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

Anoikis resistance in diffuse glioma: The potential therapeutic targets in the future

Glioma is the most common malignant intracranial tumor and exhibits diffuse metastasis and a high recurrence rate. The invasive property of glioma results from cell detachment. Anoikis is a special form of apoptosis that is activated upon cell detachment. Resistance to anoikis has proven to be a protumor factor. Therefore, it is suggested that anoikis resistance commonly occurs in glioma and promotes diffuse invasion. Several factors, such as integrin, E-cadherin, EGFR, IGFR, Trk, TGF-β, the Hippo pathway, NF-κB, eEF-2 kinase, MOB2, hypoxia, acidosis, ROS, Hsp and protective autophagy, have been shown to induce anoikis resistance in glioma. In our present review, we aim to summarize the underlying mechanism of resistance and the therapeutic potential of these molecules.

Obesity and inflammation: colorectal cancer engines

The prevalence of obesity continues to increase to the extent that it became a worldwide pandemic. An accumulating body of evidence has associated obesity with the development of different types of cancer, including colorectal cancer, which is a notorious disease with a high mortality rate. At the molecular level, colorectal cancer is a heterogenous disease characterized by a myriad of genetic and epigenetic alterations associated with various forms of genomic instability (detailed in Supplementary Materials). Recently, the microenvironment has emerged as a major factor in carcinogenesis. Our aim is to define the different molecular alterations leading to the development of colorectal cancer in obese patients with a focus on the role of the microenvironment in carcinogenesis. We also highlight all existent molecules in clinical trials that target the activated pathways in obesity-associated colorectal cancer, whether used as single treatments or in combination. Obesity predisposes to colorectal cancer via creating a state of chronic inflammation with dysregulated adipokines, inflammatory mediators, and other factors such as immune cell infiltration. A unifying theme in obesity-mediated colorectal cancer is the activation of the PI3K/AKT, mTOR/MAPK, and STAT3 signaling pathways. Different inhibitory molecules towards these pathways exist, increasing the therapeutic choice of obesity-associated colon cancer. However, obese patients are more likely to suffer from chemotherapy overdosing. Preventing obesity through maintaining a healthy and active lifestyle remains to be the best remedy.

IPF pathogenesis is dependent upon TGFβ induction of IGF-1

Pathogenic fibrotic diseases, including idiopathic pulmonary fibrosis (IPF), have some of the worst prognoses and affect millions of people worldwide. With unclear etiology and minimally effective therapies, two-thirds of IPF patients die within 2-5 years from this progressive interstitial lung disease. Transforming Growth Factor Beta (TGFβ) and insulin-like growth factor-1 (IGF-1) are known to promote fibrosis; however, myofibroblast specific upregulation of IGF-1 in the initiation and progression of TGFβ-induced fibrogenesis and IPF have remained unexplored. To address this, the current study (1) documents the upregulation of IGF-1 via TGFβ in myofibroblasts and fibrotic lung tissue, as well as its correlation with decreased pulmonary function in advanced IPF; (2) identifies IGF-1's C1 promoter as mediating the increase in IGF-1 transcription by TGFβ in pulmonary fibroblasts; (3) determines that SMAD2 and mTOR signaling are required for TGFβ-dependent Igf-1 expression in myofibroblasts; (4) demonstrates IGF-1R activation is essential to support TGFβ-driven profibrotic myofibroblast functions and excessive wound healing; and (5) establishes the effectiveness of slowing the progression of murine lung fibrosis with the IGF-1R inhibitor OSI-906. These findings expand our knowledge of IGF-1's role as a novel fibrotic-switch, bringing us one step closer to understanding the complex biological mechanisms responsible for fibrotic diseases and developing effective therapies.

Establishment and Characterization of Two Novel Cholangiocarcinoma Cell Lines

Background

Cholangiocarcinoma (CCA) is a rare, aggressive and highly lethal tumor. The disease is very difficult to diagnose and multi-modality treatments are ineffective. To improve our understanding of the biological characteristics of CCA, and facilitate the identification of valid treatments, an in-depth characterization of two novel Chinese patient-derived primary CCA cell lines was performed.

Methods

Two CCA cell lines were developed and labelled ZJU-0826 and -1125. The two cell lines were characterized with respect to phenotypic, molecular, biomarker, functional and histological properties.

Results

Two novel cell lines were cultured for 2 years, and maintained for more than 100 passages. They retained their typical biliary epithelial morphology and ultrastructure. The population doubling times of ZJU-0826, and -1125 were 63.84 h and 44.73 h, respectively. The cells exhibited near-triploid karyotypes with complex structural aberrations. ZJU-1125 cells had mutations in TP53 exons. Short tandem repeats genotyping confirmed the human origin and difference between lines. An immunophenotype analysis showed that ZJU-0826 is positive for CD44, CD29, Pdx1, CD236, FoxA1, FoxA2, and Nanog, and ZJU-1125 positive for CD44, CD29, CD133, Pdx1, FoxA1, FoxA2, and Nanog. ZJU-1125 had greater invasion ability in vitro and tumorigenicity than those of ZJU-0826.

Conclusions

Our results confirm the validity of the ZJU-0826 and -1125 as representative models for the elucidation of the molecular pathogenesis of perihilar CCA, and intrahepatic CCA in both in vitro and in vivo studies, respectively.

Electronic supplementary material

The online version of this article (10.1245/s10434-019-07649-5) contains supplementary material, which is available to authorized users.

Insulin-Like Growth Factor-1 Signaling in Lung Development and Inflammatory Lung Diseases

Insulin-like growth factor-1 (IGF-1) was firstly identified as a hormone that mediates the biological effects of growth hormone. Accumulating data have indicated the role of IGF-1 signaling pathway in lung development and diseases such as congenital disorders, cancers, inflammation, and fibrosis. IGF-1 signaling modulates the development and differentiation of many types of lung cells, including airway basal cells, club cells, alveolar epithelial cells, and fibroblasts. IGF-1 signaling deficiency results in alveolar hyperplasia in humans and disrupted lung architecture in animal models. The components of IGF-1 signaling pathways are potentiated as biomarkers as they are dysregulated locally or systemically in lung diseases, whereas data may be inconsistent or even paradoxical among different studies. The usage of IGF-1-based therapeutic agents urges for more researches in developmental disorders and inflammatory lung diseases, as the majority of current data are collected from limited number of animal experiments and are generally less exuberant than those in lung cancer. Elucidation of these questions by further bench-to-bedside researches may provide us with rational clinical diagnostic approaches and agents concerning IGF-1 signaling in lung diseases.

IGF-1R inhibition induces schedule-dependent sensitization of human melanoma to temozolomide

Prior studies implicate type 1 IGF receptor (IGF-1R) in mediating chemo-resistance. Here, we investigated whether IGF-1R influences response to temozolomide (TMZ), which generates DNA adducts that are removed by O6-methylguanine-DNA methyltransferase (MGMT), or persist causing replication-associated double-strand breaks (DSBs). Initial assessment in 10 melanoma cell lines revealed that TMZ resistance correlated with MGMT expression (r = 0.79, p = 0.009), and in MGMT-proficient cell lines, with phospho-IGF-1R (r = 0.81, p = 0.038), suggesting that TMZ resistance associates with IGF-1R activation. Next, effects of IGF-1R inhibitors (IGF-1Ri) AZ3801 and linsitinib (OSI-906) were tested on TMZ-sensitivity, cell cycle progression and DSB induction. IGF-1Ri sensitized BRAF wild-type and mutant melanoma cells to TMZ in vitro, an effect that was independent of MGMT. Cells harboring wild-type p53 were more sensitive to IGF-1Ri, and showed schedule-dependent chemo-sensitization that was most effective when IGF-1Ri followed TMZ. This sequence sensitized to clinically-achievable TMZ concentrations and enhanced TMZ-induced apoptosis. Simultaneous or prior IGF-1Ri caused less effective chemo-sensitization, associated with increased G1 population and reduced accumulation of TMZ-induced DSBs. Clinically relevant sequential (TMZ → IGF-1Ri) treatment was tested in mice bearing A375M (V600E BRAF, wild-type p53) melanoma xenografts, achieving peak plasma/tumor IGF-1Ri levels comparable to clinical Cmax, and inducing extensive intratumoral apoptosis. TMZ or IGF-1Ri caused minor inhibition of tumor growth (gradient reduction 13%, 25% respectively), while combination treatment caused supra-additive growth delay (72%) that was significantly different from control (p < 0.01), TMZ (p < 0.01) and IGF-1Ri (p < 0.05) groups. These data highlight the importance of scheduling when combining IGF-1Ri and other targeted agents with drugs that induce replication-associated DNA damage.

