Overexpressed IGF-I receptors reduce estrogen growth requirements, enhance survival, and promote E-cadherin-mediated cell-cell adhesion in human breast cancer cells

Loss of E-cadherin Induces IGF1R Activation and Reveals a Targetable Pathway in Invasive Lobular Breast Carcinoma

No special-type breast cancer [NST; commonly known as invasive ductal carcinoma (IDC)] and invasive lobular carcinoma (ILC) are the two major histological subtypes of breast cancer with significant differences in clinicopathological and molecular characteristics. The defining pathognomonic feature of ILC is loss of cellular adhesion protein, E-cadherin (CDH1). We have previously shown that E-cadherin functions as a negative regulator of the IGF1R and propose that E-cadherin loss in ILC sensitizes cells to growth factor signaling that thus alters their sensitivity to growth factor-signaling inhibitors and their downstream activators. To investigate this potential therapeutic vulnerability, we generated CRISPR-mediated CDH1 knockout (CDH1 KO) IDC cell lines (MCF7, T47D, and ZR75.1) to uncover the mechanism by which loss of E-cadherin results in IGF pathway activation. CDH1 KO cells demonstrated enhanced invasion and migration that was further elevated in response to IGF1, serum and collagen I. CDH1 KO cells exhibited increased sensitivity to IGF resulting in elevated downstream signaling. Despite minimal differences in membranous IGF1R levels between wild-type (WT) and CDH1 KO cells, significantly higher ligand-receptor interaction was observed in the CDH1 KO cells, potentially conferring enhanced downstream signaling activation. Critically, increased sensitivity to IGF1R, PI3K, Akt, and MEK inhibitors was observed in CDH1 KO cells and ILC patient-derived organoids.

IMPLICATIONS

Overall, this suggests that these targets require further exploration in ILC treatment and that CDH1 loss may be exploited as a biomarker of response for patient stratification.

Obesity and endocrine therapy resistance in breast cancer: Mechanistic insights and perspectives

The incidence of obesity, a recognized risk factor for various metabolic and chronic diseases, including numerous types of cancers, has risen dramatically over the recent decades worldwide. To date, convincing research in this area has painted a complex picture about the adverse impact of high body adiposity on breast cancer onset and progression. However, an emerging but overlooked issue of clinical significance is the limited efficacy of the conventional endocrine therapies with selective estrogen receptor modulators (SERMs) or degraders (SERDs) and aromatase inhibitors (AIs) in patients affected by breast cancer and obesity. The mechanisms behind the interplay between obesity and endocrine therapy resistance are likely to be multifactorial. Therefore, what have we actually learned during these years and which are the main challenges in the field? In this review, we will critically discuss the epidemiological evidence linking obesity to endocrine therapeutic responses and we will outline the molecular players involved in this harmful connection. Given the escalating global epidemic of obesity, advances in understanding this critical node will offer new precision medicine-based therapeutic interventions and more appropriate dosing schedule for treating patients affected by obesity and with breast tumors resistant to endocrine therapies.

Anodic formation and biomedical properties of hafnium-oxide nanofilms

Hafnium dioxide (HfO₂) is attracting attention for bio-related applications due to its good cytocompatibility, high density, and resistance to corrosion and mechanical damage. Here we synthesize two types of hafnium-oxide thin films on substrates via self-organized electrochemical anodization: (1) an array of hierarchically structured nanorods anchored to a thin oxide layer and (2) a microscopically flat oxide film. The nanostructured film is composed of a unique mixture of HfO₂, suboxide Hf₂O₃, and oxide-hydroxide compound HfO₂·nH₂O whereas the flat film is mainly HfO₂. In vitro interaction of the two films with MG-63 osteoblast-like cells and Gram-negative E. coli bacteria is studied for the first time to assess the potential of the films for biomedical application. Both films reveal good cytocompatibility and affinity for proteins, represented by fibronectin and especially albumin, which is absorbed in a nine times larger amount. The morphology and specific surface chemistry of the nanostructured film cause a two-fold enhanced antibacterial effect, better cell attachment, significantly improved proliferation of cells, five-fold rise in the cellular Young's modulus, slightly stronger production of reactive oxygen species, and formation of cell clusters. Compared with the flat film, the nanostructured one features the weakening of AFM-measured adhesion force at the cell/surface interface, probably caused by partially lifting the nanorods from the substrate due to the strong contact with cells. The present findings deepen the understanding of biological processes at the living cell/metal-oxide interface, underlying the role of surface chemistry and the impact of nanostructuring at the nanoscale.

