Neuronal Activity Regulates Matrin 3 Abundance and Function in a Calcium-dependent Manner Through Calpain-mediated Cleavage and Calmodulin Binding

RNA-binding protein (RBP) dysfunction is a fundamental hallmark of amyotrophic lateral sclerosis (ALS) and related neuromuscular disorders. Abnormal neuronal excitability is also a conserved feature in ALS patients and disease models, yet little is known about how activity-dependent processes regulate RBP levels and functions. Mutations in the gene encoding the RBP Matrin 3 (MATR3) cause familial disease, and MATR3 pathology has also been observed in sporadic ALS, suggesting a key role for MATR3 in disease pathogenesis. Here, we show that glutamatergic activity drives MATR3 degradation through an NMDA receptor-, Ca-, and calpain-dependent mechanism. The most common pathogenic mutation renders it resistant to calpain degradation, suggesting a link between activity-dependent MATR3 regulation and disease. We also demonstrate that Ca regulates MATR3 through a nondegradative process involving the binding of Ca/calmodulin to MATR3 and inhibition of its RNA-binding ability. These findings indicate that neuronal activity impacts both the abundance and function of MATR3, underscoring the effect of activity on RBPs and providing a foundation for further study of Ca-coupled regulation of RBPs implicated in ALS and related neurological diseases.