Calcium mobilization is required for nuclear vesicle fusion in vitro: implications for membrane traffic and IP3 receptor function.
We studied the fusion of nuclear vesicles bound to chromatin in Xenopus egg extracts. Fusion was inhibited by 5 mM BAPTA, a Ca2+ buffer that suppresses cytosolic [Ca2+] gradients. The BAPTA-inhibited step in fusion was biochemically distinct from, and occurred later than, the GTP gamma S-sensitive step mediated by the monomeric GTPase, ADP-ribosylation factor. Exogenous inositol 1,4,5-trisphosphate (IP3), which triggers Ca2+ release from lumenal stores via IP3 receptors, stimulated fusion in the presence of BAPTA. This rescue was specific, because inositol 1,3,4-trisphosphate had no effect. Heparin, a potent antagonist of IP3 receptors, independently blocked fusion in an IP3-reversible manner. We suggest that phosphoinositide signaling may regulate nuclear vesicle fusion.
Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
K M
KM
Sullivan
W B
WB
Busa
K L
KL
Wilson
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology*; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008561:Membrane Fusion / Q000187:drug effects*; D009685:Nuclear Envelope / Q000378:metabolism*; D010063:Ovum; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear; D015398:Signal Transduction; D013094:Spermatozoa; D014981:Xenopus
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D006493:Heparin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium