IGFBP-3 and IGFBP-5 production by human intestinal muscle: reciprocal regulation by endogenous TGF-beta1

Malnourishment affects gene expression along the length of the small intestine

Malnourishment is a risk factor for childhood mortality, jeopardizing the health of children by aggravating pneumonia/acute respiratory infections and diarrheal diseases. Malnourishment causes morphophysiological changes resulting in stunting and wasting that have long-lasting consequences such as cognitive deficit and metabolic dysfunction. Using a pig model of malnutrition, the interplay between the phenotypic data displayed by the malnourished animals, the gene expression pattern along the intestinal tract, microbiota composition of the intestinal contents, and hepatic metabolite concentrations from the same animals were correlated using a multi-omics approach. Samples from the duodenum, jejunum, and ileum of malnourished (protein and calorie-restricted diet) and full-fed (no dietary restrictions) piglets were subjected to RNA-seq. Gene co-expression analysis and phenotypic correlations were made with WGCNA, while the integration of transcriptome with microbiota composition and the hepatic metabolite profile was done using mixOmics. Malnourishment caused changes in tissue gene expression that influenced energetic balance, cell proliferation, nutrient absorption, and response to stress. Repression of antioxidant genes, including glutathione peroxidase, in coordination with induction of metal ion transporters corresponded to the hepatic metabolite changes. These data indicate oxidative stress in the intestine of malnourished animals. Furthermore, several of the phenotypes displayed by these animals could be explained by changes in gene expression.

Insulin-like growth factor-binding protein-4 inhibits epithelial growth and proliferation in the rodent intestine

Insulin-like growth factor-binding protein-4 (IGFBP-4) is a binding protein that modulates the action of insulin-like growth factor-1 (IGF-1), a growth factor whose presence is required for the intestinotrophic effects of glucagon-like peptide-2 (GLP-2). GLP-2 is a gut hormone that uses both IGF-1 and epidermal growth factor (EGF) as intermediary factors to promote intestinal growth. Therefore, to elucidate the mechanism through which IGFBP-4 regulates IGF-1 activity in the intestine, proliferation assays were conducted using rat intestinal epithelial cells (IEC-6). IGF-1 and EGF synergistically enhanced proliferation, an effect that was dose-dependently decreased by IGFBP-4 ( P < 0.05-0.001) in an IGF-1 receptor (R)- and MEK1/2- but not a phosphatidylinositol 3-kinase-dependent manner ( P > 0.05 for IGFBP-4 effects with IGF-1R and MEK1/2 inhibitors). Intestinal organoids derived from IGFBP-4 knockout mice demonstrated significantly greater Ki-67 expression and an enhanced surface area increase in response to IGF-1 treatment, compared with organoids from control mice ( P < 0.05-0.01). GLP-2 is also known to increase the mucosal expression of IGFBP-4 mRNA. To investigate whether this occurs through the actions of its intermediaries, IGF-1 and EGF, inducible intestinal epithelial-IGF-1R knockout and control mice were treated for 10 days with and without the pan-ErbB inhibitor, CI-1033. However, no differences in mucosal IGFBP-4 mRNA expression were found for any of the treatment groups ( P > 0.05). Consistently, IEC-6 cells treated with IGF-1 and/or EGF displayed no alteration in IGFBP-4 mRNA or in cellular and secreted IGFBP-4 protein ( P > 0.05). Overall, this study establishes that endogenous IGFBP-4 plays an important role in inhibiting IGF-1-induced intestinal epithelial proliferation and that mucosal IGFBP-4 expression is independent of IGF-1 and EGF. NEW & NOTEWORTHY This study demonstrates, for the first time, the inhibitory role of locally expressed insulin-like growth factor-binding protein-4 (IGFBP-4) on the intestinal proliferative actions of IGF-1 and supports the notion of the synergistic roles of IGF-1 and EGF in promoting intestinal epithelial growth. In turn, intestinal IGFBP-4 expression was not found to be regulated by IGF-1 and/or EGF.

