Differential neuronal targeting of a new and 2 known calcium channel β4 subunit splice variants correlates with their regulation of gene expression

The β subunits of voltage-gated calcium channels regulate surface expression and gating of CaV1 and CaV2 α1 subunits, and thus contribute to neuronal excitability, neurotransmitter release and calcium-induced gene regulation. In addition certain β 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 β isoforms derived from four genes and abundant alternative splicing, little is known about the roles of individual β variants in specific neuronal functions. In the present study, an alternatively spliced β4 subunit lacking the variable N-terminus (β4e) 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 β4 variants (β4a, β4b) β4e is most abundantly expressed in the distal axon, but lacks nuclear targeting properties. To examine the importance of nuclear targeting of β4 subunits for transcriptional regulation, we performed whole genome expression profiling of CGCs from lethargic mice individually reconstituted with β4a, β4b, and β4e. Notably, the number of genes regulated by each β4 splice variant correlated with the rank order of their nuclear targeting properties (β4b> β4a> β4e). Together these findings support isoform-specific functions of β4 splice variant in neurons, with β4b playing a dual role in channel modulation and gene regulation, while the newly detected β4e variant serves exclusively in calcium channel-dependent functions. We used microarrays to identify gene expression changes caused by β4 splice variants (β4a, β4b and β4e) of the voltage gated calcium channel in cultured cerebellar granule cells of lethargic mice Cultured cerebellar granule cells from lethargic (129/SvJ background) mice reconstituted with the β4 splice variants (β4a, β4b and β4e) were compared to eGFP transfected controls