Vol. August
170,
No.
BIOCHEMICAL
3, 1990
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
1325-1330
Pages
16, 1990
NATURAL REGULATORYMECHANISMS OF INSULIN DEGRADATION BY INSULIN DEGRADING ENZYME Hiroyuki
Akiyama. Koichi
Yokono’. Kozui Shii*, Wataru Ogawa, Hiroshi Shigeaki Baba+, and Masato Kasuga
Second Department of Internal Kobe University School of Medicine, * Hyogo Institute Received
July
9,
for Research
in Adult
Taniguchi,
Medicine, Kobe 650, Japan
Disease,
Akashi
673, Japan
1990
SUMHARY: Insulin-degrading enzyme (IDE) accounts for most of the insulin degrading activity in extracts of several tissues and plays an important role in the intracellular degradation of insulin. Using newly developed sandwich radioimmunoassay for rat IDE, this enzyme was detectable in all tissues we examined and liver had the highest level of IDE. The ratio of insulin degrading activity to IDE concentration was roughly the same in liver, brain and muscle, however, twice as high in kidney as compared with other tissues. On the its degrading activity in these tissue extracts, including kidney, was contrary, completely lost after immunoprecipitation of IDE. These results suggest that IDE degrades insulin in the initial step of cleavage and that there are some mechanisms to regulate insulin degrading activity by IDE in the tissues. @1990 Academic Press, Inc.
After
binding
to ceII
eventually
degraded.
terminate
the insulin
However,
protease
occurring
(4).
been indicated
consensus lines
into
‘To whom correspondence
degradation
the signal
enzyme (IDE) DNA coding
sequences
of this
and
may be to
of insulin
and the loci
Consequently,
for the cell.
of insulin yet.
(1.2)
We have been
or insulin
for human erythrocyte
IDE
the deduced sequence of this
for any of the known classes
novel enzyme in insulin
of evidence,
IDE could
enzyme could
is internalized
have not been established
insulin-degrading
by several
monoclonal antibodies
of insulin
process
a complementary
The importance
(51, or that this
in this
and sequenced.
enzyme did not contain
role
insulin
or to modulate
in the cells
Recently,
has been isolated protease
action
an enzyme called (3).
receptors,
One suggested
the enzymes involved
degradation studying
surface
especially
inhibit
insulin
be cross-linked
with
of
metabolism
that microinjection degradation
““I-insulin
in intact
has of cells
via a receptor-
should be addressed.
Abbreviations: IDE, insulin-degrading enzyme; BSA, bovine serum albumin: TCA, trichloroacetic
1325
HBS, Hepes-buffered acid.
saline;
0006-291x/90 $1.50 Copyighr 0 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
Vol.
170,
No.
3, 1990
BIOCHEMICAL
mediated and energy-dependent this
pathway
enzyme has been demonstrated
patients,
whose fat
tissues
almost identical
to those of IDE (7).
measured IDE concentrations compared IDE levels
with
cases of insulin degrading
insulin
resistant activity
of
diabetic than
activity
were
there
tissues,
and thus the changes in insulin
reflect specific
in the cytosolic their
of this
significance
However,
we have developed antibodies
COMMUNJCATIONS
The clinical
more insulin
in various
may not correctly study,
(6).
RESEARCH
The enzyme characteristics
which could degrade insulin In the present
in vivo
contained
subjects.
rat IDE using monoclonal
BIOPHYSICAL
in certain
those of control
degrading activity
AND
may be a number of enzymes
those of IDE. the sandwich
radioimmunoassay
for this
enzyme.
fraction
from various
degrading
Furthermore, tissues
for we and
activities.
