Polarized subcellular distribution of the 1-, 4- and 5-phosphatase activities that metabolize inositol 1,4,5-trisphosphate in intestinal epithelial cells.
In intestinal epithelial cells, Ins(1,4,5)P3 is metabolized both by an intracellular 5-phosphatase and by less specific extracellular phosphatases [Rubiera, Velasco, Michell, Lazo & Shears (1988) Biochem. J. 255, 131-137]. A total of 91% of intracellular Ins(1,4,5)P3 5-phosphatase was particulate, and was preferentially associated with plasma membranes rather than with other subcellular organelles. A soluble Ins(1,4,5)P3 3-kinase activity was also characterized, further supporting the idea that inositol phosphates are important in enterocyte function. We have studied the distribution of Ins(1,4,5)P3 phosphatase activities in basolateral and brush-border domains of the plasma membrane. Compared with homogenates, the extracellular phosphatases were 13-17-fold enriched in brush-border membranes, but only 2-fold enriched in basolateral membranes. The 1- and 4-phosphates of Ins(1,4,5)P3 were hydrolysed at equal rates by the extracellular phosphatases; these enzymes are proposed to have digestive functions. The intracellular particulate 5-phosphatase was 2-fold enriched in brush-border membranes and 13-fold enriched in basolateral membranes, at the same pole of the cell where Ins(1,4,5)P3 is believed to be generated. This is opposite to the polarized distribution of particulate 5-phosphatase in hepatocytes [Shears, Evans, Kirk & Michell (1988) Biochem. J. 256, 363-369]; these differences in subcellular distribution may be important in determining cell-specific metabolism of Ins(1,4,5)P3.
Rubiera
C
C
Departamento de Biologia Funcional, Universidad de Oviedo, Spain.
Lazo
P S
PS
Shears
S B
SB
D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002851:Chromatography, High Pressure Liquid; D004848:Epithelium / Q000201:enzymology / Q000648:ultrastructure; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D000072181:Inositol Polyphosphate 5-Phosphatases; D007422:Intestines / Q000201:enzymology / Q000648:ultrastructure*; D008871:Microvilli / Q000201:enzymology; D010744:Phosphoric Monoester Hydrolases / Q000032:analysis* / Q000378:metabolism; D010766:Phosphorylation; D010770:Phosphotransferases / Q000032:analysis; D017853:Phosphotransferases (Alcohol Group Acceptor); D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology*
D005958:Glucosephosphates; D019298:Glucose-6-Phosphate; D015544:Inositol 1,4,5-Trisphosphate; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases