[Leu27] insulin-like growth factor II is highly selective for the type-II IGF receptor in binding, cross-linking and thymidine incorporation experiments

IGF2 prevents dopaminergic neuronal loss and decreases intracellular alpha-synuclein accumulation in Parkinson's disease models

Parkinson's disease (PD) is the second most common late-onset neurodegenerative disease and the predominant cause of movement problems. PD is characterized by motor control impairment by extensive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). This selective dopaminergic neuronal loss is in part triggered by intracellular protein inclusions called Lewy bodies, which are composed mainly of misfolded alpha-synuclein (α-syn) protein. We previously reported insulin-like growth factor 2 (IGF2) as a key protein downregulated in PD patients. Here we demonstrated that IGF2 treatment or IGF2 overexpression reduced the α-syn aggregates and their toxicity by IGF2 receptor (IGF2R) activation in cellular PD models. Also, we observed IGF2 and its interaction with IGF2R enhance the α-syn secretion. To determine the possible IGF2 neuroprotective effect in vivo we used a gene therapy approach in an idiopathic PD model based on α-syn preformed fibrils intracerebral injection. IGF2 gene therapy revealed a significantly preventing of motor impairment in idiopathic PD model. Moreover, IGF2 expression prevents dopaminergic neuronal loss in the SN together with a decrease in α-syn accumulation (phospho-α-syn levels) in the striatum and SN brain region. Furthermore, the IGF2 neuroprotective effect was associated with the prevention of synaptic spines loss in dopaminergic neurons in vivo. The possible mechanism of IGF2 in cell survival effect could be associated with the decrease of the intracellular accumulation of α-syn and the improvement of dopaminergic synaptic function. Our results identify to IGF2 as a relevant factor for the prevention of α-syn toxicity in both in vitro and preclinical PD models.

The imprinted Igf2-Igf2r axis is critical for matching placental microvasculature expansion to fetal growth

In all eutherian mammals, growth of the fetus is dependent upon a functional placenta, but whether and how the latter adapts to putative fetal signals is currently unknown. Here, we demonstrate, through fetal, endothelial, hematopoietic, and trophoblast-specific genetic manipulations in the mouse, that endothelial and fetus-derived IGF2 is required for the continuous expansion of the feto-placental microvasculature in late pregnancy. The angiocrine effects of IGF2 on placental microvasculature expansion are mediated, in part, through IGF2R and angiopoietin-Tie2/TEK signaling. Additionally, IGF2 exerts IGF2R-ERK1/2-dependent pro-proliferative and angiogenic effects on primary feto-placental endothelial cells ex vivo. Endothelial and fetus-derived IGF2 also plays an important role in trophoblast morphogenesis, acting through Gcm1 and Synb. Thus, our study reveals a direct role for the imprinted Igf2-Igf2r axis on matching placental development to fetal growth and establishes the principle that hormone-like signals from the fetus play important roles in controlling placental microvasculature and trophoblast morphogenesis.

Two Distinct Lysosomal Targeting Strategies Afford Trojan Horse Antibodies With Pan-Filovirus Activity

Multiple agents in the family Filoviridae (filoviruses) are associated with sporadic human outbreaks of highly lethal disease, while others, including several recently identified agents, possess strong zoonotic potential. Although viral glycoprotein (GP)-specific monoclonal antibodies have demonstrated therapeutic utility against filovirus disease, currently FDA-approved molecules lack antiviral breadth. The development of broadly neutralizing antibodies has been challenged by the high sequence divergence among filovirus GPs and the complex GP proteolytic cleavage cascade that accompanies filovirus entry. Despite this variability in the antigenic surface of GP, all filoviruses share a site of vulnerability-the binding site for the universal filovirus entry receptor, Niemann-Pick C1 (NPC1). Unfortunately, this site is shielded in extracellular GP and only uncovered by proteolytic cleavage by host proteases in late endosomes and lysosomes, which are generally inaccessible to antibodies. To overcome this obstacle, we previously developed a 'Trojan horse' therapeutic approach in which engineered bispecific antibodies (bsAbs) coopt viral particles to deliver GP:NPC1 interaction-blocking antibodies to their endo/lysosomal sites of action. This approach afforded broad protection against members of the genus Ebolavirus but could not neutralize more divergent filoviruses. Here, we describe next-generation Trojan horse bsAbs that target the endo/lysosomal GP:NPC1 interface with pan-filovirus breadth by exploiting the conserved and widely expressed host cation-independent mannose-6-phosphate receptor for intracellular delivery. Our work highlights a new avenue for the development of single therapeutics protecting against all known and newly emerging filoviruses.

Insulin-like growth factor II prevents oxidative and neuronal damage in cellular and mice models of Parkinson's disease

Oxidative distress and mitochondrial dysfunction, are key factors involved in the pathophysiology of Parkinson's disease (PD). The pleiotropic hormone insulin-like growth factor II (IGF-II) has shown neuroprotective and antioxidant effects in some neurodegenerative diseases. In this work, we demonstrate the protective effect of IGF-II against the damage induced by 1-methyl-4-phenylpyridinium (MPP+) in neuronal dopaminergic cell cultures and a mouse model of progressive PD. In the neuronal model, IGF-II counteracts the oxidative distress produced by MPP + protecting dopaminergic neurons. Improved mitochondrial function, increased nuclear factor (erythroid-derived 2)-like2 (NRF2) nuclear translocation along with NRF2-dependent upregulation of antioxidative enzymes, and modulation of mammalian target of rapamycin (mTOR) signalling pathway were identified as mechanisms leading to neuroprotection and the survival of dopaminergic cells. The neuroprotective effect of IGF-II against MPP + -neurotoxicity on dopaminergic neurons depends on the specific IGF-II receptor (IGF-IIr). In the mouse model, IGF-II prevents behavioural dysfunction and dopaminergic nigrostriatal pathway degeneration and mitigates neuroinflammation induced by MPP+. Our work demonstrates that hampering oxidative stress and normalising mitochondrial function through the interaction of IGF-II with its specific IGF-IIr are neuroprotective in both neuronal and mouse models. Thus, the modulation of the IGF-II/IGF-IIr signalling pathway may be a useful therapeutic approach for the prevention and treatment of PD.

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IGF-II hampers oxidative damage and promotes survival in a cellular model of PD.

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IGF-II avoids mitochondrial damage in dopaminergic cells in a model of PD.

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IGF-II receptor mediates the neuroprotective effect of IGF-II in a cellular model of PD.

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IGF-II prevents nigrostriatal degeneration and inflammation in a mice model of PD.

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IGF-II prevents behavioural dysfunction in a mice model of PD.

Environmental Factor-Mediated Transgenerational Inheritance of Igf2r Hypomethylation and Pulmonary Allergic Response via Targeting Dendritic Cells

The developmental origin of allergic diseases has been suggested, but the molecular basis remains enigmatic. Exposure to environmental factors, such as di-(2-ethylhexyl) phthalate (DEHP; a common plasticizer), is suggested to be associated with increased childhood allergic asthma, but the causal relationship and its underlying mechanism remain unknown. This study explored the transgenerational mechanism of DEHP on allergic asthma and dendritic cell (DC) homeostasis through epigenetic modification. In a murine model, ancestral exposure of C57BL/6 mice to low-dose DEHP led to trans-generational promoter hypomethylation of the insulin-like growth factor 2 receptor (Igf2r), concomitant with enhanced Igf2r expression and increased apoptosis prominently in CD8α⁺ DCs upon ligand stimulation, with consequent reduction in their IL-12 secretion and subsequent T cell-derived IFN-γ, thereby promoting a default Th2-associated pulmonary allergic response. Increased apoptosis was also noted in circulating IGF2R^high human DCs. Further, in human placenta, the methylation level at the orthologous IGF2R promoter region was shown to be inversely correlated with the level of maternal DEHP intake. These results support the importance of ancestral phthalate exposure in conferring the trans-generational risk of allergic phenotypes, featuring hypo-methylation of the IGF2R gene and dysregulated DC homeostasis.

