Insulin-like growth factor (IGF)-I regulates IGF-binding protein-5 gene expression through the phosphatidylinositol 3-kinase, protein kinase B/Akt, and p70 S6 kinase signaling pathway

The Pregnancy-Associated Plasma Protein-A (PAPP-A) Story

Pregnancy-associated plasma protein-A (PAPP-A) was first identified in the early 1970s as a placental protein of unknown function, present at high concentrations in the circulation of pregnant women. In the mid-to-late 1990s, PAPP-A was discovered to be a metzincin metalloproteinase, expressed by many nonplacental cells, that regulates local insulin-like growth factor (IGF) activity through cleavage of high-affinity IGF binding proteins (IGFBPs), in particular IGFBP-4. With PAPP-A as a cell surface-associated enzyme, the reduced affinity of the cleavage fragments results in increased IGF available to bind and activate IGF receptors in the pericellular environment. This proteolytic regulation of IGF activity is important, since the IGFs promote proliferation, differentiation, migration, and survival in various normal and cancer cells. Thus, there has been a steady growth in investigation of PAPP-A structure and function outside of pregnancy. This review provides historical perspective on the discovery of PAPP-A and its structure and cellular function, highlights key studies of the first 50 years in PAPP-A research, and introduces new findings from recent years.

A Phase Ib/II study of IGF-neutralising antibody xentuzumab with enzalutamide in metastatic castration-resistant prostate cancer

BACKGROUND

This multicentre, open-label, Phase Ib/II trial evaluated the insulin-like growth factor (IGF) 1/2 neutralising antibody xentuzumab plus enzalutamide in metastatic castrate-resistant prostate cancer (mCRPC).

METHODS

The trial included Phase Ib escalation and expansion parts and a randomised Phase II part versus enzalutamide alone. Primary endpoints in the Phase Ib escalation, Phase Ib expansion and Phase II parts were maximum tolerated dose (MTD), prostate-specific antigen response and investigator-assessed progression-free survival (PFS), respectively. Patients in the Phase Ib escalation and Phase II parts had progressed on/after docetaxel/abiraterone.

RESULTS

In the Phase Ib escalation (n = 10), no dose-limiting toxicities were reported, and xentuzumab 1000 mg weekly plus enzalutamide 160 mg daily (Xe1000 + En160) was defined as the MTD and recommended Phase 2 dose. In the Phase Ib expansion (n = 24), median PFS was 8.2 months, and one patient had a confirmed, long-term response. In Phase II (n = 86), median PFS for the Xe1000 + En160 and En160 arms was 7.4 and 6.2 months, respectively. Subgroup analysis suggested trends towards benefit with Xe1000 + En160 in patients whose tumours had high levels of IGF1 mRNA or PTEN protein. Overall, the combination was well tolerated.

CONCLUSIONS

Xentuzumab plus enzalutamide was tolerable but lacked antitumour activity in unselected patients with mCRPC.

CLINICAL TRIAL REGISTRATION

EudraCT number 2013-004011-41.

IGF/mTORC1/S6 Signaling Is Potentiated and Prolonged by Acute Loading of Subtoxicological Manganese Ion

The insulin-like growth factor (IGF)/insulin signaling (IIS) pathway is involved in cellular responses against intracellular divalent manganese ion (Mn2+) accumulation. As a pathway where multiple nodes utilize Mn2+ as a metallic co-factor, how the IIS signaling patterns are affected by Mn2+ overload is unresolved. In our prior studies, acute Mn2+ exposure potentiated IIS kinase activity upon physiological-level stimulation, indicated by elevated phosphorylation of protein kinase B (PKB, also known as AKT). AKT phosphorylation is associated with IIS activity; and provides direct signaling transduction input for the mammalian target of rapamycin complex 1 (mTORC1) and its downstream target ribosomal protein S6 (S6). Here, to better define the impact of Mn2+ exposure on IIS function, Mn2+-induced IIS activation was evaluated with serial concentrations and temporal endpoints. In the wild-type murine striatal neuronal line STHdh, the acute treatment of Mn2+ with IGF induced a Mn2+ concentration-sensitive phosphorylation of S6 at Ser235/236 to as low as 5 μM extracellular Mn2+. This effect required both the essential amino acids and insulin receptor (IR)/IGF receptor (IGFR) signaling input. Similar to simultaneous stimulation of Mn2+ and IGF, when a steady-state elevation of Mn2+ was established via a 24-h pre-exposure, phosphorylation of S6 also displayed higher sensitivity to sub-cytotoxic Mn2+ when compared to AKT phosphorylation at Ser473. This indicates a synergistic effect of sub-cytotoxic Mn2+ on IIS and mTORC1 signaling. Furthermore, elevated intracellular Mn2+, with both durations, led to a prolonged activation in AKT and S6 upon stimulation. Our data demonstrate that the downstream regulator S6 is a highly sensitive target of elevated Mn2+ and is well below the established acute cytotoxicity thresholds (<50 μM). These findings indicate that the IIS/mTORC1 pathways, in which Mn2+ normally serves as an essential co-factor, are dually responsible for the cellular changes in exposures to real-world Mn2+ concentrations.

Perturbation of PI3K/Akt signaling affected autophagy modulation in dystrophin-deficient myoblasts

BACKGROUND

The absence of dystrophin has gave a massive impact on myotube development in Muscular Dystrophy pathogenesis. One of the conserved signaling pathways involved in skeletal muscle differentiation is the PI3K/Akt/mTOR pathway that plays a vital role in autophagy regulation. To further understand and establish targeted therapy in dystrophin-deficient myoblasts, protein expression profiling has been determined which provides information on perturbed autophagy modulation and activation.

METHODS

In this study, a dystrophin-deficient myoblast cell line established from the skeletal muscle of a dystrophic (mdx) mouse was used as a model. The dfd13 (dystrophin-deficient) and C2C12 (non-dystrophic) myoblasts were cultured in low mitogen conditions for 10 days to induce differentiation. The cells were subjected to total protein extraction prior to Western blotting assay technique. Protein sub-fractionation has been conducted to determine protein localization. The live-cell analysis of autophagy assay was done using a flow cytometer.

RESULTS

In our culture system, the dfd13 myoblasts did not achieve terminal differentiation. PTEN expression was profoundly increased in dfd13 myoblasts throughout the differentiation day subsequently indicates perturbation of PI3K/Akt/mTOR regulation. In addition, rictor-mTORC2 was also found inactivated in this event. This occurrence has caused FoxO3 misregulation leads to higher activation of autophagy-related genes in dfd13 myoblasts. Autophagosome formation was increased as LC3B-I/II showed accumulation upon differentiation. However, the ratio of LC3B lipidation and autophagic flux were shown decreased which exhibited dystrophic features.

CONCLUSION

Perturbation of the PTEN-PI3K/Akt pathway triggers excessive autophagosome formation and subsequently reduced autophagic flux within dystrophin-deficient myoblasts where these findings are of importance to understand Duchenne Muscular Dystrophy (DMD) patients. We believe that some manipulation within its regulatory signaling reported in this study could help restore muscle homeostasis and attenuate disease progression. Video Abstract.

miR-140 inhibits porcine fetal fibroblasts proliferation by directly targeting type 1 insulin-like growth factor receptor and indirectly inhibiting type 1 insulin-like growth factor receptor expression via SRY-box 4

Objective

This study aimed to elucidate the effect of miR-140 on the proliferation of porcine fetal fibroblasts (PFFs) and identify the target genes of miR-140 in PFFs.

Methods

In this study, bioinformatics software was used to predict and verify target genes of miR-140. Quantitative polymerase chain reaction and western blot were used to detect the relationship between miR-140 and its target genes in PFFs. Dual luciferase reporter gene assays were performed to assess the interactions among miR-140, type 1 insulin-like growth factor receptor (IGF1R), and SRY-box 4 (SOX4). The effect of miR-140 on the proliferation of PFFs was measured by CCK-8 when PFFs were transfected with a miR-140 mimic or inhibitor. The transcription factor SOX4 binding to promoter of IGF1R was detected by chromatin immunoprecipitation assay (ChIP).

Results

miR-140 directly targeted IGF1R and inhibited proliferation of PFFs. Meanwhile, miR-140 targeted transcription factor SOX4 that binds to promoter of porcine IGF1R to indirectly inhibit the expression of IGF1R. In addition, miR-140 inhibitor promoted PFFs proliferation, which is abrogated by SOX4 or IGF1R knockdown.

Conclusion

miR-140 inhibited PFFs proliferation by directly targeting IGF1R and indirectly inhibiting IGF1R expression via SOX4, which play an important role in the development of porcine fetal.

