United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
In neonatal animals, feeding stimulates skeletal muscle protein synthesis, a response that declines with development. Both the magnitude of the feeding response and its developmental decline can be reproduced by insulin infusion, suggesting that an altered responsiveness to insulin is a primary determinant of the developmental decline in the stimulation of protein synthesis by feeding. In this study, 7- and 26-day-old pigs were either fasted overnight or fed porcine milk after an overnight fast. We examined the abundance and degree of tyrosine phosphorylation of the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and IRS-2 in skeletal muscle and, for comparison, liver. We also evaluated the association of IRS-1 and IRS-2 with phosphatidylinositol 3-kinase (PI 3-kinase). The abundance of IR protein in muscle was twofold higher at 7 than at 26 days, but IRS-1 and IRS-2 abundances were similar in muscle of 7- and 26-day-old pigs. The feeding-induced phosphorylations were greater at 7 than at 26 days of age for IR (28- vs. 13-fold), IRS-1 (14- vs. 8-fold), and IRS-2 (21- vs. 12-fold) in muscle. The associations of IRS-1 and IRS-2 with PI 3-kinase were also increased by refeeding to a greater extent at 7 than at 26 days (9- vs. 5-fold and 6- vs. 4-fold, respectively). In liver, the abundance of IR, IRS-1, and IRS-2 was similar at 7 and 26 days of age. Feeding increased the activation of IR, IRS-1, IRS-2, and PI 3-kinase in liver only twofold, and these responses were unaffected by age. Thus our findings demonstrate that the feeding-induced activation of IR, IRS-1, IRS-2, and PI 3-kinase in skeletal muscle decreases with development. Further study is needed to ascertain whether the developmental decline in the feeding-induced activation of early insulin-signaling components contributes to the developmental decline in translation initiation in skeletal muscle.
protein synthesis; growth; insulin; muscle; liver
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
DIETARY AMINO ACIDS are efficiently deposited as body protein in the neonate (17, 34). This high efficiency is associated with a marked increase in protein synthesis after feeding (11, 13, 14, 16, 20), a response that declines with development. The postprandial rise in protein synthesis and the developmental decline in this response are more pronounced in skeletal muscle than in visceral tissues (5, 6, 11, 13, 16). Moreover, in muscle, the developmental decline in this response parallels the marked fall in the nutrient-induced activation of translation initiation factors involved in the binding of mRNA to the 40S ribosomal subunit (18). Thus, in muscle of the 7-day-old pig, feeding increases the phosphorylation of eukaryotic initiation factor (eIF)4E binding protein-1 (4E-BP1), resulting in a dissociation of the inactive 4E-BP1 · eIF4E complex and association of the active eIF4E · eIF4G complex. All of these changes are blunted with development.
Insulin likely plays a key role in the regulation of growth in the neonate. The feeding-induced stimulation of skeletal muscle protein synthesis in neonatal pigs can be completely reproduced by the infusion of insulin, even when glucose and amino acids are maintained at fasting levels (48). This response to insulin falls in exact parallel to the response to feeding and suggests that the developmental changes in the response to feeding reflect a change in insulin-mediated signals that stimulate translation. This hypothesis is supported by our recent findings of a developmental decline in the postprandial activation of the insulin-signaling proteins, ribosomal protein S6 kinase (S6K1) and protein kinase B (PKB), which are just upstream of translation initiation (Kimball SR, Farrell PA, Nguyen HV, Jefferson LS, and Davis TA, unpublished observations). However, the role of the early steps in the insulin-signaling pathway in the feeding-induced activation of translation initiation, and subsequent stimulation of protein synthesis, in neonatal pigs has not been elucidated.
The signaling cascade is initiated by insulin on binding to its receptor (45). This leads to activation of insulin receptor tyrosine kinase and the subsequent phosphorylation of several cytosolic substrates, primarily insulin receptor substrate (IRS)-1 (41) and IRS-2 (42). Although IRS-1 and IRS-2 are structurally similar, recent research suggests that they are differentially expressed and mediate distinct responses. IRS-1 and IRS-2 function as "docking proteins," transmitting insulin signals to several proteins that contain Src-homology 2 (SH2) domains (39, 40) including phosphatidylinositol (PI) 3-kinase, which catalyzes the phosphorylation of PI. The p85 subunit of this enzyme associates with phosphorylated IRS-1 and IRS-2, which leads to stimulation of its enzyme activity (2). The activation of PI 3-kinase triggers the downstream signaling pathway that leads to various insulin-stimulated biological responses, including glucose and amino acid transport, glycogen synthesis, and protein synthesis (22).
Feeding and developmental stage both appear to affect the early steps in the insulin-signaling pathway. Feeding stimulates the tyrosine phosphorylation of the insulin receptor and IRS-1 in rat (28) and chicken (21) liver, but not in chick muscle (21). The insulin-stimulated tyrosine phosphorylation of the insulin receptor, IRS-1, and IRS-2, as well as the association of PI 3-kinase with IRS-1 in both muscle and liver, is greater in the young adult than in the elderly rat (8, 9).
