Effects of tiazofurin on guanine nucleotide binding regulatory proteins in
HL-60 cells
SM Kharbanda, ML Sherman and DW Kufe
Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard
Medical School, Boston, MA 02115.
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.
Volume 75,
Issue 3,
pp. 583-588,
02/01/1990
Copyright © 1990 by The American Society of Hematology