Danshen (Salvia miltiorhiza) inhibits Leu27 IGF-II-induced hypertrophy in H9c2 cells

In this study, we used ICI 182 780 (ICI), an estrogen receptor (ER) antagonist, to investigate the estrogenic activity of Danshen, and to further explored whether Danshen extract can block Leu27IGF-II-induced hypertrophy in H9c2 cardiomyoblast cells. We first used an IGF-II analog Leu27IGF-II, which specifically activates IGF2R signaling cascades and induces H9c2 cardiomyoblast cell hypertrophy. However, Danshen extract completely inhibited Leu27IGF-II-induced cell size increase, ANP and BNP hypertrophic marker expression, and IGF2R induction. We also observed that Danshen extract inhibited calcineurin protein expression and NFAT3 nuclear translocation, leading to suppression of Leu27IGF-II-induced cardiac hypertrophy. Moreover, the anti-Leu27IGF-II-IGF2R signaling effect of Danshen was totally reversed by ICI, which suggest the cardio protective effect of Danshen is mediated through estrogen receptors. Our study suggests that, Danshen exerts estrogenic activity, and thus, it could be used as a selective ER modulator in IGFIIR induced hypertrophy model.

The combined inhibition of the CaMKIIδ and calcineurin signaling cascade attenuates IGF-IIR-induced cardiac hypertrophy

Cardiac hypertrophy is a common phenomenon observed in progressive heart disease associated with heart failure. Insulin-like growth factor receptor II (IGF-IIR) has been much implicated in myocardial hypertrophy. Our previous studies have found that increased activities of signaling mediators, such as calcium/calmodulin-dependent protein kinase II (CaMKII) and calcineurin induces pathological hypertrophy. Given the critical roles played by CaMKII and calcineurin signaling in the progression of maladaptive hypertrophy, we anticipated that inhibition of CaMKII and calcineurin signaling may attenuate IGF-IIR-induced cardiac hypertrophy. The current study, therefore, investigated the effects of IGF-IIR activation on the CaMKII and calcineurin signaling and whether the combinatorial inhibition of the CaMKIIδ and calcineurin signaling could ameliorate IGF-IIR-induced pathological hypertrophy. In the present study, we induced IGF-IIR through the cardiomyocyte-specific transduction of IGFII^Y27L via adeno-associated virus 2 (AAV2) to evaluate its effects on cardiac hypertrophy. Interestingly, it was observed that the activation of IGF-IIR signaling through IGFII^Y27L induces significant hypertrophy of the myocardium and increased cardiac apoptosis and fibrosis. Moreover, we found that Leu²⁷ IGF-II significantly induced calcineurin and CaMKII expression. Furthermore and importantly, the combinatorial treatment with CaMKII and calcineurin inhibitors significantly alleviates IGF-IIR-induced hypertrophic responses. Thus, it could be envisaged that the inhibition of IGF-IIR may serve as a promising candidate for attenuating maladaptive hypertrophy. Both calcineurin and CaMKII could be valuable targets for developing treatment strategies against hypertension-induced cardiomyopathies.

Inhibition of ERK-Drp1 signaling and mitochondria fragmentation alleviates IGF-IIR-induced mitochondria dysfunction during heart failure

Mitochondrial dysfunction is a major contributor to myocyte loss and the development of heart failure. Myocytes have quality control mechanisms to retain functional mitochondria by removing damaged mitochondria via specialized autophagy, i.e., mitophagy. The underlying mechanisms of fission affect the survival of cardiomyocytes, and left ventricular function in the heart is poorly understood. Here, we demonstrated the direct effect and potential mechanisms of mitochondrial functional defects associated with abnormal mitochondrial dynamics in heart failure. We observed that IGF-IIR signaling produced significant changes in mitochondrial morphology and function; such changes were associated with the altered expression and distribution of dynamin-related protein (Drp1) and mitofusin (Mfn2). IGF-IIR signaled extracellular signal-regulated kinase (ERK) activation to promote Drp1 phosphorylation and translocation to mitochondria for mitochondrial fission and mitochondrial dysfunction. Moreover, IGF-IIR signaling triggered Rab9-dependent autophagosome formation by the JNK-mediated phosphorylation of Bcl-2 at serine 87 and promoted ULK1/Beclin 1-dependent autophagic membrane formation. Excessive mitochondrial fission by Drp1 enhanced the Rab9-dependent autophagosome recognition and engulfing of damaged mitochondria and eventually decreased cardiomyocyte viability. Therefore, these results demonstrated the connection between Rab9-dependent autophagosomes and mitochondrial fission in cardiac myocytes, which provides a potential therapeutic strategy for treating heart disease.

Rab9-dependent autophagy is required for the IGF-IIR triggering mitophagy to eliminate damaged mitochondria

Mitochondria dysfunction is the major characteristic of mitophagy, which is essential in mitochondrial quality control. However, excessive mitophagy contributes to cell death in a number of diseases, including ischemic stroke and hepatotoxicity. Insulin-like growth factor II (IGF-II) and its receptor (IGF-IIR) play vital roles in the development of heart failure during hypertension. We found that IGF-II triggers IGF-IIR receptor activation, causing mitochondria dysfunction, resulting in mitophagy, and cardiomyocyte cell death. These results indicated that IGF-IIR activation triggers mitochondria fragmentation, leading to autophagosome formation, and loss of mitochondria content. These results are associated with Parkin-dependent mitophagy. Additionally, autophagic proteins Atg5, and Atg7 deficiency did not suppress IGF-IIR-induced mitophagy. However, Rab9 knockdown reduced mitophagy and maintained mitochondrial function. These constitutive mitophagies through IGF-IIR activation trigger mitochondria loss and mitochondrial ROS accumulation for cardiomyocyte viability decrease. Together, our results indicate that IGF-IIR predominantly induces mitophagy through the Rab9-dependent alternative autophagy.

Tanshinone IIA Prevents Leu27IGF-II-Induced Cardiomyocyte Hypertrophy Mediated by Estrogen Receptor and Subsequent Akt Activation

IGF-IIR plays important roles as a key regulator in myocardial pathological hypertrophy and apoptosis, which subsequently lead to heart failure. Salvia miltiorrhiza Bunge (Danshen) is a traditional Chinese medicinal herb used to treat cardiovascular diseases. Tanshinone IIA is an active compound in Danshen and is structurally similar to 17[Formula: see text]-estradiol (E[Formula: see text]. However, whether tanshinone IIA improves cardiomyocyte survival in pathological hypertrophy through estrogen receptor (ER) regulation remains unclear. This study investigates the role of ER signaling in mediating the protective effects of tanshinone IIA on IGF-IIR-induced myocardial hypertrophy. Leu27IGF-II (IGF-II analog) was shown in this study to specifically activate IGF-IIR expression and ICI 182,780 (ICI), an ER antagonist used to investigate tanshinone IIA estrogenic activity. We demonstrated that tanshinone IIA significantly enhanced Akt phosphorylation through ER activation to inhibit Leu27IGF-II-induced calcineurin expression and subsequent NFATc3 nuclear translocation to suppress myocardial hypertrophy. Tanshinone IIA reduced the cell size and suppressed ANP and BNP, inhibiting antihypertrophic effects induced by Leu27IGF-II. The cardioprotective properties of tanshinone IIA that inhibit Leu27IGF-II-induced cell hypertrophy and promote cell survival were reversed by ICI. Furthermore, ICI significantly reduced phospho-Akt, Ly294002 (PI3K inhibitor), and PI3K siRNA significantly reduced the tanshinone IIA-induced protective effect. The above results suggest that tanshinone IIA inhibited cardiomyocyte hypertrophy, which was mediated through ER, by activating the PI3K/Akt pathway and inhibiting Leu27IGF-II-induced calcineurin and NFATC3. Tanshinone IIA exerted strong estrogenic activity and therefore represented a novel selective ER modulator that inhibits IGF-IIR signaling to block cardiac hypertrophy.

