Type I insulin-like growth factor receptor activation regulates apoptotic proteins

A novel view on the mechanisms of action of insulin and other insulin superfamily peptides: involvement of adenylyl cyclase signaling system

A new signaling mechanism common to mammalian insulin, insulin-like growth factor I, relaxin and mollusc insulin-like peptide, and involving receptor-tyrosine kinase==>G(i) protein (betagamma)==>phosphatidylinositol-3-kinase==>protein kinase Czeta==>adenylyl cyclase==>protein kinase A was discovered in the muscles and some other tissues of vertebrates and invertebrates. The authors' data were used to reconsider the problem of participation of the adenylyl cyclase-cAMP system in the regulatory effects of insulin superfamily peptides. A hypothesis has been put forward according to which the adenylyl cyclase signaling mechanism producing cAMP has a triple co-ordinating role in the regulatory action of insulin superfamily peptides on the main cell processes, inducing the mitogenic and antiapoptotic effects and inhibitory influence on some metabolic effects of the peptides. It is suggested that cAMP is a key regulator responsible for choosing the transduction pathway by concerted launching of one (proliferative) program and switching off (suppression) of two others, which lead to cell death and to the predomination of anabolic processes in a cell. The original data obtained give grounds to conclude that the adenylyl cyclase signaling system is a mechanism of signal transduction not only of hormones with serpentine receptors, but also of those with receptors of the tyrosine kinase type (insulin superfamily peptides and some growth factors).

Insulin induces heterologous desensitization of G-protein-coupled receptor and insulin-like growth factor I signaling by downregulating beta-arrestin-1

beta-Arrestin-1 mediates agonist-dependent desensitization and internalization of G protein-coupled receptors (GPCRs) and is also essential for GPCR mitogenic signaling. In addition, insulin-like growth factor I receptor (IGF-IR) endocytosis is facilitated by beta-arrestin-1, and internalization is necessary for IGF-I-stimulated mitogen-activated protein (MAP) kinase activation. Here, we report that treatment of cells for 12 h with insulin (100 ng/ml) induces an approximately 50% decrease in cellular beta-arrestin-1 content due to ubiquitination of beta-arrestin-1 and proteosome-mediated degradation. This insulin-induced decrease in beta-arrestin-1 content was blocked by inhibition of phosphatidylinositol-3 kinase (PI-3 kinase) and MEK with wortmannin and PD98059, respectively. We also found a marked decrease in the association of beta-arrestin-1 with the IGF-IR and a 55% inhibition of IGF-I-stimulated MAP kinase phosphorylation. In insulin-treated, beta-arrestin-1-downregulated cells, there was complete inhibition of lysophosphatidic acid (LPA) or isoproterenol (ISO)-stimulated MAP kinase phosphorylation. This was associated with a decrease in beta-arrestin-1 association with the beta2-AR as well as a decrease in beta-arrestin-1-Src and Src-beta2-AR association. Ectopic expression of wild-type beta-arrestin-1 in insulin-treated cells in which endogenous beta-arrestin-1 had been downregulated rescued IGF-I- and LPA-stimulated MAP kinase phosphorylation. In conclusion, we found the following. (i) Chronic insulin treatment leads to enhanced beta-arrestin-1 degradation. (ii) This downregulation of endogenous beta-arrestin-1 is associated with decreased IGF-I-, LPA-, and ISO-mediated MAP kinase signaling, which can be rescued by ectopic expression of wild-type beta-arrestin-1. (iii) Finally, these results describe a novel mechanism for heterologous desensitization, whereby insulin treatment can impair GPCR signaling, and highlight the importance of beta-arrestin-1 as a target molecule for this desensitization mechanism.

Reduction of spontaneous and irradiation-induced apoptosis in small intestine of IGF-I transgenic mice

Insulin-like growth factor I (IGF-I) may promote survival of putative stem cells in the small intestinal epithelium. Mitosis and apoptosis were quantified in crypts of nonirradiated and irradiated IGF-I transgenic (TG) and wild-type (WT) littermates. The mean apoptotic index was significantly greater in WT vs. TG littermates. After irradiation, apoptotic indexes increased, and WT mice showed a more dramatic increase in apoptosis than TG mice at the location of putative stem cells. After irradiation, no mitotic figures were observed in WT crypts, whereas mitosis was maintained within the jejunal epithelium of TG mice. The abundance and localization of Bax mRNA did not differ between nonirradiated littermates. However, there was more Bax mRNA in TG vs. WT mice after irradiation. Bax mRNA was located along the entire length of the irradiated crypt epithelium, but there was less Bax protein observed in the bottom third of TG mouse crypts compared with WT littermates. IGF-I regulates cell number by stimulating crypt cell proliferation and decreasing apoptosis preferentially within the stem cell compartment.

Expression of the bcl-2 family of pro- and anti-apoptotic genes in multiple myeloma and normal plasma cells: regulation during interleukin-6(IL-6)-induced growth and survival

Aberrant expression of genes regulating apoptosis/survival seems to be essential in the stepwise development of human multiple myeloma (MM). In this paper we have compared the expression of bcl-2 family pro- and anti-apoptotic genes in MM cell lines, primary MM cells and normal plasma cells. The Bcl-2, Mcl-1, Bcl-xL/S, Bcl-w, Bax, Bak, and Bad were shown to be expressed in both malignant and non-neoplastic, normal plasma cells. Quantitative analysis revealed that the malignant phenotype seemed to correlate with an elevated expression of Mcl-1, a decreased expression of Bax and, to a lesser extent, an increased Bcl-2/Bax expression ratio. The possible influence of interleukin-6 (IL-6) in regulating the expression of the bcl-2-related genes was also examined. Using the IL-6-dependent MM cell lines U-1958 and U-266-1970 it was clearly shown that IL-6 deprivation induced cell cycle arrest in both cell lines, whereas apoptosis was only detected in the U-1958 cells. Furthermore, the anti-apoptotic proteins Bcl-2, Mcl-1 and Bcl-xL were down-regulated, while the expression of the pro-apoptotic Bax protein was increased. To conclude, we suggest that the expression pattern of the Bcl-2 family of proteins separates the malignant phenotype of MM from normal plasma cells, and that the protecting effect of IL-6 may be conducted via an altered balance between these proteins.

Insulin-like growth factor I prevents mannitol-induced degradation of focal adhesion kinase and Akt

In our laboratory, we are interested in hyperosmolarity-induced apoptosis in neuronal cells. We have shown that high concentrations of glucose or mannitol induce apoptotic cell death in dorsal root ganglia in culture and in SH-SY5Y and SH-EP human neuroblastoma cells. Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that has a critical role for transmitting integrin-mediated-signals. In this study, we report that hyperosmolar treatment mediates FAK dephosphorylation and cleavage, which is prevented by insulin-like growth factor I (IGF-I) treatment. Mannitol treatment of SH-EP cells transfected with vector (SH-EP/pSFFV) results in concentration- and time-dependent dephosphorylation and degradation of FAK. Dephosphorylation and degradation of FAK are tightly correlated with apoptotic morphological changes, including the disruption of actin stress fibers, the loss of focal adhesion sites, membrane blebbing, and cell detachment. Treatment of SH-EP/pSFFV cells with IGF-I or transfection of IGF-I receptor prevents these changes. Treatment of cells with pharmacologic inhibitors of the mitogen-activated protein kinase or phosphatidylinositol 3-kinase pathways does not affect mannitol-induced FAK dephosphorylation and degradation. However, phosphatidylinositol 3-kinase is necessary for IGF-I-mediated protection against FAK alteration. Mannitol treatment also results in the degradation of Akt. Mannitol induces the activation of caspases-3 and -9 in a time course similar to the dephosphorylation and degradation of FAK. Treatment of the cells with ZVAD, a general caspase inhibitor, blocks the mannitol-induced FAK and Akt degradation as well as cell detachment and apoptosis. These results suggest that one of the pathways of mannitol-mediated apoptosis is through the degradation of FAK and Akt and that IGF-I protects the cells from apoptosis by blocking the activation of caspases, which may be responsible for the loss of FAK and Akt.

Response of recombinant Chinese hamster ovary cells to hyperosmotic pressure: effect of Bcl-2 overexpression

In an attempt to use the hyperosmotic pressure for improved foreign protein production in recombinant Chinese hamster ovary (rCHO) cells, the response of rCHO cells producing a humanized antibody (SH2-0.32-(Delta)bcl-2 cells) to hyperosmotic pressure was determined in regard to cell growth and death, and antibody production. Further, the feasibility of Bcl-2 overexpression in improving rCHO cell viability under hyperosmotic pressure was also determined by comparing control cells (SH2-0.32-(Delta)bcl-2) with Bcl-2 overexpressing cells (14C6-bcl-2). After 3 days of cultivation in the standard medium (294 mOsm x kg(-1)), the spent medium was exchanged with the fresh media with various osmolalities (294-640 mOsm x kg(-1)). The results obtained show that hyperosmotic pressure inhibited cell growth in a dose-dependent manner, though 14C6-bcl-2 cells were less susceptible to hyperosmotic pressure than SH2-0.32-(Delta)bcl-2 cells. At 522 mOsm x kg(-1), SH2-0.32-(Delta)bcl-2 cells underwent a gradual cell death mainly through apoptosis due to the cytotoxic effect of hyperosmotic pressure. In contrast, Bcl-2 overexpression in 14C6-bcl-2 cells could delay the apoptosis induced by 522 mOsm x kg(-1) by inhibiting caspase-3 activation. Bcl-2 overexpression could also improve the cellular membrane integrity of 14C6-bcl-2 cells. When subjected to hyperosmotic pressure, the specific antibody productivity of SH2-0.32-(Delta)bcl-2 cells and 14C6-bcl-2 cells was increased in a similar extent. As a result, the final antibody concentration achieved in 14C6-bcl-2 cells at 522 mOsm x kg(-1) was 2.5-fold higher than that at 294 mOsm x kg(-1). At 580 mOsm x kg(-1), acute hyperosmotic pressure induced the rapid loss of viability in both SH2-0.32-(Delta)bcl-2 and 14C6-bcl-2 cells through necrosis rather than through apoptosis. Taken together, Bcl-2 overexpression and optimized hyperosmotic pressure could improve the antibody production of rCHO cells.

