Synergy between RNA editing and alternative splicing modulates the biological properties of the voltage-gated calcium...

Alternative splicing and adenosine-to-inosine (A-to-I) RNA editing are post-transcriptional mechanisms that promote proteomic diversity in the brain. The impact of RNA editing on brain physiology is underscored by its association with the etiology and pathogenesis of various neurological and neurodegenerative diseases. Alternative splicing of exon 43 within the CaV1.3 C-terminus produces long (CaV1.3_L) and short (CaV1.3_43S) variants exhibiting distinct gating and pharmacological properties. While the physiological role of CaV1.3 A-to-I RNA editing in brain function is still unfolding, recent findings indicate that unedited CaV1.3 channels display larger calcium (Ca²⁺) influx and enhanced neuronal excitability, suggesting that A-to-I RNA editing may act as a negative regulator of neuronal Ca²⁺ signaling. However, it remains unclear which specific splice variants of CaV1.3 undergo RNA editing. We discovered an unexpected link between alternative splicing and RNA editing, where generation of the CaV1.3_43S variant results in a threefold increase in RNA editing at the IQ site. The CaV1.3_43S variant undergoes A-to-I RNA editing at two sites within its calmodulin-binding IQ domain, giving rise to three different edited variants. Functional analysis revealed that A-to-I RNA editing markedly decreases current density and induces a depolarizing shift in the current window, aligning the edited short variant's properties with those of the long variant. Our findings suggest that A-to-I RNA editing serves as a physiological mechanism regulating the "short" gating properties of the CaV1.3_43S variant and position A-to-I RNA editing of CaV1.3_43S variant as a neuroprotective physiological mechanism that prevents Ca²⁺ overload, especially in neurons susceptible to Ca²⁺ toxicity.