Studies using intact animals and cell lines suggest that early events in the insulin-signaling pathway may play an important role in the regulation of growth and protein synthesis. Lack of the insulin receptor gene is associated with profound growth retardation in humans (44). Anti-insulin receptor antibodies in embryonic chicks (25) and null mutations of the insulin receptor and IRS-1 in mice (30, 46, 49) are associated with low body weight (25, 30, 46) and muscle protein synthesis (49). Insulin receptor tyrosine kinase activity is required for insulin-stimulated IRS-1 and PI 3-kinase activation in transgenic mice (10), and activation of IRS-1 and PI 3-kinase is required for insulin-stimulated protein synthesis in 32D cell lines (35). Mutations of IRS-1 and IRS-2 genes in mice indicate that insulin action is largely mediated by IRS-1 in skeletal muscle and IRS-2 in liver (30) and that IRS-1 plays a more critical role than IRS-2 in regulating growth (46).
The current study tested the hypothesis that the feeding-induced changes in the level and phosphorylation of the insulin receptor, IRS-1, and IRS-2, as well as the associations of IRS-1 and IRS-2 with PI 3-kinase, decrease with development in skeletal muscle in parallel with the previously observed developmental decline in the feeding-induced activation of translation initiation factors (18) and protein synthesis (11) in skeletal muscle. For comparison, we examined the developmental changes in the liver, an organ in which insulin does not increase protein synthesis (12) and which shows no decline in its response to feeding during early postnatal development (11).
![]() |
EXPERIMENTAL PROCEDURES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals. Eight crossbred (Landrace × Yorkshire × Duroc × Hampshire) pregnant sows (Agriculture Headquarters, Texas Department of Criminal Justice, Huntsville, TX) were housed in lactation crates in individual, environmentally controlled rooms 2 wk before farrowing. Sows were fed a commercial diet (5084, PMI Feeds, Richmond, IN) and provided water ad libitum. After farrowing, piglets remained with the sow but were not allowed access to the sow's diet. A total of 24 piglets from four litters, weighing ~2 and 8 kg, were studied at 7 and 26 days of age, respectively.
Pigs within each litter were randomly assigned to one of two treatment groups (n = 6 per age group per treatment group), and were either 1) fasted for 18 h or 2) fed for 1.5 h after an 18-h fast. Water was provided throughout the fasting period. Pigs that were fed after the 18-h fast were given two gavage administrations of 30 ml/kg body wt of mature porcine milk (University of Nebraska, Lincoln, NE) at 60-min intervals. Pigs in the fasting group were killed after 18 h of fasting, and pigs in the fed group were killed 30 min after the second gavage feeding. Samples of longissimus dorsi muscle and liver were rinsed in ice-cold saline and rapidly frozen. The protocol was approved by the Animal Care and Use Committee of Baylor College of Medicine and was conducted in accordance with the National Research Council's Guide for the Care and Use of Laboratory Animals.Materials.
BioMag goat anti-mouse IgG and goat anti-rabbit IgG magnetic beads were
obtained from Polysciences (Warrington, PA), and the magnetic sample
rack was from Promega (Madison, WI). Reagents for SDS-PAGE were from
Bio-Rad Laboratories (Richmond, CA). The protein assay kit was
purchased from Pierce (Rockford, IL). Anti-insulin receptor
(-subunit) antibody, anti-phosphotyrosine (PY) antibody, and
anti-IRS-1 antibody were obtained from Santa Cruz Biotechnology (Santa
Cruz, CA). Anti-IRS-2 antibody was from Upstate Biotechnology (Lake
Placid, NY). Anti-PI 3-kinase (p85) was purchased from Mbl International (Watertown, MA). The enhanced chemiluminescence Western
blotting detection kit (ECL-Plus) was obtained from Amersham (Arlington
Heights, IL). Other chemicals and reagents were from Sigma Chemical
(St. Louis, MO).
Insulin receptor content. To determine insulin receptor abundance, the samples were prepared as described by Burrin et al. (7), with slight modification as follows. The samples (±1 g) of frozen muscle and liver were pulverized in liquid nitrogen and homogenized in a buffer (buffer A) containing (in mM) 50 HEPES, pH 7.4, 150 NaCl, 10 sodium pyrophosphate, 2 Na3VO4, 1 MgCl2, 1 CaCl2, 10 NaF, 5 Na-EDTA, and 2 phenylmethylsulfonyl fluoride and 25 µg/ml leupeptin. The homogenate was centrifuged at 10,000 g for 10 min at 4°C, and the resulting supernatant was centrifuged at 100,000 g for 1 h at 4°C. The 100,000-g pellet was solubilized in 3-5 ml of buffer A containing 1% Triton X-100 overnight at 4°C. The protein concentration of the solubilized membrane-containing fraction was determined using bicinchoninic acid (BCA; Pierce) by the method of Smith et al. (38).
