Isoprenylated Human Brain Type I Inositol 1,4,5-Trisphosphate 5-Phosphatase Controls Ca2+ Oscillations Induced by ATP in Chinese Hamster Ovary Cells

Abstract

. In mouse exocrine pancreatic acinar cells, InsP 4 is effective in mobilizing Ca 2ϩ and promoting Ca 2ϩ influx in conditions where phospholipase A 2 activity, and thus arachidonic acid production, is inhibited (10). Recently, a high affinity InsP 4 -binding protein has been purified from pig platelets (11). The cDNA encoding this putative receptor encoded a GTPase-activating protein. In vitro, it shows GTPase-activating protein activity against Ras that is inhibited by phospholipids and specifically stimulated by InsP 4 (12).Both the InsP 3 3-kinase and the 5-phosphatase consist of a family of multiple isoenzymes. In particular, the various 5-phosphatases dephosphorylate InsP 3 , InsP 4 , phosphatidylinositol 4,5-bisphosphate, and phosphatidylinositol 3,4,5-trisphosphate with different specificities, K m , and V max (13)(14)(15). In vitro, type I InsP 3 5-phosphatase (also designated as the 43-kDa 5-phosphatase) can use either InsP 3 or InsP 4 as substrates but not the phosphoinositides (16 -20). Based upon kinetic analysis (K m for InsP 3 and V max values compared with other 5-phosphatases), this enzyme is generally considered as a signal-terminating enzyme for InsP 3 , analogous to the cyclic nucleotide phosphodiesterases for cyclic AMP (21).The type I 5-phosphatase has a higher affinity but lower

The Prostacyclin Receptor Is Isoprenylated

“…One of the limiting factors relating to the development of the FTase inhibitors as anti-Ras drugs relates to the issues concerning nonspecific cytotoxic effects because of their inhibition of isoprenylation of other farnesylated proteins. In addition to the four cellular Ras proteins (Ha-Ras, K1-4A, Ki-4B, and N-Ras), many other proteins have been reported to be farnesylated including the nuclear lamins A and B, the Ras-related proteins Rap2 and RhoB, phosphorylase kinase, rhodopsin kinase (GRK1), cyclic GMP phosphodiesterase ␣, the ␥ subunit of transducin, and type 1 inositol-1,4,5-triphosphate 5-phosphatase (37,42). We now add the prostacyclin receptor to this growing list.…”

“…There are two geranylgeranyl transferases: geranylgeranyl protein transferase I, which transfers geranylgeranyl to proteins containing a CAAX sequence in which X is leucine or isoleucine, and geranylgeranyl protein transferase II, which transfers geranylgeranyl to proteins terminating in -CC or -CXC (40,41). Among those proteins that are isoprenylated are the nuclear lamins A and B, the ␥ subunits of the heterotrimeric G proteins, many members of the Ha-Ras-related low molecular mass GTP-binding proteins, rhodopsin kinase, yeast mating factor a (37), and inositol-1,4,5-trisphosphate 5-phosphatase (42). Recently, a novel Ca 2ϩ -independent phospholipase A 2 , cPLA 2 -␥, which shows homology to Ca 2ϩ -dependent cytoplasmic cPLA 2 has been demonstrated to be isoprenylated (43).…”

The Structural and Functional Versatility of Inositol Phosphates

“…It is of interest that over-expression of membrane-bound 5-phosphatase activity can prevent the proper expression of Ca 2+ oscillations (47). Ca signaling was not similarly affected when the over expressed 5-phosphatase was directed to the cytosol (by mutating its isoprenylation motif) (47). Thus, an appropriate, localized metabolism of Ins(l,4,5)P 3 seems to be an important aspect of the spatiotemporal characteristics of Ca 2+ signaling.…”

“…In polarized epithelial cells, 5-phosphatase activity may subsequently be redistributed, by vesicle trafficking, to specific domains of the plasma membrane (48). It is of interest that over-expression of membrane-bound 5-phosphatase activity can prevent the proper expression of Ca 2+ oscillations (47). Ca signaling was not similarly affected when the over expressed 5-phosphatase was directed to the cytosol (by mutating its isoprenylation motif) (47).…”

“…Type I and Π 5-phosphatases are directed to the plasma membrane by isoprenylation of the carboxy terminus (40,47). In polarized epithelial cells, 5-phosphatase activity may subsequently be redistributed, by vesicle trafficking, to specific domains of the plasma membrane (48).…”