Growth hormone-stimulated insulin-like growth factor-1 expression in rainbow trout (Oncorhynchus mykiss) hepatocytes is mediated by ERK, PI3K-AKT, and JAK-STAT

Growth hormone (GH) initiates many of its growth-promoting actions by binding to GH receptors (GHR) and stimulating the synthesis and secretion of insulin-like growth factor-1 (IGF-1) from the liver and other sites. In this study, we used hepatocytes isolated from rainbow trout as a model system in which to determine the molecular signaling events of GH in fish. GH directly stimulated the phosphorylation of ERK, protein kinase B (Akt), a downstream target of phosphatidylinositol 3-kinase (PI3K), JAK2, and STAT5 in hepatocytes incubated in vitro. Activation of ERK, Akt, JAK2, and STAT5 was rapid, occurring within 5-10 min, and was concentration dependent. GH-induced ERK activation was completely blocked by the ERK pathway inhibitor, U0126, and the JAK2 inhibitor, 1,2,3,4,5,6-hexabromocyclohexane (Hex), and was partially blocked by the PI3K inhibitor LY294002. GH-stimulated Akt activation was completely blocked by LY294002 and Hex, but was not affected by U0126; whereas, STAT5 activation by GH was blocked only by Hex, and was not affected by either U0126 or LY294002. GH stimulated hepatic expression of IGF-1 mRNA as well as the secretion of IGF-1, effects that were partially or completely blocked by U0126, LY294002, and Hex. These results indicate that GHR linkage to the ERK, PI3K/Akt, or STAT pathways in trout liver cells requires activation of JAK2, and that GH-stimulated IGF-1 synthesis and secretion is mediated through the ERK, PI3K/Akt, and JAK-STAT pathways.     

Stimulation of protein kinase C modulates insulin-like growth factor-1-induced akt activation in PC12 cells

Activation of protein kinase C (PKC) plays an important role in the negative regulation of receptor signaling, but its effect on insulin-like growth factor-1 (IGF-1) receptor signaling remains unclear. In this study, we characterized the intracellular pathways involved in IGF-1-induced activation of Akt and evaluated the effects of the PKC activator phorbol 12-myristate 13-acetate (PMA) on the Akt activation by IGF-1. IGF-1 induced a time- and concentration-dependent activation of Akt. The effect of IGF-1 was blocked by the phosphatidylinositide 3-kinase (PI3K) inhibitors LY294002 (50 micrometer) and wortmannin (0.5 micrometer), but not by the MEK inhibitor PD98059 (50 micrometer) or the p70 S6 kinase pathway inhibitor rapamycin (50 nm), suggesting that the stimulation of Akt by IGF-1 is mediated by the PI3K pathway. Interestingly, cotreatment with PMA (400 nm) attenuated IGF-1-induced activation of Akt. The attenuation was blocked completely by the PKC inhibitor GO6983 (0.5 micrometer), but only partially by the MEK inhibitor PD98059 (50 micrometer), indicating that MAPK-dependent and -independent pathways are involved. PMA induced the activation of PKC in PC12 cells, and this induction was blocked by GO6983. These data further support the role of PKC in the effect of PMA. Moreover, PKCdelta is likely involved in the action of PMA on the basis of data obtained using isoform-specific inhibitors such as rottlerin. PMA also decreased IGF-1-induced tyrosine phosphorylation of insulin receptor substrate-1 and its association with PI3K. Taken together, these results suggest, for the first time, that stimulation of PKC modulates IGF-1-induced activation of Akt.     

PKC-zeta is required for angiotensin II-induced activation of ERK and synthesis of C-FOS in MCF-7 cells