Insulin-Like Growth Factor-Independent Effects of Growth Hormone on Growth Plate Chondrogenesis and Longitudinal Bone Growth

GH stimulates growth plate chondrogenesis and longitudinal bone growth directly at the growth plate. However, it is not clear yet whether these effects are entirely mediated by the local expression and action of IGF-1 and IGF-2. To determine whether GH has any IGF-independent growth-promoting effects, we generated (TamCart)Igf1r(flox/flox) mice. The systemic injection of tamoxifen in these mice postnatally resulted in the excision of the IGF-1 receptor (Igf1r) gene exclusively in the growth plate. (TamCart)Igf1r(flox/flox) tamoxifen-treated mice [knockout (KO) mice] and their Igf1r(flox/flox) control littermates (C mice) were injected for 4 weeks with GH. At the end of the 4-week period, the tibial growth and growth plate height of GH-treated KO mice were greater than those of untreated C or untreated KO mice. The systemic injection of GH increased the phosphorylation of Janus kinase 2 and signal transducer and activator of transcription 5B in the tibial growth plate of the C and KO mice. In addition, GH increased the mRNA expression of bone morphogenetic protein-2 and the mRNA expression and protein phosphorylation of nuclear factor-κB p65 in both C and KO mice. In cultured chondrocytes transfected with Igf1r small interfering RNA, the addition of GH in the culture medium significantly induced thymidine incorporation and collagen X mRNA expression. In conclusion, our findings demonstrate that GH can promote growth plate chondrogenesis and longitudinal bone growth directly at the growth plate, even when the local effects of IGF-1 and IGF-2 are prevented. Further studies are warranted to elucidate the intracellular molecular mechanisms mediating the IGF-independent, growth-promoting GH effects.

Maternal insulin-like growth factor 1 and 2 differentially affect the renin-angiotensin system during pregnancy in the guinea pig

OBJECTIVE

Insulin-like growth factors (IGFs) are known to interact with the renin-angiotensin system (RAS). We previously demonstrated that administration of IGF1 to guinea pigs in early to mid pregnancy promotes placental function and fetal growth in mid to late gestation. Early administration of IGF2 had sustained, but not acute, effects on these parameters and also on placental structural differentiation. Here, we aimed to determine whether the IGFs interact with the placental RAS in early to mid gestation to modulate placental development and increase fetal growth and survival, and if IGF2 binding the IGF2R is implicated in the sustained effects of IGF2 treatment.

DESIGN

At day 20 of pregnancy, guinea pigs were infused with 1m g/kg/day of IGF1, IGF2, (Leu27)IGF2 or vehicle for 18days and sacrificed on either day 62 (late pregnancy) or during the infusion period on day 35 (early-mid pregnancy). Placental structure at day 35 was analyzed using morphometric technique and expression of RAS genes in the placenta and placental and plasma renin activity were measured at both time points.

RESULTS

Compared with vehicle at day 35 of gestation, IGF1 infusion reduced the total midsagittal cross-sectional area of the placenta (-17%, p = 0.02) and the labyrinth area (-22%, p = 0.014) but did not alter the labyrinth volume nor labyrinth:interlobium ratios. IGF2 treatment did not affect placental structure. IGF1 did not alter placental mRNA for any of the RAS genes quantified at day 35 (AGTR1, ACE, AGT, TGFB1) but increased TGFB1 expression by more than 16-fold (p = 0.005) at day 62. IGF2 increased placental expression of AGTR1 (+88%, p = 0.03) and decreased AGT (-73%, p = 0.01) compared with the vehicle-treated group at day 35, and both IGF2 and (Leu27)IGF2 increased expression of TGFB1 at day 62 by 9-fold (p = 0.016) and 6-fold (p = 0.019) respectively. Both IGFs increased the ratio of active:total placental renin protein (+22% p = 0.026 p = 0.038) compared to vehicle compared to vehicle at day 35 but not 62. At day 62, IGF2-treated mothers showed a marked increase in total plasma renin (+495%) and active renin (+359%) compared to vehicle but decreased the ratio of active to total renin by 41% (p = 0.042). (Leu27)IGF2-treated animals had higher levels of placental active renin (+73%, p = 0.001) and total renin (+71%, p = 0.001) compared with the vehicle control.

CONCLUSIONS

The data obtained in the current study suggest the potential for alternate roles for the induction of the RAS after IGF treatment. IGF1 and 2 treatments increase the activation of prorenin to renin in the placenta, possibly due to increased protease activity. In addition, IGF2 treatment in early pregnancy may enhance the maternal adaptation to pregnancy through stimulation of renin in the kidney. The sustained effects on placental differentiation and function after IGF2 treatment suggest therapeutic potential for exogenous administration of IGFs in improving pregnancy outcomes.

Danshen mediates through estrogen receptors to activate Akt and inhibit apoptosis effect of Leu27IGF-II-induced IGF-II receptor signaling activation in cardiomyoblasts

Post-menopausal women show dramatically increased cardiovascular disease morbidity (CVD). Danshen is used widely in China for the treatment of cardiovascular disorders, including coronary heart disease. Danshen possesses lipid-soluble biologically active components with a structure similar to 17β-estrodiol (E2). This study assesses whether the cardio-protection exerted by Danshen is mediated through the ERs within H9c2 cardiomyoblast cells. Cardiomyoblast cells pretreated with Fulvestrant (ICI 182,780), an estrogen receptor antagonist was applied to investigate the estrogenic activity of Danshen. The Danshen extract preventive effects on Leu27IGF-II-induced IGF-IIR signaling activator and H9c2 cell apoptosis were identified using TUNEL assay, JC-1 staining and Western blot assay. We found that Danshen extract treatments significantly enhanced phosphorylated Akt through estrogen receptor activation to inhibit Leu27IGF-II-induced calcineurin activation and block H9c2 cell apoptosis. Danshen extracts suppressed the IGF-IIR signaling proteins, pro-apoptotic proteins and reversed the mitochondrial membrane instability induced by Leu27IGF-II. However, the cardioprotective properties of Danshen to inhibit Leu27IGF-II-induced cell apoptosis and promote cell survival were attenuated by applying ICI, which suggests that the Danshen cardioprotective effect is mediated through estrogen receptors. All our data indicated that Danshen exerts strong estrogenic activity which can be considered a novel selective estrogen receptor modulator (SERM) against IGF2R signaling that blocks cardiac apoptosis.

Action, localization and structure-function relationship of growth factors and their receptors in the prostate

Whereas the direct action of sex steroids, namely of androgens, on prostate cell division was questioned as early as in the 1970s, and remains so, the interest in prostatic growth factors (GFs) is rather recent but has expanded tremendously in the last five years. This lag period can be partly explained by the fact that, at the time, androgen receptors had just been discovered, and newly developed hormonal regimens or strategies to treat patients with prostate carcinoma (PCa) or epithelioma had generated great enthusiasm and hopes in the medical and scientific community. Another point to consider was the difficulty in maintaining prostate tissues in organ cultures and the relative novelty of culturing prostate epithelial cells in monolayers. Failures of sex steroids to elicit a direct positive response on prostate cell divisionin vitro, as seenin vivo, were interpreted as resulting from inappropriate models or culture conditions. However, the increasing number of reports confirming the lack of mitogenic activity of sex steroidsin vitro, coupled with the powerful mitogenic activity of GFs displayed in other systems, the discovery of GF receptors (GF-Rs), and the elucidation of their signalling pathways showing sex steroid receptors as potential substrates of GF-activated protein kinases gradually led to an increased interest in the putative role of GFs in prostate physiopathology. Of utmost importance was the recognition that hormone refractiveness was responsible for PCa progression, and for the poor outcome of patients with advanced disease under endocrine therapies. This problem remains a major issue and it raises several key questions that need to be solved at the fundamental and clinical levels.