Effects of chondroitin sulfate proteoglycan 4 (NG2/CSPG4) on soft-tissue sarcoma growth depend on tumor developmental stage

Sarcomas, and the mesenchymal precursor cells from which they arise, express chondroitin sulfate proteoglycan 4 (NG2/CSPG4). However, NG2/CSPG4's function and its capacity to serve as a therapeutic target in this tumor type are unknown. Here, we used cells from human tumors and a genetically engineered autochthonous mouse model of soft-tissue sarcomas (STSs) to determine NG2/CSPG4's role in STS initiation and growth. Inhibiting NG2/CSPG4 expression in established murine and human STSs decreased tumor volume by almost two-thirds and cell proliferation rate by 50%. NG2/CSPG4 antibody immunotherapy in human sarcomas established as xenografts in mice similarly decreased tumor volume, and expression of a lentivirus blocking NG2/CSPG4 expression inhibited tumor cell proliferation and increased the latency of engraftment. Gene profiling showed that Ng2/Cspg4 deletion altered the expression of genes regulating cell proliferation and apoptosis. Surprisingly, Ng2/Cspg4 deletion at the time of tumor initiation resulted in larger tumors. Gene expression profiling indicated substantial down-regulation of insulin-like growth factor binding protein (Igfbp) genes when Ng2/Cspg4 is depleted at tumor initiation, but not when Ng2/Cspg4 is depleted after tumor initiation. Such differences may have clinical significance, as therapeutic targeting of a signaling pathway such as NG2/CSPG4 may have different effects on cell behavior with tumor progression. NG2/CSPG4 depletion has divergent effects, depending on the developmental stage of sarcoma. In established tumors, IGF signaling is active, and NG2 inhibition targets cell proliferation and apoptosis.

Molecular identification of an insulin growth factor binding protein (IGFBP) and its potential role in an insulin-like peptide system of the pearl oyster, Pinctada fucata

Insulin-like growth factors (IGFs) play critical roles in regulating metabolism, growth, and reproduction in invertebrates. IGF binding proteins (IGFBPs) serve as major regulators of IGF activity and regulate endocrine system. In the present study, the full-length cDNA of an igfbp was identified from the pearl oyster, Pinctada fucata, using expressed sequence tag (EST) sequence. The 1124bp Pfigfbp cDNA contains a 465bp open reading frame (ORF) encoding a putative protein of 154 amino acids, a 5'-untranslated region (UTR) of 238bp, and a 3'-UTR of 394bp (not including polyA+). Multiple sequence alignment of the deduced IB domain sequences revealed that twelve conserved Cys and ILP binding site in PfIGFBP were well aligned with human IGFBPs1-7, Mizuhopecten yessoensis IGFBP5 and Eriocheir sinensis IGFBP7. Gene expression analysis indicated that Pfigfbp mRNA was expressed in all the tissues and developmental stages examined, with a higher level in the foot than in other tissues and a higher level in the polar body stage and 32-cell stage than in the other stages. Pfigfbp and PfILP (insulin-like peptide) mRNA levels significantly increased in the digestive gland after feeding, while levels were dramatically reduced during a week of food deprivation and increased upon refeeding. In vitro experiments indicated that Pfigfbp mRNA expression in mantle cells was affected by insulin/IGFs (IGF-I, IGF-II). Our data suggests that Pfigfbp may be involved in endocrine signaling in P. fucata via the regulation of insulin-like peptide signaling.

Development of a Whole Organism Platform for Phenotype-Based Analysis of IGF1R-PI3K-Akt-Tor Action

Aberrant regulation of the insulin-like growth factor (IGF)/insulin (IIS)-PI3K-AKT-TOR signaling pathway is linked to major human diseases, and key components of this pathway are targets for therapeutic intervention. Current assays are molecular target- or cell culture-based platforms. Due to the great in vivo complexities inherited in this pathway, there is an unmet need for whole organism based assays. Here we report the development of a zebrafish transgenic line, Tg(igfbp5a:GFP), which faithfully reports the mitotic action of IGF1R-PI3K-Akt-Tor signaling in epithelial cells in real-time. This platform is well suited for high-throughput assays and real-time cell cycle analysis. Using this platform, the dynamics of epithelial cell proliferation in response to low [Ca²⁺] stress and the distinct roles of Torc1 and Torc2 were elucidated. The availability of Tg(igfbp5a:GFP) line provides a whole organism platform for phenotype-based discovery of novel players and inhibitors in the IIS-PI3K-Akt-Tor signaling pathway.

Role of CCN5 (WNT1 inducible signaling pathway protein 2) in pancreatic islets

In search of direct targets of insulin-like growth factor (IGF)-1 action, we discovered CCN5 (WNT1 inducible signaling pathway protein 2 [WISP2]) as a novel protein expressed in pancreatic β-cells. As a member of the "CCN" ( C ysteine-rich angiogenic inducer 61 [Cyr61], C onnective tissue growth factor [CTGF in humans], and N ephroblastoma overexpressed [Nov; in chickens]) family, the expression of CCN5/WISP2 is stimulated by IGF-1 together with Wnt signaling. When overexpressed in insulinoma cells, CCN5 promotes cell proliferation and cell survival against streptozotocin-induced cell death. The cell proliferation effect seems to be caused by AKT phosphorylation and increased cyclin D1 levels. These properties resemble those of CCN2/CTGF, another isoform of the CCN family, although CCN5 is the only one within the family of six proteins that lacks the C-terminal repeat. Treatment of primary mouse islets with recombinant CCN5 protein produced similar effects to those of gene transfection, indicating that either as a matricellular protein or a secreted growth factor, CCN5 stimulates β-cell proliferation and regeneration in a paracrine fashion. This review also discusses the regulation of CCN5/WISP2 by estrogen and its involvement in angiogenesis and tumorigenesis.

IGF-I and IGF-II effects on local IGF system and signaling pathways in gilthead sea bream (Sparus aurata) cultured myocytes

The insulin-like growth factors (IGFs) have a fundamental role in a vast range of functions acting through a tyrosine-kinase receptor (IGF-IR). IGFs in muscle can affect the expression of components of the local IGF system, myogenic regulatory factors (MRFs), proliferating (proliferating cell nuclear antigen, PCNA) or differentiating molecules (myosin heavy chain, MHC) and, lead to the activation of different signaling pathways. The response of all these genes to IGFs incubation at two different times in day 4 cultured myocytes of gilthead sea bream was analyzed. Both IGFs increased the expression of IGF-I and IGFBP-5, but showed different effects on the receptors, with IGF-I suppressing the expression of both isoforms (IGF-IRa and IGF-IRb) and IGF-II up-regulating only IGF-IRb. Moreover, the protein levels of PCNA and target of rapamycin (TOR) increased after IGF-II incubation, although a decline in Myf5 and a rise in MHC gene expression was caused by IGF-I. Taken together, these results provide evidence for the importance of IGFs on controlling muscle development and growth in gilthead sea bream and suggest that each IGF may be preferentially acting through a specific IGF-IR. Moreover, the data support the hypothesis that IGF-II has a more important role during proliferation, whereas IGF-I seems to be relevant for the differentiation phase of myogenesis.

Tissue-specific changes in pregnancy associated plasma protein-A expression with age in mice

Pregnancy-associated plasma protein-A (PAPP-A) is a novel zinc metalloproteinase that functions in many systems outside of pregnancy. Data in both humans and mice suggest a role for PAPP-A in aging and age-related diseases. However, our knowledge of tissue-specific PAPP-A expression and possible changes in this expression with age is limited. Thus, the aim of this study was to determine PAPP-A mRNA expression in multiple tissues with age in both male and female mice using real-time PCR. These included the heart, liver, kidney, bone, fat, skeletal muscle, gonads, brain, thymus and spleen. In young mice, PAPP-A mRNA was expressed at relatively high levels in all tissues examined except for liver. The only difference in expression between males and females was seen in the kidney, subcutaneous fat and gonads. The highest PAPP-A mRNA expression levels were found in visceral fat and these were 10-fold higher than in subcutaneous fat. PAPP-A expression significantly increased with age in kidney, brain and gonads. PAPP-A expression significantly deceased with age in bone and skeletal muscle. In the thymus, PAPP-A mRNA showed a biphasic response with age. There were no age-related changes in PAPP-A expression seen in any of the other tissues examined. Expression of IGFBP-5 mRNA, a marker of insulin-like growth factor-I (IGF-I) bioactivity known to be regulated by PAPP-A, paralleled the changes in PAPP-A expression with age in kidney, bone, skeletal muscle and thymus. Thus, tissue-specific PAPP-A expression in mice is differentially affected during aging, and may regulate local IGF-I bioactivity in certain tissues.