Insulin-like growth factor-1 protects peroxynitrite-induced cell death by preventing cytochrome c-induced caspase-3 activation

We investigated the effect of IGF-1 on cell death induced by peroxynitrite in human neuroblastoma SH-SY5Y cells. Exposure of the cells to 3-morpholinosydnonimine (SIN-1), a peroxynitrite donor, caused cytochrome c release from the mitochondria, caspase-3-like activation, and cell death. Pre-incubation of the cells with the caspase-3 inhibitor partially prevented SIN-1-induced cell death. Simultaneous addition of IGF-1 reduced SIN-1-induced caspase-3-like activation and cell death, whereas IGF-1 failed to reduce the release of cytochrome c. IGF-1 increased Akt phosphorylation, and Akt phosphorylation was inhibited by wortmannin, an inhibitor of phosphatidylinositol 3-kinase. In addition, wortmannin prevented IGF-1-evoked inhibition of cell death and caspase-3-like activation. In a cell-free system, addition of cytochrome c to cytosolic fraction resulted in caspase-3-like activation. The activation was reduced when the cytosolic fraction prepared from IGF-1-treated cells was used. These results suggest that IGF-1 protects peroxynitrite-induced cell death downstream of cytochrome c release through the inhibition of caspase-3-like activation.

Remote delivery of rAAV-GFP to the rat brainstem through the recurrent laryngeal nerve

OBJECTIVE

To demonstrate that a recombinant adeno-associated viral vector (rAAV) carrying the gene for green fluorescent protein (GFP) could be delivered to the rat brainstem by remote injection into the recurrent laryngeal nerve.

STUDY DESIGN/METHODS

rAAV-GFP is a serotype 2 adeno-associated vector containing the cDNA of GFP and woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) under the control of the CAG promoter (obtained from Matthew During, PhD, Thomas Jefferson Medical College). Five microliters or 10 microL of 1.4 x 109 particles/microL of rAAV-GFP were injected into the right recurrent laryngeal nerve of adult Sprague-Dawley rats. Rats were killed and perfused at 3 (n = 3) and 11 weeks (n = 3). Brainstems were removed and cryosectioned. Fluorescent in-situ hybridization (FISH) was performed on cryosections from animals killed at 3 weeks using a cDNA probe for woodchuck polyribosomal enzyme within the rAAV vector. In a third group (n = 2), Fluoro-Gold (Fluorochrome, Inc., Denver, CO) was injected into the right thyroarytenoid muscle for comparison of neuronal uptake distribution. These rats were killed and perfused at 3 weeks.

RESULTS

The presence of GFP was noted in neurons throughout the medulla of all rat brainstems after unilateral rAAV-GFP injection at both 3 and 11 weeks. In contrast to the Fluoro-Gold, GFP was noted bilaterally and outside of the nucleus ambiguus. FISH confirmed the presence of virus within neurons expressing GFP at 3 weeks.

CONCLUSIONS

Remote delivery of rAAV-GFP to the rat brainstem is possible through injection into the recurrent laryngeal nerve. This has important therapeutic implications for the future treatment of recurrent laryngeal nerve injury and neurodegenerative diseases.

Akt activity in presenilin 1 wild-type and mutation transfected human SH-SY5Y neuroblastoma cells after serum deprivation and high glucose stress

The majority of early-onset familial Alzheimer disease cases are caused by mutations in the genes encoding presenilin 1 (PS1) and presenilin 2 (PS2). Presenilin mutations have been hypothesised to cause Alzheimer disease either by altering amyloid precursor protein metabolism or by increasing the vulnerability of neurons to undergo death by apoptosis. We showed previously that PS1 exon 9 deletion (PS1 DeltaE9) and L250S mutations predispose SH-SY5Y neuroblastoma cells to high glucose stress-induced apoptosis and that the anti-apoptotic effect of insulin-like growth factor I (IGF-I) is compromised by these mutations. The present study investigates whether the susceptibility of PS1 mutation transfected SH-SY5Y cells to undergo apoptosis is likely due to a downregulation of Akt/protein kinase B (Akt), a key intermediate in the phosphatidylinositol 3 (PI3)-kinase arm of the IGF-I signaling pathway. We used two methods to determine the regulation of Akt in response to the pro-apoptotic stimuli of serum deprivation and high glucose stress, as well as treatment with IGF-I. We also looked at the phosphorylatiom state of GSK-3beta at Ser9. Using a kinase assay with immunoprecipitated Akt, we detected an increased Akt activity in PS1 L250S cells at 1 hr after the combination of 20 mM glucose plus 10 nM IGF-I, when compared to the other cell types. This effect, however, was transient in that no mutation related differences were seen at either 6- or 24-hr post-treatment. Immunoblotting for Phospho-Akt as a ratio of total Akt, as well as for GSK-3beta phosphorylated at Ser9 revealed no apparent between cell type and treatment differences. This data strongly indicates that PS1 wt and mutant cells show no major differences in the pattern of Akt regulation after exposure to the pro-apoptotic stimuli of either serum deprivation or high glucose stress, or treatment with IGF-I. It is suggested that another component of IGF-I signaling is likely disrupted in these cells to increase their vulnerability to undergo death by apoptosis.

Tumor necrosis factor(alpha) and insulin-like growth factor-I in the brain: is the whole greater than the sum of its parts?

The cytokine tumor necrosis factor(alpha) (TNFalpha) and the hormone insulin-like growth factor-I (IGF-I) have both been shown to regulate inflammatory events in the central nervous system (CNS). This review summarizes the seemingly independent roles of TNFalpha and IGF-I in promoting and inhibiting neurodegenerative diseases. We then offer evidence that the combined effects of IGF-I and TNFalpha on neuronal survival can be vastly different when both receptors are stimulated simultaneously, as is likely to occur in vivo. We propose the framework of a molecular model of hormone-cytokine receptor cross talk in which disparate cell surface receptors share intracellular substrates that regulate neuronal survival.

Insulin-like growth factor 1 (IGF-1)-induced twist expression is involved in the anti-apoptotic effects of the IGF-1 receptor

In this study we investigated the molecular mechanisms whereby insulin-like growth factor 1 (IGF-1) induced Twist gene expression and the role of Twist in the anti-apoptotic actions of the IGF-1 receptor. In NIH-3T3 fibroblasts overexpressing the human IGF-1 receptor (NWTb3), treatment with IGF-1 (10(-8) m) for 1 and 4 h increased the level of Twist mRNA as well as protein by 3-fold. In contrast, insulin at physiological concentrations did not stimulate Twist expression in NIH-3T3 fibroblasts overexpressing the human insulin receptor. The IGF-1 effect was specific for the IGF-1 receptor since, in cells overexpressing a dominant negative IGF-1 receptor, IGF-1 failed to increase Twist expression. Pre-incubation with the ERK1/2 inhibitor U0126 or expression of a dominant negative MEK-1 abolished the effect of IGF-1 on Twist mRNA expression in NWTb3 cells, suggesting that Twist induction by IGF-1 occurs via the mitogen-activated protein kinase signaling pathway. In vivo, IGF-1 injection increased the mRNA level of Twist in mouse skeletal muscle, the major site of Twist expression. Finally, using an antisense strategy, we demonstrated that a reduction of 40% in Twist expression decreased significantly the ability of IGF-1 to rescue NWTb3 cells from etoposide-induced apoptosis. Taken together, these results define Twist as an important factor involved in the anti-apoptotic actions of the IGF-1 receptor.

Induction of apoptosis in mammary gland by a pure anti-estrogen ICI 182780

The antiestrogen, ICI 182780 (ICI) proves to be clinically useful for the treatment of estrogen receptor positive breast tumours. We report the assessment of the in vivo and in vitro effects of ICI on apoptosis of breast epithelial cells. In vivo, administration of rats with ICI for 3 weeks resulted in a reduction in the size of the lobular structures with the rate of mammary epithelial apoptosis equivalent to 10, 35 and 45% on treatment with 1, 1.5 and 2 mg ICI per kg body weight, respectively. Concomitantly, these treatment led to a 2.0-, 2.2- and 2.5-fold increase in Bax. Similar elevations were also observed in Bad levels which increased 1.7-, 2.6- and 2.7-fold respectively in the ICI treatment as compared to controls. This also resulted in a dose dependent decrease in Bcl-2 and Bcl-xL protein expressions. Growth inhibition and induction of apoptosis were also observed in the MCF-7 cells following in vitro treatment with ICI. This is closely associated with [1] the down-regulation of Bcl-2 and Bcl-xL proteins and [2] upregulation of Bax and Bad, whose gene products are known to be involved the regulation of apoptosis in mammalian cells. Stable over-expression of Bcl-2 resulted in protection of MCF-7 cells from apoptosis and growth inhibitory effects of ICI. Conversely, reduction of Bcl-2 by antisense transfection make MCF-7 cells more sensitive to ICI-induced growth inhibition and apoptosis. These findings suggest that modulation of Bax, Bcl-xL, Bcl-2 and Bad proteins by ICI may be, in part, responsible for the anti-proliferative and apoptotic effect of ICI seen clinically and in animal models.