Energy metabolism during anchorage-independence. Induction by osteopontin-c

The detachment of epithelial cells, but not cancer cells, causes anoikis due to reduced energy production. Invasive tumor cells generate three splice variants of the metastasis gene osteopontin, the shortest of which (osteopontin-c) supports anchorage-independence. Osteopontin-c signaling upregulates three interdependent pathways of the energy metabolism. Glutathione, glutamine and glutamate support the hexose monophosphate shunt and glycolysis and can feed into the tricarboxylic acid cycle, leading to mitochondrial ATP production. Activation of the glycerol phosphate shuttle also supports the mitochondrial respiratory chain. Drawing substrates from glutamine and glycolysis, the elevated creatine may be synthesized from serine via glycine and supports the energy metabolism by increasing the formation of ATP. Metabolic probing with N-acetyl-L-cysteine, L-glutamate, or glycerol identified differential regulation of the pathway components, with mitochondrial activity being redox dependent and the creatine pathway depending on glutamine. The multiple skewed components in the cellular metabolism synergize in a flow toward two mechanisms of ATP generation, via creatine and the respiratory chain. It is consistent with a stimulation of the energy metabolism that supports anti-anoikis. Our findings imply a coalescence in cancer cells between osteopontin-a, which increases the cellular glucose levels, and osteopontin-c, which utilizes this glucose to generate energy.

Osteopontin-a alters glucose homeostasis in anchorage-independent breast cancer cells

Invasive breast tumor cells generate three splice variants of the metastasis gene osteopontin, while non-invasive breast cells express only the unspliced form or no osteopontin at all. One role for osteopontin in tumor progression is the support of anchorage-independence. Here we show that the full-length gene product, osteopontin-a, induces a gene expression profile that is associated with tissue remodeling and directed movement/sprouting. This occurs via signals through STAT1 and STAT3 to sn-glycero-3-phosphocholine. Osteopontin-a upregulates the levels of glucose in breast cancer cells, likely through STAT3 and its transcriptional targets apolipoprotein D and IGFBP5. The splice variants osteopontin-a and osteopontin-c may synergize, with each form activating signal transduction pathways that are distinct from the other. The elevated glucose is used by osteopontin-c dependent signals to generate chemical energy (Shi et al. submitted for publication). The splice variant-specific metabolic effects of osteopontin add a novel aspect to the pro-metastatic functions of this molecule.

miR-223 functions as a potent tumor suppressor of the Lewis lung carcinoma cell line by targeting insulin-like growth factor-1 receptor and cyclin-dependent kinase 2

microRNAs (miRNAs) have been hypothesized to function as oncogenes or tumor suppressors by targeting specific cancer-related genes. Previous studies have reported that miR-223 may serve as a tumor suppressor in a number of cancer types, however, knowledge of its targets in non-small cell lung cancer (NSCLC) remains limited. In the current study, miR-223 was found to inhibit cell proliferation in vitro by CCK-8 assay, growth curves and an anchorage-independent growth assay in a Lewis lung carcinoma (LLC) cell line. miR-223 transfection in the LLC cells was observed to significantly inhibit migration and invasion, induce G₂/M arrest and decrease the expression levels of Sca-1, a marker of murine stem cells. In addition, miR-223 transfection markedly suppressed AKT and ERK signaling, as well as insulin-like growth factor-1 receptor (IGF-1R)-mediated downstream signaling, pathways that are crucial for cell proliferation and invasion in NSCLC cells. Analyses in C57BL/6 mice demonstrated that miR-223 suppresses tumorigenicity in vivo. Using a luciferase activity assay and western blot analysis, IGF-1R and cyclin-dependent kinase 2 (CDK2) were identified as direct targets of miR-223. In the present study, novel cancer-related targets of miR-223 were identified and verified in a LLC cell line, indicating that miR-223 functions as a tumor suppressor, which may fine-tune the activity of the IGF-1R pathway in lung cancer. Therefore, increasing miR-223 expression may provide a novel approach for the treatment of NSCLC.

Exosomes from triple-negative breast cancer cells can transfer phenotypic traits representing their cells of origin to secondary cells

BACKGROUND

Triple-negative breast cancer (TNBC) accounts for 15-20% of breast cancers but is responsible for a disproportionate number of deaths. We investigated the relevance, in TNBC, of nano-sized exosomes expelled from cells. Specifically, we compared effects of exosomes derived from the claudin-low TNBC cell line Hs578T and its more invasive Hs578Ts(i)8 variant, as well as exosomes from TNBC patient sera compared to normal sera.

METHODS

Exosomes were isolated from conditioned media (CM) of Hs578T and Hs578Ts(i)8 cells and from sera by filtration and ultracentrifugation. Successful isolation was confirmed by transmission electron microscopy and immunoblotting. Subsequent analysis, of secondary/recipient cells in response to exosomes, included proliferation; motility/migration; invasion; anoikis assays and endothelial tubule formation assays.

RESULTS

Hs578Ts(i)8-exosomes versus Hs578T-exosomes significantly increased the proliferation, migration and invasion capacity of all three recipient cell lines evaluated i.e. SKBR3, MDA-MB-231 and HCC1954. Exosomes from Hs578Ts(i)8 cells also conferred increased invasiveness to parent Hs578T cells. Hs578Ts(i)8-exosomes increased sensitivity of SKBR3, MDA-MB-231 and HCC1954 to anoikis when compared to the effects of Hs578T-exosomes reflecting the fact that Hs578Ts(i)8 cells are themselves innately more sensitive to anoikis. In relation to vasculogenesis and subsequent angiogenesis, Hs578Ts(i)8-exosomes versus Hs578T-exosomes stimulated significantly more endothelial tubules formation. Finally, our pilot translational study showed that exosomes from TNBC patients' sera significantly increased recipient cells' invasion when compared to those derived from age- and gender-matched healthy control sera.

CONCLUSION

This study supports the hypothesis that TNBC exosomes may be involved in cancer cell-to-cell communication, conferring phenotypic traits to secondary cells that reflect those of their cells of origin.

Disruption of the protein interaction between FAK and IGF-1R inhibits melanoma tumor growth

FAK (focal adhesion kinase) and IGF-1R (insulin-like growth factor receptor-1) directly interact with each other and thereby activate crucial signaling pathways that benefit cancer cells. Inhibition of FAK and IGF-1R function has been shown to significantly decrease cancer cell proliferation and increase sensitivity to chemotherapy and radiation treatment. As a novel approach in human melanoma, we evaluated the effect of a small-molecule compound that disrupts the protein interaction of FAK and IGF-1R. Previously, using virtual screening and functional testing, we identified a lead compound (INT2-31) that targets the known FAK-IGF-1R protein interaction site. We studied the ability of this compound to disrupt FAK-IGF-1R protein interactions, inhibit downstream signaling, decrease human melanoma cell proliferation, alter cell cycle progression, induce apoptosis and decrease tumor growth in vivo. INT2-31 blocked the interaction of FAK and IGF-1R in vitro and in vivo in melanoma cells and tumor xenografts through precluding the activation of IRS-1, leading to reduced phosphorylation of AKT upon IGF-1 stimulation. As a result, INT2-31 significantly inhibited cell proliferation and viability (range 0.05-10 μM). More importantly, 15 mg/kg of INT2-31 given for 21 d via intraperitoneal injection disrupted the interaction of FAK and IGF-1R and effectively decreased phosphorylation of tumor AKT, resulting in significant melanoma tumor regression in vivo. Our data suggest that the FAK-IGF-1R protein interaction is an important target, and disruption of this interaction with a novel small molecule (INT2-31) has potential anti-neoplastic therapeutic effects in human melanoma.

