title: Effects of tiazofurin on guanine nucleotide binding regulatory proteins in HL-60 cells.
abstract: Guanine nucleotide binding proteins (G proteins) are regulatory molecules that couple membrane receptors to effector systems such as adenylate cyclase and phospholipase C. The alpha subunits of G proteins bind to guanosine 5'-diphosphate (GDP) in the unstimulated state and guanosine 5' triphosphate (GTP) in the active state. Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide), a specific inhibitor of inosine monophosphate (IMP) dehydrogenase, decreases guanylate synthesis from IMP in HL-60 promyelocytic leukemia cells and depletes intracellular guanine nucleotide pools. This study demonstrates that treatment of HL-60 cells with tiazofurin is associated with a fourfold increase in membrane binding sites for the nonhydrolyzable analogue GDP beta S. This increase in binding sites was associated with a 3.2-fold decrease in GDP beta S binding affinity. Similar findings were obtained with GTP gamma S. These effects of tiazofurin treatment on guanine nucleotide binding were also associated with decreased adenosine diphosphate-ribosylation of specific G protein substrates by cholera and pertussis toxin. The results further demonstrate that tiazofurin treatment results in inhibition of G protein-mediated transmembrane signaling mechanisms. In this regard, stimulation of adenylate cyclase by prostaglandin E2 was inhibited by over 50% in tiazofurin-treated cells. Furthermore, tiazofurin treatment resulted in inhibition of N-formylmethionylleucylphenylalanine-induced stimulation of phospholipase C. Taken together, these results indicate that tiazofurin acts at least in part by inhibiting the ability of G proteins to function as transducers of intracellular signals.
authors.affiliation: Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115.
authors.forename: S M
authors.initials: SM
authors.lastname: Kharbanda
authors.forename: M L
authors.initials: ML
authors.lastname: Sherman
authors.forename: D W
authors.initials: DW
authors.lastname: Kufe
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism*; D006801:Humans; D007168:IMP Dehydrogenase / Q000037:antagonists & inhibitors*; D007295:Inositol Phosphates / Q000378:metabolism; D007658:Ketone Oxidoreductases / Q000037:antagonists & inhibitors*; D015470:Leukemia, Myeloid, Acute; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D037342:Pertussis Toxin; D012254:Ribavirin / Q000031:analogs & derivatives / Q000494:pharmacology*; D012263:Ribonucleosides / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D006150:Guanine Nucleotides; D007295:Inositol Phosphates; D012263:Ribonucleosides; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D012254:Ribavirin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D002772:Cholera Toxin; D007168:IMP Dehydrogenase; D007658:Ketone Oxidoreductases; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D015232:Dinoprostone; C033706:tiazofurin