Regulation of the localization and activity of inositol 1,4,5-trisphosphate 3-kinase B in intact cells by proteolysis.
IP3K (inositol 1,4,5-trisphosphate 3-kinase) catalyses the Ca2+-regulated phosphorylation of the second messenger Ins(1,4,5)P3, thereby inactivating the signal to release Ca2+ and generating Ins(1,3,4,5)P4. Here we have investigated the localization and activity of IP3KB and its modulation by proteolysis. We found that the N- and C-termini (either side of residue 262) of IP3KB localized predominantly to the actin cytoskeleton and ER (endoplasmic reticulum) respectively, both in COS-7 cells and in primary astrocytes. The functional relevance of this was demonstrated by showing that full-length (actin-localized) IP3KB abolished the histamine-induced Ca2+ response in HeLa cells more effectively than truncated constructs localized to the ER or cytosol. The superior efficacy of full-length IP3KB was also attenuated by disruption of the actin cytoskeleton. By transfecting COS-7 cells with double-tagged IP3KB, we show that the translocation from actin to ER may be a physiologically regulated process caused by Ca2+-modulated constitutive proteolysis in intact cells.
Yu
Jowie C H
JC
Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK.
Lloyd-Burton
Samantha M
SM
Irvine
Robin F
RF
Schell
Michael J
MJ
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D051381:Rats
D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D002118:Calcium