Gliclazide increases insulin receptor tyrosine phosphorylation but not p38 phosphorylation in insulin-resistant skeletal muscle cells
Signal Transduction Research Laboratory, Department of Biotechnology, National Institute of Pharmaceutical Education and Research, Punjab, India
* Author for correspondence (e-mail: csdey{at}niper.ac.in)
Accepted 23 August 2002
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: insulin resistance, skeletal muscle, insulin signaling, glucose uptake, gliclazide, p38
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Insulin stimulation results in the activation of two distinct pathways
involved in metabolic regulation: the phosphatidylinositol 3-kinase (PI
3-kinase) pathway and the mitogenic signaling pathway [mitogen-activated
protein kinase (MAPK) pathway]. The PI 3-kinase pathway
(Farese, 2001) and, more
recently, p38 MAPK activation have been implicated in glucose uptake
(Konrad et al., 2001
; Somwar
et al., 2000
,
2001a
). Insulin has been shown
to activate p38 in skeletal muscle cells
(Somwar et al., 2000
). In the
present study, the effect of gliclazide was also studied on the IR downstream
pathway and on all three MAPKs (p38 MAPK, JNK and ERK).
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell culture and treatment
C2C12 cells were cultured in DMEM supplemented with 15% FCS and antibiotics
(100IU ml-1 penicillin, 100 µg ml-1 streptomycin) in
5% CO2 at 37°C. The cells were differentiated in an equal
mixture of two serum-free media (MCDB201 and F-12 Ham medium) along with 0.05%
bovine serum albumin (BSA) in the absence (MF) or chronic presence (MFI) of
100 nmoll-1 insulin for three days. The media was changed after
every 12h. Gliclazide (2 moll-1) was added during the last 24h of
differentiation, where indicated. Gliclazide was dissolved in DMSO (dimethyl
sulfoxide), and control samples also received an equal amount of DMSO.
Preparation of extracts of C2C12 muscle cells for immunoblotting and
immunoprecipitation
Media in the differentiated cells were changed 1 h before the start of an
experiment. The cells were washed twice with Krebs-Ringer phosphate buffer
[KRP; 10 mmoll-1 phosphate (pH 7.2), 136 mmoll-1 NaCl,
4.7 mmoll-1 KCl, 1.25 mmoll-1 CaCl2, 1.25
mmoll-1 MgSO4] containing 5 mmoll-1 glucose
and 0.05% BSA. The cells were further incubated twice with KRP buffer at
37°C for 30 min. The cells were then stimulated with 100
nmoll-1 insulin for 5 min at 37°C or left unstimulated. The
cells were washed with ice-cold phosphate-buffered saline (PBS) and lysed in
lysis buffer [50 mmoll-1 Hepes (pH 7.4), 150 mmoll-1
NaCl, 1.5 mmoll-1 MgCl2, 1 mmoll-1 EGTA, 10
mmoll-1 sodium pyrophosphate, 50 mmoll-1 sodium
fluoride, 50 mmoll-1 ß-glycerophosphate, 1 mmoll-1
Na3VO4, 1% Triton X-100, 2 mmoll-1
phenylmethylsulfonyl fluoride, 10 µg ml-1 each of leupeptin,
aprotonin and soyabean trypsin inhibitor]. Lysis was carried out at 4°C
for 30 min. Cell lysate were clarified at 16,000g at 4°C
for 15 min. 500µg of protein was immunoprecipitated with antibody against
either anti-IR-ß or anti-IRS-1 with the addition of protein A-agarose.
The cell lysates or immunoprecipitates were boiled with Laemmli sample buffer
(Laemmli, 1970) for 5 min,
resolved by sodium dodecyl sulphate polyacrylamide gel electrophoresis
(SDS-PAGE) under reducing conditions and transferred to PVDF (polyvinylidene
difluoride) membranes. The membranes were blocked and incubated with the
indicated antibodies, followed by incubation with HRP-conjugated secondary
antibodies. The bands were visualized using enhanced chemiluminescence. Blots
were stripped in stripping buffer [62.5 mmoll-1 Tris-HCl (pH 6.7),
2% SDS and 100 mmoll-1 ß-mercaptoethanol] at 50°C for 30
min and reprobed with antibodies against either IR-ß or IRS-1.