Inhibition of Orai1-mediated Ca(2+) entry is a key mechanism of the antiproliferative action of sirolimus in human arterial smooth muscle

Sirolimus (rapamycin) is used in drug-eluting stent strategies and proved clearly superior in this application compared with other immunomodulators such as pimecrolimus. The molecular basis of this action of sirolimus in the vascular system is still incompletely understood. Measurements of cell proliferation in human coronary artery smooth muscle cells (hCASM) demonstrated a higher antiproliferative activity of sirolimus compared with pimecrolimus. Although sirolimus lacks inhibitory effects on calcineurin, nuclear factor of activated T-cell activation in hCASM was suppressed to a similar extent by both drugs at 10 μM. Sirolimus, but not pimecrolimus, inhibited agonist-induced and store-operated Ca(2+) entry as well as cAMP response element binding protein (CREB) phosphorylation in human arterial smooth muscle, suggesting the existence of an as-yet unrecognized inhibitory effect of sirolimus on Ca(2+) signaling and Ca(2+)-dependent gene transcription. Electrophysiological experiments revealed that only sirolimus but not pimecrolimus significantly blocked the classical stromal interaction molecule/Orai-mediated, store-operated Ca(2+) current reconstituted in human embryonic kidney cells (HEK293). A link between Orai function and proliferation was confirmed by dominant-negative knockout of Orai in hCASM. Analysis of the effects of sirolimus on cell proliferation and CREB activation in an in vitro model of arterial intervention using human aorta corroborated the ability of sirolimus to suppress stent implantation-induced CREB activation in human arteries. We suggest inhibition of store-operated Ca(2+) entry based on Orai channels and the resulting suppression of Ca(2+) transcription coupling as a key mechanism underlying the antiproliferative activity of sirolimus in human arteries. This mechanism of action is specific for sirolimus and not a general feature of drugs interacting with FK506-binding proteins.

Insulin Like Growth Factor Binding Protein-5 Regulates Excessive Vascular Smooth Muscle Cell Proliferation in Spontaneously Hypertensive Rats via ERK 1/2 Phosphorylation

Insulin-like growth factor binding proteins (IGFBPs) are important components of insulin growth factor (IGF) signaling pathways. One of the binding proteins, IGFBP-5, enhances the actions of IGF-1, which include the enhanced proliferation of smooth muscle cells. In the present study, we examined the expression and the biological effects of IGFBP-5 in vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). The levels of IGFBP-5 mRNA and protein were found to be higher in the VSMC from SHR than in those from WKY. Treatment with recombinant IGFBP-5-stimulated VSMC proliferation in WKY to the levels observed in SHR. In the VSMCs of WKY, incubation with angiotensin (Ang) II or IGF-1 dose dependently increased IGFBP-5 protein levels. Transfection with IGFBP-5 siRNA reduced VSMC proliferation in SHR to the levels exhibited in WKY. In addition, recombinant IGFBP-5 significantly up-regulated ERK1/2 phosphorylation in the VSMCs of WKY as much as those of SHR. Concurrent treatment with the MEK1/2 inhibitors, PD98059 or U0126 completely inhibited recombinant IGFBP-5-induced VSMC proliferation in WKY, while concurrent treatment with the phosphatidylinositol-3 kinase inhibitor, LY294002, had no effect. Furthermore, knockdown with IGFBP-5 siRNA inhibited ERK1/2 phosphorylation in VSMC of SHR. These results suggest that IGFBP-5 plays a role in the regulation of VSMC proliferation via ERK1/2 MAPK signaling in hypertensive rats.

Caffeic Acid phenethyl ester as a potential treatment for advanced prostate cancer targeting akt signaling

Prostate cancer is the fifth most common cancer overall in the world. Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, most prostate cancer patients receiving the androgen ablation therapy ultimately develop recurrent castration-resistant tumors within 1–3 years after treatment. The median overall survival time is 1–2 years after tumor relapse. Chemotherapy shows little effect on prolonging survival for patients with metastatic hormone-refractory prostate cancer. More than 80% of prostate tumors acquire mutation or deletion of tumor suppressor phosphatase and tensin homolog (PTEN), a negative regulator of PI3K/Akt signaling, indicating that inhibition of PI3K/Akt might be a potential therapy for advanced prostate tumors. Caffeic acid phenethyl ester (CAPE) is a strong antioxidant extracted from honeybee hive propolis. CAPE is a well-known NF-κB inhibitor. CAPE has been used in folk medicine as a potent anti-inflammatory agent. Recent studies indicate that CAPE treatment suppresses tumor growth and Akt signaling in human prostate cancer cells. We discuss the potential of using CAPE as a treatment for patients with advanced prostate cancer targeting Akt signaling pathway in this review article.

Functional roles and clinical values of insulin-like growth factor-binding protein-5 in different types of cancers

Insulin-like growth factor-binding proteins (IGFBPs) are critical regulators of the mitogenic activity of insulin-like growth factors (IGFs). IGFBP5, one of these IGFBPs, has special structural features, including a nuclear transport domain, heparin-binding motif, and IGF/extracellular matrix/acid-labile subunit-binding sites. Furthermore, IGFBP5 has several functional effects on carcinogenesis and even normal cell processes, such as cell growth, death, motility, and tissue remodeling. These biological effects are sometimes related with IGF (IGF-dependent effects) and sometimes not (IGF-independent effects). The functional role of IGFBP5 is most likely determined in a cell-type and tissue-type specific manner but also depends on cell context, especially in terms of the diversity of interacting proteins and the potential for nuclear localization. Clinical findings show that IGFBP5 has the potential to be a useful clinical biomarker for predicting response to therapy and clinical outcome of cancer patients. In this review, we summarize the functional diversity and clinical importance of IGFBP5 in different types of cancers.

Post-natal cardiomyocytes can generate iPS cells with an enhanced capacity toward cardiomyogenic re-differentation

Adult mammalian cells can be reprogrammed to a pluripotent state by forcing the expression of a few embryonic transcription factors. The resulting induced pluripotent stem (iPS) cells can differentiate into cells of all three germ layers. It is well known that post-natal cardiomyocytes (CMs) lack the capacity to proliferate. Here, we report that neonatal CMs can be reprogrammed to generate iPS cells that express embryonic-specific markers and feature gene-expression profiles similar to those of mouse embryonic stem (mES) cell and cardiac fibroblast (CF)-derived iPS cell populations. CM-derived iPS cells are able to generate chimeric mice and, moreover, re-differentiate toward CMs more efficiently then either CF-derived iPS cells or mES cells. The increased differentiation capacity is possibly related to CM-derived iPS cells retaining an epigenetic memory of the phenotype of their founder cell. CM-derived iPS cells may thus lead to new information on differentiation processes underlying cardiac differentiation and proliferation.

Transcriptional regulation of the IGF signaling pathway by amino acids and insulin-like growth factors during myogenesis in Atlantic salmon

The insulin-like growth factor signalling pathway is an important regulator of skeletal muscle growth. We examined the mRNA expression of components of the insulin-like growth factor (IGF) signalling pathway as well as Fibroblast Growth Factor 2 (FGF2) during maturation of myotubes in primary cell cultures isolated from fast myotomal muscle of Atlantic salmon (Salmo salar). The transcriptional regulation of IGFs and IGFBP expression by amino acids and insulin-like growth factors was also investigated. Proliferation of cells was 15% d⁻¹ at days 2 and 3 of the culture, increasing to 66% d⁻¹ at day 6. Three clusters of elevated gene expression were observed during the maturation of the culture associated with mono-nucleic cells (IGFBP5.1 and 5.2, IGFBP-6, IGFBP-rP1, IGFBP-2.2 and IGF-II), the initial proliferation phase (IGF-I, IGFBP-4, FGF2 and IGF-IRb) and terminal differentiation and myotube production (IGF2R, IGF-IRa). In cells starved of amino acids and serum for 72 h, IGF-I mRNA decreased 10-fold which was reversed by amino acid replacement. Addition of IGF-I and amino acids to starved cells resulted in an 18-fold increase in IGF-I mRNA indicating synergistic effects and the activation of additional pathway(s) leading to IGF-I production via a positive feedback mechanism. IGF-II, IGFBP-5.1 and IGFBP-5.2 expression was unchanged in starved cells, but increased with amino acid replacement. Synergistic increases in expression of IGFBP5.2 and IGFBP-4, but not IGFBP5.1 were observed with addition of IGF-I, IGF-II or insulin and amino acids to the medium. IGF-I and IGF-II directly stimulated IGFBP-6 expression, but not when amino acids were present. These findings indicate that amino acids alone are sufficient to stimulate myogenesis in myoblasts and that IGF-I production is controlled by both endocrine and paracrine pathways. A model depicting the transcriptional regulation of the IGF pathway in Atlantic salmon muscle following feeding is proposed.