The investigation of transcriptional repression mediated by ZEB2 in canine invasive micropapillary carcinoma in mammary gland

The E-cadherin loss has frequently been associated with transcriptional repression mediated by transcription factors, such as the Zinc Finger E-Box Binding Homeobox-2 (ZEB2). Invasive micropapillary carcinomas (IMPCs) of the breast are aggressive neoplasms frequently related to lymph node metastasis and poor overall survival. In the canine mammary gland, IMPCs has just been reported and, based on its behavioral similarity with the human IMPCs, appears to be a good spontaneous model to this human entity. This study aimed to evaluate the relationship between E-cadherin and ZEB2 in a spontaneous canine model of invasive micropapillary carcinoma of the mammary gland. The correlation among gene expression (ZEB2 and CDH1) and clinicopathological findings was also explored. Nineteen cases of IMPC of the canine mammary gland were obtained, protein and mRNA expression were investigated through immunohistochemistry and RNA In Situ Hybridization, respectively. To better understand the relationship between E-cadherin and ZEB2, immunofluorescence was performed in canine IMPCs. Immunohistochemically, most of IMPCs showed 1+ (14/19, 73.7%) for E-cadherin; and positivity for ZEB2 was diagnosed in 47.4% of the IMPCs. Regarding the RNA In Situ Hybridization (ISH), most of IMPCs showed 4+ and 0+ for E-cadherin (CDH1) and ZEB2 respectively. Through immunofluorescence, the first and second more frequent combinatorial group were E-cadherin⁺ZEB2^- and E-cadherin⁺ZEB2⁺; neoplastic cells showing concomitantly weak expression for E-cadherin and positivity for ZEB2 were frequently observed. A negative correlation was observed between E-cadherin and progesterone receptor expression in IMPCs. Based on these results, canine mammary IMPCs show E-cadherin lost and, at times reveals nuclear positivity for the transcription factor ZEB2 that seems to exert transcriptional repression of the CDH1.

Loss of E-cadherin Enhances IGF1-IGF1R Pathway Activation and Sensitizes Breast Cancers to Anti-IGF1R/InsR Inhibitors

Purpose: Insulin-like growth factor 1 (IGF1) signaling regulates breast cancer initiation and progression and associated cancer phenotypes. We previously identified E-cadherin (CDH1) as a repressor of IGF1 signaling and in this study examined how loss of E-cadherin affects IGF1R signaling and response to anti-IGF1R/insulin receptor (InsR) therapies in breast cancer.Experimental Design: Breast cancer cell lines were used to assess how altered E-cadherin levels regulate IGF1R signaling and response to two anti-IGF1R/InsR therapies. In situ proximity ligation assay (PLA) was used to define interaction between IGF1R and E-cadherin. TCGA RNA-seq and RPPA data were used to compare IGF1R/InsR activation in estrogen receptor-positive (ER+) invasive lobular carcinoma (ILC) and invasive ductal carcinoma (IDC) tumors. ER+ ILC cell lines and xenograft tumor explant cultures were used to evaluate efficacy to IGF1R pathway inhibition in combination with endocrine therapy.Results: Diminished functional E-cadherin increased both activation of IGF1R signaling and efficacy to anti-IGF1R/InsR therapies. PLA demonstrated a direct endogenous interaction between IGF1R and E-cadherin at points of cell-cell contact. Increased expression of IGF1 ligand and levels of IGF1R/InsR phosphorylation were observed in E-cadherin-deficient ER+ ILC compared with IDC tumors. IGF1R pathway inhibitors were effective in inhibiting growth in ER+ ILC cell lines and synergized with endocrine therapy and similarly IGF1R/InsR inhibition reduced proliferation in ILC tumor explant culture.Conclusions: We provide evidence that loss of E-cadherin hyperactivates the IGF1R pathway and increases sensitivity to IGF1R/InsR targeted therapy, thus identifying the IGF1R pathway as a potential novel target in E-cadherin-deficient breast cancers. Clin Cancer Res; 24(20); 5165-77. ©2018 AACR.