PI 3-kinase assay
To study PI 3-kinase activity associated with IRS-1, 1 mg of cell lysate
was used. Cell lysates were prepared after 10 min of 100 nmoll-1
insulin stimulation. Immunoprecipitates were washed twice with lysis buffer
and twice with 10 mmoll-1 Tris-HCl (pH 7.5), 100 mmoll-1
NaCl, 1 mmoll-1 EDTA and 100 µmoll-1
Na3VO4. Immunoprecipitates were resuspended in 50 µl
of 20 mmoll-1 Hepes (pH 7.5), 180 mmoll-1 NaCl followed
by addition of 25 µl of assay buffer [28 mmoll-1 Hepes (pH 7.5),
50 mmoll-1 NaCl, 0.15% (v/v) Nonidet P40, 12.5 mmoll-1
MgCl2, 0.4 mmoll-1 EGTA, 0.8 mg ml-1
L--phosphatidylinositol, 50 µmoll-1
[
-32P]ATP (370Bq per assay)]. Reactions were terminated
after 15 min at 30°C by the addition of 50 µl of 2 moll-1
HCl followed by 160 µl of chloroform, vortexed and centrifuged briefly. 60
µl of the lower phase was applied to TLC plates. TLC plates were developed
in CHCl3:CH3OH:NH4OH:H2O
(60:47:11:5 by volume), dried and visualized by autoradiography.
2-deoxyglucose uptake
After washing with KRP buffer, cells were stimulated with 100
nmoll-1 insulin in KRP buffer without glucose for 15 min.
2-deoxyglucose (2-DOG) uptake (7.4 Bq in 1 µmoll-1 of unlabelled
2-DOG) was added and cells were incubated for 10 min. Cells were washed in
ice-cold PBS three times and were solubilized in 0.1 moll-1 NaOH.
Protein concentration was measured in each sample by the bicinchoninic acid
(BCA; Smith et al., 1985)
method followed by liquid scintillation counting. The uptake measurement was
made in duplicate. The results were corrected for non-specific uptake in the
presence of 10 µmoll-1 cytochalasin B. Non-specific uptake and
absorption were always <10% of the total uptake.
Densitometric analysis
Densitometric analysis of the western blots was performed using a GS-670
Imaging Densitometer (BioRad) and Molecular Analyst software (version 1.3).
The relative values of the samples were determined by giving an arbitrary
value of 1.0 to the control samples.
Statistical analysis
The data are expressed as means ± S.E.M. For comparison of two
groups, P-values were calculated by two-tailed unpaired student's
t-test. In all cases, P<0.05 was considered to be
statistically significant.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Effect of gliclazide on tyrosine phosphorylation of IRS-1
As insulin-stimulated IR tyrosine phosphorylation was increased by
gliclazide, we determined tyrosine phosphorylation of IRS-1, as IRS-1 is the
major molecule of IR signaling in skeletal muscle
(Cusi et al., 2000). MF and MFI
cells were treated with 2 mmol l-1 gliclazide and then lysed and
immunoprecipitated with anti-IRS-1 antibody followed by immunoblotting with
phosphotyrosine. Insulin-stimulated IRS-1 phosphorylation was impaired in MFI
cells as compared with MF cells (Fig.
2A). Treatment with gliclazide did not increase IRS-1 tyrosine
phosphorylation (Fig. 2C) in
sensitive (MF) or in insulin-resistant skeletal muscle cells (MFI). Expression
of IRS-1 was unaffected by treatment with the chronic presence of either
insulin or gliclazide (Fig.
2B).
|
Effect of gliclazide on PI 3-kinase activity
Stimulation of cells with insulin causes activation of PI 3-kinase, which
results in glucose uptake. PI 3-kinase has been shown to play an important
role in insulin-stimulated glucose uptake in insulin-responsive tissues
(Farese, 2001). Therefore, we
determined whether gliclazide could affect PI 3-kinase activity.
Insulin-stimulated PI 3-kinase activity was severely reduced in MFI cells as
compared with MF cells (Fig.
3A). The treatment of cells with 2 mmol l-1 gliclazide
was able to restore IRS-1-associated PI 3-kinase activity, and a 95% increase
in activity was observed in MFI cells as compared with untreated
insulin-stimulated MFI cells. A 210% increase in drug-treated MF cells
stimulated with insulin was observed as compared with untreated
insulin-stimulated MF cells (Fig.