MATERIALS AND UETHODS Preparation of Rat Cytosolic Fraction : Male Wistar rats (200-25Og) were decapted and the liver, kidney, hind leg muscle and brain were homogenized using a Polytron homogenizer with 50 mM Hepes-buffered saline (HBS, pH 7.6). The homogenates were centrifuged at 100,000 g for 60 min at 4 “c. The supernatant was used as a cytosolic fraction. Radioimmunoassay for IDE : Monoclonal antibodies against IDE were produced by fusing spleen cells from mouse immunized with purified human erythrocyte IDE (2) with mouse myeloma cells (5). Antibodies were purified from ascites fluid on protein A-sepharose. Among four monoclonal antibodies that recognized human IDE, two antibodies (9B12 and 28Hl) were also found to recognize the rat liver Rat liver IDE which served as a standard, was affinity purified ; extracts (5). the procedure will be described in detail elsewhere. Briefly, the cytosolic fraction was applied to 9B12-coupled affigel 10 column and eluted with 75 mM sodium bicarbonate buffer (pH 11.2). The elutant was further applied to a MonoQ anion exchange column, the highest fraction of insulin degrading activity was concentrated, and finally purified by a Superlose 12 gel filtration column. The cytosolic fractions from various rat tissues obtained as described above were diluted with 50 mfl HBS containing 1 % bovine serum albumin (BSA), 1 m!l phenylmethylsulfonyIfluoride and 1 mg/ml bacitracin. Antibody 9B12 was iodinated using the chloramine T method (specific activity ; 10 pg/pCi). Fifty ~1 of another monoclonal antibody 28Hl (10 pg/ml in 20 mM bicarbonate buffer, pH 9.6) were first coated on 96mwell polyvinyl microtiter plates overnight at 4 “c. The wells were washed twice with 10 mM phosphate buffer (pH 7.4) containing 0.1 % BSA and 0.05 % Tween 20. The we1 1s were further incubated either with 50 ~1 of standard IDE, or the sample, for 2 h at room temperature. After washing twice, 50 pl of iodinated 9B12 in the same buffer was added and incubated another 2 h at 4 “c. Finally, the wells were washed, cut and counted in a Y -counter. Insulin Degradation Assay : The insulin degrading activity was estimated by determining the quantity of 7.5 % trichloroacetic acid (TCA)-soluble radioactivity produced in incubation with ““I-insulin (8). The percentage of insulin degraded was estimated as the net amount of supernatant radioactivity. In order to avoid any insulin degrading activity greater than 15 % in this assay, various rat cytosolic fractions were diluted differently. The abilities of diluted samples to degrade insulin were a linear function of the protein concentrations within this range. The results of enzyme activity were expressed as specific activity (PM insulin degraded/mg protein/min). 1326
Vol.
170,
No.
BIOCHEMICAL
3, 1990
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Immunoprecipitation of Insulin Degrading Activity : The cytosolic fraction from rat tissues was first incubated with 500 bl of various concentrations of anti body 9B12 in 50 mM HBS containing 0.2 % BSA overnight at 4 “c. The immune complex was then immunoprecipitated with 100 ~1 of 10 % staphylococcus aureus coated anti-mouse IgG (Cappel). After centrifugation, the resultant supernatant was tested for the ability to degrade ‘““I-insulin as described above. RESULTS AND DISCUSSION The specificity
and the stability
using the standard liver
dilution
curve and the percent
IDE added to the sample.
The purity
reduced 7.5% SDS polyacrylamide of 110 Kd (9). of rat
liver
cytosolic related
Figure
The lower
fraction.
occurred
of both liver
When 50 rig/ml purified cytosolic
fractions,
Using this various
1 shows a typical
sensitive
rat tissues
concentration
and kidney
standard
rat
liver
assay,
was 20 rig/ml,
liver
The serial to the standard liver
in the cytosolic
or kidney dilution curve.
or kidney
among the tissues
which
of them were almost equal,
except
serial
3-
from
has the highest
we examined.
was standardized
1).
fractions
Table 2 shows that the liver
in these tissues
band
and a dose-
of IDE was between 90 % and 98 % (Table
IDE concentrations
of IDE per protein
a single
by
the radioimmunoassay
curve of the rat
IDE was added to various
the recovery
rat
IDE was confirmed
curve for
for detection
assessed
of purified
demonstrating
samples were parallel
were measured.