Anoikis resistance: an essential prerequisite for tumor metastasis

Metastasis is a multistep process including dissociation of cancer cells from primary sites, survival in the vascular system, and proliferation in distant target organs. As a barrier to metastasis, cells normally undergo an apoptotic process known as “anoikis,” a form of cell death due to loss of contact with the extracellular matrix or neighboring cells. Cancer cells acquire anoikis resistance to survive after detachment from the primary sites and travel through the circulatory and lymphatic systems to disseminate throughout the body. Because recent technological advances enable us to detect rare circulating tumor cells, which are anoikis resistant, currently, anoikis resistance becomes a hot topic in cancer research. Detailed molecular and functional analyses of anoikis resistant cells may provide insight into the biology of cancer metastasis and identify novel therapeutic targets for prevention of cancer dissemination. This paper comprehensively describes recent investigations of the molecular and cellular mechanisms underlying anoikis and anoikis resistance in relation to intrinsic and extrinsic death signaling, epithelial-mesenchymal transition, growth factor receptors, energy metabolism, reactive oxygen species, membrane microdomains, and lipid rafts.

Cell therapy for spinal cord repair: optimization of biologic scaffolds for survival and neural differentiation of human bone marrow stromal cells

BACKGROUND AIMS

The suppression of cell apoptosis using a biodegradable scaffold to replace the missing or altered extracellular matrix (ECM) could increase the survival of transplanted cells and thus increase the effectiveness of cell therapy.

METHODS

We studied the best conditions for the proliferation and differentiation of human bone marrow stromal cells (hBMSC) when cultured on different biologic scaffolds derived from fibrin and blood plasma, and analyzed the best concentrations of fibrinogen, thrombin and calcium chloride for favoring cell survival. The induction of neural differentiation of hBMSC was done by adding to these scaffolds different growth factors, such as nerve growth factor (NGF), brain-derived-neurotrophic factor (BDNF) and retinoic acid (RA), at concentrations of 100 ng/mL (NGF and BDNF) and 1 micro/mL (RA), over 7 days.

RESULTS

Although both types of scaffold allowed survival and neural differentiation of hBMSC, the results showed a clear superiority of platelet-rich plasma (PRP) scaffolds, mainly after BDNF administration, allowing most of the hBMSC to survive and differentiate into a neural phenotype.

CONCLUSIONS

Given that clinical trials for spinal cord injury using hBMSC are starting, these findings may have important clinical applications.

Hollow spheroids in ascites of ovarian clear cell carcinoma: how are they formed and how do they behave?

OBJECTIVE

Although the multicellular aggregates (spheroids) in malignant ascites are usually solid throughout, they sometimes have acellular hollow spaces, especially in ascites of ovarian clear cell carcinoma. The purpose of this study is to analyse the origin and behaviour of hollow spheroids.

METHODS

Archival cytological and histological specimens of 32 ovarian carcinomas, including 12 clear cell carcinomas, were reviewed. HAC-2, a clear cell carcinoma cell line, was injected into the abdominal cavity of nude mice for direct comparison of ascitic cytology and tumour histology. Spheroids that were collected from nude mice ascites were cultured in vitro to observe their behaviour.

RESULTS

Five of six clear cell carcinomas with hollow spheroids showed spherule-like hyaluronan-rich stroma in their tumour tissue, whereas those without hollow spheroids did not. After heterotransplantation, both ascites and tumour imprints showed small or large hollow spheroids. Hyaluronan was detected in the former but not in the latter. The abdominal tumours showed compact spherule-like hyaluronan-rich stroma, enlarged oedematous stroma or intermediate stroma. In both size and hyaluronan status, small and large hollow spheroids were approximately comparable to spherule-like hyaluronan-rich stroma and oedematous stroma, respectively. During culture in vitro, hollow spheroids were maintained as hollow spheroids in suspension, and produced daughter hollow spheroids.

CONCLUSIONS

The hollow space in the spheroids originates from spherule-like hyaluronan-rich stroma, where water trapping by hyaluronan causes enlargement of the space. The matrix within the hollow space serves as a scaffold that regulates cell polarity and matrix production.

Will targeting insulin growth factor help us or hurt us?: An oncologist's perspective

The insulin/insulin growth factor (IGF) pathway is a critical mediator of longevity and aging. Efforts to extend longevity by altering the insulin/IGF pathway may have varying effects on other physiological processes. Reduced insulin/IGF levels may decrease the incidence of certain cancers as well as the risk of developing metastatic disease. However, it may also increase the risk of developing cardiovascular disease as well as cardiovascular related mortality. Pursuing the right insulin/IGF pathway targets will require striking a balance between inhibiting cancer cell development and progression and avoiding damage to tissues under normal insulin/IGF-mediated control. This review will discuss the roles of the insulin/IGF pathway in aging and longevity and the development of cancer cell metastasis and considerations in taking insulin/IGF directed targets to the oncology clinic.

Insulin-like growth factor-I-forkhead box O transcription factor 3a counteracts high glucose/tumor necrosis factor-α-mediated neuronal damage: implications for human immunodeficiency virus encephalitis

In HIV patients, antiretroviral medications trigger metabolic abnormalities, including insulin resistance. In addition, the inflammatory cytokine tumor necrosis factor-α (TNFα), which is elevated in human immunodeficiency virus encephalitis (HIVE), also induces insulin resistance and inflicts neuronal damage in vitro. In differentiated PC12 cells and rat cortical neurons, high glucose (HG; 25 mM) triggers reactive oxygen species (ROS) accumulation, contributing to the retraction of neuronal processes, with only a minimal involvement of neuronal apoptosis. In the presence of TNFα, HG-treated neurons undergo massive apoptosis. Because mammalian homolog of the Forkhead family of transcription factors, Forkhead box O transcription factor 3a (FOXO3a), controls ROS metabolism, we asked whether FOXO3a could affect the fate of differentiated neurons in the paradigm of HIVE. We observed FOXO3a nuclear translocation in HG-treated neuronal cultures, accompanied by partial loss of mitochondrial potential and gradual retraction of neuronal processes. Addition of TNFα to HG-treated neurons increased expression of the FOXO-dependent proapoptotic gene Bim, which resulted in extensive apoptotic death. Insulin-like growth factor-I (IGF-I) significantly lowered intracellular ROS, which was accompanied by IGF-I-mediated FOXO3a nuclear export and decrease in its transcriptional activity. The clinical relevance of these findings is supported by detection of nuclear FOXO3a in TUNEL-positive cortical neurons from HIVE, especially in brain areas characterized by elevated TNFα.

Long-term IGF-I exposure decreases autophagy and cell viability

A reduction in IGF-I signaling has been found to increase lifespan in multiple organisms despite the fact that IGF-I is a trophic factor for many cell types and has been found to have protective effects against multiple forms of damage in acute settings. The increase in longevity seen in response to reduced IGF-I signaling suggests that there may be differences between the acute and chronic impact of IGF-I signaling. We have examined the possibility that long-term stimulation with IGF-I may have a negative impact at the cellular level using quiescent human fibroblasts. We find that fibroblast cells exposed to IGF-I for 14 days have reduced long-term viability as judged by colony forming assays, which is accompanied by an accumulation of senescent cells. In addition we observe an accumulation of cells with depolarized mitochondria and a reduction in autophagy in the long-term IGF-I treated cultures. An examination of mice with reduced IGF-I levels reveals evidence of enhanced autophagy and fibroblast cells derived from these mice have a larger mitochondrial mass relative to controls indicating that changes in mitochondrial turnover occurs in animals with reduced IGF-I. The results indicate that chronic IGF-I stimulation leads to mitochondrial dysfunction and reduced cell viability.