Expression of insulin-like growth factor-1 receptor in circulating tumor cells of patients with breast cancer is associated with patient outcomes

In patients with breast cancer, markers of aggressiveness such as dysregulation of the insulin-like growth factor receptor (IGF1R) system and E-cadherin loss are commonly observed. Reduced IGF1R expression is correlated with decreased E-cadherin levels and increased cell motility. We assessed IGF1R and E-cadherin expression in circulating tumor cells (CTCs) in patients with breast cancer. Peripheral blood mononuclear cells of early (n = 87)- and metastatic (n = 126)-stage breast cancer patients (obtained prior to adjuvant and first-line chemotherapy) were evaluated using double immunofluorescence (IF) staining for cytokeratin (CK) and IGF1R. Triple IF using CK, IGF1R, and E-cadherin antibodies was performed in selected CTC(+) patients. IGF1R(+) CTCs were more frequently observed in early disease than in metastatic disease (86% vs 68% of CTCs, P = 0.04) stage, whereas IGF1R(-) CTCs were more common in metastatic than in early disease (32% vs 14% of CTCs, P = 0.002). 100% of CTC(+) patients with early disease, compared to 79% of those with metastatic disease, harbored IGF1R(+) CTCs (P = 0.007). Patients with early disease and exclusively IGF1R(+) CTCs had longer disease-free (P = 0.02) and overall survival (P = 0.001) compared to patients with both IGF1R(+) and IGF1R(-) CTC populations. 67% of early-stage CTC(+) patients evaluated had exclusively IGF1R(+)/E-cadherin(+) CTCs, 33% also had IGF1R(-)/E-cadherin(-) CTCs, and none had exclusively IGF1R(-)/E-cadherin(-) CTCs compared to 17%, 75%, and 8% of metastatic patients, respectively (P = 0.027). Similarly, in paired samples of patients with early disease that progressed to metastatic disease, the proportion of IGF1R(+)/E-cadherin(+) CTCs was reduced and IGF1R(-)/E-cadherin(-) CTCs were increased in the metastatic stage compared to early disease stage. IGF1R(+) CTCs are commonly detected in breast cancer, and their frequency decreases in the metastatic disease stage. IGF1R(+)/E-cadherin(+) CTCs also decrease in metastatic patients. IGF1R(+) CTCs are associated with favorable outcomes in early disease stage, suggesting that IGF1R expression is correlated with reduced metastatic potential in breast cancer.

The WNT-less wonder: WNT-independent β-catenin signaling

β-catenin is known as an Armadillo protein that regulates gene expression following WNT pathway activation. However, WNT-independent pathways also activate β-catenin. During the establishment of the melanocyte lineage, β-catenin plays an important role. In the context of physiopathology, β-catenin is activated genetically or transiently in various cancers, including melanoma, where it can be found in the nucleus of tumors. In this review, we discuss alternative pathways that activate β-catenin independent of WNTs and highlight what is known regarding these pathways in melanoma. We also discuss the role of β-catenin as a transcriptional regulator in various cell types, with emphasis on the different transcription factors it associates with independent of WNT induction. Finally, the role of WNT-independent β-catenin in melanocyte development and melanomagenesis is also discussed.

IGF-1 Receptor and Adhesion Signaling: An Important Axis in Determining Cancer Cell Phenotype and Therapy Resistance

IGF-1R expression and activation levels generally cannot be correlated in cancer cells, suggesting that cellular proteins may modulate IGF-1R activity. Strong candidates for such modulation are found in cell-matrix and cell-cell adhesion signaling complexes. Activated IGF-1R is present at focal adhesions, where it can stabilize β1 integrin and participate in signaling complexes that promote invasiveness associated with epithelial mesenchymal transition (EMT) and resistance to therapy. Whether IGF-1R contributes to EMT or to non-invasive tumor growth may be strongly influenced by the degree of extracellular matrix engagement and the presence or absence of key proteins in IGF-1R-cell adhesion complexes. One such protein is PDLIM2, which promotes both cell polarization and EMT by regulating the stability of transcription factors including NFκB, STATs, and beta catenin. PDLIM2 exhibits tumor suppressor activity, but is also highly expressed in certain invasive cancers. It is likely that distinct adhesion complex proteins modulate IGF-1R signaling during cancer progression or adaptive responses to therapy. Thus, identifying the key modulators will be important for developing effective therapeutic strategies and predictive biomarkers.

