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RNA Editing‐Mediated Modulation of Calcium‐Dependent Activator Protein for Secretion 1 (CAPS1) Function
Author(s) -
Emeson Ronald B,
Ulbricht Randi J,
Lazarenko Roman M,
DelBove Claire E,
Zhang Qi
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.807.4
Subject(s) - rna editing , biology , microbiology and biotechnology , rna , gene isoform , secretion , biochemistry , gene
CAPS1 is a priming factor, involved in the regulated release of hormones, peptides and neurotransmitters from large dense‐core secretory granules and synaptic vesicles. Tran‐scripts encoding CAPS1 are modified by an adenosine‐to‐inosine (A‐to‐I) RNA editing event in which a genomically‐encoded glutamate (GAG) is converted to a glycine (GIG) codon. This non‐synonymous amino acid change is located within the essential carboxyl‐terminal domain of the protein which mediates the CAPS1 interaction with peptide and hormone‐containing vesicles, suggesting that RNA editing modulates the contribution of CAPS1 to evoke vesicular release. Editing of CAPS1 was found to be conserved in vertebrate species from humans to zebrafish, indicating its importance in regulated secretion, an essential cellular function in the nervous and endocrine systems. Quantitative analysis of editing for CAPS1 transcripts in dissected mouse brain regions and peripheral endocrine organs revealed that editing was highest in the cortex of the brain (~24%) and lowest in the testes (~2%). Furthermore, the sequences necessary for editing were found to be contained within a predicted duplex region of the pre‐mRNA formed by two halves of a 32 base‐pair inverted repeat surrounding the editing site (exon 27) and within intron 27. Electrophysiological analyses of primary neuronal cultures from postnatal rat hippocampus revealed that neuronal synapses were enhanced by overexpression of the non‐edited CAPS1 isoform. Surprisingly, FM 1–43 dye loading and unloading studies suggested that synaptic vesicle release and retrieval were less complete with the non‐edited CAPS1 isoform. Tracking the fate of synaptic vesicle protein recycling during exocytosis and endocytosis, using a red fluorescence pH‐sensor (pHTomato) fused to the synpatophysin luminal domain, revealed that the non‐edited CAPS1 isoform promoted fast, but incomplete, fusion (i.e. kiss‐and‐run) that is often exerted by docking vesicles. These data suggests that CAPS1 editing may serve as a molecular mechanism to fine tune synaptic connectivity through less appreciated vesicle docking and recycling kinetics at pre‐synaptic terminals. These studies provide insights into the functional importance of CAPS1 editing in the regulation of neuronal network connectivity, as well as suggest a broader role for CAPS1 RNA editing in vertebrate physiology. Support or Funding Information Joel G. Hardman Chair in Pharmacology (RBE) and NIH OD008761 (QZ)