PTK6 regulates IGF-1-induced anchorage-independent survival

BACKGROUND

Proteins that are required for anchorage-independent survival of tumor cells represent attractive targets for therapeutic intervention since this property is believed to be critical for survival of tumor cells displaced from their natural niches. Anchorage-independent survival is induced by growth factor receptor hyperactivation in many cell types. We aimed to identify molecules that critically regulate IGF-1-induced anchorage-independent survival.

METHODS AND RESULTS

We conducted a high-throughput siRNA screen and identified PTK6 as a critical component of IGF-1 receptor (IGF-1R)-induced anchorage-independent survival of mammary epithelial cells. PTK6 downregulation induces apoptosis of breast and ovarian cancer cells deprived of matrix attachment, whereas its overexpression enhances survival. Reverse-phase protein arrays and subsequent analyses revealed that PTK6 forms a complex with IGF-1R and the adaptor protein IRS-1, and modulates anchorage-independent survival by regulating IGF-1R expression and phosphorylation. PTK6 is highly expressed not only in the previously reported Her2(+) breast cancer subtype, but also in high grade ER(+), Luminal B tumors and high expression is associated with adverse outcomes.

CONCLUSIONS

These findings highlight PTK6 as a critical regulator of anchorage-independent survival of breast and ovarian tumor cells via modulation of IGF-1 receptor signaling, thus supporting PTK6 as a potential therapeutic target for multiple tumor types. The combined genomic and proteomic approaches in this report provide an effective strategy for identifying oncogenes and their mechanism of action.

ROS accumulation and IGF-IR inhibition contribute to fenofibrate/PPARalpha -mediated inhibition of glioma cell motility in vitro

BACKGROUND

Glioblastomas are characterized by rapid cell growth, aggressive CNS infiltration, and are resistant to all known anticancer regimens. Recent studies indicate that fibrates and statins possess anticancer potential. Fenofibrate is a potent agonist of peroxisome proliferator activated receptor alpha (PPARalpha) that can switch energy metabolism from glycolysis to fatty acid beta-oxidation, and has low systemic toxicity. Fenofibrate also attenuates IGF-I-mediated cellular responses, which could be relevant in the process of glioblastoma cell dispersal.

METHODS

The effects of fenofibrate on Glioma cell motility, IGF-I receptor (IGF-IR) signaling, PPARalpha activity, reactive oxygen species (ROS) metabolism, mitochondrial potential, and ATP production were analyzed in human glioma cell lines.

RESULTS

Fenofibrate treatment attenuated IGF-I signaling responses and repressed cell motility of LN-229 and T98G Glioma cell lines. In the absence of fenofibrate, specific inhibition of the IGF-IR had only modest effects on Glioma cell motility. Further experiments revealed that PPARalpha-dependent accumulation of ROS is a strong contributing factor in Glioma cell lines responses to fenofibrate. The ROS scavenger, N-acetyl-cysteine (NAC), restored cell motility, improved mitochondrial potential, and increased ATP levels in fenofibrate treated Glioma cell lines.

CONCLUSIONS

Our results indicate that although fenofibrate-mediated inhibition of the IGF-IR may not be sufficient in counteracting Glioma cell dispersal, PPARalpha-dependent metabolic switch and the resulting ROS accumulation strongly contribute to the inhibition of these devastating brain tumor cells.

Obesity, the PI3K/Akt signal pathway and colon cancer

Obesity is currently reaching epidemic levels worldwide and is a major predisposing factor for a variety of life-threatening diseases including diabetes, hypertension and cardiovascular diseases. Recently, it has also been suggested to be linked with cancer. Epidemiological studies have shown that obesity increases the risk of colon cancer by 1.5-2 fold with obesity-associated colon cancer accounting for 14-35% of total incidence. Several factors, altered in obesity, may be important in cancer development including increased levels of blood insulin, insulin-like growth factor I, leptin, TNF-alpha, IL-6 as well as decreased adiponectin. A unifying characteristic of all these factors is that they increase the activity of the PI3K/Akt signal pathway. The PI3K/Akt signal pathway in turn activates signals for cell survival, cell growth and cell cycle leading to carcinogenesis. Here we review the evidence that PI3K/Akt and its downstream targets are important in obesity-associated colon cancer and thus, that targeted inhibition of this pathway could be employed for the prevention of obesity-associated colon cancer and incorporated into the therapy regime for those with irremovable colon cancers.

The type I insulin-like growth factor receptor regulates cancer metastasis independently of primary tumor growth by promoting invasion and survival

The type I insulin-like growth factor receptor (IGF1R) regulates multiple aspects of malignancy and is the target of several drugs currently in clinical trials. While IGF1R’s role in proliferation and survival is well-studied, the regulation of metastasis by IGF1R is not as clearly delineated. Previous work showed that disruption of IGF1R signaling via overexpression of a dominant negative IGF1R inhibited metastasis. To establish a clinically applicable approach to inhibition of metastasis by targeting IGF1R, the effect of an inhibitory antibody against IGF1R, EM164 and its humanized version, AVE1642 on metastasis of cancer cells was examined. EM164 and AVE1642 did not affect primary tumor growth of MDA-435A/LCC6 cells but inhibited metastasis of these cells. Consistent with this inhibition in the formation of metastatic nodules, disruption of IGF1R also resulted in a decreased number of circulating tumor cells in blood of tumor-bearing mice. Disruption of IGF1R with a dominant negative construct or antibody inhibited invasion across Matrigel in vitro. When tumor cells were directly injected into the circulation via the lateral tail vein of mice, IGF1R disruption also resulted in significant reduction of pulmonary nodules, suggesting that regulation of invasion is not the only function of IGF1R signaling. Further, disruption of IGF1R rendered cells more susceptible to anoikis. Thus, IGF1R regulated metastasis independently of tumor growth. The multiple phenotypes regulated by IGF1R must be considered during development of this therapeutic strategy as inhibition of metastasis independent of inhibition of tumor growth is not easily assessed in phase II clinical trials.

Autocrine VEGF-A/KDR loop protects epithelial ovarian carcinoma cells from anoikis

Epithelial ovarian carcinoma (EOC) patients are usually diagnosed at an advanced stage, characterized by interperitoneal carcinomatosis and production of large volumes of ascites. Vascular endothelial growth factor-A (VEGF-A) and its main signaling receptor VEGFR2 (KDR) are coexpressed in primary ovarian tumors, ascitic cells and metastases, suggesting the existence of an autocrine VEGF-A/KDR loop in EOC cells. In the present study, we examined this possibility and explored the role of this autocrine loop in protecting EOC cells from apoptosis under anchorage free growth conditions (anoikis). We found that 3 different EOC cell lines (Caov3, OVCAR3, SKOV3) express both VEGF-A and its receptors, including KDR. In these cells, KDR is constitutively phosphorylated and is detected both in the cell plasma membrane and in the nucleus. Treating EOC cells with specific internal inhibitors of KDR kinase activity or a VEGF-A neutralizing antibody abolished KDR autophosphorylation and resulted in significant increase in apoptosis when cells were grown in single-cell, anchorage-free conditions. By contrast, these blocking reagents had no effect on cell viability when EOC cells were grown in adhesive monolayers. In summary, our results indicate that an autocrine VEGF-A/KDR loop exists in EOC cells and that it plays a role in protecting the cells from anoikis. Our results imply that treating EOC patients with VEGF blocking agents may potentially reduce peritoneal dissemination by decreasing vascular permeability as well as inducing apoptosis of shed ovarian cancer cells in ascites.