Evaluation of 99mTc-Z IGF1R:4551-GGGC affibody molecule, a new probe for imaging of insulin-like growth factor type 1 receptor expression

Overexpression of insulin-like growth factor-1 receptor (IGF-1R) in several cancers is associated with resistance to therapy. Radionuclide molecular imaging of IGF-1R expression in tumors may help in selecting the patients that will potentially respond to IGF-1R-targeted therapy. Affibody molecules are small (7 kDa) non-immunoglobulin-based scaffold proteins that are well-suited probes for radionuclide imaging. The aim of this study was the evaluation of an anti-IGF-1R affibody molecule labeled with technetium-99m using cysteine-containing peptide-based chelator GGGC at C-terminus. Z_IGF1R:4551-GGGC was efficiently and stably labeled with technetium-99m (radiochemical yield 97 ± 3 %). ^99mTc-Z_IGF1R:4551-GGGC demonstrated specific binding to IGF-1R-expressing DU-145 (prostate cancer) and MCF-7 (breast cancer) cell lines and slow internalization in vitro. The tumor-targeting properties were studied in BALB/c nu/nu mice bearing DU-145 and MCF-7 xenografts. [^99mTc(CO)₃]⁺-(HE)₃-Z_IGF1R:4551 was used for comparison. The biodistribution study demonstrated high tumor-to-blood ratios (6.2 ± 0.9 and 6.9 ± 1.0, for DU-145 and MCF-7, respectively, at 4 h after injection). Renal radioactivity concentration was 16-fold lower for ^99mTc-Z_IGF1R:4551-GGGC than for [^99mTc(CO)₃]⁺-(HE)₃-Z_IGF1R:4551 at 4 h after injection. However, the liver uptake of ^99mTc-Z_IGF1R:4551-GGGC was 1.2- to 2-fold higher in comparison with [^99mTc(CO)₃]⁺-(HE)₃-Z_IGF1R:4551. A possible reason for the elevated hepatic uptake of ^99mTc-Z_IGF1R:4551-GGGC is a high lipophilicity of amino acids in the binding site of Z_IGF1R:4551, which is not compensated in ^99mTc-Z_IGF1R:4551-GGGC. In conclusion, ^99mTc-Z_IGF1R:4551-GGGC can visualize the IGF-1R expression in human tumor xenografts and provides low retention of radioactivity in kidneys. Further development of this imaging agent should include molecular design aimed at reducing the hepatic uptake.

The small GTPase Rap1 promotes cell movement rather than stabilizes adhesion in epithelial cells responding to insulin-like growth factor I

The Ras-related GTPase Rap1 promotes cell adhesion and migration. Although the significance of Rap1 contribution to cell migration is increasingly being recognized, little is known about the biochemical mechanisms driving this process. In the present study, we discovered a previously unidentified regulatory role of insulin-like growth factor type I (IGF-I) receptor (IGF-IR) in CRK Src homology 3 (SH3)-binding guanine-nucleotide-releasing protein (C3G)-Rap1-fascin-actin axis promoting cell movement. We demonstrate that a burst of Rap1 activity, rather than presumed hyperactivation, is imperative for the onset of cell movement. We show that while autophosphorylated IGF-IR signals to C3G to activate Rap1, subsequent IGF-IR internalization promotes gradual inactivation of Rap1 by putative Rap1 GTPase-activating protein (GAP). Additionally, IGF-IR signalling recruits active Rap1 at sites of cell motile protrusions. C3G depletion prevents IGF-I-induced fascin accumulation at actin microspikes and blocks protrusions. In the absence of IGF-IR activity, the wild-type (WT) Rap1 and the constitutively active V12Rap1 mutant remain in cell-cell contacts. Forced inactivation of Rap1 signalling by overexpressing dominant negative N17Rap1, Rap1GAP or by silencing C3G has a detrimental effect on filamentous (F)-actin and cell adhesion irrespective of IGF-IR signalling. We conclude that the basal levels of Rap1 activity holds up cell adhesion, whereas sequential regulation of C3G and GAP by IGF-IR reverses the labile Rap1 function from supporting adhesion to promoting migration.

