Upregulation of synaptotagmin IV inhibits transmitter release in PC12 cells with targeted synaptotagmin I knockdown.
BACKGROUND
The function of synaptotagmins (syt) in Ca2+-dependent transmitter release has been attributed primarily to Ca2+-dependent isoforms such as syt I. Recently, syt IV, an inducible Ca2+-independent isoform has been implicated in transmitter release. We postulated that the effects of syt IV on transmitter release are dependent on the expression of syt I.


RESULTS
To test this, we increased syt IV expression in PC12 cells by either upregulation with forskolin treatment or overexpression with transfection. Two separately generated stable PC12 cell lines with syt I expression abolished by RNAi targeting were used and compared to control cells. We measured catecholamine release from single vesicles by amperometry and neuropeptide Y release from populations of cells by an immunoassay. In syt I targeted cells with forskolin-induced syt IV upregulation, amperometry measurements showed a reduction in the number of release events and the total amount of transmitter molecules released per cell. In cells with syt IV overexpressed, similar amperometry results were obtained, except that the rate of expansion for full fusion was slowed. Neuropeptide Y (NPY) release from syt I knockdown cells was decreased, and overexpression of syt IV did not rescue this effect.


CONCLUSIONS
These data support an inhibitory effect of syt IV on release of vesicles and their transmitter content. The effect became more pronounced when syt I expression was abolished.
Moore-Dotson
Johnnie M
JM
Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St, Louis, MO 63104, USA.
Papke
Jason B
JB
Harkins
Amy B
AB
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D004563:Electrochemistry; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D051379:Mice; D008854:Microscopy, Electron; D009478:Neuropeptide Y / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D016716:PC12 Cells; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D050863:Synaptotagmin I / Q000096:biosynthesis* / Q000235:genetics; D050857:Synaptotagmins / Q000096:biosynthesis* / Q000502:physiology; D014162:Transfection; D015854:Up-Regulation / Q000502:physiology
D002395:Catecholamines; D009478:Neuropeptide Y; D018377:Neurotransmitter Agents; D034741:RNA, Small Interfering; D050863:Synaptotagmin I; D050857:Synaptotagmins; D005576:Colforsin; D002118:Calcium