Immunoprecipitation of insulin receptor protein.
To determine insulin receptor abundance and tyrosine phosphorylation,
protein samples from membrane preparations were immunoprecipitated with
anti-insulin receptor- antibody. The immunoprecipitation procedure
was conducted as described by Fox et al. (23). Briefly, equal amounts of membrane protein (500 µg protein in 500 µl buffer) were incubated overnight at 4°C with anti-insulin receptor-
antibody in 2.5% Triton X-100/PBS. BioMag goat anti-mouse IgG or goat
anti-rabbit IgG magnetic beads (1 ml/tube) were washed three times in
low-salt buffer (20 mM Tris, 150 mM NaCl, 5 mM disodium EDTA, 0.5%
Triton X-100, and 0.1%
-mercaptoethanol, pH 7.4) with the use of a
magnetic sample rack and were resuspended in 500 µl of low-salt
buffer containing 1% dry skim milk. Each sample was added to 500 µl
of resuspended beads and rocked for at least 1 h at 4°C. The
beads were captured using a magnetic rack and were washed twice in
low-salt buffer and once in high-salt buffer (50 mM Tris, 500 mM NaCl, 5 mM disodium EDTA, 1% Triton X-100, 0.6% sodium deoxycholate, 0.1%
SDS, and 0.04%
-mercaptoethanol, pH 7.4). The captured beads were
resuspended in 100 µl 1× sample buffer [2% SDS, 100 mM
Tris · HCl, pH 6.8, 5%
-mercaptoethanol, 12% (vol/vol)
glycerol, and 0.02% (wt/vol) Bromphenol blue], boiled for 5 min, and
stored at
80°C until electrophoresis.
Preparation of tissue extracts. Samples for immunoblotting were prepared as described by Goodyear et al. (27). Briefly, samples of frozen muscle and liver were pulverized and homogenized in ice-cold buffer A with 1% IGEPAL and 10% glycerol added. The homogenate was incubated for 45 min at 4°C with gentle mixing and then centrifuged at 35,000 g for 1 h at 4°C. The supernatant was collected, and an aliquot was assayed for protein concentration with BCA (37). Supernatants were used to determine IRS-1 and IRS-2 abundance, tyrosine phosphorylation of insulin receptor, IRS-1, and IRS-2, and the association of PI 3-kinase (p85) with IRS-1 and IRS-2.
Immunoprecipitation of PY, IRS-1 and IRS-2 proteins. To determine the abundance and tyrosine phosphorylation of the insulin receptor, IRS-1, and IRS-2 and the association of PI 3-kinase (p85) with IRS-1 and IRS-2, protein samples from tissue extract preparations were immunoprecipitated with anti-mouse PY, anti-human IRS-1, or anti-human IRS-2 antibodies. The immunoprecipitation procedure was similar to that described for the insulin receptor.
Western blot analysis. Equal amounts of protein were subjected to SDS-PAGE (8% wt/vol; Mini-PROTEAN II electrophoresis system, Bio-Rad), as described by Laemmli (33). Electrophoretic separation was carried out in 1% SDS, 25 mM Tris, and 200 mM glycine (pH 8.4) at 200 V for 45-60 min at room temperature. The proteins were then transferred to an activated polyvinylidene difluoride (PVDF) membrane (Immobilon-P; Millipore, Bedford, MA) in 25 mM Tris, 192 mM glycine, and 20% methanol (vol/vol; pH 8.3) for 1 h at 4°C. The membrane was incubated for 1 h at room temperature in a Tris-buffered saline-Tween 20 solution (TBS-T) containing 10 mM Tris, 0.5 M NaCl, and 0.5% Tween 20, pH 7.4, with 5% (wt/vol) nonfat dried milk. After the blocking step, the membrane was incubated with one primary antibody (anti-insulin receptor, IRS-1, IRS-2, PI 3-kinase/p85, or PY) for 1 h and washed four times in rinsing solution. Membranes were then incubated with secondary antibody (horseradish peroxidase-conjugated IgG fraction of goat anti-rabbit IgG or goat anti-mouse IgG) diluted 1:2,000 in TBS-T. The membranes were then washed in TBS-T three times for 10 min and developed with an enhanced chemiluminescence detection kit (ECL-Plus, Amersham Pharmacia, Piscataway, NJ) before exposure onto Kodak-X-Omat film. The blots were quantified by computerized densitometry (Molecular Dynamics, Sunnyvale, CA).
Statistics. Analysis of variance (general linear modeling) was used to assess the effects of feeding, age, and their interaction. If there was an interaction between feeding and age, Student's t-test was used to test for differences between treatment groups. Probability values of <0.05 were considered statistically significant. Data are presented as means ± SE.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Insulin receptor, IRS-1, and IRS-2 abundance in muscle and liver.