IGF-IR promotes prostate cancer growth by stabilizing α5β1 integrin protein levels

Dynamic crosstalk between growth factor receptors, cell adhesion molecules and extracellular matrix is essential for cancer cell migration and invasion. Integrins are transmembrane receptors that bind extracellular matrix proteins and enable cell adhesion and cytoskeletal organization. They also mediate signal transduction to regulate cell proliferation and survival. The type 1 insulin-like growth factor receptor (IGF-IR) mediates tumor cell growth, adhesion and inhibition of apoptosis in several types of cancer. We have previously demonstrated that β1 integrins regulate anchorage-independent growth of prostate cancer (PrCa) cells by regulating IGF-IR expression and androgen receptor-mediated transcriptional functions. Furthermore, we have recently reported that IGF-IR regulates the expression of β1 integrins in PrCa cells. We have dissected the mechanism through which IGF-IR regulates β1 integrin expression in PrCa. Here we report that IGF-IR is crucial for PrCa cell growth and that β1 integrins contribute to the regulation of proliferation by IGF-IR. We demonstrate that β1 integrin regulation by IGF-IR does not occur at the mRNA level. Exogenous expression of a CD4 - β1 integrin cytoplasmic domain chimera does not interfere with such regulation and fails to stabilize β1 integrin expression in the absence of IGF-IR. This appears to be due to the lack of interaction between the β1 cytoplasmic domain and IGF-IR. We demonstrate that IGF-IR stabilizes the β1 subunit by protecting it from proteasomal degradation. The α5 subunit, one of the binding partners of β1, is also downregulated along with β1 upon IGF-IR knockdown while no change is observed in the expression of the α2, α3, α4, α6 and α7 subunits. Our results reveal a crucial mechanistic role for the α5β1 integrin, downstream of IGF-IR, in regulating cancer growth.

Discovering causal pathways linking genomic events to transcriptional states using Tied Diffusion Through Interacting Events (TieDIE)

MOTIVATION

Identifying the cellular wiring that connects genomic perturbations to transcriptional changes in cancer is essential to gain a mechanistic understanding of disease initiation, progression and ultimately to predict drug response. We have developed a method called Tied Diffusion Through Interacting Events (TieDIE) that uses a network diffusion approach to connect genomic perturbations to gene expression changes characteristic of cancer subtypes. The method computes a subnetwork of protein-protein interactions, predicted transcription factor-to-target connections and curated interactions from literature that connects genomic and transcriptomic perturbations.

RESULTS

Application of TieDIE to The Cancer Genome Atlas and a breast cancer cell line dataset identified key signaling pathways, with examples impinging on MYC activity. Interlinking genes are predicted to correspond to essential components of cancer signaling and may provide a mechanistic explanation of tumor character and suggest subtype-specific drug targets.

AVAILABILITY

Software is available from the Stuart lab's wiki: https://sysbiowiki.soe.ucsc.edu/tiedie.

CONTACT

jstuart@ucsc.edu.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

HT-29 human colon cancer cell proliferation is regulated by cytosolic phospholipase A(2)α dependent PGE(2)via both PKA and PKB pathways

Cytosolic phospholipase A(2)α (cPLA(2)α) up-regulation has been reported in human colorectal cancer cells, thus we aimed to elucidate its role in the proliferation of the human colorectal cancer cell line, HT-29. EGF caused a rapid activation of cPLA(2)α which coincided with a significant increase in cell proliferation. The inhibition of cPLA(2)α activity by pyrrophenone or by antisense oligonucleotide against cPLA(2)α (AS) or inhibition of prostaglandin E(2) (PGE(2)) production by indomethacin resulted with inhibition of cell proliferation, that was restored by addition of PGE(2). The secreted PGE(2) activated both protein kinase A (PKA) and PKB/Akt pathways via the EP2 and EP4 receptors. Either, the PKA inhibitor (H-89) or the PKB/Akt inhibitor (Ly294002) caused a partial inhibition of cell proliferation which was restored by PGE(2). But, inhibited proliferation in the presence of both inhibitors could not be restored by addition of PGE(2). AS or H-89, but not Ly294002, inhibited CREB activation, suggesting that CREB activation is mediated by PKA. AS or Ly294002, but not H-89, decreased PKB/Akt activation as well as the nuclear localization of β-catenin and cyclin D1 and increased the plasma membrane localization of β-catenin with E-cadherin, suggesting that these processes are regulated by the PKB pathway. Similarly, Caco-2 cells exhibited cPLA(2)α dependent proliferation via activation of both PKA and PKB/Akt pathways. In conclusion, our findings suggest that the regulation of HT-29 proliferation is mediated by cPLA(2)α-dependent PGE(2) production. PGE(2)via EP induces CREB phosphorylation by the PKA pathway and regulates β-catenin and cyclin D1 cellular localization by PKB/Akt pathway.

