J. Biol. Chem., Vol. 262, Issue 11, 5180-5187, Apr, 1987
In vitro modulation of rat liver glucocorticoid receptor by urea
VK Moudgil, L Vandenheede, C Hurd, N Eliezer and G Lombardo
We have examined the influence of urea on the properties of the rat liver
glucocorticoid receptor (GR). A 1-h incubation of hepatic cytosol with 1-3
M urea at 0 or at 23 degrees C caused a progressive decrease in the steroid
binding efficiency of GR. Urea treatment of cytosol incubated with 20 nM
[3H]triamcinolone acetonide caused transformation of
glucocorticoid-receptor complexes (GRc) and resulted in an increase in the
binding of GRc to DNA-cellulose and ATP-Sepharose. The transforming effect
was maximal with 2.5 M urea at 0 degrees C for 1 h, and it caused a shift
in the rate of sedimentation of the 9 S untransformed GRc to a 4 S form,
similar to that observed upon incubation of the cytosol GRc at 23 degrees
C. This 9 to 4 S transformation could also be observed in the presence of
Na2MoO4. The Stokes radii of the GRc eluted from a Bio-Gel-A-0.5m agarose
column were determined to be 5.9 and 4.9 nm in the absence and presence of
2.5 M urea. The aqueous two-phase partitioning analysis revealed a
significant change in surface properties of GR following urea treatment;
the observed partition coefficient values (cpm upper phase/bottom phase)
were 0.022, 0.208, and 0.60 for GRc, GRc + 23 degrees C, and GRc + 2.5 M
urea, respectively. Furthermore, the urea treatment rendered the GRc less
negatively charged, forcing their appearance in the flow-through fractions
of a DEAE-Sephacel column. These results suggest that urea is a potent in
vitro modulator of the physicochemical behavior of GR, influencing both the
steroid binding and the process of receptor transformation.
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