Differential neuronal targeting of a new and two 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 interact directly 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 (CGCs) and modulates P/Q-type calcium currents in tsA201 cells and CaV2.1 surface expression in neurons. Compared with the other two known full-length β4 variants (β4a and β4b), β4e is most abundantly expressed in the distal axon, but lacks nuclear-targeting properties. To determine the importance of nuclear targeting of β4 subunits for transcriptional regulation, we performed whole-genome expression profiling of CGCs from lethargic (β4-null) 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 variants in neurons, with β4b playing a dual role in channel modulation and gene regulation, whereas the newly detected β4e variant serves exclusively in calcium-channel-dependent functions.
Department of Physiology and Medical Physics, Medical University Innsbruck, 6020 Innsbruck, Austria; Center of Physiology and Pharmacology, Department of Neurophysiology and Pharmacology, Medical University Vienna, 1090 Vienna, Austria; Division of Molecular Pathophysiology, Biocenter; Division of Molecular Biology; Biocenter; Medical University Innsbruck, 6020 Innsbruck, Austria; and Experimental and Clinical Pharmacology and Toxicology, University of Saarland, 66421 Homburg, Germany.
Solmaz
S
Etemad
Gerald J
GJ
Obermair
Daniel
D
Bindreither
Ariane
A
Benedetti
Ruslan
R
Stanika
Valentina
V
Di Biase
Verena
V
Burtscher
Alexandra
A
Koschak
Reinhard
R
Kofler
Stephan
S
Geley
Alexandra
A
Wille
Alexandra
A
Lusser
Veit
V
Flockerzi
Bernhard E
BE
Flucher
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D015220:Calcium Channels / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015870:Gene Expression / Q000235:genetics*; D006624:Hippocampus / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
C491530:Cacnb4 protein, mouse; D015220:Calcium Channels; D020033:Protein Isoforms; D021122:Protein Subunits
Ca2+ channel; CaV2.1; Cacnb4; cerebellar granule cells; hippocampal neurons; lethargic mice