Insulin-like growth factor-I overexpression attenuates cerebellar apoptosis by altering the expression of Bcl family proteins in a developmentally specific manner

In studies of transgenic (Tg) mice that overexpress insulin-like growth factor-I (IGF-I) exclusively in the CNS, we demonstrated a dramatic increase in cerebellar granule cell number that appeared to be attributable predominantly to enhanced survival. IGF-I anti-apoptotic actions are well established in cultured neurons, but comparable studies in vivo are few. Using the same Tg mice, therefore, we set out to document IGF-I anti-apoptotic effects during cerebellar development and to probe IGF-I signaling mechanisms. Compared with cerebella (CBs) of non-Tg littermates, those of Tg mice had fewer apoptotic cells at postnatal day 7 (P7) and showed a similar tendency at P14 and P21. At each age studied, procaspase-3 and caspase-3 were decreased in CBs of Tg mice. The caspase-3 decline was accompanied by decreases in the 85 kDa fragment of Poly(ADP-ribose) polymerase, a known product of caspase cleavage, suggesting decreased caspase activity. At P7 decreased apoptosis in Tg mice was associated with increased expression of the anti-apoptotic Bcl genes, Bcl-x(L) and Bcl-2. The mRNA expression of the proapoptotic Bcl genes, Bax and Bad, also was increased, but no changes were observed in the abundance of their proteins. At P14 Bcl-xL and Bcl-2 expression were similar in normal and Tg mice; Bax mRNA was unchanged in Tg mice, but its protein abundance was decreased, and both Bad mRNA and protein abundance were decreased. At P21 Bcl-xL and Bcl-2 expression were unchanged, but Bax and Bad expression were decreased. Our data show that IGF-I exerts anti-apoptotic actions during cerebellar development, and thereby alters the magnitude of naturally occurring apoptosis. IGF-I appears to affect multiple steps in the apoptotic pathway in a developmentally specific manner. IGF-I decreases caspase-3 availability and activity, increases the expression of anti-apoptotic Bcl-x(L) and Bcl-2 during early postnatal development, and decreases proapoptotic Bax and Bad expression at later developmental stages.

Receptor-mediated control of regulatory volume decrease (RVD) and apoptotic volume decrease (AVD)

A fundamental property of animal cells is the ability to regulate their own cell volume. Even under hypotonic stress imposed by either decreased extracellular or increased intracellular osmolarity, the cells can re-adjust their volume after transient osmotic swelling by a mechanism known as regulatory volume decrease (RVD). In most cell types, RVD is accomplished mainly by KCl efflux induced by parallel activation of K+ and Cl- channels. We have studied the molecular mechanism of RVD in a human epithelial cell line (Intestine 407). Osmotic swelling results in a significant increase in the cytosolic Ca2+ concentration and thereby activates intermediate-conductance Ca2+-dependent K+ (IK) channels. Osmotic swelling also induces ATP release from the cells to the extracellular compartment. Released ATP stimulates purinergic ATP (P2Y2) receptors, thereby inducing phospholipase C-mediated Ca2+ mobilization. Thus, RVD is facilitated by stimulation of P2Y2 receptors due to augmentation of IK channels. In contrast, stimulation of another G protein-coupled Ca2+-sensing receptor (CaR) enhances the activity of volume-sensitive outwardly rectifying Cl- channels, thereby facilitating RVD. Therefore, it is possible that Ca2+ efflux stimulated by swelling-induced and P2Y2 receptor-mediated intracellular Ca2+ mobilization activates the CaR, thereby secondarily upregulating the volume-regulatory Cl- conductance. On the other hand, the initial process towards apoptotic cell death is coupled to normotonic cell shrinkage, called apoptotic volume decrease (AVD). Stimulation of death receptors, such as TNF receptor and Fas, induces AVD and thereafter biochemical apoptotic events in human lymphoid (U937), human epithelial (HeLa), mouse neuroblastoma x rat glioma hybrid (NG108-15) and rat phaeochromocytoma (PC12) cells. In those cells exhibiting AVD, facilitation of RVD is always observed. Both AVD induction and RVD facilitation as well as succeeding apoptotic events can be abolished by prior treatment with a blocker of volume-regulatory K+ or Cl- channels, suggesting that AVD is caused by normotonic activation of ion channels that are normally involved in RVD under hypotonic conditions. Therefore, it is likely that G protein-coupled receptors involved in RVD regulation and death receptors triggering AVD may share common downstream signals which should give us key clues to the detailed mechanisms of volume regulation and survival of animal cells. In this Topical Review, we look at the physiological ionic mechanisms of cell volume regulation and cell death-associated volume changes from the facet of receptor-mediated cellular processes.

IGF-I differentially regulates Bcl-xL and Bax and confers myocardial protection in the rat heart

Bcl-2 family proteins play a crucial role in the cytoprotective action of insulin-like growth factor-I (IGF-I) by regulating cell death signaling at the mitochondrial level. The present study examined the effect of IGF-I on the expression of Bcl-2 family proteins in the rat heart mitochondria in relation to myocardial protection against ischemia-reperfusion injury. Systemic IGF-I (1 mg) treatment in the rat increased Bcl-xL and attenuated Bax 12-24 h later in the heart mitochondria fraction. Permeability transition and cytochrome c release occurred in a Ca(2+) concentration-dependent manner in the vehicle-treated mitochondria. This was significantly inhibited by the IGF-I-pretreatment. Moreover, ATP synthesis was significantly greater in the IGF-I-pretreated mitochondria. IGF-I pretreatment 24 h before 25 min of global ischemia in the isolated rat heart model significantly improved recovery of isovolumic left ventricular function and inhibited creatine kinase release during reperfusion. This was associated with a significantly less number of terminal transferase labeling-positive myocytes and nonmyocytes 2 h after reperfusion. These results suggest that IGF-1 differentially regulates Bcl-xL and Bax in heart mitochondria, which may be causally related to myocardial protection against ischemia-reperfusion injury.

Insulin-like growth factor-I and over-expression of Bcl-xL prevent glucose-mediated apoptosis in Schwann cells

Schwann cells (SCs), the myelinating cells of the peripheral nervous system, are lost or damaged in patients suffering from diabetic neuropathy. In the current study, 2 model systems are used to study the mechanism of SC damage in diabetic neuropathy: the streptozotocin (STZ)-treated diabetic rat and cultures of purified SCs in vitro. Electron microscopy of dorsal root ganglia from STZ-treated rats reveals classic ultrastructural features of apoptosis in SCs, including chromatin clumping and prominent vacuolation. Bisbenzamide staining of SCs cultured in hyperglycemic defined media shows nuclear blebbing of apoptotic cells. Insulin-like growth factor-I (IGF-I) is protective. LY294002, a phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, blocks the effect of IGF-I. High glucose induces caspase cleavage in apoptotic SCs--an effect that is blocked by bok-asp-fmk (BAF), a caspase inhibitor. Although Bcl-xL expression remains unchanged in experimental conditions, over-expression of Bcl-xL protects SCs from apoptosis. In summary, hyperglycemia induces caspase activation and morphologic changes in SCs consistent with apoptotic death, both in vivo and in vitro. Over-expression of Bcl-xL, or IGF-I, signaling via PI 3-kinase, protects SCs from glucose-mediated apoptosis in vitro. IGF-I may be useful in preventing hyperglycemia-induced damage to SCs in patients suffering from diabetic neuropathy.

Insulin-like growth factor-I and Bcl-X(L) inhibit c-jun N-terminal kinase activation and rescue Schwann cells from apoptosis

We previously reported that Schwann cells undergo apoptosis after serum withdrawal. Insulin-like growth factor-I, via phosphatidylinositol-3 kinase, inhibits caspase activation and rescues Schwann cells from serum withdrawal-induced apoptosis. In this study, we examined the role of c-jun N-terminal protein kinase (JNK) in Schwann cell apoptosis induced by serum withdrawal. Activation of both JNK1 and JNK2 was detected 1 h after serum withdrawal with the maximal level detected at 2 h. A dominant negative JNK mutant, JNK (APF), blocked JNK activation induced by serum withdrawal and Schwann cell apoptosis, suggesting JNK activation participates in Schwann cell apoptosis. Serum withdrawal-induced JNK activity was caspase dependent and inhibited by a caspase 3 inhibitor, Ac-DEVD-CHO. Because insulin-like growth factor-I and Bcl-X(L) are both Schwann cell survival factors, we tested their effects on JNK activation during apoptosis. Insulin-like growth factor-I treatment decreased both JNK1 and JNK2 activity induced by serum withdrawal. LY294002, a phosphatidylinositol-3 kinase inhibitor, blocked insulin-like growth factor-I inhibition on JNK activation, suggesting that phosphatidylinositol-3 kinase mediates the effects of insulin-like growth factor-I. Overexpression of Bcl-X(L) also resulted in less Schwann cell death and inhibition of JNK activation after serum withdrawal. Collectively, these results suggest JNK activation is involved in Schwann cell apoptosis induced by serum withdrawal. Insulin-like growth factor-I and Bcl family proteins rescue Schwann cells, at least in part, by inhibition of JNK activity.