Igf1r signaling is indispensable for preimplantation development and is activated via a novel function of E-cadherin

Insulin-like growth factor I receptor (Igf1r) signaling controls proliferation, differentiation, growth, and cell survival in many tissues; and its deregulated activity is involved in tumorigenesis. Although important during fetal growth and postnatal life, a function for the Igf pathway during preimplantation development has not been described. We show that abrogating Igf1r signaling with specific inhibitors blocks trophectoderm formation and compromises embryo survival during murine blastocyst formation. In normal embryos total Igf1r is present throughout the membrane, whereas the activated form is found exclusively at cell contact sites, colocalizing with E-cadherin. Using genetic domain switching, we show a requirement for E-cadherin to maintain proper activation of Igf1r. Embryos expressing exclusively a cadherin chimera with N-cadherin extracellular and E-cadherin intracellular domains (NcEc) fail to form a trophectoderm and cells die by apoptosis. In contrast, homozygous mutant embryos expressing a reverse-structured chimera (EcNc) show trophectoderm survival and blastocoel cavitation, indicating a crucial and non-substitutable role of the E-cadherin ectodomain for these processes. Strikingly, blastocyst formation can be rescued in homozygous NcEc embryos by restoring Igf1r signaling, which enhances cell survival. Hence, perturbation of E-cadherin extracellular integrity, independent of its cell-adhesion function, blocked Igf1r signaling and induced cell death in the trophectoderm. Our results reveal an important and yet undiscovered function of Igf1r during preimplantation development mediated by a unique physical interaction between Igf1r and E-cadherin indispensable for proper receptor activation and anti-apoptotic signaling. We provide novel insights into how ligand-dependent Igf1r activity is additionally gated to sense developmental potential in utero and into a bifunctional role of adhesion molecules in contact formation and signaling.

One of the most important steps during mammalian development is the formation of a blastocyst before implantation. Proper blastocyst development is fundamentally reliant on the function of the E-cadherin adhesion molecule, which cannot be replaced by another highly related member of the cadherin family. We have addressed the question of how E-cadherin unfolds its unique function during this central embryonic process. We generated mouse mutants that allow specific domain swapping of extra- and intracellular protein domains of E-cadherin with the corresponding portion of N-cadherin. Upon E-cadherin (Cdh1) depletion, apoptosis is induced in cells that are required to form the trophectoderm, the outer cells of a functional blastocyst. Uncoupling of the two E-cadherin domains demonstrated that specifically the presence of the extracellular domain is indispensable in providing essential survival cues. To establish a proper trophectoderm the insulin-like growth factor I receptor (Igf1r) is intimately connected to the E-cadherin–mediated suppression of apoptosis. By interaction of the two proteins Igf1r is efficiently activated to allow embryo survival, blastocyst formation, and implantation. This novel and adhesion-independent function of E-cadherin may serve as paradigm for bifunctionality of adhesion molecules and how they are particularly utilized to interpret signal transduction activities in specific cellular contexts.

Nuclear IGF1R is a transcriptional co-activator of LEF1/TCF

Recent findings suggest that nuclear IGF1R binds to enhancer regions and functions as a transcriptional cofactor. However, the downstream transcriptional regulators of this pathway remain to be defined. Here, we show that nuclear IGF1R associates with the transcription factor LEF1 and increases promoter activity of LEF1 downstream target genes cyclin D1 and axin2. Furthermore, nuclear IGF1R augments protein levels of cyclin D1 and axin2. Our findings suggest a novel function for IGF1R, thus further emphasizing the important role of this receptor in cancer biology.

Decorin antagonizes IGF receptor I (IGF-IR) function by interfering with IGF-IR activity and attenuating downstream signaling

We have recently discovered that the insulin-like growth factor receptor I (IGF-IR) is up-regulated in human invasive bladder cancer and promotes migration and invasion of transformed urothelial cells. The proteoglycan decorin, a key component of the tumor stroma, can positively regulate the IGF-IR system in normal cells. However, there are no available data on the role of decorin in modulating IGF-IR activity in transformed cells or in tumor models. Here we show that the expression of decorin inversely correlated with IGF-IR expression in low and high grade bladder cancers (n = 20 each). Decorin bound with high affinity IGF-IR and IGF-I at distinct sites and negatively regulated IGF-IR activity in urothelial cancer cells. Nanomolar concentrations of decorin promoted down-regulation of IRS-1, one of the critical proteins of the IGF-IR pathway, and attenuated IGF-I-dependent activation of Akt and MAPK. This led to decorin-evoked inhibition of migration and invasion upon IGF-I stimulation. Notably, decorin did not cause down-regulation of the IGF-IR in bladder, breast, and squamous carcinoma cells. This indicates that decorin action on the IGF-IR differs from its known activity on other receptor tyrosine kinases such as the EGF receptor and Met. Our results provide a novel mechanism for decorin in negatively modulating both IGF-I and its receptor. Thus, decorin loss may contribute to increased IGF-IR activity in the progression of bladder cancer and perhaps other forms of cancer where IGF-IR plays a role.