Activation of insulin-like growth factor II receptor induces mitochondrial-dependent apoptosis through G(alpha)q and downstream calcineurin signaling in myocardial cells

In previous studies, we have found that IGF-II and IGF-II receptor (IGF-IIR) dose dependently correlated with the progression of pathological hypertrophy after complete abdominal aorta ligation, which may play a critical role in angiotensin II-induced cardiomyocyte apoptosis. However, the detail mechanisms of IGF-IIR in the regulation of cell apoptosis in response to IGF-II remain unclear. By using IGF-IR short hairpin RNA to inhibit IGF-IR expression and using Leu27 IGF-II analog to activate specifically the IGF-IIR, we investigated the role of IGF-II/IGF-IIR activation and its downstream signaling. Our results revealed that IGF-II synergistically increased the cell apoptosis induced by suppressing of IGF-IR in neonatal rat ventricular myocytes. After binding of Leu27IGF-II, IGF-IIR became associated with alpha-q polypeptide, acted like a protein-coupled receptor to activate calcineurin, led to the translocation of Bad into mitochondria and release of cytochrome c into cytoplasm, and contributed to mitochondrial-dependent apoptosis in neonatal rat ventricular myocytes. Furthermore, inhibition of IGF-IIR, alpha-q polypeptide, or calcineurin by RNA interference could block the Leu27IGF-II-induced cell apoptosis. Together, this study provides a new insight into the effects of the IGF-IIR and its downstream signaling in myocardial apoptosis. Suppression of IGF-IIR signaling pathways may be a good strategy for both the protection against myocardial cell apoptosis and the prevention of heart failure progression.

Single transmembrane domain insulin-like growth factor-II/mannose-6-phosphate receptor regulates central cholinergic function by activating a G-protein-sensitive, protein kinase C-dependent pathway

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor is a single-pass transmembrane glycoprotein that plays an important role in the intracellular trafficking of lysosomal enzymes and endocytosis-mediated degradation of IGF-II. However, its role in signal transduction after IGF-II binding remains unclear. In the present study, we report that IGF-II/M6P receptor in the rat brain is coupled to a G-protein and that its activation by Leu27IGF-II, an analog that binds rather selectively to the IGF-II/M6P receptor, potentiates endogenous acetylcholine release from the rat hippocampal formation. This effect is mediated by a pertussis toxin (PTX)-sensitive GTP-binding protein and is dependent on protein kinase Calpha (PKCalpha)-induced phosphorylation of downstream substrates, myristoylated alanine-rich C kinase substrate, and growth associated protein-43. Additionally, treatment with Leu27IGF-II causes a reduction in whole-cell currents and depolarization of cholinergic basal forebrain neurons. This effect, which is blocked by an antibody against the IGF-II/M6P receptor, is also sensitive to PTX and is mediated via activation of a PKC-dependent pathway. These results together revealed for the first time that the single transmembrane domain IGF-II/M6P receptor expressed in the brain is G-protein coupled and is involved in the regulation of central cholinergic function via the activation of specific intracellular signaling cascades.

Birth insults involving hypoxia produce long-term increases in hippocampal [125I]insulin-like growth factor-I and -II receptor binding in the rat

Insulin-like growth factors-I and -II and insulin are structurally related mitogenic growth factors with multiple actions in the developing nervous system and adult CNS. Previous studies have demonstrated acute induction of insulin-like growth factors and their receptors, over a time course of several days, in response to hypoxic/ischemic insult to developing or adult brain. The current study tested whether birth insults involving hypoxia may produce long term changes in brain insulin-like growth factor or insulin receptor levels, lasting into adulthood. For this, rats were born vaginally (controls), by cesarean section, or by cesarean section with 15 min of added global anoxia (cesarean section+anoxia), and brain [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin receptor binding sites were assessed autoradiographically at adulthood. [125I]Insulin-like growth factor-I receptor binding sites were increased in all hippocampal subfields (CA1-CA3, dentate gyrus) in rats born either by cesarean section or by cesarean section+anoxia, compared with vaginal birth. [125I]Insulin-like growth factor-II binding was increased in all hippocampal subfields only in rats born by cesarean section+anoxia compared with either vaginal birth or cesarean section groups. [125I]Insulin-like growth factor-I and [125I]insulin-like growth factor-II binding in frontal cortex, striatum and cerebellum were unaffected by birth group, except for increased [125I]insulin-like growth factor-I binding in the cerebellar molecular layer of cesarean-sectioned animals. Birth group had no significant effect on [125I]insulin binding in any brain region. Affinity cross-linking experiments performed with hippocampal membranes from the three birth groups showed that i) [125I]insulin-like growth factor-I and [125I]insulin-like growth factor-II recognized bands of molecular weights characteristic of insulin-like growth factor-I and insulin-like growth factor-II receptors, respectively, and ii) [125I]insulin-like growth factor-I and [125I]insulin-like growth factor-II were displaced more potently by their respective unlabeled ligands than by related molecules. It is concluded that birth insults involving hypoxia can induce lasting increases in insulin-like growth factor-I and -II receptors in the CNS. There is specificity with respect to the subtype of insulin-like growth factor receptor affected by the particular birth insult and the brain region affected. It is suggested that enduring increases in levels of insulin-like growth factor receptors consequent to hypoxic birth insult may help to maintain hippocampal function at adulthood, and could modulate responsiveness to insulin-like growth factor administration.

Insulin-like growth factor-binding protein 3 induces caspase-dependent apoptosis through a death receptor-mediated pathway in MCF-7 human breast cancer cells

Insulin-like growth factor-binding protein (IGFBP)-3 has been shown to potently inhibit cell proliferation in various cell systems. However, the specific mechanisms involved in the antiproliferative action of IGFBP-3 have yet to be elucidated. In the present study, we demonstrate that IGFBP-3 induces apoptosis in an insulin-like growth factor (IGF)-independent manner through the activation of caspases involved in a death receptor-mediated pathway in MCF-7 human breast cancer cells. Induction of IGFBP-3 using an ecdysone-inducible expression system inhibited DNA synthesis in an IGF-IGF receptor axis-independent fashion and resulted in the subsequent induction of apoptosis and an increase in caspase activity. Similar results were obtained when cells were transfected with GGG-IGFBP-3, an IGFBP-3 mutant unable to bind IGFs, corroborating the IGF-independent action of IGFBP-3. Additional caspase activity studies and immunoblot analyses using specific caspase substrates and/or caspase inhibitors revealed that the growth-inhibitory effect of IGFBP-3 results mainly from its induction of apoptosis (in particular, activation of caspase-8 and -7). Analyses of caspase-9 activity and release of cytochrome c into the cytosol confirmed that the mitochondria-mediated pathway is not involved. Taken together, these results show that IGFBP-3 expression leads to the induction of apoptosis through the activation of caspases involved in a death receptor-mediated pathway and that IGFBP-3 functions as a negative regulator of breast cancer cell growth, independent of the IGF-IGF receptor axis.

Pregnancy-associated plasma protein a gene expression as a target of inflammatory cytokines

Pregnancy-associated plasma protein A (PAPP-A) cleaves IGF-binding protein-4 (IGFBP-4) and appears to enhance local IGF bioavailability in response to injury. In this study we determined the effects of growth factors and cytokines involved in the healing process on PAPP-A expression in human dermal fibroblasts. There was no effect of platelet-derived growth factor, epidermal growth factor, or basic fibroblast growth factor on PAPP-A mRNA expression in these cells. However, treatment with the proinflammatory cytokines, TNFalpha and IL-1 beta, resulted in time- and dose-dependent increases in PAPP-A mRNA and protein expression (3- to 4-fold maximal effects), which were prevented by actinomycin D. On the other hand, interferon-gamma (IFN gamma) treatment markedly inhibited PAPP-A expression. IGFBP-4 proteolytic activity was increased 4-fold in medium from TNFalpha- and IL-1 beta-treated (1 nm) cells and decreased 40% in medium from IFN gamma-treated (1 nm) cells. IGF-I-stimulated [(3)H]thymidine incorporation was significantly enhanced by pretreatment with 1 nm TNFalpha, and this enhancement was blocked in the presence of protease-resistant IGFBP-4. In conclusion, PAPP-A expression is regulated by inflammatory cytokines in adult human fibroblasts, with functional consequences on IGFBP-4 protease activity and IGF-I bioavailability. These data provide a mechanism for the regulation of PAPP-A in response to injury and further implicate PAPP-A in the wound-healing processes.