Blunted satellite cell response is associated with dysregulated IGF-1 expression after exercise with age

PURPOSE

Insulin-like growth factor-1 (IGF-1) regulates protein synthesis and cell cycle kinetics. Given that aging is associated with anabolic resistance, we sought to determine if the attenuated exercise-induced satellite cell (SC) expression in older muscle is associated with a blunted IGF-1 response.

METHODS

SC expression (Pax7⁺ cells) and protein (Western blot) and mRNA (RT-PCR) expression of IGF-1 splice variants and ubiquitous (IGFBP4) and muscle-specific (IGFBP3 and -5) IGF-1 binding proteins were measured in skeletal muscle of young (Y: 22 ± 2, n = 7) and older (O: 70 ± 2, n = 7) adults up to 48 h after an acute bout of resistance exercise.

RESULTS

SC expression was greater in Y compared to O (age; P < 0.01) and increased (interaction; P < 0.05) by 24 h after exercise in Y only. IGF-1Ea and IGF-1Eb mRNA tended to be greater in O (age; P < 0.06-0.09). IGF-1Eb mRNA increased at 48 h (time; P < 0.05), whereas IGF-1Ec mRNA increased (interaction; P < 0.05) at 24 and 48 h in O only. IGF binding protein (IGFBP)4 mRNA was greater (age; P < 0.01) in O with the increase at 24 h and 48 h (time; P < 0.01) primarily driven by changes in O (interaction; P < 0.01). Despite IGFBP3 mRNA being greater in O (age; P < 0.01) and increasing at 48 h (time; P < 0.01), there was no effect of age or exercise on IGFBP3 protein expression. In contrast, IGFBP5 mRNA was greater (age; P < 0.01) despite IGFBP5 protein expression being lower (age; P < 0.01) in O compared to Y.

CONCLUSIONS

The greater muscle-specific expression of IGF-1 family members with a blunted post-exercise SC expression may be a compensatory attempt to rescue age-related anabolic resistance.

IGF binding proteins in cancer: mechanistic and clinical insights

The six members of the family of insulin-like growth factor (IGF) binding proteins (IGFBPs) were originally characterized as passive reservoirs of circulating IGFs, but they are now understood to have many actions beyond their endocrine role in IGF transport. IGFBPs also function in the pericellular and intracellular compartments to regulate cell growth and survival - they interact with many proteins, in addition to their canonical ligands IGF-I and IGF-II. Intranuclear roles of IGFBPs in transcriptional regulation, induction of apoptosis and DNA damage repair point to their intimate involvement in tumour development, progression and resistance to treatment. Tissue or circulating IGFBPs might also be useful as prognostic biomarkers.

Insulin-like growth factor-binding protein-5 stimulates growth of human intestinal muscle cells by activation of G{alpha}i3

In human intestinal smooth muscle cells, endogenous insulin-like growth factor-I (IGF-I) regulates growth and IGF-binding protein-5 (IGFBP-5) expression. The effects of IGF-I are facilitated by IGFBP-5. We previously showed that IGFBP-5 acts independently of IGF-I in human intestinal muscle to stimulate proliferation and upregulate IGF-I production by activation of Erk1/2 and p38 MAPK. Thus a positive feedback loop exists between IGF-I and IGFBP-5, whereby both stimulate muscle growth and production of the other factor. In Crohn's disease, IGF-I and IGFBP-5 expression are increased and contribute to stricture formation through this effect on muscle growth. To determine the signaling pathways coupling IGFBP-5 to MAPK activation and growth, smooth muscle cells were isolated from muscularis propria of human intestine and placed into primary culture. Erk1/2 and p38 MAPK activation and type I collagen production were measured by immunoblot. Proliferation was measured by [(3)H]thymidine incorporation. Activation of specific G proteins was measured by ELISA. AG1024, an IGF-I receptor tyrosine kinase inhibitor, was used to isolate the IGF-I-independent effects of IGFBP-5. IGFBP-5-induced phosphorylation of Erk1/2 and p38 MAPK and proliferation were abolished by pertussis toxin, implying the participation of Gi. IGFBP-5 specifically activated Gi3 but not other G proteins. Transfection of an inhibitory Galphai minigene specifically inhibited MAPK activation, proliferation, and both collagen-I and IGF-I production. Our results indicate that endogenous IGFBP-5 activates Gi3 and regulates smooth muscle growth, IGF-I production, and collagen production via the alpha-subunit of Gi3, independently of IGF-I, in normal human intestinal muscle cells.