To determine whether there were effects of feeding and development on
the relative amount of insulin receptor in skeletal muscle and liver,
equal amounts of membrane protein were subjected to immunoblotting
using antibody to the -subunit of the insulin receptor. Insulin
receptor abundance in skeletal muscle was twofold higher in 7- than in
26-day-old pigs (P < 0.05; Fig.
1). Insulin receptor abundance in liver
was unaffected by age. Feeding did not alter insulin receptor abundance
in either skeletal muscle or liver of 7- and 26-day-old pigs.
|
Insulin receptor, IRS-1, and IRS-2 phosphorylation in muscle and
liver.
The effects of feeding and development on tyrosine phosphorylation of
the insulin receptor -subunit, IRS-1, and IRS-2 were determined by subjecting an equal amount of protein extracts from skeletal muscle and liver to immunoprecipitation with an
anti-phosphotyrosine (
PY) antibody. After SDS-PAGE and
electrotransfer, PVDF membrane was incubated with anti-insulin receptor
-subunit antibody, anti-IRS-1, or anti-IRS-2 antibodies.
The amount of tyrosine-phosphorylated insulin receptor
-subunit in both skeletal muscle and liver was increased
by feeding (P < 0.001 and P < 0.05, respectively; Fig. 2). The
feeding-induced stimulation of insulin receptor phosphorylation in
skeletal muscle was greater (P < 0.05) in 7-day-old
(16-fold) than in 26-day-old pigs (4-fold). In contrast, the
feeding-induced phosphorylation of the insulin receptor in liver did
not differ between 7- and 26-day-old pigs (both 2-fold). The baseline
fasting level of phosphorylation of the insulin receptor appeared to be lower, and the magnitude of the response to feeding appeared to be
higher, in skeletal muscle than in liver.
|
|
Association of PI 3-kinase with IRS-1 and IRS-2 in muscle and
liver.
To determine the association of PI 3-kinase with IRS-1 and IRS-2 in
response to feeding and development, equal amounts of skeletal muscle
and liver extracts were immunoprecipitated with anti-IRS-1 or IRS-2
antibody, followed by immunoblotting with anti-PI 3-kinase (p85)
antibody. The representative blots (Fig. 4) showed that feeding increased the
association of PI 3-kinase (p85) with IRS-1 and IRS-2 in both skeletal
muscle and liver. The feeding-induced stimulation of the association of
PI 3-kinase (p85) with IRS-1 in skeletal muscle was greater
(P < 0.05) in 7- than in 26-day-old pigs (9- vs.
5-fold). Similarly, the association of PI 3-kinase (p85) with IRS-2 in
skeletal muscle was greater in 7- than in 26-day-old pigs (6- vs.
4-fold, P < 0.05) after eating. In the liver, there
were no differences between 7- and 26-day-old pigs in the
feeding-induced stimulation of the association of PI 3-kinase with both
IRS-1 (3- vs. 3-fold) and IRS-2 (2- vs. 2-fold.) The baseline fasting
level of association of PI 3-kinase with IRS-1 and IRS-2 appeared to be
lower, and the magnitude of the response to feeding appeared to be
higher in skeletal muscle than in liver.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Effect of development on insulin receptor, IRS-1, and IRS-2 abundance. The rapid growth of skeletal muscle in the neonate is supported by an elevated rate of skeletal muscle protein synthesis (15, 19, 26, 50). To identify the mechanisms that regulate the high rate of protein deposition during early postnatal development, we have utilized the neonatal pig model (36). Pigs are studied at 7 days of age to avoid the complications of endocytosis of ingested protein in the newborn and at 26 days of age for comparison with a more advanced stage of development but before diet composition changes. We have demonstrated previously (11) that, in response to feeding, skeletal muscle protein synthesis increases from 15 to 24% per day at 7 days of age, but from only 4 to 6% per day at 26 days of age. By contrast, protein synthesis in liver increases after feeding from 76 to 93% per day at 7 days of age and from 63 to 72% per day at 26 days of age. Thus the overall developmental decline in protein synthesis is more pronounced in skeletal muscle than in liver (11). In addition, both the magnitude of the feeding-induced stimulation of protein synthesis and the developmental decline in this response to feeding are more profound in skeletal muscle than in liver. This stimulation of protein synthesis by feeding in muscle, but not in liver, of the 7- and 26-day-old pig can be reproduced by the infusion of insulin (12, 48). In the current study, we wished to determine whether the developmental changes in feeding-induced stimulation of skeletal muscle protein synthesis are associated with developmental changes in either the abundance or activation of early insulin-signaling components in skeletal muscle. For comparison, we also examined the effect of development on these signaling components in the liver, an organ in which the developmental changes in protein synthesis contrast sharply with those in skeletal muscle.