GP88 (PC-Cell Derived Growth Factor, progranulin) stimulates proliferation and confers letrozole resistance to aromatase overexpressing breast cancer cells

Background

Aromatase inhibitors (AI) that inhibit breast cancer cell growth by blocking estrogen synthesis have become the treatment of choice for post-menopausal women with estrogen receptor positive (ER⁺) breast cancer. However, some patients display de novo or acquired resistance to AI. Interactions between estrogen and growth factor signaling pathways have been identified in estrogen-responsive cells as one possible reason for acquisition of resistance. Our laboratory has characterized an autocrine growth factor overexpressed in invasive ductal carcinoma named PC-Cell Derived Growth Factor (GP88), also known as progranulin. In the present study, we investigated the role GP88 on the acquisition of resistance to letrozole in ER⁺ breast cancer cells

Methods

We used two aromatase overexpressing human breast cancer cell lines MCF-7-CA cells and AC1 cells and their letrozole resistant counterparts as study models. Effect of stimulating or inhibiting GP88 expression on proliferation, anchorage-independent growth, survival and letrozole responsiveness was examined.

Results

GP88 induced cell proliferation and conferred letrozole resistance in a time- and dose-dependent fashion. Conversely, naturally letrozole resistant breast cancer cells displayed a 10-fold increase in GP88 expression when compared to letrozole sensitive cells. GP88 overexpression, or exogenous addition blocked the inhibitory effect of letrozole on proliferation, and stimulated survival and soft agar colony formation. In letrozole resistant cells, silencing GP88 by siRNA inhibited cell proliferation and restored their sensitivity to letrozole.

Conclusion

Our findings provide information on the role of an alternate growth and survival factor on the acquisition of aromatase inhibitor resistance in ER⁺ breast cancer.

Elevated insulin-like growth factor 1 receptor signaling induces antiestrogen resistance through the MAPK/ERK and PI3K/Akt signaling routes

INTRODUCTION

Insulin-like growth factor 1 (IGF-1) receptor (IGF-1R) is phosphorylated in all breast cancer subtypes. Past findings have shown that IGF-1R mediates antiestrogen resistance through cross-talk with estrogen receptor (ER) signaling and via its action upstream of the epidermal growth factor receptor and human epidermal growth factor receptor 2. Yet, the direct role of IGF-1R signaling itself in antiestrogen resistance remains obscure. In the present study, we sought to elucidate whether antiestrogen resistance is induced directly by IGF-1R signaling in response to its ligand IGF-1 stimulation.

METHODS

A breast cancer cell line ectopically expressing human wild-type IGF-1R, MCF7/IGF-1R, was established by retroviral transduction and colony selection. Cellular antiestrogen sensitivity was evaluated under estrogen-depleted two-dimensional (2D) and 3D culture conditions. Functional activities of the key IGF-1R signaling components in antiestrogen resistance were assessed by specific kinase inhibitor compounds and small interfering RNA.

RESULTS

Ectopic expression of IGF-1R in ER-positive MCF7 human breast cancer cells enhanced IGF-1R tyrosine kinase signaling in response to IGF-1 ligand stimulation. The elevated IGF-1R signaling rendered MCF7/IGF-1R cells highly resistant to the antiestrogens tamoxifen and fulvestrant. This antiestrogen-resistant phenotype involved mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and phosphatidylinositol 3-kinase/protein kinase B pathways downstream of the IGF-1R signaling hub and was independent of ER signaling. Intriguingly, a MAPK/ERK-dependent agonistic behavior of tamoxifen at low doses was triggered in the presence of IGF-1, showing a mild promitogenic effect and increasing ER transcriptional activity.

CONCLUSIONS

Our data provide evidence that the IGF-1/IGF-1R signaling axis may play a causal role in antiestrogen resistance of breast cancer cells, despite continuous suppression of ER transcriptional function by antiestrogens.

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.