Enteral nutrients potentiate the intestinotrophic action of glucagon-like peptide-2 in association with increased insulin-like growth factor-I responses in rats

Glucagon-like peptide-2 (GLP-2) is a nutrient-dependent, intestinotrophic hormone derived from posttranslational processing of proglucagon in the distal bowel. GLP-2 is thought to act through indirect mediators, such as IGF-I. We investigated whether intestinal expression of GLP-2 and IGF-I system components are increased with the mucosal growth induced by enteral nutrient (EN) and/or a low dose of GLP-2 in parenterally fed rats. Rats were randomized to four treatment groups using a 2 x 2 design and maintained with parenteral nutrition (PN) for 7 days: PN alone, EN, GLP-2, and EN+GLP-2; n = 7-9. The two main treatment effects are +/-GLP-2 (100 microg.kg body wt(-1).day(-1)) and +/-EN (43% of energy needs, days 4-6). Combination treatment with EN+GLP-2 induced synergistic intestinal growth in ileum, resulting in greater mucosal cellularity, sucrase segmental activity, and gain of body weight (ENxGLP-2, P < 0.04). In addition, EN+GLP-2 induced a significant 28% increase in plasma concentration of bioactive GLP-2, a significant 102% increase in ileal proglucagon mRNA with no change in ileal dipeptidyl peptidase-IV (DPP-IV) specific activity, and significantly reduced plasma DPP-IV activity compared with GLP-2. This indicates that EN potentiates the intestinotrophic action of GLP-2. Proliferation of enterocytes due to GLP-2 infusion was associated with greater expression of ileal proglucagon, GLP-2 receptor, IGF-I, IGF binding protein-3 mRNAs, and greater IGF-I peptide concentration in ileum (P < 0.032). Ileal IGF-I mRNA was positively correlated with expression of proglucagon, GLP-2R, and IGFBP-5 mRNAs (R2 = 0.43-0.56, P < 0.0001). Our findings support the hypothesis that IGF-I is one of the downstream mediators of GLP-2 action in a physiological model of intestinal growth.

Colostrum supplementation restores insulin-like growth factor -1 levels and alters muscle morphology following massive small bowel resection

BACKGROUND

Colostrum protein concentrate (CPC) contains a high level of insulin-like growth factor-1 (IGF-1). IGF-1 and IGF binding protein (IGFBPs) may play an important role during the postresection adaptation response. As smooth muscle is an important site for IGF-1 action in the intestine, this study aims to (1) investigate the effect of CPC supplementation on circulating levels and tissue expression of IGF-1, IGF-1 receptor, and IGFBPs following massive small bowel resection (MSBR), and (2) characterize the effect of CPC on the muscular adaptation response following MSBR.

METHODS

Four-week-old piglets underwent either a 75% MSBR or sham operation. Piglets received either a polymeric infant formula (PIF) diet or PIF supplemented with CPC for 8 weeks. Serum was analyzed by enzyme-linked immunosorbent assay, and ileal tissue assessed by molecular and histological analysis.

RESULTS

There was no difference in IGF-1 or IGFBPs mRNA among groups. CPC treatment resulted in significant increases in circulating levels of IGF-1 and IGFBPs and a concurrent increase in muscle width and the number of muscle cells, but did not alter muscle cell size.