The results show that the insulin receptor concentration in skeletal muscle was twofold higher in 7- than in 26-day-old pigs. Studies have shown that insulin receptor abundance in muscle is also higher in suckling than in adult rats and dogs (1, 29). However, in those studies, age-related changes in insulin receptor abundance were confounded by changes in diet composition. In the current study, 7- and 26-day-old pigs were suckled until studied, and thus the results indicate that insulin receptor number is indeed developmentally regulated. However, neither feeding nor development altered the relative amount of IRS-1 and IRS-2 proteins in skeletal muscle of neonatal pigs, suggesting that the amount of IRS-1 and IRS-2 protein is not limiting for downstream signaling events, such as translation initiation, in neonatal skeletal muscle. The developmental decline in insulin receptor abundance in skeletal muscle in the current study is consistent with our recent findings (Kimball SR, Farrell PA, Nguyen HV, Jefferson LS, and Davis TA, unpublished observations) of a developmental decline in the abundance in muscle of components of the insulin signal transduction pathway that are downstream of PI 3- kinase (4, 38), i.e., PKB and the protein kinase mammalian target of rapamycin (mTOR). In addition, the developmental changes in the abundance of these signaling proteins paralleled the developmental change in both the activity of translation initiation factors that regulate the binding of met-tRNA to the 40S ribosomal subunit complex, i.e., eIF2 (18), and the overall rate of muscle protein synthesis (11). These responses are consistent with the hypothesis that the reduction in insulin receptor abundance in skeletal muscle during early postnatal development contributes to the long-term changes in muscle protein synthesis that occur over the course of development. In the liver, however, the abundance of insulin receptor, IRS-1, and IRS-2 did not change between 7 and 26 days of age, even though we had previously found a modest reduction in liver protein synthesis with development (11). This suggests that the developmental decline in liver protein synthesis is regulated by factors other than insulin receptor abundance. We have previously reported that the activation of a translation initiation factor, eIF2B, which regulates the binding of met-tRNA to the 40S ribosomal subunit, decreases with postnatal development in liver (18).Effects of feeding and development on the activation of insulin
receptor, IRS-1, IRS-2, and PI 3-kinase.
Insulin binding is followed by autophosphorylation of tyrosine residues
of the insulin receptor -subunit (45). This
event greatly enhances its tyrosine kinase activity toward endogenous substrates such as IRS-1 and IRS-2 and is considered important for the
biological effects of insulin. Insulin binding also activates PI
3-kinase by causing insulin receptor substrates to bind to the SH2
domain of the p85 subunit of PI 3-kinase (37, 40). In this
study, feeding increased the tyrosine phosphorylation of the insulin
receptor
-subunit, IRS-1, and IRS-2, as well as the association of
the p85 subunit of PI 3-kinase with both IRS-1 and IRS-2 in skeletal
muscle. By contrast, feeding has no effect on the phosphorylation of
the insulin receptor and IRS-1 in muscle of mature chickens
(21).
Perspectives. Our observation that insulin receptor abundance in skeletal muscle decreased with development, in parallel with the overall developmental decline in muscle protein synthesis (11), supports the hypothesis that insulin receptor abundance plays a role in the developmental regulation of muscle protein synthesis. The feeding-induced activation of the insulin receptor, IRS-1, IRS-2, and PI 3-kinase in skeletal muscle decreased with development, in parallel with the developmental decline in the feeding-induced activation of downstream signaling proteins (Kimball SR, Farrell PA, Nguyen HV, Jefferson LS, and Davis TA, unpublished observations), translation initiation factors (18), and protein synthesis (11) in skeletal muscle and the ability of insulin to stimulate skeletal muscle protein synthesis (48). In contrast, insulin receptor abundance and the modest feeding-induced activation of the early insulin-signaling components in liver did not change with development. Together, these results support the hypothesis that the developmental decline in the response of muscle protein synthesis to food consumption results from a reduction in the capacity of the insulin-signaling pathway in muscle to transduce to the translational apparatus the stimulus provided by the postprandial rise in circulating insulin concentration. If supported by further studies, the results imply that the enhanced activation of the insulin-signaling pathway in skeletal muscle of the neonate after food consumption plays a crucial role in determining the high rate of protein deposition in skeletal muscle and the more efficient use of dietary amino acids for growth in the neonate.
![]() |
ACKNOWLEDGEMENTS |
---|
We thank M. Fiorotto, P. Reeds, and D. Burrin for helpful discussions, P. O'Connor and W. Liu for the laboratory assistance, J. Cunningham and F. Biggs for care of animals, and L. Loddeke for editorial review.
![]() |
FOOTNOTES |
---|
This work is a publication of the United States Department of Agriculture/Agricultural Research Service (USDA/ARS) Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston, TX. This project has been funded in part by National Institute of Arthritis and Musculoskeletal and Skin Diseases Institute Grant R01-AR-44474 (T. A. Davis) and the USDA/ARS under Cooperative Agreement no. 58-6250-6-001 (T. A. Davis). The contents of this publication do not necessarily reflect the views or policies of the US Department of Agriculture, nor does mention of trade names, commercial products or organization imply endorsement by the US Government.