We examined the signalling pathways responsible for the Ang II induction of growth in MCF-7 human breast cancer cells. Ang II in MCF-7 cells induced: (a) the translocation from the cytosol to membrane and nucleus of atypical protein kinase C-zeta (PKC-zeta) but not of PKC-alpha, -delta, - epsilon and -eta; (b) the expression of c-fos mRNA and protein; (c) the phosphorylation of the extracellular signal-regulated protein kinases 1 and 2 (ERK1/2). All these effects were due to the activation of the Ang II type I receptor (AT1) since they were blocked by the AT1 antagonist losartan. The Ang II-stimulated ERK1/2 phosphorylation was blocked by (a) high doses of staurosporine, inhibitor of PKC-zeta, and by a synthetic myristoylated peptide with sequences based on the endogenous PKC-zeta pseudosubstrate region (zeta-PS); (b) PD098059, a mitogen-activated protein kinase kinase inhibitor (MAPKK/MEK); and, moreover, (c) the inhibitors of phosphoinositide 3-kinases (PI3K), LY294002 and wortmannin, thus indicating that PI3K may act upstream of ERK1/2. The Ang II-evoked c-fos induction was blocked only by high doses of staurosporine and by zeta-PS whilst PD098059, LY294002 and wortmannin were ineffective, thus indicating that c-fos induction is not due to ERK1/2 activity. When the epidermal growth factor-receptor (EGFR) tyrosine kinase activity was inhibited by the use of its inhibitor AG1478, Ang II was still able to induce ERK1/2 phosphorylation and c-fos expression, therefore proving that the transactivation of EGFR was not required for these Ang II effects in MCF-7 cells. The previously reported proliferation of MCF-7 cells induced by Ang II was blocked by PD098059 and by wortmannin in a dose-dependent manner, thereby indicating that in MCF-7 cells the PI3K and ERK pathways mediate the mitogenic signalling of AT1. Our results suggest that in MCF-7 cells Ang II activates multiple signalling pathways involving PKC-zeta, PI3K and MAPK; of these pathways only PKC-zeta appears responsible for the induction of c-fos.     

The cyclin-dependent kinase inhibitor p21CIP/WAF is a positive regulator of insulin-like growth factor I-induced cell proliferation in MCF-7 human breast cancer cells

To study the role of IGF-I receptor signaling on cell cycle events we utilized MCF-7 breast cancer cells. IGF-I at physiological concentrations increased the level of p21CIP/WAF mRNA after 4has well as protein after 8hby 10- and 6-fold, respectively, in MCF-7 cells. This IGF-1 effect was reduced by 50% in MCF-7-derived cells (SX13), which exhibit a 50% reduction in IGF-1R expression, demonstrating that IGF-1 receptor activation was involved in this process. Preincubation with the ERK1/2 inhibitor U0126 significantly reduced the IGF-1 effect on the amount of p21CIP/WAF protein in MCF-7 cells. These results were confirmed by the expression of a dominant negative construct for MEK-1 suggesting that the increase of the abundance of p21CIP/WAF in response to IGF-1 occurs via the ERK1/2 mitogen-activated protein kinase pathway. Using an antisense strategy, we demonstrated that abolition of p21CIP/WAF expression decreased by 2-fold the IGF-1 effect on cell proliferation in MCF-7. This latter result is explained by a delay in G1 to S cell cycle progression due partly to a reduction in the activation of some components of cell cycle including the induction of cyclin D1 expression in response to IGF-1. MCF-7 cells transiently overexpressing p21 showed increased basal and IGF-I-induced thymidine incorporation. Taken together, these results define p21CIP/WAF as a positive regulator in the cell proliferation induced by IGF-1 in MCF-7 cells.     

IGF-1-induced epithelial–mesenchymal transition in MCF-7 cells is mediated by MUC1

Metastases are the major cause of death from cancer. IGF-1 signaling pathway has been shown to have strong implication in the epithelial–mesenchymal transition (EMT) process. However, the mechanisms of how IGF-1 promotes EMT have not been fully elucidated. Mucin 1 (MUC1), a transmembrane glycoprotein, engages in multiple cancer-related signaling pathways and functions as an oncoprotein that contributes to metastases. Here we provide evidence showing that IGF-1 upregulates MUC1 expression in MCF-7 cells in a PI3K/Akt signaling pathway-dependent manner. The overexpression of MUC1 is critical for IGF-1-induced EMT of MCF-7 cells because the knockdown of MUC1 prevented the EMT of MCF-7 cells as demonstrated by various EMT markers including the expression of E-cadherin, N-cadherin, vimentin, fibronectin and the nuclear translocalization of β-catenin. On the other hand, the knockdown of MUC1 had no impact on IGF-1-induced activation of PI3K/Akt or MAPK. In summary, our study demonstrated MUC1 as a critical downstream effector that mediates IGF-1-induced EMT of MCF-7 cells and suggested that MUC1 might be a potential therapeutic target for preventing tumor metastases.     