CONCLUSIONS

Strategies aimed at increasing muscular adaptation may decrease Gl transit and allow greater mucosal contact time for absorption. We have shown that CPC supplementation following resection results in increased levels of circulating IGF-1, IGFBP-2, and IGFBP-3 and muscular hypertrophy. Our results suggest that IGF-1 and its mediators may play a role in the muscular adaptation response and warrant further exploration as a treatment option for short bowel syndrome.

Upregulation of N-acetylaspartic acid alters inflammation, transcription and contractile associated protein levels in the stomach and smooth muscle contractility

N-acetylaspartic acid (NAA) is converted into aspartate and acetate by aspartoacylase. Abnormal levels of the enzyme leads to accumulation of NAA and these changes have been observed in Canavan disease and type 2 diabetes. How upregulation of NAA affect the gastrointestine protein levels and the function is not known. Incubation of rat stomach tissue with NAA 1.5 mM, 1.5 microM and 1.5 nM induced inflammatory agents TNFalpha, p38MAPK, iNOS, PKC, COX2 and ICAM3; transcription factors phospho-NF-kBp65, cjun and cfos; contractile proteins MLCK and phospho MLC; and calcium channel alpha1C and calcium channel, voltage-dependent, beta 3 subunit compared to their respective control. Incubation of circular smooth muscle cells with the above doses of NAA induced contractility compared to the control. These studies suggest that NAA alters proteins levels and smooth muscle contractility and these changes likely to contribute to gastrointestinal disorder seen in these diseases.

Intestinotrophic effects of exogenous IGF-I are not diminished in IGF binding protein-5 knockout mice

IGF binding protein-5 (IGFBP-5) modulates the availability of IGF-I to its receptor and potentiates the intestinotrophic action of IGF-I. Our aim was to test the hypothesis that stimulation of intestinal growth due to coinfusion of IGF-I with total parenteral nutrition (TPN) solution is dependent on increased expression of IGFBP-5 through conducting our studies in IGFBP-5 knockout (KO) mice. IGFBP-5 KO, heterozygote (HT) and wild type (WT) male and female mice were maintained with TPN or TPN plus coinfusion of IGF-I [recombinant human (rh)IGF-I; 2.5 mg x kg(-1) x day(-1)] for 5 days. The concentration of IGF-I in serum was 73% greater (P < 0.0001) in mice given TPN + IGF-I infusion compared with TPN alone. IGF-I attenuated the 2-3 g loss of body weight associated with TPN in WT mice, whereas KO and HT mice did not show improvement in body weight with IGF-I treatment. KO and HT mice had significantly greater levels of circulating IGF-I binding proteins (IGFBPs) compared with WT mice. Intestinal growth due to IGF-I was observed in all groups treated with IGF-I based on greater concentrations of protein and DNA in small intestine and colon and significantly greater crypt depth and muscularis thickness in jejunum. Jejunal expression of IGFBP-5 mRNA was greater in WT mice, whereas IGFBP-3 mRNA was greater in KO mice treated with IGF-I. In summary, the absence of the IGFBP-5 gene did not block the ability of IGF-I to stimulate intestinal growth, possibly because greater jejunal expression of IGFBP-3 compensates for the absence of IGFBP-5.

Effect of NS398 on metastasis-associated gene expression in a human colon cancer cell line

AIM: To investigate the effect of NS398 on the metastasis-associated gene expression in LoVo colorectal cancer cells.

METHODS: LoVo cells were treated with NS398 at the concentration of 100 mmol/L for 24 and 48 h respectively. Total RNA was extracted with TRIzol reagents and reverse transcribed with Superscript II and hybridized with cDNA microarray (containing oncogenes, tumor suppressor genes, signal transduction molecules, adhesive molecules, growth factors, and ESTs) fabricated in our laboratory. After normalization, the ratio of gene expression of NS398 treated to untreated LoVo cells was either 2-fold up or 0.5-fold down was defined as the differentially expressed genes. Semi-quantitative RT-PCR was used to validate the microarray results.

