J. Biol. Chem., Vol. 261, Issue 16, 7311-7315, Jun, 1986
Effects of alpha-amanitin and cycloheximide on 1,25-dihydroxyvitamin D3- dependent calbindin-D28K and its mRNA in vitamin D3-replete chick intestine
G Theofan and AW Norman
We have examined the effects of the transcriptional inhibitor alpha-
amanitin and the translational inhibitor cycloheximide on levels of
calbindin-D28K (28-kDa calcium binding protein, CaBP) and CaBP-mRNA in the
vitamin D-replete chick intestine. Chicks were raised on one of four diets:
"normal" (1% calcium, 0.6% phosphorus); high calcium (3.3% calcium, 0.5%
phosphorus); low calcium (0.3% calcium, 0.6% phosphorus); or low phosphorus
(1% calcium, 0.09% phosphorus). Chicks were then treated either with
alpha-amanitin (20 micrograms/chick) or cycloheximide (600
micrograms/chick) 2 h prior to a dose of 6.5 nmol of 1,25-dihydroxyvitamin
D3. Duodenal mucosa was collected from 0 to 120 min afterward and assayed
for CaBP-mRNA by dot blot hybridization and for CaBP using an enzyme-linked
immunosorbent assay. In the absence of inhibitor, CaBP levels were
depressed by high calcium and elevated by low calcium or low phosphorus, as
expected. These changes occurred, however, without a change in CaBP-mRNA
levels. alpha-Amanitin had no effect on CaBP or on CaBP-mRNA levels in
chicks raised on any of the diets. Cycloheximide inhibited CaBP levels, and
surprisingly also inhibited CaBP-mRNA levels in all four dietary groups.
These results indicate that continual protein synthesis is necessary for
the expression of CaBP-mRNA, suggesting the existence of a rapidly turned
over protein that may be required for stabilization or for processing of
the chick intestinal CaBP messenger RNA.