all
rat
over the range of 2,000 &ml.
when the IDE concentration degrade insulin,
of standard
dilution
limit
were first
of recovery
gel electrophoresis
IDE and a representative
response
curves
of radioimmunoassay
However,
by the ability
for the kidney.
to
Since
dilution
OL /’ oylo
’ “““” IDE
100
concentration
’ “1”“’
1,000
’ ’
(rig/ml)
Figure 1. Typical standard curve of rat liver IDE (0) and a representative dilution curve of rat liver (0) or kidney (0) cytosolic fraction. Rat liver IDE was determined with antibody 28Hl as a solid phase and ““I-labeled antibody 9812. 1321
Vol.
170,
No.
3, 1990
BIOCHEMICAL
Table
1.
Recovery test
BIOPHYSICAL
RESEARCH
of radioimmunoassay
Purified IDE (ng)
IDE in the cytosolic fraction (nd Liver
AND
COMMUNICATIONS
for rat IDE
Expected
Measured
Recovery
(ng)
(ng)
(%)
246 123 61 30
50 50 50 50
296 173 111 80
290 164 108 74
98 95 97 93
95 47
50 50
145 97
130 92
90 95
Kidney
Purified rat liver IDE (50 ng) was added to various amounts of rat liver or kidney cytosolic fraction. The IDE concentration in the sample was measured as described in Materials and Methods.
IDE seems to account various
tissues
degrading
The insulin
degrading
IDE degrades
IDE are incapable finding
to IDE level
Rat tissue
Liver Kidney Brain Muscle
after
initial
step
insulin
by evidence are consistent
mediates found in the cell
Table 2.
was lost
of degrading
(13-15).
is shown
Comparison
2.93 1.38 1.05 0.38
: ? i i
tissues,
9B12 and the resultant
insulin
of cleavage, it
with
the nature
0.28 0.17 0.23 0.07
of IDE,
0.87 0.76 0.35 0.11
f f -t i
0.06 0.08 0.03 0.01
suggesting
that other
degraded
by IDE.
high ratio
inter
of degrading
may contain
degrading
a
activity
Relative ratio (activity/ concentration) 1.00 1.86 1.12 0.97
The relative ratio of insulin degrading activity to IDE concentration in the liver cytosolic fraction was provisionally considered as 1.00. Values are means i SE of 4 experiments. 1328
than
in a limited
of the peptide
tissue
was
Thus,
proteases
Insulin degrading activity ““I-insulin degraded/ mg protein/min)
(PM
kidney, M.
insulin
Since a reIatively this
including
is partially
IDE cleaves
2).
of lo-”
while
that
in the kidney,
(Figure
extracts,
the removal
before
how IDE
To examine
antibody
tissue
of
IDE in the cytosolic
of IDE concentration and insulin in various tissues
IDE concentration (,ug/mg protein)
in extracts and insulin
interest.
to degrade
in various
in the
which
activity
by 9B12 at a concentration
activity
is supported
number of places activity
in these
the ability
activity
insulin
is of
by monoclonal
immunoprecipitated degrading
This
for
degrading
of IDE concentration
in the kidney
degradation
was tested
completely insulin
as shown
was immunoprecipitated
supernatant
insulin
the discrepancy
to insulin
fraction
most of the
(lo-12),
activity
contributes
for
Vol.
170,
No.
BIOCHEMICAL
3, 1990
AND
RESEARCH
I
I
I
0
10-g
10-a
Antlbody
Figure 2.