Activation of Akt Kinase Inhibits Apoptosis and Changes in Bcl-2 and Bax Expression Induced by Nitric Oxide in Primary Hippocampal Neurons

Emerging data indicate that growth factors such as insulin-like growth factor-1 (IGF-1) prevent neuronal death due to nitric oxide (NO) toxicity. On the other hand, growth factors can promote cell survival by acting on phosphatidylinositol 3-kinase (PI3-kinase) and its downstream target, serine-threonine kinase Akt, in various types of cells. Here, we examined the mechanism by which IGF-1 inhibits neuronal apoptosis induced by NO in primary hippocampal neurons. IGF-1 was capable of preventing apoptosis and caspase-3-like activation induced by a NO donor, sodium nitroprusside or 3-morpholin-osydnonimine. Incubation of neurons with a P13-kinase inhibitor, wortmannin or LY294002, blocked the effects of IGF-1 on NO-induced neurotoxicity and caspase-3-like activation. In addition, the P13-kinase inhibitors blocked the effect of IGF-1 on down-regulation in Bcl-2 and upregulation in Bax expression induced by NO. Adenovirus-mediated overexpression of the activated form of Akt significantly inhibited NO-induced cell death, caspase-3-like activation, and changes in Bcl-2 and Bax expression. Moreover, expression of the kinase-defective form of Akt almost completely blocked the effects of IGF-1. These findings suggest that activation of Akt is necessary and sufficient for the effect of IGF-1 and is capable of preventing NO-induced apoptosis by modulating the NO-induced changes in Bcl-2 and Bax expression.     

IGF-1 activates hEAG K(+) channels through an Akt-dependent signaling pathway in breast cancer cells: role in cell proliferation

Previous work from our laboratory has shown that human ether à go-go (hEAG) K(+) channels are crucial for breast cancer cell proliferation and cell cycle progression. In this study, we investigated the regulation of hEAG channels by an insulin-like growth factor-1 (IGF-1), which is known to stimulate cell proliferation. Acute applications of IGF-1 increased K(+) current-density and hyperpolarized MCF-7 cells. The effects of IGF-1 were inhibited by hEAG inhibitors. Moreover, IGF-1 increased mRNA expression of hEAG in a time-dependent manner in parallel with an enhancement of cell proliferation. The MCF-7 cell proliferation induced by IGF-1 is inhibited pharmacologically by Astemizole or Quinidine or more specifically using siRNA against hEAG channel. Either mitogen-activated protein kinase (MAPK) or phosphatidylinositol 3-kinase (PI3K) are known to mediate IGF-1 cell proliferative signals through the activation of extracellular signal-regulated kinase 1/2 (Erk 1/2) and Akt, respectively. In MCF-7 cells, IGF-1 rapidly stimulated Akt phosphorylation, whereas IGF-1 had little stimulating effect on Erk 1/2 which seems to be constitutively activated. The application of wortmannin was found to block the effects of IGF-1 on K(+) current. Moreover, the inhibition of Akt phosphorylation by the application of wortmannin or by a specific reduction of Akt kinase activity reduced the hEAG mRNA levels. Taken together, our results show, for the first time, that IGF-1 increases both the activity and the expression of hEAG channels through an Akt-dependent pathway. Since a hEAG channel is necessary for cell proliferation, its regulation by IGF-1 may thus play an important role in IGF-1 signaling to promote a mitogenic effect in breast cancer cells.     

Effects of insulin and insulin-like growth factor 1 on osteoblast proliferation and differentiation: differential signalling via Akt and ERK

Insulin and insulin-like growth factor 1 (IGF-1) are evolutionarily conserved hormonal signalling molecules, which influence a wide array of physiological functions including metabolism, growth and development. Using genetic mouse studies, both insulin and IGF-1 have been shown to be anabolic agents in osteoblasts and bone development primarily through the activation of Akt and ERK signalling pathways. In this study, we examined the temporal signalling actions of insulin and IGF-1 on primary calvarial osteoblast growth and differentiation. First, we observed that the IGF-1 receptor expression decreases whereas insulin receptor expression increases during osteoblast differentiation. Subsequently, we show that although both insulin and IGF-1 promote osteoblast differentiation and mineralization in vitro, IGF-1, but not insulin, can induce osteoblast proliferation. The IGF-1-induced osteoblast proliferation was mediated via both MAPK and Akt pathways because the IGF-1-mediated cell proliferation was blocked by U0126, an MEK/MAPK inhibitor, or LY294002, a PI3-kinase inhibitor. Osteocalcin, an osteoblast-specific protein whose expression corresponds with osteoblast differentiation, was increased in a dose- and time-dependent manner after insulin treatment, whereas it was decreased with IGF-1 treatment. Moreover, insulin treatment dramatically induced osteocalcin promoter activity, whereas IGF-1 treatment significantly inhibited it, indicating direct effect of insulin on osteocalcin synthesis.     