RESULTS: Among the 447 metastasis-associated genes, 9 genes were upregulated and 8 genes were downregulated in LoVo cells treated with NS398 for 24 h compared to untreated cells. While 31 genes were upregulated and 14 genes were downregulated in LoVo cells treated with NS398 for 48 h. IGFBP-5, PAI-2, JUN, REL, BRCA1, and BRCA2 might be the new targets of NS398 in treatment of colorectal cancer.

CONCLUSION: NS398 might exert its anti-metastasis effect on colorectal cancer by affecting several metastasis-associated gene expression.

Insulin-like growth factor binding proteins 3 and 5 are overexpressed in idiopathic pulmonary fibrosis and contribute to extracellular matrix deposition

Idiopathic pulmonary fibrosis (IPF) is a fibrotic disease of unknown etiology that results in significant morbidity and mortality. The pathogenesis of IPF is not completely understood. Because recent studies have implicated insulin-like growth factor-I (IGF-I) in the pathogenesis of fibrosis, we examined the expression and function of insulin-like growth factor binding proteins (IGFBP)-3 and -5 in IPF. IGFBP-3 and -5 levels were increased in vivo in IPF lung tissues and in vitro in fibroblasts cultured from IPF lung. The IGFBPs secreted by IPF fibroblasts are functionally active and can bind IGF-I, and IGFBPs secreted by primary fibroblasts bind extracellular matrix components. Our results also suggest that IGFBPs may be involved in the initiation and/or perpetuation of fibrosis by virtue of their ability to induce the production of extracellular matrix components such as collagen type I and fibronectin in normal primary adult lung fibroblasts. Although transforming growth factor-beta increased IGFBP-3 production by primary fibroblasts in a time-dependent manner, IGFBP-5 levels were not increased by transforming growth factor-beta. Taken together, our results suggest that IGFBPs play an important role in the development of fibrosis in IPF.

Endogenous IGF-I protects human intestinal smooth muscle cells from apoptosis by regulation of GSK-3 beta activity

We have previously shown that endogenous IGF-I regulates human intestinal smooth muscle cell proliferation by activation of phosphatidylinositol 3 (PI3)-kinase- and Erk1/2-dependent pathways that jointly regulate cell cycle progression and cell division. Whereas insulin-like growth factor-I (IGF-I) stimulates PI3-kinase-dependent activation of Akt, expression of a kinase-inactive Akt did not alter IGF-I-stimulated proliferation. In other cell types, Akt-dependent phosphorylation of glycogen synthase kinase-3 beta (GSK-3 beta) inhibits its activity and its ability to stimulate apoptosis. The aim of the present study was to determine whether endogenous IGF-I regulates Akt-dependent GSK-3 beta phosphorylation and activity and whether it regulates apoptosis in human intestinal muscle cells. IGF-I elicited time- and concentration-dependent GSK-3 beta phosphorylation (inactivation) that was measured by Western blot analysis using a phospho-specific GSK-3beta antibody. Endogenous IGF-I stimulated GSK-3 beta phosphorylation and inhibited GSK-3 beta activity (measured by in vitro kinase assay) in these cells. IGF-I-dependent GSK-3 beta phosphorylation and the resulting GSK-3 beta inactivation were mediated by activation of a PI3-kinase-dependent, phosphoinositide-dependent kinase-1 (PDK-1)-dependent, and Akt-dependent mechanism. Deprivation of serum induced beta-catenin phosphorylation, increased in caspase 3 activity, and induced apoptosis of muscle cells, which was inhibited by either IGF-I or a GSK-3 beta inhibitor. Endogenous IGF-I inhibited beta-catenin phosphorylation, caspase 3 activation, and apoptosis induced by serum deprivation. IGF-I-dependent inhibition of apoptosis, similar to GSK-3 beta activity, was mediated by a PI3-kinase-, PDK-1-, and Akt-dependent mechanism. We conclude that endogenous IGF-I exerts two distinct but complementary effects on intestinal smooth muscle cell growth: it stimulates proliferation and inhibits apoptosis. The growth of intestinal smooth muscle cells is regulated jointly by the net effect of these two processes.