In vivo analysis of gene expression in long-lived mice lacking the pregnancy-associated plasma protein A (PappA) gene

Mice lacking the pregnancy-associated plasma protein A (PappA) gene exhibit diminished localized IGF-1 bioavailability and a 30% increase in mean life span. However, it is uncertain which tissues exhibit reduced IGF-1 signals in the PappA(-/-) mouse, and whether effects of this mutation parallel those of mutations that diminish IGF-1 in serum. Across a panel of 21 tissues, we used RT-PCR to evaluate the effects of the PappA(-/-) mutation on expression of Igfbp5, which served as an in vivo indicator of IGF-1 signaling. Among these tissues, expression of Igfbp5 was significantly reduced by PappA(-/-) only in kidney. A broader survey of IGF-associated genes in six organs identified five other genes responsive to PappA(-/-) in kidney, with stronger effects in this organ relative to other tissues. Renal expression of Irs1 and Mt1 was increased by PappA(-/-) as well as by mutations that reduce IGF-1 in serum (i.e., Ghr(-/-), Pit1(dw/dw) and Prop1(df/df)), and we demonstrate that expression of these genes is regulated by growth hormone-treatment and calorie restriction. These results provide in vivo data on an important new model of mammalian aging, and characterize both similar and contrasting expression patterns between long-lived mice with reduced local IGF-1 availability and diminished IGF-1 in serum.

Role of insulin-like growth factor-binding protein 5 (IGFBP5) in organismal and pancreatic beta-cell growth

A family of IGF-binding proteins (IGFBP) exerts biological actions both dependent on and independent of IGF-I. A major effector of the insulin/IGF-I signaling pathway, the serine/threonine protein kinase Akt, mediates cellular processes such as glucose uptake, protein synthesis, cell survival, and growth. IGF-I is required for normal organismal growth, and in the pancreatic beta-cell, the insulin/IGF-I signaling pathway is critical for normal and adaptive maintenance of beta-cell mass. Expression of myrAkt1, an activated form of Akt, in the endocrine pancreas drives beta-cell expansion through dramatic increases in both islet and beta-cell size and number. Herein we present a comparative expression profiling of myrAkt1 transgenic islets that demonstrates the increased abundance of transcripts encoding proteins associated with growth, suppression of apoptosis, RNA processing, and metabolism. Although IGFBP5 is identified as a gene induced by Akt1 activation in the beta-cell, Igfbp5 expression is not necessary for myrAkt1 to augment beta-cell size or mass in vivo. However, in the absence of Igfbp5, mice demonstrate an increase in size and mild glucose intolerance. This is accentuated during diet-induced obesity, when Igfbp5-deficient mice have increased adiposity compared with wild-type mice on the same diet. These studies reveal a novel role for Igfbp5 in the control of growth and metabolism.

Subtractive hybridization identifies genes differentially expressed by olfactory ensheathing cells and neural stem cells

The in vitro differentiation of embryonic stem cells into glia has received relatively limited attention to date when compared with the interest in the generation of neurons. We are interested in a particular glial phenotype, the aldynoglia, and their differentiation from multipotential neural precursors (MNP), since this type of glia can promote neuronal regeneration. We constructed cDNA libraries from cultures of purified olfactory ensheathing cells (OEC), an aldynoglia cell type, and MNP to perform subtractive hybridization. As a result, we isolated four genes from the OEC: one tenascin C (Tn-C) isoform, Insulin-like growth factor binding protein 5 (Igfbp-5), cytochrome oxidase subunit I (COX1) and a phosphodiesterase for cyclic nucleotides (CNPase). With the exception of CNPase, these genes are expressed more strongly in the OEC than in the MNP and moreover, the expression of all four is induced when MNP were exposed to OEC conditioned media. The data suggest a role for these genes in MNP differentiation, and their products appear to represent characteristic proteins of the aldynoglia phenotype.

Nuclear factor I transcription factors regulate IGF binding protein 5 gene transcription in human osteoblasts

Insulin-like growth factor binding protein 5 (IGFBP5) is expressed in many cell types including osteoblasts and modulates IGF activities. IGFBP5 may affect osteoblasts and bone formation, in part by mechanisms independent of binding IGFs. The highly conserved IGFBP5 proximal promoter within 100 nucleotides of the start of transcription contains functional cis regulatory elements for C/EBP, Myb and AP-2. We report evidence for a functional Nuclear Factor I (NFI) cis element that mediates activation or repression of IGFBP5 transcription by the NFI gene family. All four NFI genes were expressed in human osteoblast cultures and osteosarcoma cell lines. Co-transfection with human IGFBP5 promoter luciferase reporter and murine Nfi expression vectors showed that Nfib was the most active in stimulating transcription. Nfix was less active and Nfia and Nfic were inhibitory. Knockdown of NFIB and NFIC expression using siRNA decreased and increased IGFBP5 expression, respectively. Analysis of IGFBP5 promoter deletion and mutation reporter constructs identified a functional NFI cis element. All four NFI proteins bound the NFI site in electrophoretic mobility shift experiments and NFIB bound in chromatin immunoprecipitation assays. Results suggest that NFI proteins are important regulators of IGFBP5 expression in human osteoblasts and thus in modulating IGFBP5 functions in bone.

Induction of cellular senescence by insulin-like growth factor binding protein-5 through a p53-dependent mechanism

The insulin-like growth factor (IGF) signaling pathway plays a crucial role in the regulation of cell growth, differentiation, apoptosis, and aging. IGF-binding proteins (IGFBPs) are important members of the IGF axis. IGFBP-5 is up-regulated during cellular senescence in human dermal fibroblasts and endothelial cells, but the function of IGFBP-5 in cellular senescence is unknown. Here we show that IGFBP-5 plays important roles in the regulation of cellular senescence. Knockdown of IGFBP-5 in old human umbilical endothelial cells (HUVECs) with IGFBP-5 micro-RNA lentivirus caused partial reduction of a variety of senescent phenotypes, such as changes in cell morphology, increases in cell proliferation, and decreases in senescence-associated beta-galactosidase (SA-beta-gal) staining. In addition, treatment with IGFBP-5 protein or up-regulation of IGFBP-5 in young cells accelerates cellular senescence, as confirmed by cell proliferation and SA-beta-gal staining. Premature senescence induced by IGFBP-5 up-regulation in young cells was rescued by knockdown of p53, but not by knockdown of p16. Furthermore, atherosclerotic arteries exhibited strong IGFBP-5-positive staining along intimal plaques. These results suggest that IGFBP-5 plays a role in the regulation of cellular senescence via a p53-dependent pathway and in aging-associated vascular diseases.

Genetic deletion of pregnancy-associated plasma protein-A is associated with resistance to atherosclerotic lesion development in apolipoprotein E-deficient mice challenged with a high-fat diet

Pregnancy-associated plasma protein-A (PAPP-A), a metalloproteinase in the insulin-like growth factor (IGF) system, is markedly upregulated in human atherosclerotic plaque. To determine whether PAPP-A plays an active role in the development of atherosclerosis, we crossed mice lacking apolipoprotein E (ApoE) with PAPP-A-deficient mice, generating ApoE knock-out (KO), PAPP-A KO, wild-type (WT/WT), and ApoE/PAPP-A double KO (KO/KO) mice. These mice were fed a high-fat diet starting at 7 weeks of age. Total serum cholesterol levels were elevated similarly in the ApoE KO and KO/KO mice and were 10-fold higher than in the WT/WT and PAPP-A KO mice. WT/WT and PAPP-A KO mice showed little or no lesion development even after 20 weeks of diet. ApoE KO mice had a progressive increase in aortic lesion area over 20 weeks of diet. In comparison, lesion area was reduced 60% to 80% in KO/KO mice. Lesions of ApoE KO aortas had 8- to 20-fold increases in PAPP-A, IGFBP-4, and IGF-I mRNA levels compared with nonlesional areas, whereas IGF-I receptor levels were equivalent--conditions for enhanced lesional IGF activity. Consistent with this, an in vivo marker of IGF-I receptor-mediated action was increased 10-fold in lesions from ApoE KO compared with KO/KO aortas. These data indicate that PAPP-A plays a critical role in lesion development in a mouse model of atherosclerosis, at least in part, through amplification of local IGF-I bioavailability.