Regulation of breast cancer metastasis by IGF signaling

The insulin-like growth factors (IGFs) signaling via the type I insulin-like growth factor receptor (IGF-1R) regulate multiple aspects of malignancy. The importance of IGF-1R in regulating the malignant phenotype is currently being validated in numerous clinical trials for cancer including breast cancer. This review discusses the regulation of breast cancer metastasis by IGF-1R. IGF-1R stimulates invasion and survival in anchorage independent conditions. The regulation of metastasis independently of tumor growth by IGF-1R is also discussed. Finally, the impact of this on clinical trial design and outcomes, and the need for biomarkers, other than reduction in tumor size, are discussed in light of the fact that inhibition of metastasis is not measured in conventional clinical trial design.

Gene expression analysis of pancreatic cystic neoplasm in SV40Tag transgenic mice model

AIM: To study the gene expression changes in pancreatic cystic neoplasm in SV40Tag transgenic mice model and to provide information about the prevention, clinical diagnosis and therapy of pancreatic cancer.

METHODS: Using the pBC-SV40Tag transgenic mice model of pancreatic cystic neoplasm, we studied the gene expression changes by applying high-density microarrays. Validation of part gene expression profiling data was performed using real-time PCR.

RESULTS: By using high-density oligonucleotide microarray, of 14 113 genes, 453 were increased and 760 decreased in pancreatic cystic neoplasm, including oncogenes, cell-cycle-related genes, signal transduction-related genes, skeleton-related genes and metabolism-related genes. Among these, we confirmed the changes in Igf, Shh and Wnt signal pathways with real-time PCR. The results of real-time PCR showed similar expression changes in gene chip.

CONCLUSION: all the altered expression genes are associated with cell cycle, DNA damage and repair, signal pathway, and metabolism. SV40Tag may cooperate with several proteins in promoting tumorigenesis.

Focal adhesion kinase mediates cell survival via NF-kappaB and ERK signaling pathways

Focal adhesion kinase (FAK) is important to cellular functions such as proliferation, migration, and survival of anchorage-dependent cells. We investigated the role of FAK in modulating normal cellular responses, specifically cell survival in response to inflammatory stimuli and serum withdrawal, using FAK-knockout (FAK(-/-)) embryonic fibroblasts. FAK(-/-) fibroblasts were more vulnerable to TNF-alpha-induced apoptosis, as measured by terminal deoxynucleotidyl transferase positivity. FAK(-/-) fibroblasts also demonstrated increased procaspase-3 cleavage to p17 subunit, whereas this was undetectable in FAK(+/+) fibroblasts. Insulin receptor substrate-1 expression was completely abolished and NF-kappaB activity was reduced, with a concomitant decrease in abundance of the anti-apoptotic protein Bcl-x(L) in FAK(-/-) cells. Upon serum withdrawal, FAK(+/+) cells exhibited marked attenuation of basal ERK phosphorylation, while FAK(-/-) cells, in contrast, maintained high basal ERK phosphorylation. Moreover, inhibition of ERK phosphorylation potentiated serum withdrawal-induced caspase-3 activity. This was paralleled by increased insulin receptor substrate (IRS)-2 expression in FAK(-/-) cells, although both insulin- and IGF-1-mediated phosphorylation of Akt/PKB and GSK-3 were impaired. This suggests that IRS-2 protects against apoptosis upon serum withdrawal via the ERK signaling pathway. The specific role of FAK to protect cells from apoptosis is regulated by activation and phosphorylation of NF-kappaB and interaction between activated growth factor anti-apoptotic signaling pathways involving both phosphatidylinositol 3-kinase/Akt and MAPK/ERK1/2. We demonstrate that FAK is necessary for upregulation of the anti-apoptotic NF-kappaB response, as well as for normal expression of growth factor signaling proteins. Thus we propose a novel role for FAK in protection from cytokine-mediated apoptosis.

Inhibition of IGF-I receptor in anchorage-independence attenuates GSK-3beta constitutive phosphorylation and compromises growth and survival of medulloblastoma cell lines

We have previously reported that insulin-like growth factor-I (IGF-I) supports growth and survival of mouse and human medulloblastoma cell lines, and that IGF-I receptor (IGF-IR) is constitutively phosphorylated in human medulloblastoma clinical samples. Here, we demonstrate that a specific inhibitor of insulin-like growth factor-I receptor (IGF-IR), NVP-AEW541, attenuated growth and survival of mouse (BsB8) and human (D384, Daoy) medulloblastoma cell lines. Cell cycle analysis demonstrated that G1 arrest and apoptosis contributed to the action of NVP-AEW54. Interestingly, very aggressive BsB8 cells, which derive from cerebellar tumors of transgenic mice expressing viral oncoprotein (large T-antigen from human polyomavirus JC) became much more sensitive to NVP-AEW541 when exposed to anchorage-independent culture conditions. This high sensitivity to NVP-AEW54 in suspension was accompanied by the loss of GSK-3beta constitutive phosphorylation and was independent from T-antigen-mediated cellular events (Supplementary Materials). BsB8 cells were partially rescued from NVP-AEW541 by GSK3beta inhibitor, lithium chloride and were sensitized by GSK3beta activator, sodium nitroprusside (SNP). Importantly, human medulloblastoma cells, D384, which demonstrated partial resistance to NVP-AEW541 in suspension cultures, become much more sensitive following SNP-mediated GSK3beta dephosphorylation (activation). Our results indicate that hypersensitivity of medulloblastoma cells in anchorage-independence is linked to GSK-3beta activity and suggest that pharmacological intervention against IGF-IR with simultaneous activation of GSK3beta could be highly effective against medulloblastomas, which have intrinsic ability of disseminating the CNS via cerebrospinal fluid.

IGF-I mediated survival pathways in normal and malignant cells

The type-I and -II insulin-like growth factors (IGF-I, II) are now established as survival- or proliferation-factors in many in vitro systems. Of note IGFs provide trophic support for multiple cell types or organ cultures explanted from various species, and delay the onset of programmed cell death (apoptosis) through the mitochondrial (intrinsic pathway) or by antagonizing activation of cytotoxic cytokine signaling (extrinsic pathway). In some instances, IGFs protect against other forms of death such as necrosis or autophagy. The effect of IGFs on cell survival appears to be context specific, being determined both by the cell origin (tissue specific) and the cellular stress that induces loss of cellular viability. In many human cancers, there is a strong association with dysregulated IGF signaling, and this association has been extensively reviewed recently. IGF-regulation is also disrupted in childhood cancers as a consequence of chromosomal translocations. IGFs are implicated also in acute renal failure, traumatic injury to brain tissue, and cardiac disease. This article focuses on the role of IGFs and their cellular signaling pathways that provide survival signals in stressed cells.

The insulin-like growth factor I receptor is required for Akt activation and suppression of anoikis in cells transformed by the ETV6-NTRK3 chimeric tyrosine kinase

Signaling through the insulin-like growth factor I receptor (IGF-IR) axis is essential for transformation by many dominantly acting oncoproteins. However, the mechanism by which IGF-IR contributes to oncogenesis remains unknown. To examine this, we compared transformation properties of the oncogenic ETV6-NTRK3 (EN) chimeric tyrosine kinase in IGF-IR-null R- mouse embryo fibroblasts with R- cells engineered to reexpress IGF-IR (R+ cells). We previously showed that R- cells expressing EN (R- EN cells) are resistant to transformation but that transformation is restored in R+ cells. We now show that while R- EN cells have intact Ras-extracellular signal-regulated kinase signaling and cell cycle progression, they are defective in phosphatidylinositol-3-kinase (PI3K)-Akt activation and undergo detachment-induced apoptosis (anoikis) under anchorage-independent conditions. In contrast, R+ cells expressing EN (R+ EN cells) suppress anoikis and are fully transformed. The requirement for IGF-IR in R- EN cells is overcome by ectopic expression of either activated Akt or a membrane-targeted form of EN. Moreover, compared to R- EN cells, R+ EN cells show a dramatic increase in membrane localization of insulin receptor substrate 1 (IRS-1) in association with EN. Since EN is known to bind IRS-1 as an adaptor protein, our findings suggest that IGF-IR may function to localize EN/IRS-1 complexes to cell membranes, in turn facilitating PI3K-Akt activation and suppression of anoikis.

