Targeting the CACNA1A IRES as a Treatment for Spinocerebellar Ataxia Type 6

Cerebellum. 2018 Feb;17(1):72-77. doi: 10.1007/s12311-018-0917-6.


We have discovered that the P/Q-type voltage-gated Ca2+ channel (VGCC) gene, CACNA1A, encodes both the α1A (Cav2.1) subunit and a newly recognized transcription factor, α1ACT, by means of a novel internal ribosomal entry site (IRES) within the α1A C-terminal coding region. α1ACT, when mutated with an expansion of the polyglutamine tract in the C-terminus, gives rise to spinocerebellar ataxia type 6 (SCA6). Because silencing of the entire CACNA1A gene would result in the loss of the essential Cav2.1 channel, the IRES controlling α1ACT expression is an excellent target for selective silencing of α1ACT as a therapeutic intervention for SCA6. We performed a high-throughput screen of FDA-approved small molecules using a dual luciferase reporter system and identified ten hits able to selectively inhibit the IRES. We identified four main candidates that showed selective suppression of α1ACT relative to α1A in HEK cells expressing a native CACNA1A vector. We previously pursued another avenue of molecular intervention through miRNA silencing. We studied three human miRNAs (miRNA-711, -3191-5p, -4786) that would potentially bind to sequences within the CACNA1A IRES region, based on an miRNA prediction program. Only miRNA-3191-5p was found to selectively inhibit the translation of α1ACT in cells. We developed a hyperacute model of SCA6 in mice by injecting a pathogenic form of the IRES-mediated α1ACT (AAV9-α1ACTQ33). Finally, we tested the effectiveness of the miRNA therapy by co-expressing either control miRNA or miRNA-3191-5p and found that miRNA-3191-5p decreased the levels of α1ACTQ33 and prevented the hyperacute disease in mice. These studies provide the proof of principle that a therapy directed at selectively preventing α1ACT expression could be used to treat SCA6.

Keywords: Cap; IRES; Independent; SCA6; Small molecules; Spinocerebellar; Therapeutics; miRNA.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Ajmaline / pharmacology
  • Animals
  • Calcium Channels / genetics
  • Calcium Channels / metabolism*
  • Calcium Channels, L-Type / genetics
  • Calcium Channels, L-Type / metabolism*
  • Disease Models, Animal
  • Dose-Response Relationship, Drug
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / physiology*
  • HEK293 Cells
  • Humans
  • Inhibitory Concentration 50
  • Internal Ribosome Entry Sites / drug effects
  • Internal Ribosome Entry Sites / physiology*
  • MicroRNAs / genetics
  • MicroRNAs / metabolism
  • Mutation / genetics
  • Receptors, Atrial Natriuretic Factor / genetics
  • Receptors, Atrial Natriuretic Factor / metabolism
  • Spinocerebellar Ataxias / drug therapy*
  • Spinocerebellar Ataxias / genetics
  • Transfection
  • Voltage-Gated Sodium Channel Blockers / pharmacology


  • CACNA1A protein, human
  • Calcium Channels
  • Calcium Channels, L-Type
  • Internal Ribosome Entry Sites
  • L-type calcium channel alpha(1C)
  • MicroRNAs
  • Voltage-Gated Sodium Channel Blockers
  • Ajmaline
  • Receptors, Atrial Natriuretic Factor
  • atrial natriuretic factor receptor C