Protein kinase Cdelta participates in insulin-induced activation of PKB via PDK1

PKCdelta has been shown to be activated by insulin and to interact with insulin receptor and IRS. PKB(Akt) plays an important role in glucose transport and glycogen synthesis. In this study, we investigated the possibility that PKCdelta may be involved in insulin-induced activation of PKB. Studies were conducted on primary cultures of rat skeletal muscle. PKB was activated by insulin stimulation within 5min and reached a peak by 15-30min. Insulin also increased the physical association between PKCdelta with PKB and with PDK1. The insulin-induced PKCdelta-PKB association was PI3K dependent. PKB-PKCdelta association was accounted for by the involvement of PDK1. Overexpression of dominant negative PKCdelta abrogated insulin-induced association of PKCdelta with both PKB and PDK1. Blockade of PKCdelta also decreased insulin-induced Thr308 PKB phosphorylation and PKB translocation. Moreover, PKCdelta inhibition reduced insulin-induced GSK3 phosphorylation. The results indicate that insulin-activated PKCdelta interacts with PDK1 to regulate PKB.

Sepsis and inflammatory insults downregulate IGFBP-5, but not IGFBP-4, in skeletal muscle via a TNF-dependent mechanism

The purpose of the present study was to determine whether catabolic stimuli that induce muscle atrophy alter the muscle mRNA abundance of insulin-like growth factor binding protein (IGFBP)-4 and -5, and if so determine the physiological mechanism for such a change. Catabolic insults produced by endotoxin (LPS) and sepsis decreased IGFBP-5 mRNA time- and dose-dependently in gastrocnemius muscle. This reduction did not result from muscle disuse because hindlimb immobilization increased IGFBP-5. Continuous infusion of a nonlethal dose of tumor necrosis factor-α (TNF-α) decreased IGFBP-5 mRNA 70%, whereas pretreatment of septic rats with a neutralizing TNF binding protein completely prevented the reduction in muscle IGFBP-5. The addition of LPS or TNF-α to cultured C2C12myoblasts also decreased IGFBP-5 expression. Although exogenously administered growth hormone (GH) increased IGFBP-5 mRNA 2-fold in muscle from control rats, muscle from septic animals was GH resistant and no such elevation was detected. In contrast, exogenous administration of IGF-I as part of a binary complex composed of IGF-I/IGFBP-3 produced comparable increases in IGFBP-5 mRNA in both control and septic muscle. Concomitant determinations of IGF-I mRNA content revealed a positive linear relationship between IGF-I and IGFBP-5 mRNA in the same muscle in response to LPS, sepsis, TNF-α, and GH treatment. Although dexamethasone decreased muscle IGFBP-5, pretreatment of rats with the glucocorticoid receptor antagonist RU486 did not prevent the sepsis-induced decrease in IGFBP-5 mRNA. In contrast, muscle IGFBP-4 mRNA abundance was not significantly altered by LPS, sepsis, or hindlimb immobilization. In summary, these data demonstrate that various inflammatory insults decrease muscle IGFBP-5 mRNA, without altering IGFBP-4, by a TNF-dependent glucocorticoid-independent mechanism. Finally, IGF-I appears to be a dominant positive regulator of IGFBP-5 gene expression in muscle under both normal and catabolic conditions.

Several acidic amino acids in the N-domain of insulin-like growth factor-binding protein-5 are important for its transactivation activity

Insulin-like growth factor-binding protein (IGFBP)-5 is a secreted protein that binds to IGFs and modulates IGF actions. IGFBP-5 is also found in the nuclei of cultured cells and has transactivation activity. Here we report the nuclear localization of endogenous IGFBP-5 in mouse embryonic skeletal cells. Chromatin immunoprecipitation experiments indicated that IGFBP-5 interacts with the nuclear histone-DNA complex. Using a series of deletion mutants, the transactivation domain of IGFBP-5 was mapped to its N-terminal region. Intriguingly, the transactivation activity of IGFBP-5 is masked by negative regulatory elements located in the L- and C-domains. Among the other IGFBPs, the N-domains of IGFBP-2 and -3 also had strong transactivation activity, whereas those of IGFBP-1 and -6 had no activity. The IGFBP-4 N-domain had modest activity. Sequence analysis revealed several amino acids in the IGFBP-5 N-domain that are not present in IGFBP-1. The activities of mutants in which these residues were changed to the corresponding IGFBP-1 sequence were determined. Mutations that changed acidic residues to neutral residues (e.g. E8A, D11S, E12A, E30S/P31A, E43L, and E52A) or a polar to a basic residue (e.g. Q56R) significantly reduced transactivation activity. The E8A/D11S/E12A triple mutant and E52A/Q56R double mutants showed further reduced activity. The combinatory mutants had essentially no transactivation activity. Taken together, our results indicate that there are several conserved residues in the IGFBP-5 N-terminal region that are critical for transactivation and that IGFBP-2 and -3 also have strong transactivation activity in their N-domains.

Insulin and oxidative stress modulate proliferation of rat ovarian theca-interstitial cells through diverse signal transduction pathways

Insulin and moderate oxidative stress stimulate proliferation of ovarian theca-interstitial cells. The effects of these agents on selected signal transduction pathways were examined. PD98059 (inhibitor of MAP2K1, also known as MEK-1, upstream of extracellular signal-regulated protein kinases MAPK3/1, also known as ERK1/2), wortmannin (inhibitor of PIK3C2A, also known as PI3K), and rapamycin (inhibitor of FRAP1, also known as mTOR, upstream of RPS6KB1) each significantly decreased insulin and oxidative stress-induced proliferation of theca-interstitial cells. The greatest inhibition was observed in the presence of rapamycin; this effect occurred without a significant change in cell viability. Phosphorylation of AKT was stimulated by insulin only, while phosphorylation of MAPK3/1 and RPS6KB1 was increased by insulin and oxidative stress. Insulin-induced and oxidative stress-induced phosphorylation of RPS6KB1 was partly inhibited by wortmannin and partly by PD98059; the greatest inhibition was observed in the presence of a combination of wortmannin plus PD98059. Effects of insulin and oxidative stress on phosphorylation of RPS6KB1 were confirmed by kinase activity assays. These findings indicate that actions of insulin and oxidative stress converge on MAPK3/1 and RPS6KB1. Furthermore, we speculate that activation of RPS6KB1 may be in part induced via the MAPK3/1 pathway.

Insulin-like growth factor-I downregulates embryonic myosin heavy chain (eMyHC) in myoblast nuclei

The obscure ability of the insulin-like growth factors (IGF-I & -II) to stimulate both myoblast proliferation and differentiation suggests that the latter effect may be mediated locally, possibly by IGF binding proteins (IGFBPs). In some cells, the growth inhibitory actions of IGFBP-5 require plasma membrane translocation and nuclear localization. Immunoreactivity of presumably endogenous IGFBP-5 was identified within proliferating rat L6 myoblast nuclei using fluorescent and confocal microscopy in separate experiments and was reduced by 100 ng/ml IGF-I in a time-dependent manner. Western blotting of nuclear and cytosolic protein identified a single anti-IGFBP-5 immunoreactive protein of approximately 200 kDa, primarily in nuclear fractions, that was downregulated in cells treated with IGF-I for 12 h. The unknown protein was immunopurified from nuclear fractions and identified as the rat homologue for embryonic myosin heavy chain (eMyHC) using matrix-associated laser desorption ionization time of flight (MALDI-TOF) mass spectroscopy. Cross-reactivity of the IGFBP-5 antiserum with eMyHC was confirmed by blotting anti-IGFBP-5 nuclear immunoprecipitates with eMyHC monoclonal antibodies (F1.652). These data indicate that eMyHC is located predominantly within the nuclei of proliferating L6 myoblasts and suggest that IGF-stimulated differentiation is associated with the rapid downregulation of nuclear eMyHC as these cells stop expressing this myosin II isoform as they differentiate. Myosin Ibeta has been identified within the nuclei of non-muscle cells where it helps to regulate gene transcription. Thus, eMyHC may serve a similar role in myoblasts that is specific only to the undifferentiated state.