Adaptive hypersensitivity following long-term estrogen deprivation: involvement of multiple signal pathways

Long-term estrogen deprivation causes hypersensitivity of MCF-7 cells to the mitogenic effect of estradiol (E₂) which is associated with activation of mitogen-activated protein kinase (MAPK). However, several lines of evidence indicate that MAPK activation is not the exclusive mechanism for E₂ hypersensitivity and multiple signal pathways might be involved. The current study explores the possible role of the PI3 kinase (PI3K) pathway in development of E₂ hypersensitivity. Basal PI3K activity in long-term estrogen deprived MCF-7 cells (LTED) was elevated as evidenced by increased phosphorylation of three downstream effectors, Akt, p70 S6 kinase, and eukaryotic initiation factor-4E binding protein (4E-BP1), which was blocked by the specific inhibitor of PI3K, LY294002. Dual blockade of both MAPK and PI3K completely reversed E₂ hypersensitivity of LTED cells. Enhancement in aromatase activity is another phenomenon accompanied with E₂ hypersensitivity. In aromatase over-expressing MCF-7 cells, aromatase activity was reduced by inhibitors of MAPK and PI3K suggesting the involvement of protein phosphorylation in the regulation of aromatase activity. Our data suggest that in addition to the MAP kinase pathway, activation of the PI3 kinase pathway is involved in E₂ hypersensitivity, which develops during adaptation of MCF-7 cells to the low estrogen environment.     

Insulin-like growth factor-1 protects H9c2 cardiac myoblasts from oxidative stress-induced apoptosis via phosphatidylinositol 3-kinase and extracellular signal-regulated kinase pathways

Oxidative stress plays a critical role in cardiac injuries during ischemia/reperfusion. Insulin-like growth factor-1 (IGF-1) promotes cell survival in a number of cell types, but the effect of IGF-1 on the oxidative stress has not been elucidated in cardiac muscle cells. Therefore, we examined the role of IGF-1 signaling pathway in cell survival against H2O2-induced apoptosis in H9c2 cardiac myoblasts. H2O2 treatment induced apoptosis in H9c2 cells, and pretreatment of cells with IGF-1 suppressed apoptotic cell death. The antiapoptotic effect of IGF-1 was blocked by LY294002 (an inhibitor of phosphatidylinositol 3-kinase) and by PD98059 (an inhibitor of extracellular signal-regulated kinase (ERK)). The protective effect of IGF-1 was also blocked by rapamycin (an inhibitor of p70 S6 kinase). Furthermore, H9c2 cells stably transfected with constitutively active PI 3-kinase (H9c2-p110*) and Akt (H9c2-Gag-Akt) constructs were more resistant to H2O2 cytotoxicity than control cells. Although H2O2 activates both p38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK), IGF-1 inhibited only JNK activation. Activated PI 3-kinase (H9c2-p110*) and pretreatment of cells with IGF-1 down-regulated Bax protein levels compared to control cells. Taken together, our results suggest that IGF-1 transmits a survival signal against oxidative stress-induced apoptosis in H9c2 cells via PI 3-kinase and ERK-dependent pathways and the protective effect of IGF-1 is associated with the inhibition of JNK activation and Bax expression.     