BIOPHYSICAL
concentraton
COMMUNICATIONS
CM)
Insulin degrading activity in the cytosolic fraction after immunoprecipitation of IDE by 9B12. Rat liver (O), kidney (0). brain (A), and muscle(A) cytosolic fractions were diluted differently to avoid any insulin degrading activity greater than 15 % in the TCA method,as described in Materials and Methods. After IDE in the cytosolic fraction was immunoprecipitated by various of 9B12, insulin degrading activity in the resultant
concentrations supernatant was
measured.
relatively high amount of nonspecific proteases in the cytosol. Another possibility is that different tissues may contain different amounts of an endogenousinhibitor
specific
of IDE is predictable,
to IDE.
The presence of an endogeneousinhibitor
since IDE is a cytosolic
the cell without an inhibitor.
In fact,
protease was partially
from a cytosolic
(16) and liver
(17).
in the cytosolic inhibitor
purified
enzyme which could be toxic
an endogeneous inhibitor fraction
fraction
from porcine liver
(18).
seemto be an important natural regulatory
degrading activity, degrading activity The liver
a relatively
low inhibitor
of insulin
of rat skeletal
We have also found an endogenous inhibitor
to
specific
muscle to IDE
Since IDE and its endogenous mechanismof insulin
level may account for the high
in the kidney.
had the highest IDE concentration
in the present study and no crude cytosolic degradation without IDE.
In addition,
regulate insulin degrading activity
amongthe various tissues tested
fraction
could initiate
in the tissues.
nonspecific proteases appear to have an effect
An endogenous inhibitor
on the insulin
of IDE. Further studies on these mechanismsare, therefore, understand the biological
significance
the insulin
there are important mechanismsto
of IDE in insulin
degrading activity necessary to
metabolism.
ACKNOWLEDGMENT This work was supported in part by Grant-inAid for Scientific Research 61480251from the Japanese Ministry of Education, Science, and Culture.
1329
and
Vol.
170,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
Yokono, K., Imamura, Y., Shii, K., Sakai, H., and Baba, S. (1981) Endocrinology 108, 1527-1532. Shii, K., Yokono, K., Baba, S., and Roth, R.A. (1986) Diabetes 35, 675-683. Duckworth, W.C., Stenz, F.B., Heinemann, M., and Kitabchi, A.E. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 635-639. Affholter J.A., Fried V-A., and Roth, R.A. (1988) Science 242, 1415-1418. Shii, K., and Roth, R.A. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 4147-4151. Hari, J., Shii, K., and Roth, R.A. (1987) Endocrinology 120, 829-831. Kitabchi, A.E., Stenz, F.B., Cole, C., and Duckworth, W.C. (1979) Diabetes Care 2, 414-417. Shii, K.. Baba, S., Yokono, K., and Roth, R.A. (1985) J. Biol. Chem. 260. 6503-6506. Yonezawa, K., Yokono, K., Shii, K., Hari, J., Yaso, St Amano, K. 7 Sakamoto, ‘I., Kawase, Y., Akiyama, H., Nagata. M., and Baba, S- (1988) Biochem. Biophys. Res. Commun. 150, 605-614. Brush, J. (1971) Diabetes 33, 140-145. Duckworth, W.C. (1976) Biochim. Biophys. Acta 437. 531-542. J. (1980) Biochem. J. 186, 351-360. Goldstein, B., and Livingston, Assoian R. K., Tager, H.S. (1981) J. Biol. Chem. 257, 9078-9085. Hamel F. G. , Posner, B. I., Bergeron, J.M., Frank, B. H., and Duckworth, W.C. (1988) J. Biol. Chem. 263, 6703-6708. Yonezawa, K., Yokono, K., Shii, K., Hari, J., Yaso, S., Sakamoto, T., Kawase, Y., Akiyama, H., Taketomi, S., and Baba, S. (1989) Endocrinology 124, 496-504. Ryan M. P., and Duckworth, W.C. (1983) Biochem. Biophys. Res. Commun. 116, 195-203. Mckenzie, R. A., and Burghen G.A. (1984) Arch. Biochem. Biophys. 2.29, 604m 611. Ogawa W i8Yo:;;;, Dlabetes. KbstS:ii, K., Yonezawa, K., and Baba, S. (1989) . .
1330
170,
No.
