Differential neuronal targeting of a new and 2 known calcium channel 4 subunit splice variants correlates with their regulation of gene expression

The subunits of voltage-gated calcium channels regulate surface expression and gating of CaV1 and CaV2 1 subunits, and thus contribute to neuronal excitability, neurotransmitter release and calcium-induced gene regulation. In addition certain subunits are targeted into the nucleus, where they directly interact with the epigenetic machinery. Whereas their involvement in this multitude of functions is reflected by a great molecular heterogeneity of isoforms derived from four genes and abundant alternative splicing, little is known about the roles of individual variants in specific neuronal functions. In the present study, an alternatively spliced 4 subunit lacking the variable N-terminus (4e) is identified. It is highly expressed in mouse cerebellum and cultured cerebellar granule cells (CGC) and modulates P/Q-type calcium currents in tsA cells and CaV2.1 surface expression in neurons. Compared to the other two known full-length 4 variants (4a, 4b) 4e is most abundantly expressed in the distal axon, but lacks nuclear targeting properties. To examine the importance of nuclear targeting of 4 subunits for transcriptional regulation, we performed whole genome expression profiling of CGCs from lethargic mice individually reconstituted with 4a, 4b, and 4e. Notably, the number of genes regulated by each 4 splice variant correlated with the rank order of their nuclear targeting properties (4b> 4a> 4e). Together these findings support isoform-specific functions of 4 splice variant in neurons, with 4b playing a dual role in channel modulation and gene regulation, while the newly detected 4e variant serves exclusively in calcium channel-dependent functions.

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Etemad S, Obermair GJ, Bindreither D, Benedetti A, Stanika R, Di Biase V, Burtscher V, Koschak A, Kofler R, Geley S, Wille A, Lusser A, Flockerzi V, Flucher BE