Transforming growth factor-beta regulation of the insulin-like growth factor binding protein-4 protease system in cultured human osteoblasts

IGFBP-4 is an inhibitor of IGF-I in bone. We show that TGF-beta regulates IGFBP-4 and enhances IGF-I-stimulated growth of cultured human bone cells through increased expression of an IGFBP-4 protease, PAPP-A. This effect of TGF-beta on IGF-I bioavailability may promote local bone formation. Insulin-like growth factor binding protein (IGFBP-4) proteolysis is implicated in the regulation of local insulin-like growth factor (IGF)-I bioavailability during bone remodeling. The IGFBP-4 protease secreted by normal adult human osteoblastic (hOB) cells in culture is a novel metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A). We have recently identified an inhibitor of PAPP-A, the precursor form of major basic protein (proMBP). Very little is known about the molecular regulation of this IGFBP-4 protease system. In the present study, we determined the effect of transforming growth factor (TGF)-beta and IGF-II, the two most abundant growth factors in human bone, on PAPP-A and proMBP expression in primary cultures of hOB cells. Treatment with TGF-beta resulted in time- and dose-dependent increases in PAPP-A mRNA expression, with a maximal 12-fold increase after 24 h of stimulation with 10 ng/ml TGF-beta. Increased PAPP-A levels in hOB cell-conditioned medium paralleled PAPP-A gene expression. In addition, TGF-beta completely suppressed proMBP expression. Treatment of hOB cells with IGF-II had no effect on PAPP-A or proMBP gene expression. However, IGFBP-4 proteolysis in cell-free assay was dependent on IGF-II, and there was increased IGF-II-dependent IGFBP-4 protease activity in conditioned medium from hOB cells that were treated with TGF-beta. IGF-I stimulation of hOB cell proliferation was markedly enhanced by pretreatment with TGF-beta and [Leu27]IGF-II, and this enhancement was prevented with protease-resistant IGFBP-4. In summary, TGF-beta regulates IGFBP-4 proteolysis in hOB cells through increased expression of the protease, PAPP-A, and decreased expression of the inhibitor, proMBP. However, functional activation of the IGFBP-4 protease system is dependent on IGF-II, which acts at a post-translational level. These data support a model whereby local TGF-beta and IGF-II in the bone microenvironment coordinately amplify IGF-I bioavailability through controlled IGFBP-4 proteolysis, which may be a means to promote bone formation.

Characteristics of binding of insulin-like growth factor (IGF)-I and IGF-II analogues to the type 1 IGF receptor determined by BIAcore analysis

Insulin-like growth factor (IGF) binding to the type 1 IGF receptor (IGF1R) elicits mitogenic effects, promotion of differentiation and protection from apoptosis. This study has systematically measured IGF1R binding affinities of IGF-I, IGF-II and 14 IGF analogues to a recombinant high-affinity form of the IGF1R using BIAcore technology. The analogues assessed could be divided into two groups: (a) those designed to investigate binding of IGF-binding protein, which exhibited IGF1R-binding affinities similar to those of IGF-I or IGF-II; (b) those generated to probe IGF1R interactions with greatly reduced IGF1R-binding affinities. The relative binding affinities of IGF-I analogues and IGF-I for the IGF1R determined by BIAcore analysis agreed closely with existing data from receptor-binding assays using cells or tissue membranes, demonstrating that BIAcore technology is a powerful tool for measuring affinities of IGFs for IGF1R. In parallel studies, IGF1R-binding affinities were related to ability to protect against serum withdrawal-induced apoptosis in three different assays including Hoechst 33258 staining, cell survival, and DNA fragmentation assays using the rat pheochromocytoma cell line, PC12. In this model system, IGF-I and IGF-II at low nanomolar concentrations are able to prevent apoptosis completely. We conclude that ability to protect against apoptosis is directly related to ability to bind the IGF1R.

Prorenin-induced myocyte proliferation: no role for intracellular angiotensin II

Cardiomyocytes bind, internalize, and activate prorenin, the inactive precursor of renin, via a mannose 6-phosphate receptor (M6PR)--dependent mechanism. M6PRs couple directly to G-proteins. To investigate whether prorenin binding to cardiomyocytes elicits a response, and if so, whether this response depends on angiotensin (Ang) II, we incubated neonatal rat cardiomyocytes with 2 nmol/L prorenin and/or 150 nmol/L angiotensinogen, with or without 10 mmol/L M6P, 1 micromol/L eprosartan, or 1 micromol/L PD123319 to block M6P and AT(1) and AT(2) receptors, respectively. Protein and DNA synthesis were studied by quantifying [(3)H]-leucine and [(3)H]-thymidine incorporation. For comparison, studies with 100 nmol/L Ang II were also performed. Neither prorenin alone, nor angiotensinogen alone, affected protein or DNA synthesis. Prorenin plus angiotensinogen increased [(3)H]-leucine incorporation (+21 +/- 5%, mean +/- SEM, P<0.01), [(3)H]-thymidine incorporation (+29 +/- 6%, P<0.01), and total cellular protein (+14 +/- 3%, P<0.01), whereas Ang II increased DNA synthesis only (+34 +/- 7%, P<0.01). Eprosartan, but not PD123319 or M6P, blocked the effects of prorenin plus angiotensinogen as well as the effects of Ang II. Medium Ang II levels during prorenin and angiotensinogen incubation were <1 nmol/L. In conclusion, prorenin binding to M6PRs on cardiomyocytes per se does not result in enhanced protein or DNA synthesis. However, through Ang II generation, prorenin is capable of inducing myocyte hypertrophy and proliferation. Because this generation occurs independently of M6PRs, it most likely depends on the catalytic activity of intact prorenin in the medium (because of temporal prosegment unfolding) rather than its intracellular activation. Taken together, our results do not support the concept of Ang II generation in cardiomyocytes following intracellular prorenin activation.

The effect of insulin-like growth factor analogs on turkey satellite cell and embryonic myoblast proliferation

The effects of several human and chicken insulin-like growth factor (IGF) analogs on turkey satellite cell and embryonic myoblast proliferation were examined in serum-free medium. Similar rates of proliferation were observed when human or chicken IGF-I or IGF-II (13.1 nM) was administered to satellite cells. The biopotency of two analogs, which were modified to prevent interaction with IGF-binding proteins, was also examined. Human Des(1-6)IGF-II was equipotent to native human and chicken IGF-II. However, the chicken LR3 IGF-I analog was significantly less active toward satellite cells and embryonic myoblasts compared with chicken IGF-I. Human [Leu27] IGF-II, an analog designed to have reduced affinity to the IGF Type I receptor but unaltered binding to IGF-binding proteins, had a diminished effect on cell proliferation. Examination of IGF receptor binding characteristics revealed that chicken LR3 IGF-I had reduced ability to compete with [125I]hIGF-I for binding to satellite cells or embryonic myoblasts compared with chicken IGF-I. The observed biological responses to IGF suggest that IGF-binding proteins have little effect on Type I IGF receptor action in these cell types in serum-free medium. The results also suggest that alterations of the IGF molecule to prevent interaction with binding proteins may also alter receptor binding affinity.