Molecular significance of excess body weight in postmenopausal breast cancer patients, in relation to expression of insulin-like growth factor I receptor and insulin-like growth factor II genes

A number of epidemiological and clinical studies have revealed that excess body weight increases the risk of postmenopausal breast cancer and also adversely affects subsequent malignant progression. To elucidate the molecular mechanisms underlying these observations, we examined mRNA expression of various genes in normal (non-cancerous) mammary gland and cancer tissue of Japanese patients with primary breast cancer, in association with their body mass index (BMI). On the basis of analysis of 106 breast cancer patients, we found that mRNA expression of insulin-like growth factor I receptor (IGF-IR) and insulin-like growth factor II (IGF-II) in the normal mammary gland showed a significant and positive association with increased BMI among postmenopausal patients. Furthermore, the positive association of increased BMI with IGF-IR mRNA expression was also found in postmenopausal breast cancer tissue, while this association was not observed among premenopausal patients. In addition, increased mRNA expression of cyclin D1 and bcl-2 was observed in association with increased mRNA levels of IGF-IR among the patients regardless of menopausal status. These findings suggest that the molecular consequence of the increased BMI is the increased expression of IGF-II and IGF-IR, resulting in development of postmenopausal breast cancer and its progression mediated through modulation of the cell cycle and apoptosis.

Insulin-like growth factor-I is a potential trophic factor for amacrine cells

In this study we show that insulin-like growth factor (IGF)-I selectively promotes survival and differentiation of amacrine neurons. In cultures lacking this factor, an initial degeneration pathway, selectively affecting amacrine neurons, led to no lamellipodia development and little axon outgrowth. Cell lysis initially affected 50% of amacrine neurons; those remaining underwent apoptosis leading to the death of approximately 95% of them by day 10. Apoptosis was preceded by a marked increase in c-Jun expression. Addition of IGF-I or high concentrations (over 1 microM) of either insulin or IGF-II to the cultures prevented the degeneration of amacrine neurons, stimulated their neurite outgrowth, increased phospho-Akt expression and decreased c-Jun expression. The high insulin and IGF-II concentrations required to protect amacrine cells suggest that these neurons depend on IGF-I for their survival, IGF-II and insulin probably acting through IGF-I receptors to mimic IGF-I effects. Inhibition of phosphatidylinositol-3 kinase (PI 3-kinase) with wortmannin blocked insulin-mediated survival. Wortmannin addition had similar effects to IGF-I deprivation: it prevented neurite outgrowth, increased c-Jun expression and induced apoptosis. These results suggest that IGF-I is essential for the survival and differentiation of amacrine neurons, and activation of PI 3-kinase is involved in the intracellular signaling pathways mediating these effects.

Measurement of caspase activity in individual cells reveals differences in the kinetics of caspase activation between cells

Most forms of apoptosis involve activation of caspases and it is likely that differences between cells in their ability to activate caspases contributes to the responsiveness of any given cell within a population to apoptotic stimuli. To study the molecular mechanisms that underlie such differences, it is necessary to measure caspase activity in individual cells. Here, we describe a method that allows the continuous monitoring of caspase activity in individual, living mammalian cells. This approach allows studies of the kinetics of caspase activation to be performed in individual cells within a population. We demonstrate that in a group of cells where some cells die and some cells survive in response to the same stimulus, the cells that die can be differentiated from those that survive based on the amount of caspase activity in each cell several hours before death occurs.

Insulin-like growth factor-binding protein-3 modulates expression of Bax and Bcl-2 and potentiates p53-independent radiation-induced apoptosis in human breast cancer cells

We report that transfection of insulin-like growth factor-binding protein-3 (IGFBP-3) cDNA in human breast cancer cell lines expressing either mutant p53 (T47D) or wild-type p53 (MCF-7) induces apoptosis. IGFBP-3 also increases the ratio of pro-apoptotic to anti-apoptotic members of the Bcl-2 family. In MCF-7, an increase in Bad and Bax protein expression and a decrease in Bcl-x(L) protein and Bcl-2 protein and mRNA were observed. In T47D, Bax and Bad proteins were up-regulated; Bcl-2 protein is undetectable in these cells. As T47D expresses mutant p53 protein, these modulations of pro-apoptotic proteins and induction of apoptosis are independent of p53. The effect of IGFBP-3 on the response of T47D to ionizing radiation (IR) was examined. These cells do not G(1) arrest in response to IR and are relatively radioresistant. Transfection of IGFBP-3 increased the radiosensitivity of T47D and increased IR-induced apoptosis but did not effect a rapid G(1) arrest. IR also caused a much greater increase in Bax protein in IGFBP-3 transfectants compared with vector controls. Thus, IGFBP-3 increases the expression of pro-apoptotic proteins and apoptosis both basally and in response to IR, suggesting it may be a p53-independent effector of apoptosis in breast cancer cells via its modulation of the Bax:Bcl-2 protein ratio.

Prevention of beta cell dysfunction and apoptosis activation in human islets by adenoviral gene transfer of the insulin-like growth factor I

Interleukin-1beta is a potent pro-inflammatory cytokine that has been shown to inhibit islet beta cell function as well as to activate Fas-mediated apoptosis in a nitric oxide-dependent manner. Furthermore, this cytokine is effective in recruiting lymphocytes that mediate beta cell destruction in IDDM onset. The insulin-like growth factor I (IGF-I) has been shown to block IL-1beta actions in vitro. We hypothesized that gene transfer of the insulin-like growth factor I to intact human islets could prevent IL-1beta-induced beta cell dysfunction and sensitization to Fas-triggered apoptosis activation. Intact human islets were infected with adenoviral vectors encoding IGF-I as well as beta-galactosidase and enhanced green fluorescent protein as controls. Adenoviral gene transfer of human IGF-I prevented IL-1beta-mediated nitric oxide production from human islets in vitro as well as the suppression of beta cell function as determined by glucose-stimulated insulin production. Moreover, IGF-I gene transfer prevented IL-1beta-induced, Fas-mediated apoptosis. These results suggest that locally produced IGF-I from cultured islets may be beneficial in maintaining beta cell function and promoting islet survival before and following islet transplantation as a potential therapy for type I diabetes.

Anti-apoptotic action of insulin-like growth factor-I during human preimplantation embryo development

Insulin-like growth factor I (IGF-I) has been shown to increase the proportion of embryos forming blastocysts and the number of inner cell mass cells in human and other mammalian preimplantation embryos. Here we examined whether the increased cell number resulted from increased cell division or decreased cell death. Normally fertilized, Day 2 human embryos of good morphology were cultured to Day 6 in glucose-free Earle's balanced salt solution supplemented with 1 mM glutamine, with (n = 42) and without (n = 45) 1.7 nM IGF-I. Apoptotic cells in Day 6 blastocysts were identified using terminal deoxynucleotidyl dUTP terminal transferase (TUNEL) labeling to detect DNA fragmentation and 4'-6-diamidino-2-phenylindole (DAPI) counterstain to evaluate nuclear morphology. The number of nuclei and extent of DNA and nuclear fragmentation was assessed using laser scanning confocal microscopy. IGF-I significantly increased the proportion of embryos developing to the blastocyst stage from 49% (control) to 74% (+IGF-I) (P < 0.05). IGF-I also significantly decreased the mean proportion of apoptotic nuclei from 16.3 +/- 2.9% (-IGF-I) to 8.7 +/- 1.4% (+IGF-I) (P < 0.05). The total number of cells remained similar between both groups (61.7 +/- 4.6 with IGF-I; 54.5 +/- 5.1 without IGF-I). The increased number of blastocysts combined with reduced cell death suggests that IGF-I is rescuing embryos in vitro which would otherwise arrest and acting as a survival factor during preimplantation human development.

Effects of voluntary ethanol drinking on [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin receptor binding in the mouse hippocampus and cerebellum

Chronic exposure to ethanol can induce widespread cell loss in the brain, in some cases even causing dementia. Although the underlying mechanism associated with ethanol toxicity has not yet been established, it is suggested that one of the ways in which ethanol disrupts neuronal functioning/survival is by targeting the actions of mitogenic growth factors. Insulin-like growth factors-I and -II and insulin are structurally related polypeptides with potent mitogenic and metabolic effects on the central and peripheral nervous systems. These growth factors and their respective receptors are widely distributed throughout the brain, including the hippocampus and cerebellum. Evidence indicates that ethanol can decrease plasma levels of insulin-like growth factors and can also inhibit the growth-promoting and cell survival effects of these growth factors under in vitro conditions. The present study was designed to determine if voluntary ethanol consumption over a 21-day period could alter [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin receptor-binding sites in the hippocampus and cerebellum-areas known to be severely affected following chronic exposure to ethanol. C57BL/6 mice were presented with either water only or a choice of water and a 10% v/v ethanol solution. Mice with access to the ethanol solution drank an average of 5.35+/-0.77 g of ethanol/kg body weight per day. [125I]Insulin-like growth factor-I receptor-binding sites were found to be significantly increased in all subfields of the hippocampal formation, but not in the cerebellum, of ethanol-treated mice compared to controls. [125I]Insulin-like growth factor-II and [125I]insulin receptor-binding sites, on the other hand, did not exhibit any alterations either in the hippocampus or cerebellum following chronic exposure to ethanol. These results, in keeping with earlier reports, suggest that hippocampal insulin-like growth factor-I is more sensitive to ethanol treatment than either insulin-like growth factor-II or insulin, and the observed increase in the [125I]insulin-like growth factor-I receptor levels possibly reflects an activity-dependent response to prevent/slow down neuronal degeneration and/or to regulate subtle functional alterations that follow chronic exposure to ethanol.

