RAPID DECLINE IN FOLYLPOLYGLUTAMATE SYNTHETASE-ACTIVITY AND GENE-EXPRESSION DURING MATURATION OF HL-60 CELLS - NATURE OF THE EFFECT, IMPACTON FOLATE COMPOUND POLYGLUTAMATE POOLS, AND EVIDENCE FOR PROGRAMMED DOWN-REGULATION DURING MATURATION
Mg. Egan et al., RAPID DECLINE IN FOLYLPOLYGLUTAMATE SYNTHETASE-ACTIVITY AND GENE-EXPRESSION DURING MATURATION OF HL-60 CELLS - NATURE OF THE EFFECT, IMPACTON FOLATE COMPOUND POLYGLUTAMATE POOLS, AND EVIDENCE FOR PROGRAMMED DOWN-REGULATION DURING MATURATION, The Journal of biological chemistry, 270(10), 1995, pp. 5462-5468
These studies in HL-60 cells examined the regulation of folylpolygluta
mate synthetase (FPGS) activity at the level of gene expression during
terminal maturation. Following addition of 210 mM Me(2)SO to cultures
of HL-60 cells at a concentration that induces maturation of 85-90% o
f the cells, FPGS activity, but not folylpolyglutamate hydrolase (FPGH
) activity, was reduced 2-7-fold within 1-5 days. The initial decline
in FPGS activity preceded any effect of Me(2)SO on rate of growth and
the increase in appearance of nitro blue tetrazolium-positive cells, a
marker of cellular maturation, and the decrease after 5 days of expos
ure to Me(2)SO was solely accounted for by a 7-fold decrease in value
for V-max. The same time and concentration dependence for Me(2)SO was
shown for the decline in FPGS activity, increase in nitro blue tetrazo
lium-positive cells, and decline in the level of a 2.1-kilobase FPGS m
RNA during exposure to this inducer. This decline in FPGS mRNA was rev
ersible when Me(2)SO was removed from the culture medium but only unti
l that time when an appreciable number of cells were committed to term
inal maturation. Following growth of HL-60 cells with [H-3]MTX, used a
s a model folate compound, a large reduction in its intracellular poly
glutamate pools was shown during maturation which quantitatively refle
cted the decline in FPGS activity as well as folate transport inward (
Sirotnak, F. M., Jacobson, D. M., and Yang, C-H. (1986) J. Biol. Chem.
261, 11150-11156). Other data showed that folate status or obviation
of the folate requirement during growth of these cells strongly influe
nced the rapidity of the onset of maturation following exposure to ind
ucer. Overall, these results show that FPGS activity in HL 60 cells is
a marker for proliferative capacity and that the underlying basis for
the decline in FPGS activity during maturation is altered cognate gen
e expression which is manifested as early reversible and late irrevers
ible phases. They also suggest that the coordinate reduction observed
in folate transport, FPGS activity, dihydrofolate reductase, and proba
bly other folate related enzymes by limiting macromolecular biosynthes
is may be early programmed events in the maturation process that influ
ence the switch from proliferation to senescence in these cells.