (Ca²⁺)-activated kinases is unknown. We investigated Ca²⁺/calmodulin-dependent protein kinases (CaMKs) as upstream regulators of REST fate and activity. We show that REST is phosphorylated by CaMKIV at Ser³²² site in the fifth-to-sixth Zn-finger domain linker. A phosphomimic mutant at Ser³²² decreased REST repressor activity and caused its transition to the cytosol, followed by degradation. Molecular dynamics simulations of the phosphomimic REST mutant revealed a sharp decrease in the stability of the REST-RE1 binding interface. Phosphorylation of REST by CaMKIV suppressed the downscaling of excitatory postsynaptic current (EPSC) frequency in response to hyperactivity. Moreover, the homeostatic effects of CaMKIV on EPSC amplitude were inhibited in the absence of REST. The results demonstrate that CaMKIV phosphorylation plays a crucial role in regulating REST levels and repressor activity and that an interplay exists between CaMKIV and REST in homeostatic plasticity mechanisms.