Dexamethasone inhibits insulin-like growth factor signaling and potentiates myoblast apoptosis

In the critically ill, glucocorticoids induce myopathy, combining profound protein catabolism and mild myotubular death. Insulin-like growth factors (IGFs) inhibit muscle catabolism through activation of phosphatidylinositol 3-kinase (PI3K). Using rat L6 myoblasts, we show that IGF-I also acts through PI3K to inhibit apoptosis induced by hyperosmolar metabolic stress with 300 mM mannitol. We find that the glucocorticoid dexamethasone inhibits this antiapoptotic effect of IGF-I by impairing PI3K signaling. Dexamethasone induces overexpression of the PI3K subunit p85alpha, which, in turn, competes with the complete PI3K heterodimer for binding at insulin receptor substrate-1, inhibiting PI3K activation. Dexamethasone blocks IGF-I-induced phosphorylation of Akt, a PI3K-dependent process. Increased cellular p85alpha abundance, induced by either 10 microM dexamethasone or transient transfection with a plasmid coding for p85alpha, significantly inhibits IGF-I rescue from apoptosis induced by mannitol, as indicated by both loss of cell viability and increased activity of caspase-3 by fluorogenic assay. Conversely, constitutively active PI3K inhibits death induced by mannitol, even in the presence of dexamethasone. These findings may have particular relevance in the pathogenesis of acute steroid myopathy in critical illness, in which catabolic glucocorticoid effects combine with acute metabolic stressors, including sepsis, fasting, and chemical denervation.

Autocrine stimulation by insulin-like growth factor 1 and insulin-like growth factor 2 mediates chondrocyte survival in vitro

OBJECTIVE

To determine the role of autocrine stimulation by insulin-like growth factor 1 (IGF-1) and IGF-2 in mediating chondrocyte survival and to determine whether chondrocytes from older individuals are more susceptible to cell death when IGF action is blocked.

METHODS

Survival was assessed in human and monkey chondrocytes cultured in suspension in alginate under serum-free conditions. The role of IGFs in mediating survival was determined by treating cultures with neutralizing antibodies to IGF-1 and IGF-2, an antibody that blocks the type 1 IGF receptor, and antisense oligonucleotides to inhibit IGF-1 production. Survival was measured in chondrocyte cultures from young and old adult monkeys in the presence and absence of the IGF receptor blocking antibody and ceramide to induce cell death.

RESULTS

Cell survival of >90% was noted when chondrocytes were cultured for as long as 107 days in alginate in a supplemented serum-free medium. Compared with controls, survival was significantly reduced by treatment with neutralizing antibodies to IGF-1 (25% cell death), neutralizing antibodies to IGF-2 (18% cell death), antibody to the IGF receptor (45% cell death), and IGF-1 antisense oligonucleotides (28% cell death). Cell death from inhibition of the type 1 IGF receptor was associated with an increase in caspase 3 activity and with positive DNA fragmentation, consistent with apoptotic cell death. Chondrocytes from old adult monkeys were more susceptible to cell death than were those from young adult monkeys when the IGF receptor was blocked and cell death was further stimulated by ceramide.

CONCLUSION

Autocrine production of IGFs helps to maintain chondrocyte survival in vitro and could play a similar role in vivo. With aging, chondrocytes may become more susceptible to factors that induce cell death.

IGF-I receptor activation and BCL-2 overexpression prevent early apoptotic events in human neuroblastoma

The type I insulin-like growth factor receptor (IGF-IR) is important for mitogenesis, transformation, and survival of tumor cells. The current study examines the effect of IGF-IR expression and activation on apoptosis in SHEP human neuroblastoma cells. SHEP cells undergo apoptosis which is prevented by IGF-I addition or overexpression of the IGF-IR (SHEP/IGF-IR cells). High mannitol treatment activates caspase-3 by 1 h in SHEP cells while caspase-3 activation is delayed by 3 h in SHEP/IGF-IR cells. Transfection with Bcl-2 (SHEP/Bcl-2 cells) prevents serum withdrawal and mannitol induced apoptosis and caspase-3 activation. Mannitol induces mitochondrial membrane depolarization in both SHEP and SHEP/IGF-IR cells. IGF-IR activation or overexpression of Bcl-2 in SHEP cells prevents mitochondrial membrane depolarization. Collectively, these results suggest that IGF-IR or Bcl-2 overexpression in neuroblastoma cells promotes cell survival by preventing mitochondrial membrane depolarization and caspase-3 activation, ultimately leading to increased tumor growth.

The cytokine hepatocyte growth factor/scatter factor inhibits apoptosis and enhances DNA repair by a common mechanism involving signaling through phosphatidyl inositol 3' kinase

Scatter factor (SF) [aka. hepatocyte growth factor (HGF)] (designated HGF/SF) is a multifunctional cytokine that stimulates tumor cell invasion and angiogenesis. We recently reported that HGF/SF protects epithelial and carcinoma cells against cytotoxicity from DNA-damaging agents and that HGF/SF-mediated cytoprotection was associated with up-regulation of the anti-apoptotic protein Bcl-XL in cells exposed to adriamycin. We now report that in addition to blocking apoptosis, HGF/SF markedly enhances the repair of DNA strand breaks caused by adriamycin or gamma radiation. Constitutive expression of Bcl-XL in MDA-MB-453 breast cancer cells not only simulated the HGF/SF-mediated chemoradioresistance, but also enhanced the repair of DNA strand breaks. The ability of HGF/SF to induce both chemoresistance and DNA repair was inhibited by wortmannin, suggesting that these activities of HGF/SF are due, in part, to a phosphatidylinositol-3'-kinase (PI3K) dependent signaling pathway. Consistent with this finding, HGF/SF induced the phosphorylation of c-Akt (protein kinase-B), a PI3K substrate implicated in apoptosis inhibition; and an expression vector encoding a dominant negative kinase inactive Akt partially but significantly inhibited HGF/SF-mediated cell protection and DNA repair. These findings suggest that HGF/SF activates a cell survival and DNA repair pathway that involves signaling through PI3K and c-Akt and stabilization of the expression of Bcl-XL; and they implicate Bcl-XL in the DNA repair process.

Akt/protein kinase B up-regulates Bcl-2 expression through cAMP-response element-binding protein

In our previous study we showed that insulin-like growth factor-I induces a cAMP-response element (CRE) site-containing Bcl-2 promoter through a novel signaling pathway involving mitogen-activated protein kinase kinase 6/p38beta mitogen-activated protein kinase/MAP kinase-activated protein kinase-3/cAMP-response element-binding protein (CREB) (Pugazhenthi, S., Miller, E., Sable, C., Young, P., Heidenreich, K. A., Boxer, L. M., and Reusch, J. E.-B. (1999) J. Biol. Chem. 274, 27529-27535). In the present investigation, we define a second pathway contributing to CREB-dependent up-regulation of Bcl-2 expression as a novel anti-apoptotic function of Akt signaling. To examine the role of Akt on Bcl-2 expression, a series of transient transfections using a luciferase reporter gene driven by the promoter region of Bcl-2 containing a CRE were carried out. Pharmacological inhibition of phosphatidylinositol (PI) 3-kinase, the upstream kinase of Akt, with LY294002 led to a 45% decrease in Bcl-2 promoter activity. The reporter activity was enhanced 2.3-fold by overexpression of active p110 subunit of PI 3-kinase and inhibited 44% by the dominant negative p85 subunit of PI 3-kinase. Cotransfection with 3-phosphoinositide-dependent kinase (PDK1), which is required for the full activation of Akt, resulted in enhanced luciferase activity. Insulin-like growth factor-I-mediated induction of Bcl-2 promoter activity was decreased significantly (p < 0.01) by the dominant negative forms of p85 subunit of PI 3-kinase, PDK1, and Akt. These data indicate that regulation of Bcl-2 expression by IGF-I involves a signaling cascade mediated by PI 3-kinase/PDK1/Akt/CREB. Furthermore, we measured the Bcl-2 mRNA in PC12 cells overexpressing Akt by real-time quantitative reverse transcription-polymerase chain reaction using the TaqMan(TM) fluorogenic probe system. We observed a 2.1-fold increase in Bcl-2 mRNA levels in the Akt cell line compared with control PC12 cells, supporting the observation that enhanced CREB activity by Akt signaling leads to increased Bcl-2 promoter activity and cell survival.

Epidermal growth factor (EGF) suppresses staurosporine-induced apoptosis by inducing mcl-1 via the mitogen-activated protein kinase pathway

Overexpression of epidermal growth factor receptor (EGFR) and establishment of transforming growth factor alpha (TGF alpha)/EGF autocrine system are frequently detected in tumor cells. In addition to mitogenic ability, we demonstrate in this report that EGF protects a human esophageal carcinoma (CE) cell line, CE81T/VGH, from staurosporine-induced apoptosis. The anti-apoptotic signal of EGF is alleviated by a MEK inhibitor PD98059 or an ERK2 dominant negative mutant but not by a phosphatidylinositol-3'-kinase (PI-3K) inhibitor wortmannin. Furthermore, v-raf blocks apoptosis induced by staurosporine. This evidence implies that the survival signal of EGF is mediated via the Raf-MEK-ERK pathway but not the PI3-K pathway. The survival effect of EGF is coincident with the induction of mcl-1, an antiapoptotic gene in the bcl-2 family. PD98059 also suppresses the induction of Mcl-1 by EGF, implying that EGF may up-regulate Mcl-1 via the MAP kinase pathway. Overexpression of mcl-1 is sufficient to protect against apoptosis, while transfection of a mcl-1 antisense plasmid causes cell death. The expression of mcl-1 antisense plasmid also suppresses the anti-apoptotic effect of EGF. Taken together, these results indicate that EGF may up-regulate Mcl-1 through the MAP kinase pathway to suppress apoptosis.