Antiproliferative effects of insulin-like growth factor-binding protein-3 in mesenchymal chondrogenic cell line RCJ3.1C5.18. relationship to differentiation stage

Chondrogenesis results from a complex equilibrium between chondrocyte proliferation and differentiation. Insulin-like growth factors (IGFs) have a crucial role in chondrogenesis, but their mechanisms of action are not well defined. IGF-binding protein-3 (IGFBP-3) is the major carrier for circulating IGFs in postnatal life, and has been shown to have IGF-independent effects on proliferation of several cancer cell lines. In this study, we have evaluated the IGF-independent and -dependent effects of IGFBP-3 on chondrocyte proliferation and the relationship of these effects with chondrocyte differentiation stage. We used the RCJ3.1C5.18 nontransformed mesenchymal chondrogenic cell line, which, over 2 weeks of culture, progresses through the differentiation pathway exhibited by chondrocytes in the growth plate. We demonstrated that IGFBP-3 inhibited, in a dose-dependent manner (1-30 nm), the proliferation of chondroprogenitors and early differentiated chondrocytes, stimulated by des-(1-3)-IGF-I and longR(3)-IGF-I (IGF-I analogs with reduced affinity for IGFBP-3), and by insulin and IGF-I. In terminally differentiated chondrocytes, IGFBP-3 retained the ability to inhibit cell proliferation stimulated by IGF-I, but had no effect on cell growth stimulated by insulin, or des-(1-3)-IGF-I or longR(3)IGF-I. By monolayer affinity cross-linking, we demonstrated a specific IGFBP-3-associated cell-membrane protein of approximately 20 kDa. We determined that IGFBP-3 has an antiproliferative effect on chondrocytes and, that this effect is related to the differentiation process. In chondroprogenitors and early differentiated chondrocytes, antiproliferative effect of IGFBP-3 is mainly IGF-independent, whereas, following terminal differentiation this effect is IGF-dependent.

Involvement of insulin-like growth factors-I and -II and their receptors in medroxyprogesterone acetate-induced growth of mouse mammary adenocarcinomas

The role of the insulin-like growth factors (IGFs) system was investigated in hormone-dependent (HD) and -independent (HI) in vivo lines of the medroxyprogesterone acetate (MPA)-induced mammary tumor model in Balb/c mice. IGF-II protein and message showed a three- to four-fold increase in HD lines growing in MPA-treated mice, as compared with HD tumors growing in untreated mice. Progression to a hormone-independent phenotype in all these lines was accompanied by a high constitutive expression of IGF-II. Similar IGF-I mRNA levels were detected in HD and HI lines. Both IGF-I and -II messages arose from the malignant epithelial cells, as shown by in situ hybridization studies. A significant decrease in Man-6P/type II IGF-R content was detected in HD tumors growing in MPA-treated mice as compared with HD lines growing in untreated mice. On the other hand, in HI tumors, notwithstanding high IGF-II synthesis, the levels of Man-6P/type II IGF-R remain high. Competitive inhibition and affinity labeling studies showed an almost exclusive binding of IGF-II to Man-6P/type II IGF-R on tumor membranes. The involvement of IGFs in the growth of epithelial primary cultures of the C4-HD line was evaluated. Exogenous IGF-I potentiated MPA stimulatory effect at concentrations of 50-100 ng/ml. Treatment of C4-HD cells with antisense oligodeoxynucleotides (ASODNs) to type I IGF-R and to IGF-II RNA resulted in a dose-dependent inhibition of MPA-mediated cell proliferation. The inhibition caused by IGF-II ASODNs could not be overcome by the addition of IGF-II up to 150 ng/ml. ASODNs to type I IGF-R at 40 microg/ml reduced by 75% the number of type I IGF-R; ASODNs to IGF-II at 1 microM decreased by 83% the levels of IGF-II protein. Our results provide support for the involvement of IGF-I and -II in MPA-induced mammary tumor growth by autocrine pathways.

Biological characterization of human epithelial ovarian carcinoma cells in primary culture: the insulin-like growth factor system

Little is known about the factors regulating epithelial ovarian cancer cell growth. This is due, in large part, to the difficulty in obtaining and culturing human ovarian cells for relevant in vitro studies. We recently developed a method for culturing epithelial carcinoma cells derived from fresh, untreated epithelial ovarian cancer specimens. The cell populations are free of fibroblasts and reflect the primary tumor as determined by chromosomal analysis. In this study we report on the cells' growth in serum-free medium and their secretion of CA-125, a glycoprotein marker for ovarian cancer. Furthermore we characterize the insulin-like growth factor (IGF) system in these primary ovarian carcinoma cell cultures. The cells secrete IGF peptides and IGF-binding proteins, possess specific type I IGF receptors, and respond to exogenous IGFs. The culture system reported here provides the basis for further study and manipulation of the IGF system as well as other regulators of epithelial ovarian cancer. Greater understanding of the cellular and molecular mediators of primary human ovarian cancer cell growth may translate into relevant clinical interventions.

Insulin-like growth factor binding protein-1 binds to placental cytotrophoblast alpha5beta1 integrin and inhibits cytotrophoblast invasion into decidualized endometrial stromal cultures

Insulin-like growth factor binding protein-1 (IGFBP-1) can bind to the alpha5beta1 integrin and stimulate cellular migration in Chinese hamster ovary (CHO) cells. IGFBP-1 is a major product of the endometrium of pregnancy (decidua), and may interact with invading cytotrophoblasts expressing alpha5beta1 integrin to modulate their invasion. The present study investigated IGFBP-1 interaction with cytotrophoblast alpha5beta1 integrin, and its effects on trophoblast attachment to fibronectin and invasion into decidualized endometrial stromal cell multilayers. IGFBP-1 incubated with cytotrophoblast extracts was co-precipitated by an antibody to the alpha5 integrin subunit. Up to 55% of radiolabeled IGFBP-1 bound to cytotrophoblasts was displaced by excess non-radioactive IGFBP-1, but not by IGFBP-3. Cytotrophoblast attachment to fibronectin was inhibited by an RGD-containing octapeptide, by antibodies to the alpha5 subunit or the alpha5beta1 heterodimer, and by IGFBP-1. Cytotrophoblasts showed limited invasion into endometrial stromal multilayers decidualized in vitro secreting abundant IGFBP-1, but invaded multilayers when IGFBP-1 production was inhibited by insulin. Invasion into insulin-treated multilayers was prevented by addition of exogenous IGFBP-1 but not by IGFBP-3. These findings suggest IGFBP-1 may modulate trophoblast invasiveness.

Paracrine/autocrine regulation of breast cancer by the insulin-like growth factors

Local environmental signals regulate the growth and development of both normal and malignant breast epithelium. Members of the insulin-like growth factor (IGF) family likely influence both of these processes. The localization of IGF2 to stroma specifically surrounding malignant breast epithelium indicates that this growth factor may play a critical role in the genesis or maintenance of this transformed phenotype. Recent studies have sought to understand the mechanism by which IGF2 expressing fibroblasts are localized to the periphery of malignant breast cancer cells. In addition, the consequences of the expression of IGF-signaling components likely expand beyond their direct effects on mitogenesis. Indirect effects predominantly associated with the IGF2 receptor could also influence the invasive potential of breast tumor cells.

Inhibition of insulin receptor activation by insulin-like growth factor binding proteins

The insulin-like growth factors (IGFs) are transported by a family of high-affinity binding proteins (IGFBPs) that protect IGFs from degradation, limit their binding to IGF receptors, and modulate IGF actions. The six classical IGFBPs have been believed to have no affinity for insulin. We now demonstrate that IGFBP-7/mac25, a newly identified member of the IGFBP superfamily that binds IGFs specifically with low affinity is a high-affinity insulin binding protein. IGFBP-7 blocks insulin binding to the insulin receptor and thereby inhibiting the earliest steps in insulin action, such as autophosphorylation of the insulin receptor beta subunit and phosphorylation of IRS-1, indicating that IGFBP-7 is a functional insulin-binding protein. The affinity of other IGFBPs for insulin can be enhanced by modifications that disrupt disulfide bonds or remove the conserved COOH terminus. Like IGFBP-7, an NH2-terminal fragment of IGFBP-3 (IGFBP-3((1-87))), also binds insulin with high affinity and blocks insulin action. IGFBPs with enhanced affinity for insulin might contribute to the insulin resistance of pregnancy, type II diabetes mellitus, and other pathological conditions.