Insulin-like growth factor (IGF)-I stimulates cell proliferation and induces IGF binding protein (IGFBP)-3 and IGFBP-5 gene expression in cultured growth plate chondrocytes via distinct signaling pathways

The bioactivity of IGF-I in the cellular microenvironment is modulated by both inhibitory and stimulatory IGF binding proteins (IGFBPs), whose production is partially under control of IGF-I. However, little is known on the IGF-mediated regulation of these IGFBPs in the growth plate. We therefore studied the effect of IGF-I on IGFBP synthesis and the involved intracellular signaling pathways in two cell culture models of rat growth plate chondrocytes. In growth plate chondrocytes in primary culture, incubation with IGF-I increased the concentrations of IGFBP-3 and IGFBP-5 in conditioned cell culture medium in a dose- and time-dependent manner. Coincubation of IGF-I with specific inhibitors of the p42/44 MAPK pathway (PD098059 or U0126) completely abolished the stimulatory effect of IGF-I on IGFBP-3 mRNA expression but did not affect increased IGFBP-5 mRNA levels. In contrast, inhibition of the phosphatidylinositol-3 kinase signaling pathway by LY294002 abrogated both IGF-I-stimulated IGFBP-3 and -5 mRNA expression. Comparable results regarding IGFBP-5 were obtained in the mesenchymal chondrogenic cell line RCJ3.1C5.18, which does not express IGFBP-3. The IGF-I-induced IGFBP-5 gene expression required de novo mRNA transcription and de novo protein synthesis. These data suggest that IGF-I modulates its activity in cultured rat growth plate chondrocytes by the synthesis of both inhibitory (IGFBP-3) and stimulatory (IGFBP-5) binding proteins. The finding that IGF-I uses different and only partially overlapping intracellular signaling pathways for the regulation of two IGFBPs with opposing biological functions might be important for the modulation of IGF bioactivity in the cellular microenvironment.

Increased level of phosphorylated akt measured by chemiluminescence-linked immunosorbent assay is a predictor of poor prognosis in primary breast cancer overexpressing ErbB-2

Introduction

Akt1, Akt2 and Akt3 kinases are downstream components of phosphoinositol 3-kinase derived signals from receptor tyrosine kinases, which influence cell growth, proliferation and survival. Akt2 overexpression and amplification have been described in breast, ovarian and pancreatic cancers. The present study was designed to investigate the prognostic significance of activated Akt in primary breast cancer and its association with other tumour biomarkers.

Methods

Using a two-site chemiluminescence-linked immunosorbent assay, we measured the quantitative expression levels of total phosphorylated (P-S473) Akt (Akt1/Akt2/Akt3) on cytosol fractions obtained from fresh frozen tissue samples of 156 primary breast cancer patients.

Results

Akt phosphorylation was not associated with nodal status or ErbB-2 protein expression levels. High levels of phosphorylated Akt correlated (P < 0.01) with poor prognosis, and the significance of this correlation increased (P < 0.001) in the subset of patients with ErbB-2 overexpressing tumours. In addition, phosphorylated Akt was found to be associated with mRNA expression levels of several proliferation markers (e.g. thymidylate synthase), measured using quantitative real-time RT-PCR.

Conclusion

Our findings demonstrate that, in breast cancer patients, Akt activation is associated with tumour proliferation and poor prognosis, particularly in the subset of patients with ErbB2-overexpressing tumours.

Global uterine genomics in vivo: microarray evaluation of the estrogen receptor alpha-growth factor cross-talk mechanism

Cross-talk between growth factor receptors and the estrogen receptor (ER) has been proposed as a signaling mechanism in estrogen target tissues, with ER(alpha) as a direct target of growth factor receptor-activated signals, leading to regulation of estrogen target genes and estrogen-like biological responses to growth factors. We evaluated whether global genomic changes in the mouse uterus in response to epidermal growth factor or IGF-I mimic those of estradiol (E2), reflecting the cross-talk mechanism. Overlapping responses to growth factors and E2 were expected in the wild type (WT) whereas no response was expected in mice lacking ER(alpha) (ER(alpha) knockout). Surprisingly, although most of the E2 response in the WT also occurred after growth factor treatment, some genes were induced only by E2. Second, although E2 did not induce gene changes in the ER(alpha) knockout, the growth factor response was almost indistinguishable from that of the WT. Differences in response of some genes to IGF-I or epidermal growth factor indicated selective regulation mechanisms, such as phosphatidylinositol 3-kinase or MAPK-dependent responses. The robust ER(alpha)-independent genomic response to growth factor observed here is surprising considering that the biological growth response is ER(alpha) dependent. We propose two mechanisms as alternatives to the cross-talk mechanism for uterine gene regulation. First, E2 increases uterine growth factors, which activate downstream signaling cascades, resulting in gene regulation. Second, growth factors and estrogen regulate similar genes. Our results suggest that the estrogen response in the uterus involves E2-specific ER(alpha)-mediated responses as well as responses resulting from convergence of growth factor and ER-initiated activities.

The LKB1 tumor suppressor negatively regulates mTOR signaling

Germline mutations in LKB1, TSC2, or PTEN tumor suppressor genes result in hamartomatous syndromes with shared tumor biological features. The recent observations of LKB1-mediated activation of AMP-activated protein kinase (AMPK) and AMPK inhibition of mTOR through TSC2 prompted us to examine the biochemical and biological relationship between LKB1 and mTOR regulation. Here, we report that LKB1 is required for repression of mTOR under low ATP conditions in cultured cells in an AMPK- and TSC2-dependent manner, and that Lkb1 null MEFs and the hamartomatous gastrointestinal polyps from Lkb1 mutant mice show elevated signaling downstream of mTOR. These findings position aberrant mTOR activation at the nexus of these germline neoplastic conditions and suggest the use of mTOR inhibitors in the treatment of Peutz-Jeghers syndrome.

Paradoxical actions of endogenous and exogenous insulin-like growth factor-binding protein-5 revealed by RNA interference analysis

Insulin-like growth factor-binding protein-5 (IGFBP-5) is abundantly expressed in bone cells. To determine the physiological role(s) of endogenous IGFBP-5 in regulating bone cell growth, differentiation, and survival, we used short double-stranded RNA (siRNA) to trigger RNA interference of IGFBP-5 in human osteosarcoma cells. The IGFBP-5 siRNA, targeting against a sequence unique to the IGFBP-5 middle domain, efficiently reduced IGFBP-5 mRNA and protein levels. The IGFBP-5 siRNA did not change the levels of IGFBP-4, a structurally related protein, or glyceraldehyde-3-phosphate dehydrogenase, a housekeeping gene. Knock-down of IGFBP-5 resulted in a significant increase in the number of transferase-mediated dUTP nick end labeling-positive cells and a decrease in a bone differentiation parameter (alkaline phosphatase activity) but had little effect on basal or insulin-like growth factor I-induced proliferation. Overexpression of a siRNA-resistant IGFBP-5 mutant in the IGFBP-5 knock-down cells restored the levels of survival to the control level; overexpression of IGFBP-4 or wild type IGFBP-5 had no such effect. Paradoxically, the addition of exogenous IGFBP-5 not only failed to rescue IGFBP-5 knock-down-induced apoptosis, it caused a further increase in apoptosis. Furthermore, the addition of exogenous IGFBP-5 alone increased apoptosis. This pro-apoptotic action of exogenous IGFBP-5 was abolished when IGF-I was added in excess, suggesting that exogenous IGFBP-5 increases apoptosis by binding to and inhibiting the activities of insulin-like growth factors. These results indicate that endogenous and exogenous IGFBP-5 exhibits opposing biological actions on cell survival and underscore the necessity and utility of studying IGFBP functions through loss-of-function approaches.

IGF-I increases IGFBP-5 and collagen alpha1(I) mRNAs by the MAPK pathway in rat intestinal smooth muscle cells

IGF-I is a potent fibrogenic growth factor that stimulates proliferation of intestinal smooth muscle cells and increases synthesis of collagen and IGF-I-binding proteins by the cells. These processes contribute to intestinal fibrosis that develops in patients with Crohn's disease and in Lewis-strain rats with experimental Crohn's disease. The aim of this study was to determine which early docking proteins are associated with IGF-I receptor signal transduction and which transduction pathway is involved in IGF-I-mediated gene regulation in intestinal smooth muscle cells. Primary cultures of smooth muscle cells isolated from the muscularis externa of the distal colon of Lewis rats were treated with IGF-I (100 ng/ml). Immunoprecipitation studies demonstrated that IGF-I stimulation resulted in tyrosine phosphorylation of IRS-1, IRS-2, and Shc. Coimmunoprecipitation demonstrated a close association between the IGF-I receptor and these three early docking proteins. Concurrent treatment with the MAPK inhibitor PD98059 (10 microM) resulted in an inhibition of the IGF-I-mediated increase in IGFBP-5 and collagen alpha(1)(I) mRNAs, while concurrent treatment with the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin (100 nM) had no effect. In additional experiments, cells were transiently transfected with adenoviral vectors dominantly expressing inactive mutant Akt or constitutively expressing wild-type Akt. In both cases, the IGF-I-mediated increase in collagen I protein did not differ from that observed in control cultures that had been transfected with an adenoviral vector carrying the LacZ reporter gene. These results suggest that the MAPK pathway is key to IGF-I-mediated gene regulation in intestinal smooth muscle cells, whereas data do not suggest a role for the Akt-dependent pathway in our system.

