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Regulation of inositol phospholipid and inositol phosphate metabolism in chemoattractant‐activated human polymorphonuclear leukocytes
Author(s) -
Dillon Susan B.,
Murray John J.,
Uhing Ronald J.,
Snyderman Ralph
Publication year - 1987
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240350409
Subject(s) - phospholipase c , biochemistry , g protein , receptor , phosphoinositide phospholipase c , phosphatidylinositol , biology , gq alpha subunit , inositol , gtp' , inositol phosphate , gtpase , chemotaxis , phospholipase , diacylglycerol kinase , gtp binding protein regulators , inositol trisphosphate , signal transduction , protein kinase c , enzyme
Binding of chemoattractants to specific cell surface receptors on polymorphonu‐clear leukocytes (PMNs) initiates a series of biochemical responses leading to cellular activation. A critical early biochemical event in chemoattractant (CTX) receptor‐mediated signal transduction is the phosphodiesteric cleavage of plasma membrane phosphatidylinositol 4,5‐bisphosphate (PIP 2 ), with concomitant production of the calcium mobilizing inositol‐1,4,5‐trisphosphate (IP 3 ) isomer, and the protein kinase C activator, 1,2‐diacylglycerol (DAG). The following lines of experimental evidence collectively suggest that CTX receptors are coupled to phospholipase C via a guanine nucleotide binding (G) protein. Receptor‐mediated hydrolysis of PIP 2 in PMN plasma membrane preparations requires both fMet‐Leu‐Phe and GTP, and incubation of intact PMNs with pertussis toxin (which ADP ribosylates and inactivates some G proteins) eliminates the ability of fMet‐Leu‐Phe plus GTP to promote PIP 2 breakdown in isolated plasma membranes. Studies with both PMN paniculate fractions and with partially purified fMet‐Leu‐Phe receptor preparations indicate that guanine nucleotides regulate CTX receptor affinity. Finally, fMet‐Leu‐Phe stimulates high‐affinity binding of GTPγS to PMN membranes as well as GTPase activity. A Ga subunit has been identified in phagocyte membranes which is different from other Ga subunits on the basis of molecular weight and differential sensitivity to ribosylation by bacterial toxins. Thus, a novel G protein may be involved in coupling CTX receptors to phospholipase C. Studies in intact and sonicated PMNs demonstrate that metabolism of 1,4,5‐IP 3 proceeds via two distinct pathways: (1) sequential dephosphorylation to 1,4‐IP 2 , 4‐IP 1 and inositol, or (2) ATP‐dependent conversion to inositol 1,3,4,5‐tetrakisphosphate (IP 4 ) followed by sequential dephosphorylation to 1,3,4‐IP 3 , 3,4‐IP 2 , 3‐IP 1 and inositol. Receptor‐mediated hydrolysis of PIP 2 occurs at ambient intracellular Ca 2+ levels; but metabolism of 1,4,5‐IP 3 via the IP 4 pathway requires elevated cytosolic Ca 2+ levels associated with cellular activation. Thus,the two pathways for 1,4,5‐IP 3 metabolism may serve different metabolic functions. Additionally, inositol phosphate production appears to be controlled by protein kinase C, as phorbol myristate acetate (PMA) abrogates PIP 2 hydrolysis by interfering with the ability ofthe activated G protein to stimulate phospholipase C. This implies a physiologic mechanism for terminating biologic responses via protein kinase C mediated feedback inhibition of PIP 2 hydrolysis.