Proliferin induces endothelial cell chemotaxis through a G protein-coupled, mitogen-activated protein kinase-dependent pathway

To investigate the mechanism of action of the placental angiogenic hormone proliferin (PLF), we analyzed the signaling components in endothelial cells that are required for PLF-induced chemotaxis. Pertussis toxin, which inactivates Gi proteins, inhibited PLF-induced chemotaxis of endothelial cells. Gi proteins can lead to activation of the mitogen-activated protein kinase (MAPK) pathway; PLF was found to stimulate MAPK activity, and this induction was blocked by both pertussis toxin and a specific inhibitor of MAPK kinase, PD 098059. Furthermore, a blockade of MAPK activation prevented endothelial cell movement in response to PLF. As PLF functionally interacts with the insulin-like growth factor II (IGF-II)/mannose 6-phosphate receptor, we also examined the effects of pertussis toxin and PD 098059 on another ligand for this receptor, a mutant form of IGF-II; both inhibitors also block the action of this factor on endothelial cells. These data suggest that chemotaxis initiated by PLF and mediated by the IGF-II/mannose 6-phosphate receptor occurs through a G protein-coupled pathway, and that MAPK activation is necessary for the chemotactic response.

Insulin-like growth factor (IGF) binding to a murine mammary epithelial cell line

The goal of this study was to relate insulin-like growth factor (IGF) binding with IGF-stimulated growth in a murine mammary epithelial (COMMA-D/MME) cell line. Affinity crosslinking with [125I]IGF-I showed major bands at 224,000 and 148,000 Mr that were ablated by the inclusion of IGF-I or -II at 130 nM. Scatchard-transformed [125I]IGF-I binding data was best fit by a two-site model, with 24,000 sites possessing a Kd of 0.33 nM and 1,000 sites possessing a Kd of 8.09 nM per cell. Competition analysis showed ED50 values for IGF-I, -II, and insulin to be 0.90 +/- 0.03, 7.15 +/- 4.27, and 335 +/- 104 nM, respectively. Affinity crosslinking of [125I]IGF-II showed three major bands of 230,000, 148,000, and 61,000 to 58,000 Mr. Unlabeled IGF-II ablated all bands, while IGF-I and insulin ablated only the 148,000 Mr band. Competition analysis showed ED50 values for unlabeled IGF-I and -II to be 0.10 +/- 0.01 and 5.31 +/- 2.04 nM, respectively. In spite of the receptor affinity differences, no significant difference was noted in IGF-I and -II in capacity to stimulate cell growth. These data indicate that COMMA-D/MME cells express IGF receptors and that both IGFs are mitogenic.

IGF-II is more active than IGF-I in stimulating L6A1 myogenesis: greater mitogenic actions of IGF-I delay differentiation

Mitogens are generally thought to inhibit myogenesis, and many cell biologists have found it hard to interpret observations that the insulin-like growth factors (IGFs) stimulate both proliferation and differentiation of muscle cells in culture. Our previous studies suggested that the Type I IGF receptor mediates these actions. However, IGF-II and insulin treatment caused myoblasts to differentiate much more extensively, suggesting that more complex mechanisms may be involved. Here we present evidence that the greater mitogenic activity of IGF-I (compared to IGF-II and insulin) delays L6A1 myoblast differentiation. Under conditions in which the mitogenic actions of IGF-I are suppressed, the stimulation of myogenesis by IGF-I approached that by IGF-II: (1) in L6A1 cultures plated at a higher cell density; (2) in L6A1 cultures in which cell proliferation was inhibited by cytosine arabinoside or aphidicolin; and (3) in cultures of primary human muscle cells, which exhibit a smaller mitogenic response to IGF-I. Further evidence that the Type I receptor plays a major role in relaying the signal for differentiation was obtained by using IGF-I and IGF-II analogs. Analogs which have reduced affinity for the Type I receptor showed a dramatic decrease in activity, while an analog with increased affinity for the Type II receptor was no more active than native IGF-I. Our results indicate that both mitogenic and myogenic actions of IGF-I are mediated by the Type I receptor. We conclude that IGF-I delays the onset of myogenesis as a result of its mitogenic actions, and only subsequently stimulates myogenesis. These observations reconcile the apparent conflict between our results with the IGFs and other investigators' reports of effects of other mitogens.

Stimulation of glucose uptake by insulin-like growth factor II in human muscle is not mediated by the insulin-like growth factor II/mannose 6-phosphate receptor

Although the growth-promoting effects of insulin-like growth factor II (IGF-II) have been intensively studied, the acute actions of this hormone on glucose metabolism have been less well evaluated, especially in skeletal muscle of humans. We and other groups have shown that IGFs reduce glycaemic levels in humans and stimulate glucose uptake in rat muscle. The purpose of the present study was to evaluate the effect of IGF-II on glucose transport in muscle of normal and obese patients with and without non-insulin-dependent diabetes mellitus (NIDDM), as well as to identify the receptor responsible for this action. 2-Deoxyglucose transport was determined in vitro using a muscle-fibre strip preparation. IGF-II were investigated in biopsy material of rectus abdominus muscle taken from lean and obese patients and obese patients with NIDDM at the time of surgery. In the lean group, IGF-II (100 nM) stimulated glucose transport 2.1-fold, which was slightly less than stimulation by insulin (2.8-fold) at the same concentration. Binding of IGF-II was approx. 25% of that of insulin at 1 nM concentrations of both hormones. Obesity with or without NIDDM significantly reduced IGF-II-stimulated glucose uptake compared with the lean group. In order to explore which receptor mediated the IGF-II effect, we compared glucose uptake induced by IGF-II and two IGF-II analogues: [Leu27]IGF-II, with high affinity for the IGF-II/Man 6-P receptor but markedly reduced affinity for the IGF-I and insulin receptors, and [Arg54,Arg55]IGF-II was similar to that of IGF-II, whereas [Leu27]IGF-II had a very diminished effect. Results show that IGF-II is capable of stimulating muscle glucose uptake in lean but not in obese subjects and this effect seems not to be mediated via an IGF-II/Man 6-P receptor.

IGF-I stimulates granulosa cell-derived insulin-like growth factor binding protein-5: evidence for medication via type I IGF receptors

Although the precise role of insulin-like growth factor binding proteins (IGFBPs) in ovarian physiology remains a matter of study, existing data suggest a possible antigonadotropic role in the context of follicular atresia. Given the above and the need for improved understanding of the regulation of ovarian IGFBPs, we have set out to explore the ability of IGF-I to modulate IGFBP levels in cultured rat granulosa cells. Specifically, granulosa cells (5 x 10(5) viable cells/dish) from immature (23-25 days old), estrogen-primed rats were cultured under serum-free conditions for 72 h in the absence or presence of IGF-I. At the conclusion of this incubation period, media samples were collected and subjected to Western ligand blotting. Treatment with IGF-I (100 ng/ml) resulted in a substantial (P < 0.05) increase in the accumulation of IGFBP-5, the major 28-29 kDa IGFBP species. Subsequent studies revealed this effect of IGF-I to be both dose- and time-dependent. A similar effect was noted for insulin at dose levels 1-10 micrograms/ml at which cross-reaction with the type I IGF receptor (but not with IGFBPs) has been amply documented. Des (1-3) IGF-I, a type I receptor-selective ligand with markedly reduced avidity for IGFBPs, proved substantially more potent (as a promoter of IGFBP-5 accumulation) than its native counterpart. In contrast, treatment with IGF-II or [Leu27]IGF-II, type II IGF receptor-selective ligands, yielded a more limited effect on IGFBP-5 accumulation in keeping with an overall rank order of potency of des (1-3) IGF-I > IGF-I > IGF-II > or = [Leu27]IGF-II.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor-I and platelet-derived growth factor-BB induce directed migration of human arterial smooth muscle cells via signaling pathways that are distinct from those of proliferation

