A Possible Role of CASK in Regulating the Function of the Mediator Complex in Neurons
Calcium/ calmodulin-dependent serine protein kinase (CASK) is a protein highly expressed in neuronal cells and associated to the etiology of neurodevelopmental disorders, such as intellectual disability and microcephaly. CASK is known to regulate the trafficking of membrane receptors at pre- and post-synaptic terminals. Accumulating evidence also suggests a role of CASK in transcriptional regulation; however, the molecular mechanism by which CASK modulate transcription in neurons is currently unknown. To investigate the underlying mechanism, I manipulated the level of CASK by infecting primary cortical neurons with a lentiviral particle carrying short hairpin (sh)RNA targeting CASK. Following CASK knockdown, I showed that the activation of neuronal activity-dependent genes induced by KCl treatment is significantly reduced in the absence of CASK. Based on the analysis of a protein-protein interactions database, I found that CASK can bind to mediator complex, which is required for transcription initiation and long-range chromatin interactions. Thus, I used chromatin immunoprecipitation followed by quantitative PCR to study the binding of mediator complex on CASK targets after the neurons were depolarized and CASK is knocked down. This study showed that the recruitment of the mediator on the regulatory regions of CASK targets is induced by neuronal activity, but it’s reduced in the absence of CASK. Such results suggest that CASK may regulate transcriptional initiation or long-range chromatin interactions via its interaction with the mediator complex. My findings provide novel insights into the mechanism by which CASK modulates activity-regulated gene expression in neuronal cells.