BIOCHEMICAL
3, 1990
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
1325-1330
Pages
16, 1990
NATURAL REGULATORYMECHANISMS OF INSULIN DEGRADATION BY INSULIN DEGRADING ENZYME Hiroyuki
Akiyama. Koichi
Yokono’. Kozui Shii*, Wataru Ogawa, Hiroshi Shigeaki Baba+, and Masato Kasuga
Second Department of Internal Kobe University School of Medicine, * Hyogo Institute Received
July
9,
for Research
in Adult
Taniguchi,
Medicine, Kobe 650, Japan
Disease,
Akashi
673, Japan
1990
SUMHARY: Insulin-degrading enzyme (IDE) accounts for most of the insulin degrading activity in extracts of several tissues and plays an important role in the intracellular degradation of insulin. Using newly developed sandwich radioimmunoassay for rat IDE, this enzyme was detectable in all tissues we examined and liver had the highest level of IDE. The ratio of insulin degrading activity to IDE concentration was roughly the same in liver, brain and muscle, however, twice as high in kidney as compared with other tissues. On the its degrading activity in these tissue extracts, including kidney, was contrary, completely lost after immunoprecipitation of IDE. These results suggest that IDE degrades insulin in the initial step of cleavage and that there are some mechanisms to regulate insulin degrading activity by IDE in the tissues. @1990 Academic Press, Inc.
After
binding
to ceII
eventually
degraded.
terminate
the insulin
However,
protease
occurring
(4).
been indicated
consensus lines
into
‘To whom correspondence
degradation
the signal
enzyme (IDE) DNA coding
sequences
of this
and
may be to
of insulin
and the loci
Consequently,
for the cell.
of insulin yet.
(1.2)
We have been
or insulin
for human erythrocyte
IDE
the deduced sequence of this
for any of the known classes
novel enzyme in insulin
of evidence,
IDE could
enzyme could
is internalized
have not been established
insulin-degrading
by several
monoclonal antibodies
of insulin
process
a complementary
The importance
(51, or that this
in this
and sequenced.
enzyme did not contain
role
insulin
or to modulate
in the cells
Recently,
has been isolated protease
action
an enzyme called (3).
receptors,
One suggested
the enzymes involved
degradation studying
surface
especially
inhibit
insulin
be cross-linked
with
of
metabolism
that microinjection degradation
““I-insulin
in intact
has of cells
via a receptor-
should be addressed.
Abbreviations: IDE, insulin-degrading enzyme; BSA, bovine serum albumin: TCA, trichloroacetic
1325
HBS, Hepes-buffered acid.
saline;
0006-291x/90 $1.50 Copyighr 0 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
Vol.
170,
No.
3, 1990
BIOCHEMICAL
mediated and energy-dependent this
pathway
enzyme has been demonstrated
patients,
whose fat
tissues
almost identical
to those of IDE (7).
measured IDE concentrations compared IDE levels
with
cases of insulin degrading
insulin
resistant activity
of
diabetic than
activity
were
there
tissues,
and thus the changes in insulin
reflect specific
in the cytosolic their
of this
significance
However,
we have developed antibodies
COMMUNJCATIONS
The clinical
more insulin
in various
may not correctly study,
(6).
RESEARCH
The enzyme characteristics
which could degrade insulin In the present
in vivo
contained
subjects.
rat IDE using monoclonal
BIOPHYSICAL
in certain
those of control
degrading activity
AND
may be a number of enzymes
those of IDE. the sandwich
radioimmunoassay
for this
enzyme.
fraction
from various
degrading
Furthermore, tissues
for we and
activities.