Estradiol rapidly activates Akt via the ErbB2 signaling pathway

Previously, we have demonstrated that the two mitogenic growth factors epidermal growth factor and IGF-I can activate Akt and estrogen receptor-alpha (ERalpha) in the hormone-dependent breast cancer cell line, MCF-7. In this report we now show that estradiol can also rapidly activate phosphatidylinositol 3-kinase (PI 3-K)/Akt and that this effect is mediated by the ErbB2 signaling pathway. Treatment of cells with estradiol resulted in phosphorylation of Akt and a 9-fold increase in Akt activity in 10 min. Akt activation was blocked by wortmannin and LY 294,002, two inhibitors of PI 3-K; by genistein, a protein tyrosine kinase inhibitor and an ER agonist; by AG825, a selective ErbB2 inhibitor; and by the antiestrogens ICI 182,780 and 4-hydroxy-tamoxifen; but not by rapamycin, an inhibitor of the ribosomal protein kinase p70S6K; nor by AG30, a selective epidermal growth factor receptor inhibitor. Akt activation by estradiol was abrogated by an arginine-to-cysteine mutation in the pleckstrin homology domain of Akt (R25C). Growth factors also activated Akt in the ER-negative variant of MCF-7, MCF-7/ADR, but estradiol did not induce Akt activity in these cells. Transient transfection of ERalpha into these cells restored Akt activation by estradiol, suggesting that estradiol activation of Akt requires the ERalpha. Estradiol did not activate Akt in MCF-7 cells stably transfected with an anti-ErbB2-targeted ribozyme, further confirming a role for ErbB2. In vitro kinase assays using immunoprecipitation and anti-Akt1, -Akt2, and -Akt3-specific antibodies demonstrated that Akt1 is activated by estradiol in MCF-7 cells whereas Akt3 is the activated isoform in ER-negative MDA-MB231 cells, implying that selective activation of Akt subtypes plays a role in the actions of estradiol. Taken together, our data suggest that estradiol, bound to membrane ERalpha, interacts with and activates an ErbB dimer containing ErbB2, inducing activation of PI 3-K/Akt.     

Pituitary tumor transforming gene: an important gene in normal cellular functions and tumorigenesis

Pituitary tumor transforming gene (PTTG) is an oncogene which is found to be highly expressed in proliferating cells and in most of the tumors analyzed to date. Overexpression of PTTG induces cellular transformation and promotes tumor development in nude mice. PTTG is regulated by various growth factors including insulin and IGF-1. PTTG is a multifunctional and multidomain protein. Some of the functions of PTTG include inhibition of separation of sister chromatids, expression and secretion of angiogenic and metastatic factors. In this review we focus on expression of PTTG in normal and tumor tissues, define its biological function, its role in tumorigenesis, and its interaction with other proteins that may play important role in mediating tumorigenic function of PTTG.     

Multiple pathways are involved in protection of MCF-7 cells against death due to protein synthesis inhibition

Previously we have shown that IGF-1 protected MCF-7 cells against death induced by the protein synthesis inhibitor cycloheximide (CHX). In the present study we investigated the ability of protein kinase C activator 12-0-tetradecanoyl-phorbol-13-acetate (TPA), the protein kinase A activator 8-bromoadenosine 3′5′-cyclic monophosphate (Br-cAMP), and the enzyme inhibitor aurintricarboxylic acid (ATA) to protect MCF-7 cells against death, due to a continuous presence of CHX. Cell death was evaluated after 48 h of incubation by several techniques (trypan blue staining, release of lactic dehydrogenase, cellular ATP content, transmission electron microscopy, and DNA fragmentation). Apoptosis which terminates in necrosis, characterized this mode of cell death. TPA and ATA at optimal concentrations of 40 ng/ml and 100 μg/ml, respectively, reduced cell death to the control level (without CHX), while Br-cAMP at an optimal concentration of 650 μg/ml reduced cell death only partially. IGF-1, TPA, and ATA, which stimulated protein synthesis in the control MCF-7 cells, had no effect on protein synthesis in the CHX-treated cells, indicating that the survival effect is not due to new protein synthesis. The protein kinase C inhibitor staurosporine blocked the survival effect of TPA and IGF-1 in a dose-dependent manner, however did not affect the survival effect of ATA. The tyrosine kinase inhibitor genistein blocked the survival effect of IGF-1, but not that of TPA and ATA. Our results provide evidence for several distinctive pathways, the activation of which protects MCF-7 cells against death, due to protein synthesis inhibition. © 1995 Wiley-Liss, Inc.     

IGF-1 Regulates Cyr61 Induced Breast Cancer Cell Proliferation and Invasion

Background

Studies from our laboratory and others have shown that cysteine-rich 61 (Cyr61) may be involved in tumor proliferation and invasion. In earlier studies, we demonstrated increased insulin-like growth factor-I (IGF-1) is associated with breast tumor formation and poor clinical outcomes. In our current study we have investigated IGF-1 regulation of Cyr61 and whether targeting IGF-1 could inhibit Cyr61 induced tumor growth and proliferation.

Methods

Several ATCC derived normal and breast cancer cell lines were used in this study: MDA-MB231, BT474, MCF-7, and SKBR3. We also tested cells stably transfected in our laboratory with active Akt1 (pAkt; SKBR3/AA and MCF-7/AA) and dominant negative Akt1 (SKBR3/DN and MCF-7/DN). In addition, we used MCF-7 cells transfected with full length Cyr61 (CYA). Monolayer cultures treated with IGF-1 were analyzed for Cyr61 expression by RT-PCR and immunohistochemical staining. Migration assays and MTT based proliferation assays were used to determine invasive characteristics in response to IGF-1/Cyr61 activation.