Address for reprint requests and other correspondence: T. A. Davis, USDA/ARS Children's Nutrition Research Center, Dept. of Pediatrics, Baylor College of Medicine, 1100 Bates St., Houston, TX 77030 (E-mail: tdavis{at}bcm.tmc.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 1 November 2000; accepted in final form 11 June 2001.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Alexandrides, T,
Moses AL,
and
Smith RJ.
Developmental expression of receptor for insulin-like growth factor I (IGF-I), and IGF-II in rat skeletal muscle.
Endocrinology
124:
1064-1076,
1989[Abstract].
2.
Backer, JM,
Myers MG,
Shoelson SE,
Chin DJ,
Sun XJ,
Miralpeix M,
Hu P,
Margolis B,
Skolnik EY,
and
Schlessinger J.
Phosphatidylinositol 3'-kinase is activated by association with IRS-1 during insulin stimulation.
EMBO J
11:
3469-3479,
1992[Abstract].
3.
Bailyes, EM,
Nave BT,
Soos MA,
Orr SR,
Hayward AC,
and
Siddle K.
Insulin receptor/IGF-I receptor hybrids are widely distributed in mammalian tissues: quantification of individual receptor species by selective immunoprecipitation and immunoblotting.
Biochem J
327:
209-215,
1997[ISI][Medline].
4.
Baretta, L,
Gingras AC,
Svitkin YV,
Hall MN,
and
Sonenberg N.
Rapamycin blocks the phosphorylation of 4E-BP1 and inhibits cap-dependent initiation of translation.
EMBO J
15:
658-664,
1996[Abstract].
5.
Burrin, DG,
Davis TA,
Fiorotto ML,
and
Reeds PJ.
Stage of development and fasting affect protein synthetic activity in the gastrointestinal tissues of suckling rats.
J Nutr
121:
1099-1108,
1991[ISI][Medline].
6.
Burrin, DG,
Davis TA,
Fiorotto ML,
and
Reeds PJ.
Hepatic protein synthesis in suckling rats: effect of stage of development and fasting.
Pediatr Res
31:
247-252,
1992[Abstract].
7.
Burrin, DG,
Wester TJ,
Davis TA,
Fiorotto MF,
and
Chang X.
Dexamethasone inhibits small intestinal growth via increased protein catabolism in neonatal pigs.
Am J Physiol Endocrinol Metab
276:
E269-E277,
1999
8.
Carvalho, CR,
Brenelli SL,
Silva AC,
Nunes ALB,
Velloso LV,
and
Saad MJA
Effect of aging on insulin receptor, insulin receptor-1, and phosphatidylinositol 3-kinase in liver and muscle of rats.
Endocrinology
137:
151-159,
1996[Abstract].
9.
Carvalho, CRO,
Maeda L,
Brenelli SL,
and
Saad MJA
Tissue-specific regulation of IRS2/PI3-kinase association in aged rats.
Biol Chem
381:
75-78,
2000[ISI][Medline].
10.
Chang, PY,
Goodyear LJ,
Benecke H,
Markuns JS,
and
Moller D.
Impaired insulin-signaling in skeletal muscles from transgenic mice expressing kinase-deficient insulin receptor.
J Biol Chem
270:
12593-12600,
1995
11.
Davis, TA,
Burrin DG,
Fiorotto ML,
and
Nguyen HV.
Protein synthesis in skeletal muscle and jejunum is more responsive to feeding in 7- than 26-day-old pigs.
Am J Physiol Endocrinol Metab
270:
E802-E809,
1996
12.
Davis, TA,
Fiorotto ML,
Beckett PR,
Burrin DG,
Reeds PJ,
Wray-Cahen D,
and
Nguyen HV.
Differential effects of insulin on peripheral and visceral tissue protein synthesis in neonatal pigs.
Am J Physiol Endocrinol Metab
280:
E770-E779,
2001
13.
Davis, TA,
Fiorotto ML,
Burrin DG,
Pond WG,
and
Nguyen HV.
Intrauterine growth restriction does not alter response of protein synthesis to feeding in newborn pigs.
Am J Physiol Endocrinol Metab
272:
E877-E884,
1997
14.
Davis, TA,
Fiorotto ML,
Nguyen HV,
Burrin DG,
and
Reeds PJ.
Response of muscle protein synthesis to fasting in suckling and weaned rats.
Am J Physiol Regulatory Integrative Comp Physiol
261:
R1337-R1380,
1991.
15.
Davis, TA,
Fiorotto ML,
Nguyen HV,
and
Reeds PJ.
Protein turnover in skeletal muscle of suckling rats.
Am J Physiol Regulatory Integrative Comp Physiol
257:
R1141-R1146,
1989
16.