IGFBP-3 activates TGF-beta receptors and directly inhibits growth in human intestinal smooth muscle cells

We have shown that human intestinal smooth muscle cells produce IGF-I and IGF binding protein-3 (IGFBP-3). Endogenous IGF-I acts in autocrine fashion to stimulate growth of these cells. IGFBP-3 inhibits the binding of IGF-I to its receptor and thereby inhibits IGF-I-stimulated growth. In several carcinoma cell lines and some normal cells, IGFBP-3 regulates growth independently of IGF-I. Two mechanisms for this effect have been identified: IGFBP-3 can directly activate transforming growth factor-beta (TGF-beta) receptors or it can undergo direct nuclear translocation. The aim of the present study was to determine whether IGFBP-3 acts independently of IGF-I and to characterize the mechanisms mediating this effect in human intestinal smooth muscle cells. The direct effects of IGFBP-3 were determined in the presence of an IGF-I receptor antagonist to eliminate its IGF-I-dependent effects. Affinity labeling of TGF-beta receptors (TGF-betaRI, TGF-betaRII, and TGF-betaRV) with 125I-labeled TGF-beta1 showed that IGFBP-3 displaced binding to TGF-betaRII and TGF-betaRV in a concentration-dependent fashion. IGFBP-3 stimulated TGF-betaRII-dependent serine phosphorylation (activation) of both TGF-betaRI and of its primary substrate, Smad2(Ser465/467). IGFBP-3 also caused IGF-I-independent inhibition of basal [3H]thymidine incorporation. The effects of IGFBP-3 on Smad2 phosphorylation and on smooth muscle cell proliferation were independent of TGF-beta1 and were abolished by transfection of Smad2 siRNA. Immunoneutralization of IGFBP-3 increased basal [3H]thymidine incorporation, implying that endogenous IGFBP-3 inhibits proliferation. We conclude that endogenous IGFBP-3 directly inhibits proliferation of human intestinal smooth muscle cells by activation of TGF-betaRI and Smad2, an effect that is independent of its effect on IGF-I-stimulated growth.

Gene expression profile in human late radiation enteritis obtained by high-density cDNA array hybridization

Late radiation enteritis is a sequela of radiation therapy to the abdomen. The pathogenic process is poorly understood at the molecular level. cDNA array analysis was used to provide new insights into the pathogenesis of this disorder. Gene profiles of six samples of fibrotic bowel tissue from patients with radiation enteritis and six healthy bowel tissue samples from patients without radiation enteritis were compared using membrane-based arrays containing 1314 cDNAs. Results were confirmed with real-time RT-PCR and Western blot analysis. Array analysis identified many differentially expressed genes involved in fibrosis, stress response, inflammation, cell adhesion, intracellular and nuclear signaling, and metabolic pathways. Increased expression of genes coding for proteins involved in the composition and remodeling of the extracellular matrix, along with altered expression of genes involved in cell- to-cell and cell-to-matrix interactions, were observed mainly in radiation enteritis samples. Stress, inflammatory responses, and antioxidant metabolism were altered in radiation enteritis as were genes coding for recruitment of lymphocytes and macrophages. The Rho/HSP27 (HSPB1)/zyxin pathway, involved in tissue contraction and myofibroblast transdifferentiation, was also altered in radiation enteritis, suggesting that this pathway could be related to the fibrogenic process. Our results provide a global and integrated view of the alteration of gene expression associated with radiation enteritis. They suggest that radiation enteritis is a dynamic process involving constant remodeling of each structural component of the intestinal tissue, i.e. the mucosa, the mesenchyme, and blood vessels. Functional studies will be necessary to validate the present results.