Results

Cells with activated Akt have increased levels of Cyr61. Conversely, cells with inactive Akt have decreased levels of Cyr61. IGF-1 treatment increased Cyr61 expression significantly and cells with high level of Cyr61 demonstrate increased invasiveness and proliferation. Cyr61 overexpression and activation led to decrease in E-cadherin and decrease in FOXO1. Inhibition of the PI3K and MAPK pathways resulted in significant decrease in invasiveness and proliferation, most notably in the PI3K pathway inhibited cells.

Conclusion

The findings of this study show that IGF-1 upregulates Cyr61 primarily through activation of the Akt-PI3K pathway. IGF-1 induced MAPK plays a partial role. Increase in Cyr61 leads to increase in breast cancer cell growth and invasion. Hence, targeting Cyr61 and associated pathways may offer an opportunity to inhibit IGF-1 mediated Cyr61 induced breast cancer growth and invasion.     

Insulin induces expression of adenosine kinase gene in rat lymphocytes by signaling through the mitogen-activated protein kinase pathway

The activity of adenosine kinase (AK) was significantly impaired in splenocytes isolated from diabetic rats. Administration of insulin to diabetic animals restored AK activity, protein, and mRNA levels in diabetic splenocytes. Experiments performed on cultured rat lymphocytes demonstrated that insulin did not change the stability of AK mRNA. Insulin induced AK gene expression in a dose- and time-dependent manner. Maximal increases in AK mRNA (3.9-fold) and activity level (3.7-fold) were observed at the fourth and fifth hours of cell incubation with 10 nM insulin, respectively. The insulin effect on AK expression was not influenced by dibutyryl cAMP (dcAMP). On the other hand dcAMP weakly increased (1.7-fold) basal expression of AK. Exposure of rat lymphocytes to wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K), or rapamycin, an inhibitor of mTOR, did not affect the ability of insulin to stimulate expression of AK. Prior treatment of the cells with 10 microM PD98059, an inhibitor of mitogen-activated protein kinase (MAPK) kinase (MEK) completely blocked insulin-stimulated expression of AK gene. Insulin produced a significant transient increase in the tyrosine phosphorylation of ERK1/2, and PD98059 inhibited this phosphorylation. Furthermore exposure of cells to insulin has resulted in transient phosphorylation of Elk-1 on Ser-383 and sustained elevation of c-Jun and c-Fos protein. The maximal phosphorylation of Elk-1 was observed at 15 min, and was blocked by PD98059. We concluded that insulin stimulates AK gene expression through a series of events occurring sequentially. This includes activation of the MAPK cascade and subsequent phosphorylation of Elk-1 followed by increased expression of c-fos and c-jun genes.     

IGF-1-Mediated Survival from Induced Death of Human Primary Cultured Retinal Pigment Epithelial Cells Is Mediated by an Akt-Dependent Signaling Pathway

Degeneration of the human retinal pigmented epithelium (hRPE) is involved in several eye disorders such as age-related macular degeneration (AMD). In this study, we investigated the protective effect of IGF-1 on human primary cultured RPE cells and its underlying mechanism. IGF-1 dose- and time-dependently promoted the survival of RPE cells from serum deprivation. Western blot showed that IGF-1 stimulated the activation of the PI3K/Akt and MAPK pathways in hRPE. Inhibition of the PI3K/Akt pathway by the PI3K-specific inhibitor, LY294002 or inhibition of Akt by Akt-specific inhibitors Akt inhibitor VIII or SN-38, or downregulation Akt with siRNA specific for Akt blocked the effect of IGF-1 on hRPE. In contrast, blockade of the MAPK pathway with a specific inhibitor PD98059 had no effect. Interestingly, vitreous IGF-1 injection reversed the inhibitory effect of light exposure (a dry AMD model) on both a wave and b wave. Immunocytochemistry showed that vitreous IGF-1 injections promoted the survival of RPE cells in rat retina and the expression of RPE65 in RPE cells from light injury. These results indicate that IGF-1 is able to protect hRPE cell from different insults in vivo and in vitro. Further detailed studies may lead the way to a therapeutic intervention for retinal diseases in which cell death is an underlying contributory mechanism.