MATERIALS AND UETHODS Preparation of Rat Cytosolic Fraction : Male Wistar rats (200-25Og) were decapted and the liver, kidney, hind leg muscle and brain were homogenized using a Polytron homogenizer with 50 mM Hepes-buffered saline (HBS, pH 7.6). The homogenates were centrifuged at 100,000 g for 60 min at 4 “c. The supernatant was used as a cytosolic fraction. Radioimmunoassay for IDE : Monoclonal antibodies against IDE were produced by fusing spleen cells from mouse immunized with purified human erythrocyte IDE (2) with mouse myeloma cells (5). Antibodies were purified from ascites fluid on protein A-sepharose. Among four monoclonal antibodies that recognized human IDE, two antibodies (9B12 and 28Hl) were also found to recognize the rat liver Rat liver IDE which served as a standard, was affinity purified ; extracts (5). the procedure will be described in detail elsewhere. Briefly, the cytosolic fraction was applied to 9B12-coupled affigel 10 column and eluted with 75 mM sodium bicarbonate buffer (pH 11.2). The elutant was further applied to a MonoQ anion exchange column, the highest fraction of insulin degrading activity was concentrated, and finally purified by a Superlose 12 gel filtration column. The cytosolic fractions from various rat tissues obtained as described above were diluted with 50 mfl HBS containing 1 % bovine serum albumin (BSA), 1 m!l phenylmethylsulfonyIfluoride and 1 mg/ml bacitracin. Antibody 9B12 was iodinated using the chloramine T method (specific activity ; 10 pg/pCi). Fifty ~1 of another monoclonal antibody 28Hl (10 pg/ml in 20 mM bicarbonate buffer, pH 9.6) were first coated on 96mwell polyvinyl microtiter plates overnight at 4 “c. The wells were washed twice with 10 mM phosphate buffer (pH 7.4) containing 0.1 % BSA and 0.05 % Tween 20. The we1 1s were further incubated either with 50 ~1 of standard IDE, or the sample, for 2 h at room temperature. After washing twice, 50 pl of iodinated 9B12 in the same buffer was added and incubated another 2 h at 4 “c. Finally, the wells were washed, cut and counted in a Y -counter. Insulin Degradation Assay : The insulin degrading activity was estimated by determining the quantity of 7.5 % trichloroacetic acid (TCA)-soluble radioactivity produced in incubation with ““I-insulin (8). The percentage of insulin degraded was estimated as the net amount of supernatant radioactivity. In order to avoid any insulin degrading activity greater than 15 % in this assay, various rat cytosolic fractions were diluted differently. The abilities of diluted samples to degrade insulin were a linear function of the protein concentrations within this range. The results of enzyme activity were expressed as specific activity (PM insulin degraded/mg protein/min). 1326
Vol.
170,
No.
BIOCHEMICAL
3, 1990
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Immunoprecipitation of Insulin Degrading Activity : The cytosolic fraction from rat tissues was first incubated with 500 bl of various concentrations of anti body 9B12 in 50 mM HBS containing 0.2 % BSA overnight at 4 “c. The immune complex was then immunoprecipitated with 100 ~1 of 10 % staphylococcus aureus coated anti-mouse IgG (Cappel). After centrifugation, the resultant supernatant was tested for the ability to degrade ‘““I-insulin as described above. RESULTS AND DISCUSSION The specificity
and the stability
using the standard liver
dilution
curve and the percent
IDE added to the sample.
The purity
reduced 7.5% SDS polyacrylamide of 110 Kd (9). of rat
liver
cytosolic related
Figure
The lower
fraction.
occurred
of both liver
When 50 rig/ml purified cytosolic
fractions,
Using this various
1 shows a typical
sensitive
rat tissues
concentration
and kidney
standard
rat
liver
assay,
was 20 rig/ml,
liver
The serial to the standard liver
in the cytosolic
or kidney dilution curve.
or kidney
among the tissues
which
of them were almost equal,
except
serial
3-
from
has the highest
we examined.
was standardized
1).
fractions
Table 2 shows that the liver
in these tissues
band
and a dose-
of IDE was between 90 % and 98 % (Table
IDE concentrations
of IDE per protein
a single
by
the radioimmunoassay
curve of the rat
IDE was added to various
the recovery
rat
IDE was confirmed
curve for
for detection
assessed
of purified
demonstrating
samples were parallel
were measured.