3B). These data suggest that gliclazide can restore PI 3-kinase
activity of insulin-resistant myotubes to the untreated insulin-stimulated
sensitive conditions, although there was no effect on IRS-1 tyrosine
phosphorylation.
|
Effect of gliclazide on 2-DOG uptake
Gliclazide has been shown to enhance glucose uptake in L6 skeletal muscle
cells (Tsiani et al., 1995).
So, the effect of the chronic presence of insulin and gliclazide was tested on
basal and insulin-stimulated glucose uptake in MF and MFI cells. Insulin
stimulated a 20% increase in 2-DOG uptake in control samples (MF); however, we
could not observe any increase in 2-DOG uptake in the C2C12 cells chronically
treated with insulin (MFI) (Fig.
4). Treatment with gliclazide could not restore the
insulin-mediated 2-DOG uptake in resistant cells. However, the MF cells
maintained sensitivity to the insulin after treatment with gliclazide.
|
Effect of gliclazide on MAPK phosphorylation in insulin-resistant
skeletal muscle
So far, glucose uptake by insulin has been shown to be mediated by two
different pathways: PI 3-kinase is the pathway that has been widely implicated
in glucose uptake (Farese,
2001; Cefalu, 2001), and, more recently, the p38 pathway
(Konrad et al., 2001
; Somwar
et al., 2000
,
2001a
) has also been shown to
play a role in glucose uptake. Although gliclazide was able to increase PI
3-kinase activity in MFI cells, we could not observe any increase in
insulin-stimulated glucose uptake in resistant cells after gliclazide
treatment. Therefore, we determined the effect of gliclazide on p38 activation
and related MAP kinases to find out whether they play any role in insulin
resistance. The results (Fig.
5A,C,D,F) show that insulin stimulation increased ERK and JNK
activation in both MF and MFI cells. The insulin-stimulated activation of p38
was impaired in MFI cells, whereas p38 was activated by insulin in MF cells
(Fig. 5G,I). Treatment with
gliclazide could not restore the activation of p38 in MFI cells; however,
insulin was able to activate p38 in MF cells. Gliclazide treatment resulted in
an increase in JNK activation; however, the increase was not statistically
significant. The expression of all three MAP kinases was unaffected by the
chronic presence of insulin and by treatment with gliclazide
(Fig. 5B,E,H). Data suggest the
role of p38 in the uptake of glucose.
|
Effect of SB203580 on 2-DOG uptake and p38 activation
SB203580, a specific inhibitor of p38 MAPK, has been shown to reduce
insulin-stimulated glucose uptake in L6 myotubes and 3T3-L1 adipocytes in
culture (Sweeney et al.,
1999). To determine whether activation of p38 plays a role in
glucose transport in C2C12 skeletal muscle cells under MF and MFI conditions,
glucose uptake was determined in the presence of SB203580. The results
(Fig. 6A) show that there was
an insignificant increase in insulin-stimulated 2-DOG uptake in MF and MFI
samples by pretreatment with SB203580 as compared with a significant increase
(20%, P<0.05, N=4) observed in MF cells in the absence of
the p38 inhibitor (Fig. 4). Insulin-stimulated 2-DOG uptake was also insignificant, even when the samples
were treated with gliclazide in the presence of the p38 inhibitor during
insulin stimulation. These results implicate the potential role of p38 in
glucose uptake in skeletal muscle cells. Results in
Fig 6B clearly demonstrate that
10 µmol l-1 SB203580 completely blocks the activation of p38 by
insulin.