The flexible evolutionary anchorage-dependent Pardee's restriction point of mammalian cells: how its deregulation may lead to cancer

Living cells oscillate between the two states of quiescence and division that stand poles apart in terms of energy requirements, macromolecular composition and structural organization and in which they fulfill dichotomous activities. Division is a highly dynamic and energy-consuming process that needs be carefully orchestrated to ensure the faithful transmission of the mother genotype to daughter cells. Quiescence is a low-energy state in which a cell may still have to struggle hard to maintain its homeostasis in the face of adversity while waiting sometimes for long periods before finding a propitious niche to reproduce. Thus, the perpetuation of single cells rests upon their ability to elaborate robust quiescent and dividing states. This led yeast and mammalian cells to evolve rigorous Start [L.H. Hartwell, J. Culotti, J. Pringle, B.J. Reid, Genetic control of the cell division cycle in yeast, Science 183 (1974) 46-51] and restriction (R) points [A.B. Pardee, A restriction point for control of normal animal cell proliferation, Proc. Natl. Acad. Sci. U. S. A. 71 (1974) 1286-1290], respectively, that reduce deadly interferences between the two states by enforcing their temporal insulation though still enabling a rapid transition from one to the other upon an unpredictable change in their environment. The constitutive cells of multi-celled organisms are extremely sensitive in addition to the nature of their adhering support that fluctuates depending on developmental stage and tissue specificity. Metazoan evolution has entailed, therefore, the need for exceedingly flexible anchorage-dependent R points empowered to assist cells in switching between quiescence and division at various times, places and conditions in the same organism. Programmed cell death may have evolved concurrently in specific contexts unfit for the operation of a stringent R point that increase the risk of deadly interferences between the two states (as it happens notably during development). But, because of their innate flexibility, anchorage-dependent R points have also the ability to readily adjust to a changing structural context so as to give mutated cells a chance to reproduce, thereby encouraging tumor genesis. The Rb and p53 proteins, which are regulated by the two products of the Ink4a-Arf locus [C.J. Sherr, The INK4a/ARF network in tumor suppression, Nat. Rev., Mol. Cell Biol. 2 (2001) 731-737], govern separable though interconnected pathways that cooperate to restrain cyclin D- and cyclin E-dependent kinases from precipitating untimely R point transit. The expression levels of the Ink4a and Arf proteins are especially sensitive to changes in cellular shape and adhesion that entirely remodel at the time when cells shift between quiescence and division. The Arf proteins further display an extremely high translational sensitivity and can activate the p53 pathway to delay R point transit, but, only when released from the nucleolus, 'an organelle formed by the act of building a ribosome' [T. Mélèse, Z. Xue, The nucleolus: an organelle formed by the act of building a ribosome, Curr. Opin. Cell Biol. 7 (1995) 319-324]. In this way, the Ink4a/Rb and Arf/p53 pathways emerge as key regulators of anchorage-dependent R point transit in mammalian cells and their deregulation is, indeed, a rule in human cancers. Thus, by selecting the nucleolus to mitigate cell cycle control by the Arf proteins, mammalian cells succeeded in forging a highly flexible R point enabling them to match cell division with a growth rate imposed by factors controlling nucleolar assembling, such as nutrients and adhesion. It is noteworthy that nutrient control of critical size at Start in budding yeast has been shown recently to be governed by a nucleolar protein interaction network [P. Jorgensen, J.L. Nishikawa, B.-J. Breitkreutz, M. Tyers, Systematic identification of pathways that couple cell growth and division in yeast, Science 297 (2002) 395-400].

Sustained Akt/PKB activation and transient attenuation of c-jun N-Terminal kinase in the inhibition of apoptosis by IGF-1 in vascular smooth muscle cells

Characteristics of hVSMC apoptosis and its inhibition by insulin-like growth factor-1 (IGF-1) remain unclear. Also unclear is whether a balance in hVSMCs exists whereby c-Jun N-terminal stress kinases (JNK) promote apoptosis while extracellular signal-regulated (ERK1/2) MAP kinases inhibit cell death. In this study, we examined the involvement of Akt/PKB and its upstream kinase, PDK1 and whether JNK activation correlated with human and rat VSMC apoptosis induced by staurosporine and by c-myc, respectively. We observed a strong, sustained JNK activation (and c-Jun phosphorylation), which correlated with VSMC apoptosis. IGF-1 (13.3 nM), during apoptosis inhibition, transiently inhibited JNK activity at 1 h in a phosphatidylinositol 3-kinase (PI3-K)- and MEK-ERK-dependent manner, as wortmannin (100 nM) or PD98059 (30 muM) partially attenuated the IGF-1 effect. PKC down-regulation had no effect on JNK inhibition by IGF-1. While IGF-1 alone produced a strong phosphorylation of Akt/PKB in hVSMCs up to 6 h, it was notably stronger and more sustained during ratmyc and hVSMCs apoptosis inhibition. Further, whereas transient expression of phosphorylated Akt protected VSMCs from apoptosis by nearly 50%, expression of dominant interfering alleles of Akt or PDK1 strongly inhibited IGF-1-mediated VSMC survival. These results demonstrate for the first time that transient inhibition of a pro-apoptotic stimulus in VSMCs may be sufficient to inhibit a programmed cell death and that sustained anti-apoptotic signals (Akt) elicited by IGF-1 are augmented during a death stimulus. Furthermore, PI3-K and ERK-MAPK pathways may cooperate to protect VSMCs from cell death.

Altered expression of type I insulin-like growth factor receptor in Crohn's disease

The fibrotic and antiapoptotic effects of insulin-like growth factors (IGF) are mediated by type I IGF receptor (IGF-1R). IGFs could play a role in intestinal stricturing and in the maintenance of inflammation in Crohn's disease (CD). We aimed to describe IGF-1R expression in CD intestinal lesions, to compare it to other intestinal inflammatory diseases and to correlate it with fibrosis and apoptosis. IGF-1R expression and apoptosis (active caspase-3) were studied by immunohistochemistry. Surgical intestinal specimens [17 CD, nine controls, six diverticulitis and four ulcerative colitis (UC)] were used. IGF-1R was expressed transmurally mainly by inflammatory cells (IC) and smooth muscle cells, both in diseased intestine and controls. IGF-1R positive IC were increased in the mucosa and the submucosa of CD (P < 0.007), and in involved areas compared to uninvolved areas (P = 0.03). In UC, the number of IGF-1R positive IC was only increased in the mucosa, and was not different from controls in the submucosa. In diverticulitis, the number of IGF-1R positive IC did not differ from controls. In CD submucosa, IGF-1R expression in IC was inversely correlated with apoptosis in uninvolved areas (P = 0.01). Expression of IGF-1R in submucosal fibroblast-like cells, subserosal adipocytes and hypertrophic nervous plexi was specific for CD. We have shown a transmural altered expression of IGF-1R in CD. This may suggest a role for IGF-1R in the maintenance of chronic inflammation and stricture formation in CD.

Direct Effects of Polymyxin B on Human Dendritic Cells Maturation

Polymyxin B is a lipopolysaccharide binding antibiotic used to inactivate potential lipopolysaccharide contaminations when evaluating the activity of different agents on innate immune cells. We report that polymyxin B is able to induce directly in monocyte-derived human dendritic cells (DCs) several functional and molecular modifications characteristic of DCs undergoing a maturation process. DCs incubated with polymyxin B up-regulate the expression of HLA class I and II, the co-stimulatory CD86 molecule, and show an increase in the fraction of adherent cells at short time, which persist at 48 h of incubation. Adhesion to the plate was required for the polymyxin B-induced DCs maturation. A transient activation of IkappaB-alpha/NF-kappaB and ERK1/2 pathways at short time and a further ERK1/2 activation at long term were also detected. Neither up-regulation of the maturation marker CD83 nor activation of p38 nor induction of cytokines secretion was observed in DCs treated with polymyxin B. We demonstrated that inhibition of IkappaB-alpha/NF-kappaB pathway abolishes polymyxin B effects. ERK1/2 inhibition instead allowed DCs treated with polymyxin B to progress in their maturation process as revealed by the increased up-regulation of the CD83 co-stimulatory molecules, the activation of p38, and the reduced adhesion to culture plates at 48 h of incubation. Our results indicate that polymyxin B induces a partial maturation of human DCs through increased adhesion to a substrate and activation of the IkappaB-alpha/NF-kappaB pathway. The increased ERK1/2 activation observed, even though correlating with the initial phases of the maturation process, actually inhibits the occurrence of full maturation.