all
rat
over the range of 2,000 &ml.
when the IDE concentration degrade insulin,
of standard
dilution
limit
were first
of recovery
gel electrophoresis
IDE and a representative
response
curves
of radioimmunoassay
However,
by the ability
for the kidney.
to
Since
dilution
OL /’ oylo
’ “““” IDE
100
concentration
’ “1”“’
1,000
’ ’
(rig/ml)
Figure 1. Typical standard curve of rat liver IDE (0) and a representative dilution curve of rat liver (0) or kidney (0) cytosolic fraction. Rat liver IDE was determined with antibody 28Hl as a solid phase and ““I-labeled antibody 9812. 1321
Vol.
170,
No.
3, 1990
BIOCHEMICAL
Table
1.
Recovery test
BIOPHYSICAL
RESEARCH
of radioimmunoassay
Purified IDE (ng)
IDE in the cytosolic fraction (nd Liver
AND
COMMUNICATIONS
for rat IDE
Expected
Measured
Recovery
(ng)
(ng)
(%)
246 123 61 30
50 50 50 50
296 173 111 80
290 164 108 74
98 95 97 93
95 47
50 50
145 97
130 92
90 95
Kidney
Purified rat liver IDE (50 ng) was added to various amounts of rat liver or kidney cytosolic fraction. The IDE concentration in the sample was measured as described in Materials and Methods.
IDE seems to account various
tissues
degrading
The insulin
degrading
IDE degrades
IDE are incapable finding
to IDE level
Rat tissue
Liver Kidney Brain Muscle
after
initial
step
insulin
by evidence are consistent
mediates found in the cell
Table 2.
was lost
of degrading
(13-15).
is shown
Comparison
2.93 1.38 1.05 0.38
: ? i i
tissues,
9B12 and the resultant
insulin
of cleavage, it
with
the nature
0.28 0.17 0.23 0.07
of IDE,
0.87 0.76 0.35 0.11
f f -t i
0.06 0.08 0.03 0.01
suggesting
that other
degraded
by IDE.
high ratio
inter
of degrading
may contain
degrading
a
activity
Relative ratio (activity/ concentration) 1.00 1.86 1.12 0.97
The relative ratio of insulin degrading activity to IDE concentration in the liver cytosolic fraction was provisionally considered as 1.00. Values are means i SE of 4 experiments. 1328
than
in a limited
of the peptide
tissue
was
Thus,
proteases
Insulin degrading activity ““I-insulin degraded/ mg protein/min)
(PM
kidney, M.
insulin
Since a reIatively this
including
is partially
IDE cleaves
2).
of lo-”
while
that
in the kidney,
(Figure
extracts,
the removal
before
how IDE
To examine
antibody
tissue
of
IDE in the cytosolic
of IDE concentration and insulin in various tissues
IDE concentration (,ug/mg protein)
in extracts and insulin
interest.
to degrade
in various
in the
which
activity
by 9B12 at a concentration
activity
is supported
number of places activity
in these
the ability
activity
insulin
is of
by monoclonal
immunoprecipitated degrading
This
for
degrading
of IDE concentration
in the kidney
degradation
was tested
completely insulin
as shown
was immunoprecipitated
supernatant
insulin
the discrepancy
to insulin
fraction
most of the
(lo-12),
activity
contributes
for
Vol.
170,
No.
BIOCHEMICAL
3, 1990
AND
RESEARCH
I
I
I
0
10-g
10-a
Antlbody
Figure 2.
BIOPHYSICAL
concentraton
COMMUNICATIONS
CM)
Insulin degrading activity in the cytosolic fraction after immunoprecipitation of IDE by 9B12. Rat liver (O), kidney (0). brain (A), and muscle(A) cytosolic fractions were diluted differently to avoid any insulin degrading activity greater than 15 % in the TCA method,as described in Materials and Methods. After IDE in the cytosolic fraction was immunoprecipitated by various of 9B12, insulin degrading activity in the resultant
concentrations supernatant was
measured.
relatively high amount of nonspecific proteases in the cytosol. Another possibility is that different tissues may contain different amounts of an endogenousinhibitor
specific
of IDE is predictable,
to IDE.