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
IRS-1 is the major signal-transducing molecule in the IR pathway in
skeletal muscle (Cusi et al.,
2000), and it has been shown that IRS-2 has no effect on
insulin-dependent glucose uptake in skeletal muscle
(Higaki et al., 1999
). Our
study on the effect of gliclazide on IRS-1 reveals that there is no
significant difference in insulin-stimulated tyrosine phosphorylation of IRS-1
with gliclazide treatment in either insulin-sensitive or insulin-resistant
myotubes. In our study, levels of IRS-1 expression remained unaltered. Some of
the studies suggest that insulin also downregulates the expression of IRS-1
(Ricort et al., 1995
;
Zhande et al., 2002
); however,
insulin did not affect IRS-1 expression in 3T3-L1 preadipocytes and mouse
embryo fibroblasts (Rui et al.,
2001
). In our study, PI 3-kinase activity associated with IRS-1
was enhanced by gliclazide treatment, although IRS-1 phosphorylation was
unchanged. IRS-1 contains over 20 putative tyrosine and 30 potential
serine/threonine sites (Myers and White,
1996
). Changes in the level of phosphorylation at any of these
sites could potentially alter the ability of IRS-1 to bind and to activate PI
3-kinase. Protein kinase B (PKB/Akt), which acts downstream of PI 3-kinase,
phosphorylates IRS-1 at serine residues within the pTyr-binding domain of
IRS-1 and protects it from the rapid actions of protein tyrosine phosphatases
and maintains the Tyr-phosphorylated active conformation of IRS-1, thus acting
as a positive regulator (Zick,
2001
). Another downstream molecule of PI 3-kinase, PKC
,
negatively regulates IRS function by inhibiting the ability of IRS-1 to
undergo insulin-stimulated tyrosine phosphorylation
(Zick, 2001
). It has also been
shown that PI 3-kinase is a dual-specificity enzyme containing an intrinsic
serine kinase activity that phosphorylates Ser608 of the p85 subunit. The
phosphorylation on this site of the enzyme inhibits its enzyme activity
(Dhand et al., 1994
). It has
also been demonstrated that tyrosine phosphorylation of the p85 subunit of PI
3-kinase may regulate the activity of the enzyme or alter the affinity of its
SH2 domain for phosphotyrosine residues (Hayashi et al.,
1992
,
1993
). Therefore, it is
apparent that a number of factors may modify the regulation of PI 3-kinase in
a complex manner, including proteinprotein interactions and alterations
in its phosphorylation state. The treatment of gliclazide may modulate any one
or all of these factors to potentiate the activation of the enzyme. The
potentiation can also occur in a completely novel way still to be identified.
Earlier, it was reported that PI 3-kinase activity was enhanced by
thiazolidinediones in Chinese hamster ovary (CHO) cells overexpressing human
insulin receptor without having any effect on the tyrosine phosphorylation of
IRS-1 (Zhang et al.,
1994
).
Treatment with gliclazide could not restore glucose uptake in
insulin-resistant myotubes despite the fact that PI 3-kinase activity was
enhanced by gliclazide treatment. It has been reported that, although PI
3-kinase activity is required for glucose uptake, there is at least one
additional pathway involved in glucose uptake as the activation of PI 3-kinase
by platelet-derived growth factor (PDGF) or interleukin 4 or through
engagement of integrin receptors does not stimulate glucose transport
(Saltiel, 2001). In addition,
two naturally occurring insulin receptor mutations were fully capable of
activating PI 3-kinase yet were unable to mediate insulin action
(Krook et al., 1997
).
Moreover, addition of a phosphatidylinositol (3,4,5)-trisphosphate
[PtdIns(3,4,5)P3] analog had no effect on glucose
transport, and treatment of adipocytes with wortmannin, insulin and the
PtdIns(3,4,5)P3 analog resulted in enhanced glucose uptake
(Jiang et al., 1998
). The
other pathway employed by the IR could be p38 activation, as recent studies
have demonstrated the requirement of p38 activation for glucose uptake
(Konrad et al., 2001
; Somwar
et al., 2000
,
2001a
). Earlier studies on
sulfonylurea on insulin-sensitive cells have indicated the enhanced basal as
well as insulin-stimulated glucose uptake by adipocytes and muscle cells
(Cooper et al., 1990
;
Rogers et al., 1987
;
Maloff and Lockwood, 1981
).
Although there was an increase in the basal glucose uptake in
insulin-resistant cells by gliclazide treatment in our study, this did not
reach significant levels.