An investigation into signal transduction mechanisms involved in insulin-induced long-term depression in the CA1 region of the hippocampus

Recent work has demonstrated that brief application of insulin to hippocampal slices can induce a novel form of long-term depression (insulin-LTD) in the CA1 region of the hippocampus; however, the molecular details of how insulin triggers LTD remain unclear. Using electrophysiological and biochemical approaches in the hippocampal slices, we show here that insulin-LTD (i) is specific to 3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor- but not NMDA receptor-mediated synaptic transmission; (ii) is induced and expressed postsynaptically but does not require the activation of ionotropic and metabotropic glutamate receptors; (iii) requires a concomitant Ca(2+) influx through l-type voltage-activated Ca(2+) channels (VACCs) and the release of Ca(2+) from intracellular stores; (iv) requires the series of protein kinases, including protein tyrosine kinase (PTK), phosphatidylinositol 3-kinase (PI3K), and protein kinase C (PKC); (v) is mechanistically distinct from low-frequency stimulation-induced LTD (LFS-LTD) and independent on protein phosphatase 1/2 A (PP1/2 A) and PP2B activation; (vi) is dependent on a rapamycin-sensitive local translation of dendritic mRNA, and (vii) is associated with a persistent decrease in the surface expression of GluR2 subunit. These results suggest that a PI3K/PKC-dependent insulin signaling, which controls postsynaptic surface AMPA receptor numbers through PP-independent endocytosis, may be a major expression mechanism of insulin-LTD in hippocampal CA1 neurons.

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.

Akt/PKB activation in gastric carcinomas correlates with clinicopathologic variables and prognosis

Akt/protein kinase B (PKB) plays an important role in cell survival. However, the role of Akt in the biology of gastric cancer has not been well studied. We sought to investigate the expression of Akt or phosphorylated Akt (pAkt) in human gastric carcinomas and to analyze the relationship between Akt or pAkt and the clinicopathologic parameters. The expressions of Akt and pAkt were evaluated immunohistochemically in 311 gastric carcinomas using the tissue array method. Akt expression was detected in 74% of the tumors and pAkt expression in 78%. pAkt was highly expressed in the early stage of pTNM (p=0.011). We also found an inverse association between pAkt and lymphatic invasion (p=0.01) or lymph node metastasis (p=0.008). pAkt expression was significantly correlated with a higher survival in patients with stage I carcinomas (p=0.0003). Interestingly, combined evaluation revealed that the group with pAkt-positive and lymph node-negative carcinomas showed a better prognosis than the other groups (p<0.0001). In addition, pAkt was shown to correlate positively with APC (p=0.002) and Smad4 (p<0.0001) expression. These findings suggest that pAkt expression may help to predict the clinical outcome of gastric cancer patients.

The insulin-like growth factor 1 receptor induces physiological heart growth via the phosphoinositide 3-kinase(p110alpha) pathway

Insulin-like growth factor 1 (IGF1) was considered a potential candidate for the treatment of heart failure. However, some animal studies and clinical trials have questioned whether elevating IGF1 chronically is beneficial. Secondary effects of increased serum IGF1 levels on other tissues may explain these unfavorable results. The aim of the current study was to examine the role of IGF1 in cardiac myocytes in the absence of secondary effects, and to elucidate downstream signaling pathways and transcriptional regulatory effects of the IGF1 receptor (IGF1R). Transgenic mice overexpressing IGF1R in the heart displayed cardiac hypertrophy, which was the result of an increase in myocyte size, and there was no evidence of histopathology. IGF1R transgenics also displayed enhanced systolic function at 3 months of age, and this was maintained at 12-16 months of age. The phosphoinositide 3-kinase (PI3K)-Akt-p70S6K1 pathway was significantly activated in hearts from IGF1R transgenics. Cardiac hypertrophy induced by overexpression of IGF1R was completely blocked by a dominant negative PI3K(p110alpha) mutant, suggesting IGF1R promotes compensated cardiac hypertrophy in a PI3K(p110alpha)-dependent manner. This study suggests that targeting the cardiac IGF1R-PI3K(p110alpha) pathway could be a potential therapeutic strategy for the treatment of heart failure.

The chemotactic and mitogenic responses of vascular smooth muscle cells to insulin-like growth factor-I require the activation of ERK1/2

Insulin-like growth factors (IGFs) play an important role in regulating vascular smooth muscle cell (VSMC) proliferation and directed migration. IGFs exert these biological actions through the activation of the IGF-I receptor and its downstream signaling network. While the involvement of the IRS-PI3 kinase-Akt pathway in mediating the chemotactic and mitogenic actions of IGFs is clear, the role of the mitogen-activated protein kinase (MAPK) signaling pathway is still under debate. In this study, the role of ERK1 and 2 in mediating the chemotactic and mitogenic actions of IGF-I in cultured porcine VSMCs was investigated. IGF-I treatment caused a significant increase in the phosphorylation state, as well as the kinase activity, of ERK1 and 2. Compared to the strong and sustained MAPK activation induced by platelet-derived growth factor-BB, the IGF-I-induced MAPK activation was weaker and more transient. Specific inhibition of the MAPK activation by PD98059 or U0126, two selective MEK inhibitors, significantly inhibited IGF-I-stimulated cell proliferation, and reduced the number of cells that migrated towards IGF-I. The p38 MAPK inhibitor SB203580 had no such effect. Likewise, depletion of ERK1/2 using antisense oligonucleotides abolished the IGF-I-induced VSMC migration and proliferation. These results suggest that the chemotactic and mitogenic responses of VSMCs to IGF-I require the activation of ERK1 and 2.

Oscillatory shear stress increases smooth muscle cell proliferation and Akt phosphorylation

PURPOSE

Hemodynamic forces affect smooth muscle cell (SMC) proliferation and migration both in vitro and in vivo. However, the effects of oscillatory shear stress (SS) on SMC proliferation and signal transduction pathways that control survival are not well described.

METHODS

Bovine aortic SMC were exposed to arterial levels of oscillatory SS (14 dyne/cm(2)) with an orbital shaker; control cells were exposed to static conditions (0 dyne/cm(2)). Cell number and (3)[H]thymidine incorporation were measured after 1, 3, or 5 days of SS. Activation of the Akt pathway was assessed with the Western blot technique. Specificity of the phosphatidylinositol 3-kinase (PI3K) pathway was determined with the Western blot technique with the inhibitors LY294002 (10 micromol/L) or wortmannin (25 nmol/L).

RESULTS

Arterial levels of oscillatory SS increased SMC cell number by 20.1 +/- 3.7% and (3)[H]thymidine incorporation by 33.4% +/- 6.8% at 5 days. To identify whether SS increased activity of the SMC survival pathway, Akt activation was measured. SMC exposed to SS demonstrated increased Akt phosphorylation compared with control cells, with maximal phosphorylation at 60 minutes. Both PI3K inhibitors specifically inhibited the increase in Akt phosphorylation in SMC exposed to oscillatory SS.

CONCLUSION

SMC directly respond to oscillatory SS by increasing DNA synthesis, proliferation, and activation of the PI3K-Akt signal transduction pathway. These results suggest a mechanism of SMC survival and proliferation in response to endothelial-denuding arterial injury.

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.

Regulation of TRAIL expression by the phosphatidylinositol 3-kinase/Akt/GSK-3 pathway in human colon cancer cells

The intestinal mucosa is a rapidly-renewing tissue characterized by cell proliferation, differentiation, and eventual apoptosis with progression up the vertical gut axis. The inhibition of phosphatidylinositol (PI) 3-kinase by specific chemical inhibitors or overexpression of the lipid phosphatase PTEN enhances enterocyte-like differentiation in human colon cancer cell models of intestinal differentiation. In this report, we examined the role of PI 3-kinase inhibition in the regulation of apoptotic gene expression in human colon cancer cell lines HT29, HCT-116, and Caco-2. Inhibition of PI 3-kinase with the chemical inhibitor wortmannin increased TNF-related apoptosis-inducing ligand (TRAIL; Apo2) mRNA and protein expression. Similarly, overexpression of the tumor suppressor protein PTEN, an antagonist of PI 3-kinase signaling, resulted in the increased expression of TRAIL. Activation of PI 3-kinase by pretreatment with IGF-1, a gut trophic factor, markedly attenuated the induction of TRAIL by wortmannin. Moreover, overexpression of active Akt, a downstream target of PI 3-kinase, or inhibition of GSK-3, a downstream target of active Akt, completely blocked the induction of TRAIL by wortmannin. Consistent with findings that TRAIL is induced by agents that enhance intestinal cell differentiation, TRAIL expression was specifically localized to the differentiated cells of the colon and small bowel. Adenovirus-mediated overexpression of TRAIL increased DNA fragmentation of HCT-116 cells, demonstrating the functional activity of TRAIL induction. Taken together, our findings demonstrate induction of the TRAIL by inhibition of PI 3-kinase in colon cancer cell lines. These results identify TRAIL, a novel TNF family member, as a downstream target of the PI 3-kinase/Akt/GSK-3 pathway and may have important implications for better understanding the role of the PI 3-kinase pathway in intestinal cell homeostasis.