IGF-I stimulates human intestinal smooth muscle cell growth by regulation of G1 phase cell cycle proteins

Autocrine production of insulin-like growth factor-I (IGF-I) regulates growth of human intestinal muscle cells by activation of distinct phosphatidylinositol 3-kinase (PI3-kinase)-dependent and ERK1/2-dependent pathways. The aim of the present study was to determine the mechanisms by which IGF-I regulates the G(1) phase of the cell cycle and muscle cell proliferation. Incubation of quiescent cells with IGF-I stimulated time-dependent cell cycle progression measured by using fluorescence-activated cell sorting analysis and by incorporation of [(3)H]thymidine. Studies using a microarray-based approach were used initially to identify genes expressed in human intestinal muscle encoding proteins known to participate in the G(1) phase of the cell cycle that were regulated by IGF-I. Incubation of muscle cells for 24 h with IGF-I elicited greater than fivefold increase in the expression of cyclin D1 and greater than twofold increase in retinoblastoma protein (Rb1). IGF-I elicited a time-dependent increase in cyclin D1 protein levels mediated jointly by ERK1/2-dependent and PI3-kinase-dependent mechanisms. Increase in cyclin D1 levels was accompanied by a time-dependent increase in cyclin D1-dependent cyclin-dependent kinase-4 (CDK4) activity. IGF-I also elicited a rapid time-dependent increase in Rb-(Ser807/811) phosphorylation, the specific target of the cyclin D(1)-dependent CDK4 kinase, and a slower increase in total Rb protein levels. We conclude that IGF-I stimulates G(1) phase progression, DNA synthesis, and cell proliferation of human intestinal smooth muscle cells. Effects of IGF-I on proliferation are mediated jointly by ERK1/2-dependent and PI3-kinase-dependent pathways that regulate cyclin D1 levels, CDK4 activity, and Rb activity.

IGF-I elicits growth of human intestinal smooth muscle cells by activation of PI3K, PDK-1, and p70S6 kinase

Endogenous IGF-I regulates growth of human intestinal smooth muscle cells by jointly activating phosphatidylinositol 3-kinase (PI3K) and ERK1/2. The 70-kDa ribosomal S6 kinase (p70S6 kinase) is a key regulator of cell growth activated by several independently regulated kinases. The present study characterized the role of p70S6 kinase in IGF-I-induced growth of human intestinal smooth muscle cells and identified the mechanisms of p70S6 kinase activation. IGF-I-induced growth elicited via either the PI3K or ERK1/2 pathway required activation of p70S6 kinase. IGF-I elicited concentration-dependent activation of PI3K, 3-phosphoinositide-dependent kinase-1 (PDK-1), and p70S6 kinase that was sequential and followed similar time courses. IGF-I caused time-dependent and concentration-dependent phosphorylation of p70S6 kinase on Thr(421)/Ser(424), Thr(389), and Thr(229) that paralleled p70S6 kinase activation. p70S6 kinase(Thr(421)/Ser(424)) phosphorylation was PI3K dependent and PDK-1 independent, whereas p70S6 kinase(Thr(389)) and p70S6 kinase(Thr(229)) phosphorylation and p70S6 kinase activation were PI3K dependent and PDK-1 dependent. IGF-I elicited sequential Akt(Ser(308)), Akt(Ser(473)), and mammalian target of rapamycin(Ser(2448)) phosphorylation; however, transfection of muscle cells with kinase-inactive Akt1(K179M) showed that these events were not required for IGF-I to activate p70S6 kinase and stimulate proliferation of human intestinal muscle cells.

Mesenchymal IGF-I overexpression: paracrine effects in the intestine, distinct from endocrine actions

Local IGF-I expression is frequently increased in intestinal mesenchyme during adaptive growth of intestinal epithelium, but paracrine growth effects of IGF-I in vivo are not defined. We tested whether overexpression of IGF-I in intestinal mesenchyme increases epithelial growth and if effects are distinct from known effects of circulating IGF-I. SMP8-IGF-I-transgenic (TG) mice overexpress IGF-I driven by an alpha-smooth muscle actin promoter. Mucosal and muscularis growth were assessed in the jejunum, ileum, and colon of SMP8-IGF-I-TG mice and wild-type littermates. Abundance of the SMP8-IGF-I transgene and IGF binding protein (IGFBP)-3 and -5 mRNAs was determined. Mucosal growth was increased in SMP8-IGF-I-TG ileum but not jejunum or colon; muscularis growth was increased throughout the bowel. IGFBP-5 mRNA was increased in SMP8-IGF-I-TG jejunum and ileum and was specifically upregulated in ileal lamina propria. Overexpression of IGF-I in intestinal mesenchymal cells has preferential paracrine effects on the ileal mucosal epithelium and autocrine effects on the muscularis throughout the bowel. Locally expressed IGF-I has distinct actions on IGFBP expression compared with circulating IGF-I.