The effect on ERK observed in the present study is in line with the study
by Kahn and co-workers (Cusi et al.,
2000), where it was shown that the ERK pathway is unaffected in
skeletal muscle of type 2 diabetic subjects. White and co-workers have
implicated the role of JNK in insulin resistance caused by tumor necrosis
factor
(TNF-
) in Chinese hamster ovary cells overexpressing
human insulin receptor (Aguirre et al.,
2000
). In C2C12 skeletal muscle cells, there was no difference in
JNK activity in insulin-resistant myotubes induced by the chronic presence of
insulin. In the present study, activation of p38 was impaired in
insulin-resistant cells. The treatment of cells with gliclazide could not
restore p38 activation by insulin in insulin-resistant cells. These data are
in accord with the data obtained on glucose uptake. Another antihyperglycemic
drug,
-lipoic acid, has been shown to enhance glucose uptake by
increasing the activation of p38 (Konrad, 2001). Recently, it has also been
shown that inhibition of p38 activity by the p38 inhibitor SB203580 results in
the blockage of glucose uptake by insulin in rat skeletal muscle
(Somwar et al., 2000
).
Moreover, it has been shown that protein-synthesis inhibitors, such as
anisomycin, which activates p38 and JNK, can stimulate glucose uptake
(Clancy et al., 1991
) and that
GLUT-4 (glucose transporter 4) translocation and glucose transport are
differentially regulated by PI 3-kinase inhibition, possibly through the
activation of the p38 MAPK pathway (Somwar
et al., 2001b
). At a lower concentration of wortmannin (10 nmol
l-1), GLUT-4 translocation and Akt activity were unaffected, but
glucose transport and p38 MAPK kinase activity were shown to be impaired,
implicating the role of p38 activation in glucose transport
(Somwar et al., 2001b
). In our
study, the activation of p38 by insulin and corresponding stimulation of
glucose uptake was blocked by SB203580, implicating the potential role of p38
in glucose uptake. Although we have observed an increase in insulin-stimulated
tyrosine phosphorylation of IR and PI 3-kinase activity in resistant cells by
treatment with gliclazide, we did not observe the corresponding increase in
glucose uptake, as was the case with the insulin-stimulated p38 activation.
Based on these data, we propose the role of p38 in glucose uptake.
In conclusion, we show that gliclazide can enhance insulin signaling in skeletal muscle by increasing tyrosine phosphorylation of IR and PI 3-kinase activity. Gliclazide treatment could not restore insulin-stimulated IRS-1 phosphorylation, glucose uptake and p38 activation. We conclude that p38 plays an important role in glucose uptake and can be a potential therapeutic target for anti-diabetic drugs to enhance glucose uptake. Further studies in this regard are needed to find the exact role of p38 in glucose uptake and insulin resistance in type 2 diabetic subjects.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Aguirre, V., Uchida, T., Yenush, L., Davis, R. and White, M.
F. (2000). The c-Jun NH2-terminal kinase promotes
insulin resistance during association with insulin receptor substrate-1 and
phosphorylation of Ser307. J. Biol. Chem.
275,9047
-9054.
Bak, J. F., Schmitz, O., Sorensen, N. S. and Pederson, O. (1989). Postreceptor effects of sulfonylurea on skeletal muscle glycogen synthase activity in type II diabetic subjects. Diabetes 38,1343 -1350.[Abstract]
Clancy, B. M., Harrison, S. A., Buxton, J. M. and Czech, M.
P. (1991). Protein synthesis inhibitors activate glucose
transport without increasing plasma membrane glucose transporters in 3T3-L1
adipocytes. J. Biol. Chem.
266,10122
-10130.
Cooper, D. R., Vila, M. C., Watson, J. E., Nair, G., Pollet, R. J., Standaert, M. and Farese, R. V. (1990). Sulfonylurea-stimulated glucose transport association with diacylglycerol like activation of protein kinase C in BC3H1 myocytes. Diabetes 39,1399 -1407.[Abstract]
Cusi, K., Maezono, K., Osman, A., Pendergrass, M., Patti, M. E.,
Pratipanawatr, T., DeFronzo, R. A., Kahn, C. R. and Mandarino, L. J.
(2000). Insulin resistance differentially affects the PI
3-kinase- and MAP kinase-mediated signaling in human muscle. J.
Clin. Invest. 105,311
-320.