Davis, TA,
Fiorotto ML,
Nguyen HV,
and
Reeds PJ.
Enhanced response of muscle protein synthesis and plasma insulin to food intake in suckled rats.
Am J Physiol Regulatory Integrative Comp Physiol
265:
R334-R340,
1993
17.
Davis, TA,
Fiorotto ML,
and
Reeds PJ.
Amino acid compositions of body and milk protein change during the suckling period in rats.
J Nutr
123:
947-956,
1993[ISI][Medline].
18.
Davis, TA,
Nguyen HV,
Suryawan A,
Bush JA,
Jefferson LS,
and
Kimball SR.
Developmental changes in the feeding-induced stimulation of translation initiation in skeletal muscle and liver of neonatal pigs.
Am J Physiol Endocrinol Metab
279:
E1226-E1234,
2000
19.
Denne, SC,
and
Kalhan SC.
Leucine metabolism in human newborns.
Am J Physiol Endocrinol Metab
253:
E608-E615,
1987
20.
Denne, SC,
Rossi EM,
and
Kalhan SC.
Leucine kinetics during feeding in normal newborns.
Pediatr Res
30:
23-27,
1991[Abstract].
21.
Dupont, J,
Derouet M,
Simon J,
and
Taouis M.
Nutritional state regulates insulin receptor and IRS-1 phosphorylation and expression in chicken.
Am J Physiol Endocrinol Metab
274:
E308-E316,
1998.
22.
Egawa, K,
Sharma PM,
Nakashima N,
Huang Y,
Huver E,
Boss GR,
and
Olefsky JM.
Membrane-targeted phosphatidylinositol 3-kinase mimics insulin actions and induces a state of cellular insulin resistance.
J Biol Chem
274:
14306-14314,
1999
23.
Fox, HL,
Pham PT,
Kimball SR,
Jefferson LS,
and
Lynch CJ.
Amino acid effects on translational repressor 4E-BP1 are mediated primarily by L-leucine in isolated adipocytes.
Am J Physiol Cell Physiol
275:
C1232-C1238,
1998
24.
Frasca, F,
Pandini G,
Scalia P,
Sciacca L,
Mineo R,
Costantino A,
Goldfine ID,
Belfiore A,
and
Vigneri R.
Insulin receptor isoform A, a newly recognized, high-affinity insulin-like growth factor II receptor in fetal and cancer cells.
Mol Cell Biol
19:
3278-3288,
1999
25.
Girbau, M,
Lesniak MA,
Gomez JA,
and
De Pablo F.
Insulin action in early embryonic life: anti-insulin receptor antibodies retard chicken embryo growth but not muscle differentiation in vivo.
Biochem Biophys Res Commun
31:
142-148,
1988.
26.
Goldspink, DF,
and
Kelly FJ.
Protein turnover and growth in the whole body, liver and kidney of the rat from the foetus to senility.
Biochem J
217:
507-516,
1984[ISI][Medline].
27.
Goodyear, LJ,
Giorgino F,
Sherman LA,
Carey J,
Smith RJ,
and
Dohm GL.
Insulin receptor phosphorylation, insulin receptor substrate-1 phosphorylation, and phosphatidylinositol 3-kinase activity are decreased in intact skeletal muscle strips from obese subjects.
J Clin Invest
95:
2195-2204,
1995[ISI][Medline].
28.
Ito, Y,
Ariga M,
Takahashi SI,
Takenaka A,
Hidaka T,
and
Noguchi T.
Changes in tyrosine phosphorylation of insulin receptor and insulin receptor substrate-1 (IRS-1) and association of p85 subunit of phosphatidylinositol 3-kinase after feeding in rat liver in vivo.
J Endocrinol
154:
267-273,
1997[Abstract].
29.
Johnston, V,
Frazzani V,
Davidheiser S,
Przybylski RJ,
and
Kliegman RM.
Insulin receptor number and binding affinity in newborn dogs.
Pediatr Res
29:
611-614,
1991[Abstract].
30.
Kido, Y,
Burks DJ,
Withers D,
Bruning JC,
Kahn CR,
White MF,
and
Accili D.
Tissue-specific insulin resistance in mice with mutation in the insulin receptor, IRS-1 and IRS-2.
J Clin Invest
105:
199-205,
2000
31.
Kimball, SR,
Jefferson LS,
Nguyen HV,
Suryawan A,
Bush JA,
and
Davis TA.
Feeding stimulates protein synthesis in muscle and liver of neonatal pigs through an mTOR-dependent process.
Am J Physiol Endocrinol Metab
279:
E1080-E1087,
2000
33.
Laemmli, UK.
Cleavage of structural proteins during the assembly of the head of bacteriophage T4.
Nature
227:
680-685,
1970[ISI][Medline].
34.
McCraken, KJ,
Eddie SM,
and
Stevenson WG.
