Dahimene, S. | Search bioRxiv

bioRxiv2023

The interplay between splicing of exons 18a and 47 differentially affects membrane targeting and function of human CaV2.2

N-type calcium channels (CaV2.2) are predominantly localized in presynaptic terminals, and are particularly important for pain transmission in the spinal cord. Furthermore, they have multiple isoforms, conferred by alternatively-spliced or cassette exons, which are differentially expressed. Here we have examined alternatively-spliced exon47 variants that encode a long or short C-terminus in human CaV2.2. In the Ensembl database, all short exon47-containing transcripts were associated with the absence of exon 18a, therefore we also examined effect of inclusion or absence of exon18a, combinatorially with the exon47 splice variants. We found that long exon47, only in the additional presence of exon18a, results in CaV2.2 currents that have a 3.6-fold greater maximum conductance than the other three combinations. In contrast, cell surface expression of CaV2.2 in both tsA-201 cells and hippocampal neurons is increased [~]4-fold by long exon47 relative to short exon47, in either the presence or absence of exon18a. This surprising discrepancy between trafficking and function indicates that cell surface expression is enhanced by long exon47, independently of exon 18a. However, in the presence of exon47, exon18a mediates an additional permissive effect on CaV2.2 gating. We also investigated the SNP in exon47 that has been linked to schizophrenia and Parkinsons disease, which we found is only non-synonymous in the short exon47 C-terminal isoform, resulting in two minor alleles. This study highlights the importance of investigating the combinatorial effects of exon inclusion, rather than each in isolation, in order to increase our understanding of calcium channel function. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/557884v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@132c8fborg.highwire.dtl.DTLVardef@12910ccorg.highwire.dtl.DTLVardef@10de072org.highwire.dtl.DTLVardef@a86f7_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Identification that ADAM17 mediates proteolytic maturation of calcium channel auxiliary α2δ subunits, and enables calcium current enhancement

The auxiliary 2{delta} subunits of voltage-gated calcium (CaV) channels are key to augmenting expression and function of CaV1 and CaV2 channels, and are also important drug targets in several therapeutic areas, including neuropathic pain. The 2{delta} proteins are translated as pre-proteins encoding both 2 and {delta}, and post-translationally proteolysed into 2 and {delta} subunits, which remain associated as a complex. In this study we have identified ADAM17 as a key protease involved in proteolytic processing of pro-2{delta}-1 and 2{delta}-3 subunits. We provide three lines of evidence: firstly, proteolytic cleavage is inhibited by chemical inhibitors of particular metalloproteases, including ADAM17. Secondly, proteolytic cleavage of both 2{delta}-1 and 2{delta}-3 is markedly reduced in cell lines by knockout of ADAM17 but not ADAM10. Thirdly, proteolytic cleavage is reduced by the N-terminal active domain of TIMP-3 (N-TIMP-3), which selectively inhibits ADAM17. We have found previously that proteolytic cleavage into mature 2{delta} is essential for the enhancement of CaV function, and in agreement, knockout of ADAM17 inhibited the ability of 2{delta}-1 to enhance both CaV2.2 and CaV1.2 calcium currents. Thus, our study identifies ADAM17 as a key protease required for proteolytic maturation of 2{delta}-1 and 2{delta}-3, and thus a potential drug target in neuropathic pain.

neuroscience↗