Complexin 2 modulates vesicle-associated membrane protein (VAMP) 2-regulated zymogen granule exocytosis in pancreatic acini.
Complexins are soluble proteins that regulate the activity of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes necessary for vesicle fusion. Neuronal specific complexin 1 has inhibitory and stimulatory effects on exocytosis by clamping trans-SNARE complexes in a prefusion state and promoting conformational changes to facilitate membrane fusion following cell stimulation. Complexins are unable to bind to monomeric SNARE proteins but bind with high affinity to ternary SNARE complexes and with lower affinity to target SNARE complexes. Far less is understood about complexin function outside the nervous system. Pancreatic acini express the complexin 2 isoform by RT-PCR and immunoblotting. Immunofluorescence microscopy revealed complexin 2 localized along the apical plasma membrane consistent with a role in secretion. Accordingly, complexin 2 was found to interact with vesicle-associated membrane protein (VAMP) 2, syntaxins 3 and 4, but not with VAMP 8 or syntaxin 2. Introduction of recombinant complexin 2 into permeabilized acini inhibited Ca(2+)-stimulated secretion in a concentration-dependent manner with a maximal inhibition of nearly 50%. Mutations of the central α-helical domain reduced complexin 2 SNARE binding and concurrently abolished its inhibitory activity. Surprisingly, mutation of arginine 59 to histidine within the central α-helical domain did not alter SNARE binding and moreover, augmented Ca(2+)-stimulated secretion by 130% of control. Consistent with biochemical studies, complexin 2 colocalized with VAMP 2 along the apical plasma membrane following cholecystokinin-8 stimulation. These data demonstrate a functional role for complexin 2 outside the nervous system and indicate that it participates in the Ca(2+)-sensitive regulatory pathway for zymogen granule exocytosis.
Falkowski
Michelle A
MA
Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706, USA.
Thomas
Diana D H
DD
Groblewski
Guy E
GE
D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D000681:Amylases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002766:Cholecystokinin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis; D015151:Immunoblotting; D008297:Male; D008856:Microscopy, Fluorescence; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D046790:Pancreas, Exocrine / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D022142:Secretory Vesicles / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D050988:Vesicle-Associated Membrane Protein 2 / Q000235:genetics / Q000378:metabolism*
D033942:Adaptor Proteins, Vesicular Transport; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D050765:Qa-SNARE Proteins; D050988:Vesicle-Associated Membrane Protein 2; C410885:cholecystokinin 8; C095993:complexin II; D002766:Cholecystokinin; D000681:Amylases; D002118:Calcium