Alzheimer's disease presenilin-1 exon 9 deletion and L250S mutations sensitize SH-SY5Y neuroblastoma cells to hyperosmotic stress-induced apoptosis

Mutations in the presenilin-1 (PS1) and presenilin-2 (PS2) genes account for the majority of early-onset familial Alzheimer's disease cases. Recent studies suggest that presenilin gene mutations predispose cells to apoptosis by mechanisms involving altered calcium homeostasis and oxidative damage. In the present study, we determined whether PS1 mutations also sensitize cells to hyperosmotic stress-induced apoptosis. For this, we established SH-SY5Y neuroblastoma cell lines stably transfected with wild-type PS1 or either the PS1 exon 9 deletion (deltaE9) or PS1 L250S mutants. Cultured cells were exposed to an overnight (17 h) serum deprivation, followed by a 30 min treatment with either 20 mM glucose, 10 nM insulin-like growth factor-1 or 20 mM glucose + 10 nM insulin-like growth factor-1. Cells were then cultured for a further 3, 6 or 24 h and stained for apoptotic condensed nuclei using propidium iodide. Confirmation that cells were undergoing an active apoptotic process was achieved by labelling of DNA strand breaks using the terminal dUTP nick end labelling (TUNEL) technique. We also determined cell viability using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction. Propidium iodide staining revealed that all cell lines and controls showed an increased number of apoptotic cells appearing with condensed nuclei at 24 h compared with 6 h and 3 h. High glucose-induced hyperosmotic stress resulted in significantly more apoptotic cells in the PS1 deltaE9 and PS1 L250S mutation cell lines at 24 h, compared with the wild-type PS1 lines (P < 0.001, ANOVA for both comparisons). Mean values (+/-S.D.) for the percentage number of apoptotic cells at 24 h following high glucose treatment were 16.1 +/- 3.5%, 26.7 +/- 5.5% and 31.0 +/- 5.7% for the wild-type PS1, PS1 deltaE9 and PS1 L250S lines, respectively. The pro-apoptotic effects of high glucose treatment were reversed by 10 nM insulin-like growth factor-1, although to a lesser extent in the mutation cell lines (5.8 +/- 2.4%, 15.2 +/- 7.3% and 13.2 +/- 2.0% for the wild-type PS1, PS1 deltaE9 (P < 0.01 for comparison with wild-type PS1) and PS1 L250S (P < 0.01 for comparison with wild-type PS1) transfected lines, respectively. TUNEL labelling of cells at 24 h following treatment gave essentially the same results pattern as obtained using propidium iodide. The percentage number of apoptotic cells with DNA strand breaks (means +/- S.D.) following high glucose treatment was 15.4 +/- 2.6% for the wild-type PS1, 26.8 +/- 3.2% for the PS1 deltaE9 (P < 0.001 for comparison with wild-type PS1) and 29.7 +/- 6.1% for the PS1 L250S transfected lines (P < 0.001 for comparison with wild-type PS1). The PS1 deltaE9 and PS1 L250S transfected lines also showed a higher number of apoptotic cells with DNA strand breaks at 24 h following high glucose plus insulin-like growth factor-1 treatment (11.4 +/- 2.0% and 14.3 +/- 2.8%, respectively), compared with values for the wild-type PS1 lines (8.5 +/- 2.4%). These differences were significant (P < 0.01) for the comparison of wild-type PS1 and PS1 L250S, but not PS1 deltaE9 lines. The mutation-related increases in number of apoptotic cells at 24 h following high glucose treatment were not accompanied by significant differences in cell viability at this time-point. Our results indicate that PS1 mutations predispose to hyperosmotic stress-induced apoptosis and that the anti-apoptotic effects of insulin-like growth factor-1 are compromised by these mutations. Perturbations of insulin-like growth factor-1 signalling may be involved in PS1 mutation-related apoptotic neuronal cell death in Alzheimer's disease.

Understanding factors that limit the productivity of suspension-based perfusion cultures operated at high medium renewal rates

One of the key parameters in perfusion culture is the rate of medium replacement (D). Intensifying D results in enhanced provision of nutrients, which can lead to an increase in the viable cell density (X(v)). The daily MAb production of hybridoma cells can thus be increased proportionally without modifying the bioreactor scale, provided that both viable cell yield per perfusion rate (Y(Xv/D)) and specific MAb productivity (q(MAb)) remain constant at higher D. To identify factors prone to limit productivity in perfusion, a detailed kinetic analysis was carried out on a series of cultures operated within a D range of 0.48/4.34 vvd (volumes of medium/reactor volume/day) in two different suspension-based systems. In the Celligen/vortex-flow filter system, significant reductions in Y(Xv/D) and q(MAb) resulting from the use of gas sparging were observed at D > 1.57 vvd (X(v) > 15 x 10(6) cells/mL). Through glucose supplementation, we have shown that the decrease in Y(Xv/D) encountered in presence of sparging was not resulting from increased cellular destruction or reduced cell growth, but rather from glucose limitation. Thus, increases in hydrodynamic shear stress imparted to the culture via intensification of gas sparging resulted in a gradual increase in specific glucose consumption (q(glc)) and lactate production rates (q(lac)), while no variations were observed in glutamine-consumption rates. As a result, while glutamine was the sole limiting-nutrient under non-sparging conditions, both glutamine and glucose became limiting under sparging conditions. Although a reduction in q(MAb) was observed at high-sparging rates, inhibition of MAb synthesis did not result from direct impact of bubbles, but was rather associated with elevated lactate levels (25-30 mM), resulting from shear stress-induced increases in q(lac), q(glc), and Y(lac/glc). Deleterious effects of sparging on Y(Xv/D) and q(MAb) encountered in the Celligen/vortex-flow filter system were eliminated in the sparging-free low-shear environment of the Chemap-HRI/ultrasonic filter system, allowing for the maintenance of up to 37 x 10(6) viable cells/mL. A strategy aimed at reducing requirements for sparging in large-scale perfusion cultures by way of a reduction in the oxygen demand using cellular engineering is discussed.

Circulating IGF-I and its protective role in the pathogenesis of diabetic angiopathy

Poor glycaemic control in type 1 diabetes is associated with elevated serum IGFBP-1 levels and reduced rather than elevated serum IGF-I levels. Increasing age is accompanied by a further decrease in serum IGF-I levels as well as an increase in IGFBP-l levels in adult diabetic type 1 and type 2 subjects. This is especially observed in diabetic type 1 subjects with manifest microvascular complications. IGFBP-I has been proposed as one of the IGF-I inhibitors in the serum of diabetics. Lowered IGF-I and increased IGFBP-1 levels in the blood may thus result in decreased IGF-I bioavailability at the tissue level. We hypothesize that the premature and progressive decline in serum IGF-I bioactivity during ageing in diabetics ultimately results in insufficient protective effects by IGF-I in the kidneys, eyes and neurones, and thus the progression of diabetic microvascular complications. If this hypothesis is proven to be right, treatment of diabetic patients with IGF-I (eventually complexed to IGFBPs) as an adjunct to insulin might prevent and not worsen the development of diabetic microvascular complications.

Insulin-like growth factor I is the key growth factor in serum that protects neuroblastoma cells from hyperosmotic-induced apoptosis

Neuroblastoma is a childhood tumor of the peripheral nervous system that remains largely uncurable by conventional methods. Mannitol induces apoptosis in neuroblastoma cell types and insulin-like growth factor I (IGF-I) protects these cells from hyperosmotic-induced apoptosis by affecting apoptosis-regulatory proteins. In the current study, we investigate factors that enable SH-SY5Y neuroblastoma cells to survive in the presence of an apoptotic stimulus. When SH-SY5Y cells are exposed to high mannitol concentrations, more than 60% of the cells are apoptotic within 48 h. Normal CS prevents hyperosmotic-induced apoptosis in a dose-dependent manner, with 0.6% CS protecting 50% of the cells, and 3% CS rescuing more than 70% of the cells from apoptosis. Serum also delays the commitment point for SH-SY5Y cells from 9 h to 35 h. A survey of several growth factors, including epidermal growth factor (EGF), platelet-derived growth factor (PDGF), nerve growth factor (NGF), fibroblast growth factor (FGF), and IGF-I reveals that IGF-I is a component of serum necessary for protection of neuroblastoma cells from death. Mitochondrial membrane depolarization occurs in greater than 40% of the cells after mannitol exposure and caspase-3 activation is increased in high mannitol conditions after 9 h. IGF-I blocks both the mitochondrial membrane depolarization and caspase-3 activation normally induced by hyperosmotic treatment in neuroblastoma cells. Our results suggest that (1) IGF-I is a key factor in serum necessary for protection from death and (2) IGF-I acts upstream from the mitochondria and the caspases to prevent apoptosis in human neuroblastoma.