Structure, developmental expression, and physiological regulation of zebrafish IGF binding protein-1

The biological activity and availability of IGFs are regulated by a group of secreted proteins that belong to the IGF-binding protein (IGFBP) gene family. Although six IGFBPs have been identified and studied in mammals, their nonmammalian orthologs remain poorly defined. In this study, we cloned and characterized the full-length zebrafish IGFBP-1. Sequence analysis indicated that its structure is homologous to mammalian IGFBP-1. Using in situ RNA hybridization and RT-PCR, we discovered that IGFBP-1 mRNA was present in all early embryonic stages albeit at very low levels. IGFBP-1 mRNA was initially expressed in multiple embryonic tissues but became restricted to the liver shortly after hatching. In the adult stage, IGFBP-1 mRNA was found only in the liver at low levels. Prolonged food deprivation caused a significant increase in the hepatic IGFBP-1 mRNA levels, and refeeding restored the IGFBP-1 mRNA to the basal levels. When adult fish or embryos were subjected to hypoxic conditions, the IGFBP-1 mRNA expression increased dramatically. Intriguingly, the hypoxia-induced IGFBP-1 expression operated in different embryonic tissues in a developmental-stage-dependent manner. In early embryos, hypoxia-stimulated IGFBP-1 mRNA expression in the pharyngeal arches, ventricle, atrium, and brain. After hatching, the hypoxia-induced IGFBP-1 expression became liver specific. These results not only provide new information about the structural conservation, developmental expression, and physiological regulation of the IGFBP-1 gene but also present the opportunity to elucidate the developmental role of IGFBP-1 using a unique vertebrate model organism.

Expression of insulin-like growth factor-binding protein 5 in neuroblastoma cells is regulated at the transcriptional level by c-Myb and B-Myb via direct and indirect mechanisms

Neuroblastoma (NB), a malignant childhood tumor deriving from the embryonic neural crest, is sensitive to the growth-stimulating effects of insulin-like growth factors (IGFs). Aggressive cases of this disease often acquire autocrine loops of IGF production, but the mechanisms through which the different components of the IGF axis are regulated in tumor cells remain unclear. Upon conditional expression of c-Myb in a NB cell line, we detected up-regulation of IGF1, IGF1 receptor, and insulin-like growth factor-binding protein 5 (IGFBP-5) expression. Analysis of the IGFBP-5 promoter revealed two potential Myb binding sites at position -59 to -54 (M1) and -429 to -424 (M2) from the transcription start site; both sites were bound by c-Myb and B-Myb in vitro and in vivo. Reporter assays carried out using the proximal region of the human IGFBP-5 promoter demonstrated that c-Myb and B-Myb enhanced transcription. However, site-directed mutagenesis and deletion of the Myb binding sites coupled with reporter assays revealed that M2 but not M1 was important for Myb-dependent transactivation of the IGFBP-5 promoter. The double mutant M1/M2 was still transactivated by c-Myb, suggesting the existence of Myb binding-independent mechanisms of IGFBP-5 promoter regulation. A constitutively active AKT transactivated the IGFBP-5 promoter, whereas the phosphatidylinositol 3-kinase inhibitor LY294002 suppressed it. Moreover, the kinase dead dominant negative K179M AKT mutant was able to inhibit transcription from the M2 and M1/M2 IGFBP-5 mutant promoters. Deletion analysis of the IGFBP-5 promoter revealed that the AKT-responsive region lies between nucleotides -334 and -83. Together, these data suggest that the Myb binding-independent transactivation of the IGFBP-5 promoter was due to the activation of the phosphatidylinositol 3-kinase/AKT pathway likely mediated by IGF1 receptor-dependent signals. Finally, IGFBP-5 was able to modulate proliferation of NB cells in a manner dependent on its concentration and on the presence of IGFs.

Transcriptional effects of chronic Akt activation in the heart

Akt activation reduces cardiomyocyte death and induces cardiac hypertrophy. To help identify effector mechanisms, gene expression profiles in hearts from transgenic mice with cardiac-specific expression of activated Akt (myr-Akt) were compared with littermate controls. 40 genes were identified as differentially expressed. Quantitative reverse transcription-PCR confirmed qualitative results of transcript profiling for 9 of 10 genes examined, however, there were notable quantitative discrepancies between the quantitative reverse transcription-PCR and microarray data sets. Interestingly Akt induced significant up-regulation of insulin-like growth factor-binding protein-5 (IGFBP-5), which could contribute to its anti-apoptotic effects in the heart. In addition, Akt-mediated down-regulation of peroxisome proliferator-activated receptor (PPAR) gamma coactivator-1 (PGC-1) and PPAR-alpha may shift myocytes toward glycolytic metabolism shown to preserve cardiomyocyte function and survival during transient ischemia. IGFBP-5 transcripts also increased after adenoviral gene transfer of myr-Akt to cultured cardiomyocytes, suggesting that this represents a direct effect of Akt activation. In contrast, substantial induction of growth differentiation factor-8 (GDF-8), a highly conserved inhibitor of skeletal muscle growth, was observed in transgenic hearts but not after acute Akt activation in vitro, suggesting that GDF-8 induction may represent a secondary effect perhaps related to the cardiac hypertrophy seen in these mice. Thus, microarray analysis reveals previously unappreciated Akt regulation of genes that could contribute to the effects of Akt on cardiomyocyte survival, metabolism, and growth.

Interaction of Btk and Akt in B cell signaling

Reactive oxygen species (ROS) or reactive oxygen intermediates (ROIs) mediate complex signaling involving multiple pathways. In this report, we demonstrate for the first time that endogenous Bruton's tyrosine kinase (Btk) and Akt can interact with each other in DT40 chicken B cells and human Nalm6 B cells and that this interaction is inducible following H2O2 stimulation. This interaction is supported by visualizing the co-localization of Btk and Akt in the perinuclear region and membrane ruffles in COS-7 cells. We have also shown the involvement of phosphatidylinositol 3-kinase (PI 3-K) and Btk in the phosphorylation of Akt following stimulation by hydrogen peroxide (H2O2). Interestingly, Akt phosphorylation was found in the presence of Btk even in the absence of oxidative stress. In addition, we have investigated the involvement of PI 3-K in the MAPKs and ERK and JNK phosphorylation, in the presence or absence of Btk. Phosphorylation of both ERK and JNK increased when the PI 3-K pathway was inhibited and both pathways were modulated positively by Btk. Taken together, based on the study of endogenous conditions, we show the novel interaction of Btk and Akt in H2O2 signaling in B cells.

Effects of the Pit1 mutation on the insulin signaling pathway: implications on the longevity of the long-lived Snell dwarf mouse

Mutations in Caenorhabditis elegans and mice have identified candidate genes that increase their lifespan via hormonal signal transduction, i.e. the insulin/IGF-1-like pathway. In this study we propose that longevity of the Snell dwarf (Pit1(dw)/Pit1(dw)) mouse is associated with a decrease of the insulin/IGF-1 signaling pathway caused by the Pit1 mutation. We recently demonstrated that the growth hormone deficiency of the dwarf mouse alters circulating insulin levels, thereby resulting in a decreased activity of the insulin/IGF-1 signaling pathway, which is a determining factor in the increased nematode lifespan. The decreased activity of the insulin/IGF-1 signaling pathway is indicated by decrease of (a) IRS-two pool levels; (b) docking of p85 alpha to IRS-2; (c) docking of p 85 alpha to p110 alpha or p110 beta, and (d) IRS-2-associated PI3K activity. In this study we present data suggesting that the InR beta-IRS-1-PI3K pathway is attenuated in the Snell dwarf mouse liver. Our data show that the PI3K activity associated with IRS-1, the docking of IRS-1 to InR beta and the docking of p85 alpha to IRS-1 are attenuated in the aged Snell dwarf. Our studies suggest that the Pit1 mutation results in a decreased activity of the insulin/IGF-1 pathway; that this plays a key role in the longevity of the Snell dwarf mouse and conforms to the nematode longevity paradigm.