The promise of transcription profiling for understanding the pathogenesis of scleroderma

Transcription profiling, expression fingerprinting, and microarray analysis are terms that describe the cataloging of mRNA levels in a given tissue. Recent profiling technologies allow the determination of thousands of mRNA transcript levels simultaneously. The application of this technology to scleroderma has already offered insights into the disease. This article reviews these recent findings and also describes the technology itself in its several variations, along with cost comparisons. Finally, the types of information we might derive from transcription profiling are reviewed and it is asked whether this technology will significantly advance our understanding of scleroderma.

Regulation of IGFBP-4 levels in human intestinal muscle by an IGF-I-activated, confluence-dependent protease

Human intestinal smooth muscle cells in culture produce insulin-like growth factor-I (IGF-I), IGF binding protein-3 (IGFBP-3), IGFBP-4, and IGFBP-5, which can modulate the effects of IGF-I on growth. This study examined the role of IGFBP-4 on IGF-I-induced growth and the mechanisms regulating IGFBP-4 levels. IGFBP-4 inhibited IGF-I-induced [(3)H]thymidine incorporation. IGFBP-4 mRNA levels were not altered by IGF-I. IGF-I caused a concentration-dependent activation of an endogenous IGFBP-4 protease, resulting in time-dependent degradation of intact IGFBP-4 into inactive fragments. Protease activity was measured in a cell-free assay using smooth muscle cell conditioned medium containing the IGFBP-4 protease. The protease was inhibited by EDTA and benzamidine. Protease activity was highest in proliferating cells and lowest in postconfluent cells. The role of endogenous IGF-I in regulating IGFBP-4 degradation was confirmed by the ability of an IGF-I antagonist to inhibit IGF-I-activated IGFBP-4 proteolysis in intact cells. We conclude that in human intestinal smooth muscle cells levels of secreted IGFBP-4 are determined by the confluence-dependent production of a cation-dependent serine protease that is activated by endogenous IGF-I.

Endogenous IGF-I regulates IGF binding protein production in human intestinal smooth muscle cells

Human intestinal smooth muscle in culture produces insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP)-3, IGFBP-4, and IGFBP-5, which modulate the effects of IGF-I. This study examined the regulation of IGFBP production by endogenous IGF-I. R3-IGF-I, an agonist unaffected by IGFBPs, elicited concentration-dependent increase in growth, measured by [(3)H]thymidine incorporation, and production of IGFBP-3, IGFBP-4, and IGFBP-5, measured by Western blot. Antagonists of the IGF-I receptor, IGF-I Analog or monoclonal antibody 1H7, elicited concentration-dependent inhibition of growth and decrease in IGFBP-3, IGFBP-4, and IGFBP-5 production, implying that endogenous IGF-I stimulated growth and IGFBP production. R3-IGF-I-induced increase in IGFBP-3, IGFBP-4, and IGFBP-5 production was partially inhibited by a mitogen-activated protein (MAP) kinase or a phosphatidylinositol-3-kinase (PI 3-kinase) inhibitor and abolished by the combination. We conclude that endogenous IGF-I stimulates growth and IGFBP-3, IGFBP-4, and IGFBP-5 production in human intestinal smooth muscle cells. Regulation of IGFBP production by IGF-I is mediated by activation of distinct MAP kinase and PI 3-kinase pathways, the same pathways through which IGF-I stimulates growth.