Interactions between bcl-2 and the IGF system control apoptosis in the developing mouse brain

The IGF system and the pro-survival Bcl-2 proteins protect cells from apoptosis and play a key role in brain development. In order to examine a possible relationship between these two potent anti-apoptotic systems, we utilised two transgenic mice models overexpressing either Bcl-2 or IGF-I proteins in olfactory bulb (OB) or cerebellar neurons, respectively. We have demonstrated that while the organization of the defined layers of the OB from the bcl-2 transgenic and wildtype mice cultured in serum free medium (SF) was similarly poor, the mitral cell layer from the transgenic mice was expanded and their neurons were well preserved. Addition of IGF-I improved the definition of the layers normally present within the OB, in both wildtype and bcl-2 transgenic mice, and restored wildtype mitral cell layer structure and neuronal survival similar to that in bcl-2 mice, whose mitral cell survival was not further enhanced by IGF-I. Immunoreactivity for IGF-I and IGFBP-2 was markedly increased in these Bcl-2-expressing mitral cells compared to wildtype mice. In newborn IGF-I transgenic mice, cerebellar Purkinje cells overexpressing IGF-I showed markedly increased immunoreactivity for Bcl-2 and IGFBP-2. These studies indicate that in the developing brain IGF-I modulates expression of its major binding protein IGFBP-2, as well as the Bcl-2 protein. In addition apoptosis caused by culturing OBs in SF medium, is inhibited by expression of Bcl-2 in the mitral neurons and is associated with enhanced expression of the IGF system, including IGF-I and IGFBP-2. The later may thus play a role in IGF targeting. This complex interaction between the two potent anti-apoptotic systems is likely to provide a robust system of cell protection during brain development and repair.

Insulin-like growth factor-I prevents caspase-mediated apoptosis in Schwann cells

Both neurons and glia succumb to programmed cell death (PCD) when deprived of growth factors at critical periods in development or following injury. Insulin-like growth factor-I (IGF-I) prevents apoptosis in neurons in vitro. To investigate whether IGF-I can protect Schwann cells (SC) from apoptosis, SC were harvested from postnatal day 3 rats and maintained in serum-containing media until confluency. When cells were switched to serum-free defined media (DM) for 12-72 h, they underwent PCD. Addition of insulin or IGF-I prevented apoptosis. Bisbenzamide staining revealed nuclear condensation and formation of apoptotic bodies in SC grown in DM alone, but SC grown in DM plus IGF-I had normal nuclear morphology. The phosphatidylinositol 3-kinase (PI 3-K) inhibitor LY294002 blocked IGF-I-mediated protection. Caspase-3 activity was rapidly activated upon serum withdrawal in SC, and the caspase inhibitor BAF blocked apoptosis. These results suggest that IGF-I rescues SC from apoptosis via PI 3-K signaling which is upstream from caspase activation.

Multiple signaling pathways of the insulin-like growth factor 1 receptor in protection from apoptosis

The type 1 insulin-like growth factor receptor (IGF-1R), activated by its ligands, protects several cell types from a variety of apoptotic injuries. The main signaling pathway for IGF-1R-mediated protection from apoptosis has been previously elucidated and rests on the activation of phosphatidylinositol 3-kinase, Akt/protein kinase B, and the phosphorylation and inactivation of BAD, a member of the Bcl-2 family of proteins. In 32D cells (a murine hemopoietic cell line devoid of insulin receptor substrate 1 [IRS-1]), the IGF-1R activates alternative pathways for protection from apoptosis induced by withdrawal of interleukin-3. One of these pathways leads to the activation of mitogen-activated protein kinase, while a third pathway results in the mitochondrial translocation of Raf and depends on the integrity of a group of serines in the C terminus of the receptor that are known to interact with 14.3.3 proteins. All three pathways, however, result in BAD phosphorylation. The presence of multiple antiapoptotic pathways may explain the remarkable efficacy of the IGF-1R in protecting cells from apoptosis.

Neurons undergo apoptosis in animal and cell culture models of diabetes

Recent clinical trials indicate that the severity of diabetic neuropathy is correlated with the level of patient glycemic control. In the current study, hyperglycemia induces apoptotic changes in dorsal root ganglion neurons and Schwann cells in vivo both in streptozotocin-treated diabetic rats and in rats made acutely hyperglycemic with infused glucose. Typical apoptotic nuclear and cytoplasmic changes are observed. In addition mitochondrial changes recently reported to occur as part of the apoptotic cascade, such as ballooning of mitochondria and disruption of the internal cristae, are seen in diabetic dorsal root ganglion neurons and Schwann cells. Similar changes have been reported in neurons in the presence of oxidative stress. In order to study the neurotoxic effects of high glucose we developed an in vitro model using rat dorsal root ganglion neurons. In dorsal root ganglion cultured in defined medium, addition of moderate glucose levels results in neurite degeneration and apoptosis. These changes are coupled with activation of caspase-3, dependent on the concentration of glucose. The apoptotic changes observed in vitro are similar to those observed in vivo. In contrast, addition of IGF-I, even at physiological concentrations, prevents activation of caspase-3 and neuronal apoptosis in vitro. We suggest that oxidative stress may promote the mitochondrial changes in diabetic animals and lead to activation of programmed cell death caspase pathways. These results imply a new pathogenetic mechanism for diabetic sensory neuropathy.

Lack of internucleosomal DNA fragmentation is related to Cl(-) efflux impairment in hematopoietic cell apoptosis

The heterodimeric DNA fragmentation factor (DFF) is responsible for DNA degradation into nucleosomal units during apoptosis. This process needs the caspase-dependent release of ICAD/DFF-45, the inhibitory subunit of DFF. Here we report that triggering apoptosis via a hyperosmotic shock in hematopoietic cells causes the appearance of mitochondrial and cytosolic alterations, activation of caspases, chromatin condensation, nuclear disruption, and DNA fragmentation. However, oligonucleosomal but not high molecular weight (50-150 kb) DNA cleavage is abolished if Cl(-) efflux is prevented by using NaCl to raise extracellular osmolarity or by Cl(-) channel blockers, even when apoptosis is initiated by other agents (staurosporine, anti-Fas antibody). In these conditions, all the apoptosis hallmarks investigated remain detectable, including the cleavage of ICAD/DFF-45. In vitro assays with lysates of cells in which Cl(-) efflux is blocked confirm the lack of internucleosomal DNA degradation. These findings establish that neither caspase activation nor ICAD/DFF-45 processing per se is sufficient to induce oligonucleosomal DNA fragmentation and that high molecular weight DNA degradation and chromatin condensation appear independently of it. Finally, they suggest that Cl(-) efflux is a necessary cofactor that intervenes specifically in the activation of the DFF endonuclease.

Expression of the wild-type insulin-like growth factor II receptor gene suppresses growth and causes death in colorectal carcinoma cells

The insulin-like growth factor II receptor (IGFIIR) has been implicated as a tumor suppressor gene in human malignancy. Frequent mutation, loss of heterozygosity, and microsatellite instability (MSI) directly affecting the IGFIIR gene have been reported in several primary human tumor types. However, to our knowledge, dynamic functional evidence of a growth-suppressive role for IGFIIR has not yet been provided. We identified one MSI-positive colorectal carcinoma cell line, SW48, with monoallelic mutation in IGFIIR identical to that seen in primary colorectal carcinomas. A zinc-inducible construct containing the wild-type IGFIIR cDNA was stably transfected into SW48 cells. Growth rate and apoptosis were compared between zinc-treated, untreated, and untransfected cells. A twofold increase in IGFIIR protein expression was detected after zinc treatment in discrete clonal isolates of transfected SW48 cells. Moreover, zinc induction of exogenous wild-type IGFIIR expression reproducibly decreased growth rate and increased apoptosis. These data prove that wild-type IGFIIR functions as a growth suppressor gene in colorectal cancer cells and provide dynamic in vitro functional support for the hypothesis that IGFIIR is a human growth suppressor gene.

Apoptosis-resistant E1B-19K-expressing NS/0 myeloma cells exhibit increased viability and chimeric antibody productivity under perfusion culture conditions

We have shown previously that recombinant NS/0 myelomas expressing sufficient amounts of E1B-19K were resistant to apoptosis occurring in the late phase of batch culture and under stressful conditions such as cultivation in glutamine-free medium or following heat shock. However, no significant increase in monoclonal antibodies (MAb) was observed during the prolonged stationary phase of these batch cultures. Here, we show that E1B-19K can enhance cell survival and improve MAb productivity in high cell density perfusion culture. Typically, lymphoid cells grown under steady state in perfusion exhibit decreasing viabilities with concomitant accumulation of apoptotic cells. By modulating the ability of these cells to resist to induction of apoptosis in low nutrient environment, a 3-fold decrease in specific death rate from 0.22 day-1 for NS/0 control to 0.07 day-1 for E1B-19K cells was achieved, resulting in a significant improvement in cell viability throughout perfusion. E1B-19K cells at the perfusion plateau phase also exhibited a 3-fold reduction in specific growth rate concomitant with a lower percentage of S and higher percentage of G1 phase cells. This was associated with a 40% decrease in specific oxygen consumption rate, likely related to a reduction in the specific consumption rates of limiting nutrient(s). Expression of E1B-19K consequently had a significant impact on the steady-state viable cell density, allowing maintenance of 11.5 x 10(6) E1B-19K cells/mL versus 5.9 x 10(6) control NS/0 cells/mL for the same amount of fresh medium brought into the system (half a volume per day). Whereas MAb concentrations found in perfusion culture of control NS/0 myelomas were almost 3-fold higher than those found in batch culture; in the case of E1B-19K-expressing myelomas, the MAb concentration in perfusion was more than 7-fold higher than in batch. This was attributable to the 2-fold increase in viable cell plateau and to a 40% increase in the perfusion to batch ratio of specific MAb productivity (2.2-fold for E1B-19K myelomas versus 1.6-fold for NS/0 control).