Dhand, R., Hara, K., Hiles, I., Bax, B., Gout, I., Panayotou, G., Fry, M. J., Yonezawa, K., Kasuga, M. and Waterfield, M. D. (1994). PI 3-kinase: structural and functional analysis of intersubunit interactions. EMBO J. 13,522 -533.[Abstract]
Farese, R. V. (2001). Insulin-sensitive
phospholipid signaling systems and glucose transport. Update II.
Exp. Biol. Med. 226,283
-295.
Firth, R. G., Bell, P. M. and Rizza, R. A. (1986). Effects of tolazamide and exogenous insulin on insulin action in patients with non-insulin-dependent diabetes mellitus. New Engl. J. Med. 314,1280 -1286.[Abstract]
Hayashi, H., Kamohara, S., Nishioka, Y., Kanai, F., Miyake, N.,
Fukui, Y., Shibasaki, F., Takenawa, T. and Ebina, Y. (1992).
Insulin treatment stimulates the tyrosine phosphorylation of the alpha-type
85-kDa subunit of phosphatidylinositol 3-kinase in vivo. J. Biol.
Chem. 267,22575
-22580.
Hayashi, H., Nishioka, Y., Kamohara, S., Kanai, F., Ishii, K.,
Fukui, Y., Shibasaki, F., Takenawa, T., Kido, H. and Katsunuma, N.
(1993). The alpha-type 85-kDa subunit of phosphatidylinositol
3-kinase is phosphorylated at tyrosines 368, 580, and 607 by the insulin
receptor. J. Biol. Chem.
268,7107
-7117.
Higaki, Y., Wojtaszewski, J. F., Hirshman, M. F., Withers, D.
J., Towery, H., White, M. F. and Goodyear, L. J. (1999).
Insulin receptor substrate-2 is not necessary for insulin- and
exercise-stimulated glucose transport in skeletal muscle. J. Biol.
Chem. 274,20791
-20795.
Inoue, G., Cheatham, B. and Kahn, C. R. (1996).
Different pathways of postreceptor desensitization following chronic insulin
treatment and in cells overexpressing constitutively insulin receptors.
J. Biol. Chem. 271,28206
-28211.
Jiang, T., Sweeney, G., Rudolf, M. T., Klip, A., Traynor-Kaplan,
A. and Tsien, R. Y. (1998). Membrane-permeant esters of
phosphatidyl-inositol 3,4,5-triphosphate. J. Biol.
Chem. 273,11017
-11024.
Kolterman, O. G., Gray, R. S., Shapiro, G., Scarlett, J. and Olefsky, J. M. (1984). The acute and chronic effects of sulfonylurea therapy in type II diabetic subjects. Diabetes 33,346 -354.[Abstract]
Konrad, D., Somwar, R., Sweeney, G., Yaworsky, K., Hayashi, M.,
Ramlal, T. and Klip, A. (2001). The antihyperglycemic drug
-lipoic acid stimulates glucose uptake via both GLUT4 translocation and
GLUT4 activation. Diabetes
50,1464
-1471.
Krook, A., Whitehead, J. P., Dobson, S. P., Griffiths, M. R.,
Ouwens, M., Baker, C., Hayward, A. C., Sen, S. K., Maassen, J. A., Siddle, K.,
Tavare, J. M. and O'Rahilly, S. (1997). Two naturally
occurring insulin receptor tyrosine kinase domain mutants provide evidence
that phosphoinositide 3-kinase activation alone is not sufficient for the
mediation of insulin's metabolic and mitogenic effects. J. Biol.
Chem. 272,30208
-30214.
Laemmli, U. K. (1970). Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature 227,680 -685.[Medline]
Lebovitz, H. E. (1984). Cellular loci of sulfonylurea actions. Diabetes Care 7 (Suppl. 1),67 -71.[Medline]
Maloff, B. L. and Lockwood, D. H. (1981). In vitro effects of a sulfonylurea on insulin action in adipocytes. J. Clin. Invest. 68,85 -90.[Medline]
Myers, M. G. and White, M. F. (1996). Insulin signal transduction and IRS proteins. Annu. Rev. Pharmacol. Toxicol. 36,615 -658.[Medline]
Pulido, N., Casha, A., Suarez, A. I., Rodriguez, E., Casanova, B. and Rovira, A. (1996). Sulfonylurea stimulates glucose uptake in rats through an ATP-sensitive K+ channel dependent mechanism. Diabetologia 39, 22-27.[Medline]
Ricort, J. M., Tanti, J. F., Obberghen, E. V. and Marchand-Brustel, Y. L. (1995). Alterations in insulin signaling pathway induced by prolonged insulin treatment of 3T3-L1 adipocytes. Diabetologia 38,1148 -1156.[Medline]
Rogers, B. J., Standaert, M. L. and Pollet, R. J. (1987). Direct effects of sulfonylurea agents on glucose transport in the BC3H1 myocyte. Diabetes 36,1292 -1296.[Abstract]
Rui, L., Fisher, T. L., Thomas, J. and White, M. F.