Energy and protein nutrition of early-weaned pigs. Effect of energy intake and energy: protein on growth, efficiency and nitrogen utilization of pigs between 8-32 d.
Br J Nutr
43:
289-304,
1980[ISI][Medline].
35.
Mendez, R,
Myers MG,
White MF,
and
Rhoads RE.
Stimulation of protein synthesis, eukaryotic translation initiation factor 4E phosphorylation, and PHAS-1 phosphorylation by insulin requires insulin receptor substrate 1 and phosphatidylinositol 3-kinase.
Mol Cell Biol
16:
2857-2864,
1996[Abstract].
36.
Moughan, PJ,
and
Rowan AM.
The pig as a model animal for human nutrition research.
Proc Nutr Soc
14:
116-123,
1989.
37.
Myers, MG,
Backer JM,
Sun XJ,
Shoelson S,
Hu P,
Schlessinger J,
Yoakim M,
Schaffhausen B,
and
White MF.
IRS-1 activates phosphatidylinositol 3'-kinase by associating with src homology 2 domains of p85.
Proc Natl Acad Sci USA
89:
10350-10354,
1992[Abstract].
38.
Smith, PK,
Krohn RI,
Hermanson GT,
Maillia AK,
Gartner FH,
Provenzano MD,
Fujimoto EK,
Goeke NM,
Olson BJ,
and
Klenk DC.
Measurement of protein using bicinchoninic acid.
Anal Biochem
150:
76-85,
1985[ISI][Medline].
39.
Solow, BT,
Harada S,
Goldstein BJ,
Smith JA,
White MF,
and
Jarett L.
Differential modulation of the tyrosine phosphorylation state of the insulin receptor by IRS (insulin receptor substrate) proteins.
Mol Endocrinol
13:
1784-1798,
1999
40.
Sun, XJ,
Crimmins DL,
Myers MG,
Miralpeix M,
and
White MF.
Pleiotropic insulin signals are engaged by multisite phosphorylation of IRS-1.
Mol Cell Biol
13:
7418-7428,
1993[Abstract].
41.
Sun, XJ,
Rothenberg P,
Kahn CR,
Backer JM,
Araki E,
Cahill PA,
Goldstein BJ,
and
White MF.
Structure of the insulin receptor substrate IRS-1 defines a unique signal transduction protein.
Nature
352:
73-77,
1991[ISI][Medline].
42.
Sun, XJ,
Wang LM,
Zhang Y,
Yenush L,
Myers MG,
Glasheen E,
Lane WS,
Pierce JH,
and
White MF.
Role of IRS-2 in insulin and cytokine signalling.
Nature
377:
173-177,
1995[ISI][Medline].
43.
Takayama, S,
White MF,
and
Kahn CR.
Phorbol ester-induced serine phosphorylation of insulin receptor decreases its tyrosine kinase activity.
J Biol Chem
263:
3440-3447,
1988
44.
Wertheimer, E,
Lu SP,
Backeljaum PF,
Davenport ML,
and
Taylor SI.
Homozygous deletion of the human insulin receptor gene results in leprechaunism.
Nat Genet
5:
71-73,
1993[ISI][Medline].
45.
White, MF,
and
Kahn CR.
The insulin-signaling system.
J Biol Chem
269:
1-4,
1994
46.
Withers, DJ,
Burks DJ,
Towery TH,
Altamuro SL,
Flint CL,
and
White MF.
IRS-2 coordinates IGF-1 receptor-mediated -cell development and peripheral insulin-signaling.
Nat Genet
23:
32-40,
1999[ISI][Medline].
47.
Wray-Cahen, D,
Beckett PR,
Nguyen HV,
and
Davis TA.
Insulin-stimulated amino acid utilization during glucose and amino acid clamps decreases with development.
Am J Physiol Endocrinol Metab
273:
E305-E314,
1997
48.
Wray-Cahen, D,
Nguyen HV,
Burrin DG,
Beckett PR,
Fiorotto ML,
Reeds PJ,
Wester TJ,
and
Davis TA.
Response of skeletal muscle protein synthesis to insulin in suckling pigs decreases with development.
Am J Physiol Endocrinol Metab
275:
E602-E609,
1998
49.
Yamauchi, T,
Tobe K,
Tamemoro H,
Ueki K,
Kaburagi Y,
Yamamoto-Honda R,
Takahashi Y,
Yoshizawa F,
Aizawa S,
Akanuma Y,
Soneberg N,
Yazaki Y,
and
Kadowaki T.
Insulin-signaling and insulin action in muscles and livers of insulin-resistant, insulin substrate 1-deficient mice.
Mol Cell Biol
16:
3074-3084,
1996[Abstract].
50.
Young, VR.
The role of skeletal and cardiac muscle in the regulation of protein metabolism.
In: Mammalian Protein Metabolism, edited by Munro HN. New York: Academic, 1970, vol. 4, p. 585-674.