The IGF axis and programmed cell death

Insulin-like growth factors (IGF) are mitogenic peptides that have been implicated as positive regulators of cellular proliferation. In recent years, several studies have suggested an additional role for the IGF axis in the regulation of apoptosis. Signalling through the IGF receptor has been shown to have a potent survival function and protect cells from a variety of apoptotic stimuli. The actions of IGF are regulated by a family of high-affinity IGF binding proteins (IGFBP), which sequester the IGF from the IGF receptor. However, there is some evidence that one of these binding proteins, IGFBP-3, may have its own pro-apoptotic effects that are independent of its ability to modulate IGF bioavailability. In addition, it has been suggested that the tumour suppressor p53, a crucial mediator of apoptosis in response to cellular stress, may elicit several of its apoptotic effects through manipulation of components of the IGF axis. This review summarizes what is currently known about the role of the IGF system in the regulation of apoptosis, highlighting its implications in the context of tumorigenesis.

Do insulin-like growth factors mediate the effect of alcohol on breast cancer risk?

Despite a large number of epidemiologic studies demonstrating an increased risk of breast cancer in association with alcohol consumption, a causal relationship between alcohol intake and breast cancer risk remains to be determined. Several biological mechanisms have been proposed, but none of them explains well the features of the association, i.e. a modest increase in risk, a limited range of dose-response relationship and no further increase in risk among heavy drinkers. A new mechanism underlying a possible biological role of alcohol in breast cancer is proposed in this paper. Moderate consumption of alcohol increases the production of insulin-like growth factors (IGFs) by the liver and elevated IGFs via circulation stimulate or promote the development and/or growth of breast cancer. The effect of alcohol on IGF production declines among heavy drinkers as alcohol-caused liver-function damage results in no further increase in IGF production. Therefore, compared to moderate drinkers, heavy alcohol users do not have a higher risk of breast cancer.

Cellular aspects of trophic actions in the nervous system

During the past three decades the number of molecules exhibiting trophic actions in the brain has increased drastically. These molecules promote and/or control proliferation, differentiation, migration, and survival (sometimes even the death) of their target cells. In this review a comprehensive overview of small diffusible factors showing trophic actions in the central nervous system (CNS) is given. The factors discussed are neurotrophins, epidermal growth factor, fibroblast growth factor, platelet-derived growth factor, insulin-like growth factors, ciliary neurotrophic factor and related molecules, glial-derived growth factor and related molecules, transforming growth factor-beta and related molecules, neurotransmitters, and hormones. All factors are discussed with respect to their trophic actions, their expression patterns in the brain, and molecular aspects of their receptors and intracellular signaling pathways. It becomes evident that there does not exist "the" trophic factor in the CNS but rather a multitude of them interacting with each other in a complicated network of trophic actions forming and maintaining the adult nervous system.

BCL-2 is upregulated in human SH-SY5Y neuroblastoma cells differentiated by overexpression of fibroblast growth factor 1

Fibroblast growth factor 1 (FGF1) is a multipotent factor in the development and differentiation of the central nervous system. Recent studies in PC12 cells attribute these effects to high endogenous FGF1 expression. To examine the differentiation mechanisms induced by FGF1, we performed studies in SH-SY5Y human neuroblastoma cells. We monitored the impact of FGF1 overexpression in SH-SY5Y either after addition of exogenous FGF1 and heparin or after stable transfection with the FGF1 eukaryotic expression vector. Under both conditions, the FGF1 endogenous rise caused SH-SY5Y cell differentiation with morphological changes (appearance of neuritic extensions), increased GAP-43 gene expression, decreased of N-myc gene expression, and prolonged long-term survival in serum-free media. These modifications were correlated with Bcl-2 upregulation. These results suggest that there is a link between the endogenous FGF1 signaling pathway and Bcl-2 in neuronal survival modulation.

Phosphatidylinositol 3′-Kinase, But Not S6-Kinase, Is Required for Insulin-Like Growth Factor-I and IL-4 To Maintain Expression of Bcl-2 and Promote Survival of Myeloid Progenitors

Phosphatidylinositol 3′-kinase (PI 3-kinase) catalyzes the formation of 3′ phosphoinositides and has been implicated in an intracellular signaling pathway that inhibits apoptosis in both neuronal and hemopoietic cells. Here, we investigated two potential downstream mediators of PI 3-kinase, the serine/threonine p70 S6-kinase (S6-kinase) and the antiapoptotic protein B cell lymphoma-2 (Bcl-2). Stimulation of factor-dependent cell progenitor (FDCP) cells with either IL-4 or insulin-like growth factor (IGF)-I induced a 10-fold increase in the activity of both PI 3-kinase and S6-kinase. Rapamycin blocked 90% of the S6-kinase activity but did not affect PI 3-kinase, whereas wortmannin and LY294002 inhibited the activity of both S6-kinase and PI 3-kinase. However, wortmannin and LY294002, but not rapamycin, blocked the ability of IL-4 and IGF-I to promote cell survival. We next established that IL-3, IL-4, and IGF-I increase expression of Bcl-2 by &gt;3-fold. Pretreatment with inhibitors of PI 3-kinase, but not rapamycin, abrogated expression of Bcl-2 caused by IL-4 and IGF-I, but not by IL-3. None of the cytokines affected expression of the proapoptotic protein Bax, suggesting that all three cytokines were specific for Bcl-2. These data establish that inhibition of PI 3-kinase, but not S6-kinase, blocks the ability of IL-4 and IGF-I to increase expression of Bcl-2 and protect promyeloid cells from apoptosis. The requirement for PI 3-kinase to maintain Bcl-2 expression depends upon the ligand that activates the cell survival pathway.

Akt-dependent potentiation of L channels by insulin-like growth factor-1 is required for neuronal survival

The insulin-like growth factor-1 (IGF-1)/receptor tyrosine kinase recently has been shown to mediate neuronal survival and potentiate the activity of specific calcium channel subtypes; survival requires Akt, a serine/threonine kinase. We demonstrate here that Akt mediates the IGF-1-induced potentiation of L channel currents, but not that of N channels. Transient expression of wild-type, dominant-negative, and constitutively active forms of Akt in cerebellar granule neurons causes, respectively, no change in IGF-1/L channel potentiation, complete inhibition of potentiation, and a dramatic increase in basal L currents accompanied by the loss of ability to induce further increases. In no case is the IGF-1 potentiation of N currents affected. We additionally find that IGF-1 partially mediates granule neuron survival via L channel activity and that Akt-dependent L channel modulation is a necessary component. Interestingly, very brief exposure (1 min) to IGF-1 triggers nearly complete survival and requires L channel activity. These results strongly suggest that neuronal receptor tyrosine kinases can control long-term calcium-dependent processes via the rapid control of voltage-sensitive channels.

A central role of Bcl-X(L) in the regulation of keratinocyte survival by autocrine EGFR ligands

The epidermal growth factor receptor has multiple roles in epidermal biology relating to growth, migration, and, as shown recently, survival of keratinocytes. In cultured keratinocytes activation of the epidermal growth factor receptor upregulates expression of Bcl-x(L), an anti-apoptotic Bcl-2 homolog. The functional contribution of epidermal growth factor receptor-dependent Bcl-x(L) expression to keratinocyte survival is poorly understood. Here we demonstrate that inhibition of the epidermal growth factor receptor tyrosine kinase activity with either an epidermal growth factor receptor antagonistic monoclonal antibody (MoAb 425) or an epidermal growth factor receptor-selective tyrosine kinase inhibitor (AG 1478) downregulated Bcl-x(L) expression in normal human keratinocytes but had no effect on expression of the pro-apoptotic Bcl-2 homologs Bad, Bak, and Bax. Bovine pituitary extract and insulin partially alleviated both, downregulation of Bcl-x(L) expression and cell death upon epidermal growth factor receptor inhibition. Forced expression of Bcl-x(L) attenuated cell death of immortalized keratinocytes (HaCaT) induced by either forced suspension (anoikis) or by epidermal growth factor receptor blockade. These results demonstrate that epidermal growth factor receptor-dependent signaling pathways control the balance of pro-apoptotic and anti-apoptotic Bcl-2 family members expressed in normal keratinocytes. Inappropriate survival supported by aberrant signaling through the epidermal growth factor receptor may contribute to the pathogenesis of psoriasis and of squamous cell carcinomas.

Anti-apoptotic signaling of the IGF-I receptor in fibroblasts following loss of matrix adhesion

The type 1 insulin-like growth factor receptor (IGF-IR) is known to protect cells from a variety of apoptotic injuries. In several instances, the anti-apoptotic effect of the wild type IGF-IR is more evident under conditions of anchorage-independence than in cells in monolayer cultures. We have investigated IGF-IR signaling in cells in anoikis, a form of apoptosis that occurs when cells are denied attachment to the extra-cellular matrix. IGF-I protects mouse embryo fibroblasts (MEF) from anoikis caused by withdrawal of growth factors. Survival is dependent on the concentration of IGF-I and a sufficient number of functional IGF-I receptors. In this model, IGF-I protection correlates best with ras activation and cell-to-cell aggregation, while PI3-kinase, Akt and MAP kinases seem to play a lesser, alternative role.

Insulin-like growth factor-1 (IGF-1) and growth hormone (GH) in immunity and inflammation

In recent years many efforts have been undertaken to elucidate the complex interactions between mediators of the endocrine system and the immune system. The main effector of growth hormone (GH) is insulin-like growth factor-1 (IGF-1), an endocrine mediator of growth and development under physiological conditions. Besides this important function, IGF-1 also plays a prominent role in the regulation of immunity and inflammation. This article will address the involvement of IGF-1 in innate as well as acquired immunity and host-defense. We also discuss the role of IGF-1 in the course of inflammatory disorders, including sepsis and sepsis-induced catabolism as well as degenerative arthritis. Based on recent insights, we finally examine the pathophysiological background, potential pitfalls and perspectives of IGF-1 suppletion therapy in these conditions.