The presence of an endogeneousinhibitor
since IDE is a cytosolic
the cell without an inhibitor.
In fact,
protease was partially
from a cytosolic
(16) and liver
(17).
in the cytosolic inhibitor
purified
enzyme which could be toxic
an endogeneous inhibitor fraction
fraction
from porcine liver
(18).
seemto be an important natural regulatory
degrading activity, degrading activity The liver
a relatively
low inhibitor
of insulin
of rat skeletal
We have also found an endogenous inhibitor
to
specific
muscle to IDE
Since IDE and its endogenous mechanismof insulin
level may account for the high
in the kidney.
had the highest IDE concentration
in the present study and no crude cytosolic degradation without IDE.
In addition,
regulate insulin degrading activity
amongthe various tissues tested
fraction
could initiate
in the tissues.
nonspecific proteases appear to have an effect
An endogenous inhibitor
on the insulin
of IDE. Further studies on these mechanismsare, therefore, understand the biological
significance
the insulin
there are important mechanismsto
of IDE in insulin
degrading activity necessary to
metabolism.
ACKNOWLEDGMENT This work was supported in part by Grant-inAid for Scientific Research 61480251from the Japanese Ministry of Education, Science, and Culture.
1329
and
Vol.
170,
No.
3, 1990
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
Yokono, K., Imamura, Y., Shii, K., Sakai, H., and Baba, S. (1981) Endocrinology 108, 1527-1532. Shii, K., Yokono, K., Baba, S., and Roth, R.A. (1986) Diabetes 35, 675-683. Duckworth, W.C., Stenz, F.B., Heinemann, M., and Kitabchi, A.E. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 635-639. Affholter J.A., Fried V-A., and Roth, R.A. (1988) Science 242, 1415-1418. Shii, K., and Roth, R.A. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 4147-4151. Hari, J., Shii, K., and Roth, R.A. (1987) Endocrinology 120, 829-831. Kitabchi, A.E., Stenz, F.B., Cole, C., and Duckworth, W.C. (1979) Diabetes Care 2, 414-417. Shii, K.. Baba, S., Yokono, K., and Roth, R.A. (1985) J. Biol. Chem. 260. 6503-6506. Yonezawa, K., Yokono, K., Shii, K., Hari, J., Yaso, St Amano, K. 7 Sakamoto, ‘I., Kawase, Y., Akiyama, H., Nagata. M., and Baba, S- (1988) Biochem. Biophys. Res. Commun. 150, 605-614. Brush, J. (1971) Diabetes 33, 140-145. Duckworth, W.C. (1976) Biochim. Biophys. Acta 437. 531-542. J. (1980) Biochem. J. 186, 351-360. Goldstein, B., and Livingston, Assoian R. K., Tager, H.S. (1981) J. Biol. Chem. 257, 9078-9085. Hamel F. G. , Posner, B. I., Bergeron, J.M., Frank, B. H., and Duckworth, W.C. (1988) J. Biol. Chem. 263, 6703-6708. Yonezawa, K., Yokono, K., Shii, K., Hari, J., Yaso, S., Sakamoto, T., Kawase, Y., Akiyama, H., Taketomi, S., and Baba, S. (1989) Endocrinology 124, 496-504. Ryan M. P., and Duckworth, W.C. (1983) Biochem. Biophys. Res. Commun. 116, 195-203. Mckenzie, R. A., and Burghen G.A. (1984) Arch. Biochem. Biophys. 2.29, 604m 611. Ogawa W i8Yo:;;;, Dlabetes. KbstS:ii, K., Yonezawa, K., and Baba, S. (1989) . .
1330
