Formation of inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate from inositol 1,3,4,5-tetrakisphosphate and their pathways of degradation in RBL-2H3 cells.
Previous studies with antigen-stimulated rat basophilic leukemia (RBL-2H3) cells indicated the formation of multiple isomers of each of the various categories of inositol phosphates. The identities of the different isomers have been elucidated by selective labeling of [3H]inositol 1,3,4,5-tetrakisphosphate with [32P]phosphate in the 3'-or 4',5'-positions and by following the metabolism of different radiolabeled inositol phosphates in extracts of RBL-2H3 cells. We report here that inositol 1,3,4,5-tetrakisphosphate, when incubated with the membrane fraction of extracts of RBL-2H3 cells, was converted to inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate. Further dephosphorylation of the inositol polyphosphates proceeded rapidly in whole extracts of cells, although the process was significantly retarded when ATP (2 mM) levels were maintained by an ATP-regenerating system. The degradation of inositol 1,4,5-trisphosphate proceeded with the sequential formation of inositol 1,4-bisphosphate, the inositol 4-monophosphate (with smaller amounts of the 1-monophosphate), and finally inositol. Inositol 1,3,4-trisphosphate, on the other hand, was converted to inositol 1,3-bisphosphate and inositol 3,4-bisphosphate and subsequently to inositol 4-monophosphate and inositol 1-monophosphate (stereoisomeric forms were undetermined). The possible implications of the apparent interconversion between inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in regulating histamine secretion in the RBL-2H3 cells are discussed.
Cunha-Melo
J R
JR
Laboratory of Chemical Pharmacology, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
Dean
N M
NM
Ali
H
H
Beaven
M A
MA
D000818:Animals; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D007942:Leukemia, Experimental / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D051381:Rats; D013403:Sugar Phosphates / Q000378:metabolism*; D014316:Tritium
D007295:Inositol Phosphates; D010761:Phosphorus Radioisotopes; D013403:Sugar Phosphates; D014316:Tritium; C081655:inositol-1,3,4,5-tetrakisphosphate; D015544:Inositol 1,4,5-Trisphosphate