IGF-I receptor, cell-cell adhesion, tumour development and progression

The insulin-like growth factor I receptor (IGF-IR) has been implicated in the development and progression of many common cancers and other neoplastic diseases. The tumorigenic potential of IGF-IR relies on its antiapoptotic and transforming activities. The molecular mechanisms by which IGF-IR controls the proliferation and survival of tumour cells have been extensively studied and many pathways have been delineated. However, the role of IGF-IR in the regulation of non-mitogenic cell functions is less well understood. Here we focus on IGF-IR-dependent cell-cell adhesion. Limited studies suggested that IGF-IR can regulate cell aggregation and intercellular adhesion mediated by cadherins and cadherin-associated proteins. We review the mechanisms of this process and discuss the impact of IGF-IR-dependent cell-cell adhesion on the phenotype of tumour cells.

IGF-I prevents glutamate-induced motor neuron programmed cell death

Insulin-like growth factor I (IGF-I) is currently in clinical trials for treatment of amyotrophic lateral sclerosis (ALS), but little is known about how it promotes the survival of motor neurons. In the current study, we examined IGF-I-mediated neuroprotection in an in vitro model of ALS utilizing enriched cultures of embryonic rat spinal cord motor neurons. IGF-I binds to the IGF-I receptor (IGF-IR) in motor neurons and activates MAPK and the downstream effector of phosphatidylinositol 3-kinase (PI-3K) signaling, Akt. IGF-I:IGF-IR signaling involves phosphorylation of IRS-1 and Shc, but not IRS-2. Glutamate, which is elevated in the cerebrospinal fluid of ALS patients, induced DNA fragmentation and caspase-3 cleavage in the spinal cord motor neurons. These effects of glutamate were blocked by co-treatment with IGF-I. However, a delay of IGF-I treatment for as little as 30 min eliminated its neuroprotective effect. Finally, alone, neither the MAPK pathway inhibitor PD98059 nor the PI-3K inhibitor LY294002 blocked the neuroprotective effect of IGF-I, but both inhibitors together were effective in this regard. These results suggest that the dose and timing of IGF-I administration are critical for producing a neuroprotective effect, and also suggest that both the MAPK and PI-3K/Akt pathways can promote the survival of motor neurons. We discuss our results in terms of novel strategies for ALS therapy.

Role of the insulin-like growth factor I/insulin receptor substrate 1 axis in Rad51 trafficking and DNA repair by homologous recombination

The receptor for insulin-like growth factor I (IGF-IR) controls normal and pathological growth of cells. DNA repair pathways represent an unexplored target through which the IGF-IR signaling system might support pathological growth leading to cellular transformation. However, this study demonstrates that IGF-I stimulation supports homologous recombination-directed DNA repair (HRR). This effect involves an interaction between Rad51 and the major IGF-IR signaling molecule, insulin receptor substrate 1 (IRS-1). The binding occurs within the cytoplasm, engages the N-terminal domain of IRS-1, and is attenuated by IGF-I-mediated IRS-1 tyrosine phosphorylation. In the absence of IGF-I stimulation, or if mutated IGF-IR fails to phosphorylate IRS-1, localization of Rad51 to the sites of damaged DNA is diminished. These results point to a direct role of IRS-1 in HRR and suggest a novel role for the IGF-IR/IRS-1 axis in supporting the stability of the genome.

Identifying the factors and signal pathways necessary for anchorage-independent growth of Ha-ras oncogene-transformed NIH/3T3 cells

Ha-ras(Val 12) overexpression was positively correlated with colony formation by NIH/3T3 derivative "2-12" cells harboring an inducible Ha-ras(Val 12) transgene. The ras-farnesylation inhibitor, Lovastatin, completely suppressed colony formation at higher dosages. However, Ha-ras oncogene overexpression alone could not stimulate colony formation under serum-deprived conditions, suggesting that ras is required but not sufficient for supporting colony formation. Substituting cow colostrum (AC-2) for serum did not result in colony formation from 2-12 cells in soft agar, suggesting the colostrum lacked or contained insufficient amounts of factors that stimulate colony formation. Supplementation of AC-2-containing medium with growth factors, such as insulin-like growth factor-1 (IGF-1), partially restored the capability of anchorage-independent cell growth induced by Ha-ras overexpression. Consistently, antibodies specific for IGF-1 receptors only partially blocked colony formation from 2-12 cells. The data indicate that multiple factors, including IGF-1, are required for Ha-ras-dependent colony formation. Signal transduction studies revealed that, under Ha-ras overexpression conditions, IGF-1 utilizes phosphatidyl inositol 3-kinase and NF-kappaB to transduce colony formation-related signaling.

Anoikis: roadblock to cell transplantation?

Cell therapy, in particular liver cell transplantation, holds great therapeutic potential and is partially hindered by the high rate of apoptosis during cell isolation, cryopreservation, and engraftment. Apoptosis occurring due to cell detachment from the extracellular matrix is a phenomenon termed "anoikis." The purpose of this review is to describe signaling mechanisms pertinent to anoikis in both immortalized cell lines, but particularly in primary normal epithelial cells. The mechanisms described include integrin signaling and survival molecules, caspase activation, and the role of mitochondrial proteins in anoikis. Strategies to prevent anoikis during isolation and cryopreservation of hepatocytes are discussed.

Crosstalk between the extracellular domain of the ErbB2 receptor and IGF-1 receptor signaling

Insulin-like growth factor 1 receptor (IGF-1R) plays an important role in cell growth and malignant transformation. To investigate IGF-1R-dependent signaling events and its effects on apoptosis induction and cellular proliferation, we generated a constitutively active, ligand-independent IGF-1R variant. We fused the cytoplasmic domain of the IGF-1R to the extracellular and transmembrane domains of the oncogenic ErbB2 receptor (ErbB2(V-->E)/IGF-1). A fusion protein in which the wild-type sequence of the ErbB2 receptor was used, served as a control (ErbB2(V)/IGF-1R). ErbB2(V)/IGF-1R, ErbB2(V-->E)/IGF-1R and IGF-1R were stably transfected into interleukin 3 (IL-3)-dependent BaF/3 cells. ErbB2(V-->E)/IGF-1R expressing cells exhibited ligand-independent, constitutive tyrosine phosphorylation of the receptor fusion protein. Constitutively, activated ErbB2(V-->E)/IGF-1R conferred IL-3 independence for growth and survival to the transfected BaF/3 cells. Constitutive activation of the IGF-1R results in cellular growth and protection against apoptosis upon IL-3 withdrawal in BaF/3 cells.

Cell adhesion aside from integrin system can abrogate anoikis in rat liver cells by down-regulation of FasL expression, not by activation of PI-3K/Akt and ERK signaling pathway

Epithelial cells require contact with extracellular matrix (ECM) to inhibit detachment-induced apoptosis (anoikis). The ERK and PI-3K/Akt signaling pathways have been identified to inhibit anoikis. We present here a different story. An adult rat liver cell line, ARLJ301-3, underwent apoptosis within 4h under suspension conditions even with active forms of Akt and ERK1/2. Once ARLJ301-3 cells are plated on tissue culture plates coated with synthetic polymer, such as poly-(N-p-vinyl benzyl-O-beta-D-galactopyranosyl-D-gluconamide) (PVLA), poly-L-lysine or polystyrene, instead of functional ECM such as fibronectin, they could survive and proliferate without activation of Akt and ERK1/2. The expression of Fas receptor ligand (FasL) is specifically detected in cells under suspension conditions or treated with cytochalasin-D. We present here the first report that FasL expression is up-regulated by the cytoskeletal disruption directed by cytochalasin-D treatment or cell detachment from ECM.

