Agonist-induced regulation of inositol tetrakisphosphate isomers and inositol pentakisphosphate in adrenal glomerulosa cells.
In adrenal glomerulosa cells, angiotensin II (AII) rapidly stimulates the formation of inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) and causes marked long-term changes in the levels of highly phosphorylated inositols. Glomerulosa cells prelabeled with [3H]inositol for 48 h and exposed to AII for 10 min showed prominent increases in inositol 1,3,4,5-tetrakisphosphate (Ins-1,3,4,5-P4) and smaller increases in two additional tetrakisphosphates, Ins-1,3,4,6-P4 and another (Ins-3,4,5,6-P4) eluting in the position of Ins-3,4,5,6-P4 and its stereoisomer, Ins-1,4,5,6-P4, on anion exchange liquid chromatography. A concomitant decrease in InsP5 indicates that an increase in Ins-1,4,5,6-P4, the breakdown product of InsP5, is probably responsible for the initial rise in Ins-3,4,5,6-P4 during 10 min stimulation by AII. During prolonged stimulation by AII, Ins-1,3,4,5-P4 began to decline from its high, stimulated level after the first hour but the level of Ins-1,3,4,6-P4 remained elevated for several hours. There were also progressive increases in the levels of Ins-3,4,5,6-P4 and InsP5 during stimulation for up to 16 h with AII. Treatment of adrenal cells for 16 h with the cyclic AMP-mediated secretagogue, adrenocorticotropic hormone (ACTH), slightly increased basal levels of Ins-1,3,4,6-P4, Ins-3,4,5,6-P4, and InsP5, and enhanced the subsequent AII-stimulated increases in the two additional tetrakisphosphate isomers but not of inositol trisphosphates or Ins-1,3,4,5-P4. This change in the pattern of the higher inositol phosphate response to AII was manifested within 2 h after exposure to ACTH, and was mimicked by treatment with 8-bromo cyclic AMP or forskolin. Treatment with 50 microM cycloheximide abolished the ACTH-induced increases in inositol polyphosphate responses during AII stimulation, but had no effect on the responses of untreated cells to AII. The conversion of [3H]Ins-1,3,4-P3 to [3H]Ins-1,3,4,6-P4, a reaction linking the receptor-mediated InsP3 response to higher inositol phosphates, was enhanced in permeabilized cells that were pretreated for 16 h with either ACTH or AII. These results demonstrate that the reactions by which Ins-1,3,4,6-P4 and Ins-3,4,5,6-P4 are formed and converted to InsP5 are influenced by agonist-stimulated regulatory processes that include both calcium-dependent and cyclic AMP-dependent mechanisms of target cell activation. They also reveal changes consistent with agonist-induced conversion of InsP5 to its dephosphorylated metabolite, Ins-1,4,5,6-P4, during short-term stimulation by AII.
Balla
T
T
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Baukal
A J
AJ
Hunyady
L
L
Catt
K J
KJ
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D007294:Inositol / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D007536:Isomerism; D007700:Kinetics; D013403:Sugar Phosphates / Q000378:metabolism*; D015384:Zona Glomerulosa / Q000187:drug effects / Q000378:metabolism*
D007295:Inositol Phosphates; D013403:Sugar Phosphates; C081655:inositol-1,3,4,5-tetrakisphosphate; C081653:inositol-1,3,4,6-tetrakisphosphate; D000804:Angiotensin II; C081652:inositol-3,4,5,6-tetrakisphosphate; C081651:inositol-1,4,5,6-tetrakisphosphate; C013571:inositol pentaphosphate; D007294:Inositol; D000324:Adrenocorticotropic Hormone