(2001). Regulation of insulin/insulin-like growth factor-1
signaling by proteasome-mediated degradation of insulin receptor substrate-2.
J. Biol. Chem. 276,40362
-40367.
Saltiel, A. R. (2001). New perspectives into the molecular pathogenesis and treatment of type 2 diabetes. Cell 104,517 -529.[Medline]
Santos, R. F., Nomizo, R., Oliveira, E., Ursich, M., Wajchenberg, B., Reaven, G. M. and Azhar, S. (2000). Erythrocyte insulin receptor tyrosine kinase activity is increased in gluburide-treated patients with type 2 diabetes in good glycaemic control. Diabetes Obes. Metab. 2,237 -241.[Medline]
Smith, P. K., Krohn, R. I., Hermanson, G. T., Mallia, A. K., Gartner, F. H., Provenzano, M. D., Fujimoto, E. K., Goeke, N. M., Olson, B. J. and Klenk, D. C. (1985). Measurement of protein using bicinchoninic acid. Anal. Biochem. 150, 76-85.[Medline]
Somwar, R., Perreault, M., Kapur, S., Taha, C., Sweeney, G.,
Ramlal, T., Kim, D. Y., Keen, J., Cote, C. H., Klip, A. and Marette, A.
(2000). Activation of p38 mitogen-activated protein kinase
and ß by insulin and contraction in rat skeletal muscle.
Diabetes 49,1794
-1800.[Abstract]
Somwar, R., Kim, D. Y., Sweeney, G., Huang, C., Niu, W., Lador, C., Ramlal, T. and Klip, A. (2001a). GLUT4 translocation precedes the stimulation of glucose uptake by insulin in muscle cells: potential activation of GLUT4 via p38 mitogen-activated protein kinase. Biochem. J. 359,639 -649.[Medline]
Somwar, R., Niu, W., Kim, D. Y., Sweeney, G., Randhawa, V. K.,
Huang, C., Ramlal, T. and Klip, A. (2001b). Differential
effects of phosphatidylinositol 3-kinase inhibition on intracellular signals
regulating GLUT4 translocation and glucose transport. J. Biol.
Chem. 276,46079
-46087.
Sweeney, G., Somwar, R., Ramlal, T., Volchuk, A., Ueyama, A. and
Klip, A. (1999). An inhibitor of p38 mitogen-activated
protein kinase prevents insulin-stimulated glucose transport but not glucose
transporter translocation in 3T3-L1 adipocytes and L6 myotubes. J.
Biol. Chem. 274,10071
-10078.
Tsiani, E., Ramlal, T., Leiter, L. A., Klip, A. and Fantus, I. G. (1995). Stimulation of glucose uptake and increased plasma membrane content of glucose transporters in L6 skeletal muscle cells by sulfonylureas gliclazide and glyburide. Endocrinol. 136,2505 -2512.[Abstract]
Zhande, R., Mitchell, J. J., Wu, J. and Sun, X. J.
(2002). Molecular mechanism of insulin-induced degradation of
insulin receptor substrate-1. Mol. Cell. Biol.
22,1016
-1026.
Zhang, B., Szalkowski, D., Diaz, E., Hayes, N., Smith, R. and
Berger, J. (1994). Potentiation of insulin stimulation of
phosphatidylinositol 3-kinase by thiazolidinediones-derived antidiabetic
agents in Chinese hamster ovary cells expressing human insulin receptors and
L6 myotubes. J. Biol. Chem.
269,25735
-25741.
Zick, Y. (2001). Insulin resistance: a phosphorylation-based uncoupling of insulin signaling. Trends Cell Biol. 11,437 -441.[Medline]