Induction of inducible nitric oxide synthase by Epstein-Barr virus B95-8-derived LMP1 in Balb/3T3 cells promotes stress-induced cell death and impairs LMP1-mediated transformation

The latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV) causes cellular transformation and activation of several intracellular signaling events. In this report, we show that BLMP1 (encoded by the LMP1 gene derived from the B95-8 strain of EBV) triggers the expression of inducible nitric oxide synthase (iNOS) in Balb/3T3 fibroblasts. Intriguingly, NLMP1, a natural sequence variant of LMP1 identified in EBV-positive nasopharyngeal carcinoma biopsy, does not similarly induce iNOS expression. BLMP1-induced iNOS in Balb/3T3 cells is active to produce nitric oxide (NO), and NO production can be blocked by several iNOS inhibitors. When subjected to environmental stress, Balb/3T3 cells that produce NO lose viability more rapidly than non NO-producing cells. Blockage of NO generation by iNOS inhibitors enhances the viability of NO-producing cells under stress conditions. The activities of caspase-3 and c-Jun N-terminal kinase, two important regulators mediating stress-induced apoptosis, are significantly potentiated following heat shock treatment of BLMP1-expressing/NO-producing cells, compared to parental and NLMP1-expressing cells. Furthermore, treatment with iNOS inhibitor augmented the cloning efficiency (in culture) and tumor growth (in nude mice) of BLMP1-expressing/NO-producing cells. Collectively, the results demonstrate that BLMP1 induces iNOS expression and NO production in Balb/3T3 cells, which leads to the alteration of cell functions, including sensitivity to environmental stress, capability to colonize independent of anchorage and tumorigenicity in nude mice. Our data additionally implicate that the differential iNOS induction potential of the two LMP1 forms may represent the basis of a functional difference between the two LMP1 proteins.

Insulin-like growth factor-I receptor - a potential therapeutic target in medulloblastomas

Medulloblastomas represent nearly 25% of all paediatric intracranial neoplasms. These highly malignant tumours arise from the cerebellum and affect predominantly children between the ages of 5 and 15. Although the aetiology of medulloblastomas has not been elucidated, several reports show that the insulin-like growth factor-I (IGF-I) signalling system is highly activated in medulloblastoma cell lines, medulloblastoma animal models and medulloblastoma biopsies, suggesting its contribution to the development and/or progression of these tumours. In addition, reports from multiple laboratories confirm a critical role for the IGF-I receptor (IGF-IR) in the process of cellular transformation. Taken together, these observations prompt the investigation of different strategies to impair the function of IGF-IR as a potential therapeutic tool, which by compromising growth and survival of medulloblastoma cells could supplement conventional therapeutic regiments against these malignant neoplasms of childhood.

Expression of an IGF-I receptor dominant negative mutant induces apoptosis, inhibits tumorigenesis and enhances chemosensitivity in Ewing's sarcoma cells

IGF-IR plays an essential role in the establishment and maintenance of the transformed phenotype of ES cells and interference with the IGF-IR pathways causes reversal of the malignant potential of this neoplasm. In this report, we stably transfected a dominant negative IGF-IR expression plasmid in an ES cell line to determine the effectiveness of this strategy against the in vitro and in vivo growth of ES cells. DXR sensitivity of TC-71 cells expressing dominant negative mutants of IGF-IR was also examined. The mutated IGF-IR that we used carries a mutation in the ATP-binding domain of the intracellular beta subunit, while the extracellular, ligand-binding alpha subunit remains unchanged. Cells carrying the dominant mutant IGF-IR had a marked decrease in proliferation, a significant increase in anoikis-induced apoptosis and a severely reduced ability to form colonies in soft agar. In vivo, when cells carrying dominant negative IGF-IR were injected into nude mice, the tumor formation and metastatic abilities of ES cells were reduced and survival increased. Furthermore, transfected clones showed significantly higher sensitivity to DXR, a major drug in the treatment of ES. These results indicate that the IGF/IGF-IR stimulation of ES cells may be inhibited by expression of mutated IGF-IR on their surfaces and that this strategy may be considered a possible alternative to impair this important target of ES cells, whose therapeutic potential was further confirmed.

Control of cell survival by IGF signaling pathways

The insulin-like growth factor system efficiently signals to cells to grow, differentiate, and survive. One central player in the prevention of cell death is the IGF-I receptor. Transduction of signals through this receptor leads to multiple series of intracellular phosphorylation events and the activation of several signaling pathways. Mechanisms of IGF system signaling that prevent cell death continue to be identified, suggesting that cells have alternative ways to avert death signals in addition to primary protective pathways. This review describes current knowledge of the mechanisms utilized by the IGF system to promote cell survival.

Prevention of cytokine-induced apoptosis by insulin-like growth factor-I is independent of cell adhesion molecules in HT29-D4 colon carcinoma cells-evidence for a NF-kappaB-dependent survival mechanism

We have previously established that insulin-like growth factor (IGF)-I, -II and insulin exert a strong protective effect against tumor necrosis factor-alpha (TNF)-induced apoptosis in interferon-gamma (IFN)-sensitized HT29-D4 human colon carcinoma cells. In this study, we report that this effect was still operative when cells were cultured in the absence of integrin- and E-cadherin-mediated cell-extracellular matrix and cell-cell interactions. In this model, IGF-I did not activate the focal adhesion kinase, whereas it induced tyrosine phosphorylation of the insulin receptor substrate-1 and activation of the extracellular signal-related kinase 1 and 2, p38, phosphatidylinositol 3'-kinase and protein kinase B/Akt. However, the use of specific inhibitors indicated that these pathways did not play a role in the adhesion-independent IGF-I anti-apoptotic signal. In contrast, inhibition of the NF-kappaB activation induced a complete reversal of the IGF-I anchorage-independent protective effect. Correspondingly, IGF-I markedly enhanced the TNF- and IFN/TNF-induced NF-kappaB-dependent interleukin-8 production. Our results provide evidence that IGF-I induces resistance against cytokine-induced cell death even in the absence of cell adhesion-mediated signaling. NF-kappaB appears to be a key mediator of this anti-apoptotic effect that should contribute to the resistance of colon cancer cells to immune-destruction during metastasis.

Effectiveness of insulin-like growth factor I receptor antisense strategy against Ewing's sarcoma cells

The insulin-like growth factor I receptor (IGF-IR) plays an essential role in the establishment and maintenance of transformed phenotype of Ewing's sarcoma (ES) cells, and interference with the IGF-IR pathways by a neutralizing antibody causes reversal of the malignant potential of this neoplasm. In this paper, we stably transfected an IGF-IR antisense mRNA expression plasmid in an ES cell line to determine the effectiveness of antisense strategies against the in vitro and in vivo growth of ES cells. Doxorubicin sensitivity of TC-71 cells expressing antisense targeted to IGF-IR mRNA was also examined. Cells carrying antisense IGF-IR had a reduced expression of the receptor, a modest decrease in cell proliferation, a significant increase in anoikis-induced apoptosis, and a severely reduced ability to form colonies in soft agar. Moreover, TC/AS cells showed a marked reduction in their motility. In vivo, when cells carrying antisense IGF-IR were injected subcutaneously in nude mice, tumor formation was delayed and survival increased. Metastatic ability of ES cells was also significantly reduced. Furthermore, TC/AS clones showed a significantly higher sensitivity to doxorubicin - a major drug in the treatment of ES. These results indicate that inhibiting IGF-IR by antisense strategies may be relevant to the clinical treatment of ES patients by reducing the malignant potential of these cells and enhancing the effectiveness of chemotherapy.