Directed migration or chemotaxis of arterial smooth muscle cells (SMC) contributes to intimal SMC accumulation, a key event in the development of atherosclerotic lesions and in restenosis after angioplasty. The present study compares and contrasts insulin-like growth factor I (IGF-I) and platelet-derived growth factor (PDGF-BB) as chemoattractants and mitogens for human arterial SMC. Compared with PDGF-BB, IGF-I is a weaker SMC mitogen. Thus, PDGF-BB, but not IGF-I, evokes a strong and rapid activation of mitogen-activated protein (MAP) kinase kinase and MAP kinase. However, IGF-I is a potent stimulator of directed migration of human arterial SMC, as measured in a Boyden chamber assay. The half-maximal concentration for migration is similar to the Kd for IGF-I receptor interaction. An IGF-I receptor-blocking antibody blocks the effects of IGF-I, IGF-II, and insulin, indicating that the effects are indeed mediated through the IGF-I receptor. The maximal effect of IGF-I on directed migration ranges between 50% and 100% of the effect of PDGF-BB, the strongest known chemoattractant for SMC. The ability of IGF-I and PDGF-BB to induce chemotaxis coincides with their ability to stimulate phosphatidylinositol turnover, diacylglycerol formation, and intracellular Ca2+ flux and suggests that these signaling pathways, but not activation of the MAP kinase cascade, are required for chemotaxis of human arterial SMC.

Analysis of the interaction of IGF-I analogs with the IGF-I receptor and IGF binding proteins

Distinct domains of IGF-I are important for maintaining high affinity for the IGF-I receptor and for the various species of IGFBPs. The analogs that selectively bind the receptor have proven useful in determining the relative importance of IGFBPs in the regulation of the biological activity of IGF-I. Analogs with poor affinity for the receptor have also been useful in order to demonstrate that a given activity of IGF-I is mediated by the type 1 IGF receptor. These studies confirm that the role of these various proteins in IGF-I action is complex, and may be cell or tissue-type specific.

Insulin-like growth factor (IGF) suppression of IGFBP-1 production: evidence for mediation by the type I IGF receptor

The regulation of insulin-like growth factor binding protein-1 (IGFBP-1) by its ligands, IGF-I and IGF-II, was studied in continuous cultures of HepG2 human hepatoma cells. Both IGF-I and IGF-II in concentrations as low as 1-10 nmol/l caused significant suppression of IGFBP-I protein levels. This suppression was accompanied by decreased IGFBP-1 mRNA levels occurring within 2-4 h of exposure to IGF-I or IGF-II, and by a significant decrease in IGFBP-1 promoter activity. IGF-I and IGF-II were equipotent in suppressing basal levels of IGFBP-1 protein, mRNA and promoter activity. IGF-I, IGF-II, and IGF-analogs with low IGFBP-1 affinity, (des 1-3)IGF-I and long R3IGF-I, all potently suppressed the previously characterized increase in IGFBP-1 protein levels and promoter activity induced by cAMP and theophylline. In contrast, [Leu-27]IGF-II, which interacts with the type II but not type I IGF receptor, had no effect on IGFBP-1 protein levels or promoter activity. Our data indicate that IGFBP-1 production is inhibited by its ligands, IGF-I and IGF-II, and that this effect is probably mediated at the transcriptional level. The effects of IGF-I and IGF-II apparently occur as a result of binding to the type I IGF receptor, and are similar to the previously characterized suppressive effects of insulin on IGFBP-1 transcription mediated through the insulin receptor. When considered with previous data regarding expression of IGFBP-1 and the type I IGF receptor, our results suggest that IGF regulation of IGFBP-1 may play an as yet undefined role in fetal development and postnatal hepatic regeneration.

Insulinlike growth factors and binding proteins in colon cancer

Insulinlike growth factors (IGFs) express anabolic and mitogenic activity on wide variety of cells. Besides endocrine effects, IGFs have major autocrine and paracrine effects on many cellular functions. Two factors that significantly affect the extent of cellular response to IGFs include the membrane receptors for IGFs and the soluble binding proteins (BPs), which modulate the action of IGFs at the receptor level. IGFs, IGF receptors, and IGFs and their BPs (IGF-BPs) thus constitute three components of the IGF system. A role of IGFs in the transformation and proliferation of cancer cells has become increasingly evident in the past few years. Studies from several laboratories show that all three components of the IGF system may play an important role in the proliferation of colon cancers. It was recently shown that the relative expression of IGFs and IGF/BPs may critically control the metastatic potential of colon cancers. The purpose of this article is to summarize our current knowledge of the IGF system and to present support for a significant role of IGFs in the initiation and growth of colon cancers. The expression and structural aspects of IGFs, their receptors, and BPs are outlined first, followed by a discussion of the role of IGFs in gastrointestinal functions and in colon cancers.

Biosynthesis of 10 kDa and 7.5 kDa insulin-like growth factor II in a human rhabdomyosarcoma cell line

In the present study we have analysed the expression of insulin-like growth factor II (IGF-II) in the human rhabdomyosarcoma cell line IN157.IN157 cells express high levels of three IGF-II mRNAs of 6.0 kb, 4.8 kb and 4.2 kb. In contrast, normal skeletal muscle expresses a negligible amount of IGF-II mRNA. Two forms of IGF-II with molecular masses of 7.5 kDa and 10 kDa, corresponding to the mature IGF-II and IGF-II with a C-terminal extension of 21 amino acids (IGF-IIE21), were secreted into the culture medium at amounts of 17 ng/ml (2.3 nM) and 15 ng/ml (1.5 nM), respectively. IN157 cells also produce IGF binding protein-2. The bioactivity of recombinant IGF-IIE21 was compared with human IGF-I and IGF-II. IGF-I, IGF-II and IGF-IIE21 bound with high affinity to human IGF-I receptors (Kd approximately 1 nM), whereas the human IGF-II/mannose 6-phosphate (IGF-II/Man 6-P) receptor bound IGF-II and IGF-IIE21 with Kd values of 0.5 nM and 2 nM, respectively, and IGF-I with about 500 times lower affinity. IGF-II and IGF-IIE21 stimulated DNA synthesis via the IGF-I receptor, whereas the IGF-II/Man 6-P receptor mediated their rapid internalization and inactivation. During culture of IN157 cells about 50% of their IGF-I receptors were occupied by endogenous IGF-II. We conclude that IN157 cells express high levels of bioactive 10 kDa IGF-II and 7.5 kDa IGF-II that may stimulate the proliferation of rhabdomyosarcomas by interaction with IGF-I receptors on the cells.

Insulin-like growth factor II acts through an endogenous growth pathway regulated by imprinting in early mouse embryos

We present evidence that insulin-like growth factor II (IGF-II) mediates growth in early mouse embryos and forms a pathway in which imprinted genes influence development during preimplantation stages. mRNA and protein for IGF-II were expressed in preimplantation mouse embryos, but the related factors IGF-I and insulin were not. IGF-I and insulin receptors and the IGF-II/mannose-6-phosphate receptor were expressed. Exogenous IGF-II or IGF-I increased the cell number in cultured blastocysts, but a mutant form of IGF-II that strongly binds only the IGF-II receptor did not. Reduction of IGF-II expression by antisense IGF-II oligonucleotides decreased the rate of progression to the blastocyst stage and decreased the cell number in blastocysts. Preimplantation parthenogenetic mouse embryos expressed mRNA for the IGF-II receptor but not for either IGF-II ligand or the IGF-I receptor, indicating that the latter genes are not expressed when inherited maternally. These data imply that some growth factors and receptors, regulated by genomic imprinting, may control cell proliferation from the earliest stages of embryonic development.