Ras-related protein 1 and the insulin-like growth factor type I receptor are associated with risk of progression in patients diagnosed with carcinoma in situ

Currently, there are no applied molecular markers to aid in predicting risk of carcinoma in situ (CIS) progression to invasive cancer, and therefore, all women diagnosed with CIS undergo surgery. Standard assessment of protein expression in fixed tissue by immunohistochemistry (IHC) is not quantitative and hence is not well suited for measuring biomarkers. In this study, we developed an original analytical method for IHC quantification. Using our novel image-based uniplex (IBU) method, quantitative protein profiling was performed on 90 samples of the breast (17 histologically normal tissues, 16 benign lesions, 15 CIS, and 42 invasive carcinomas). Differences between groups were assessed using analysis of variance (ANOVA) and mixed effects models. Measuring protein expression on a continuous scale revealed a significant increase in Ras-related protein 1 (Rap1) and the insulin-like growth factor type I receptor (IGF-IR) in conjunction with the presence of cancer invasion. Women with invasive cancers were four times more likely to have increased levels of Rap1 [odds ratio (OR) = 3.91; P = 0.0002] and IGF-IR (OR=4.33; P<0.0001) than women with non-invasive lesions. Furthermore, expression of both proteins was also increased significantly in CIS adjacent to invasive tumors compared with non-cancerous tissue. These novel findings of a significant up-regulation of Rap1 and IGF-IR in CIS progressing to invasive cancers warrant further investigation of Rap1 and IGF-IR together as a dual biomarker to aid in predicting risk of progression and ultimately providing non-surgical treatment options to those at lower risk.

The insulin-like growth factor receptor I promotes motility and invasion of bladder cancer cells through Akt- and mitogen-activated protein kinase-dependent activation of paxillin

The insulin-like growth factor receptor I (IGF-IR) plays an essential role in transformation by promoting cell growth and protecting cancer cells from apoptosis. Aberrant IGF-IR signaling is implicated in several types of tumors, including carcinomas of the lung, breast, prostate, pancreas, liver, and colon. However, the contribution of the IGF-IR to the development of the transformed phenotype in urothelial cells has not been clearly established. In this study we demonstrated that the IGF-IR is overexpressed in invasive bladder cancer tissues compared with nonmalignant controls. We have investigated the role of the IGF-IR in bladder cancer by using urothelial carcinoma-derived 5637 and T24 cells. Although activation of the IGF-IR did not appreciably affect their growth, it did promote migration and stimulate in vitro wound closure and invasion. These effects required the activation of the Akt and Mitogen-activated protein kinase (MAPK) pathways as well as IGF-I-induced Akt- and MAPK-dependent phosphorylation of paxillin, which relocated at dynamic focal adhesions and was necessary for promoting motility in bladder cancer cells. Our results provide the first evidence for a role of the IGF-IR in motility and invasion of bladder cancer cells and support the hypothesis that the IGF-IR may play a critical role in the establishment of the invasive phenotype in urothelial neoplasia. Thus, the IGF-IR may also serve as a novel biomarker for bladder cancer.

Nuclear IRS-1 predicts tamoxifen response in patients with early breast cancer

Insulin receptor substrate-1 (IRS-1) is a cytoplasmic scaffolding protein that is phosphorylated by insulin-like growth factor-I receptor and recruits downstream effectors. Recent evidence suggests that IRS-1 has a nuclear localization and function. Here we investigated whether nuclear and cytoplasmic IRS-1 levels are associated with clinico-pathological characteristics and clinical outcome in breast cancer patients. Tissue microarrays from 1,097 patients with stage I-II breast cancer were stained by immunohistochemistry for IRS-1. Nuclear and cytoplasmic IRS-1 were scored separately according to the Allred score. Nuclear IRS-1 showed a positive association with estrogen receptor (ER) (r = 0.09, P = 0.003) and progesterone receptor (PR) (r = 0.08, P = 0.008) status and a negative correlation with lymph node involvement (r = -0.10, P = 0.001). Cytoplasmic IRS-1 did not correlate with ER or PR but showed a positive correlation with tumor size (r = 0.10, P = 0.001) and S-phase fraction (r = 0.16, P < 0.001). In univariate analysis, tamoxifen-treated patients with tumors showing positive nuclear IRS-1 had a better recurrence-free survival (RFS) (P = 0.009) and overall survival (OS) (P = 0.0007), while no association was shown between cytoplasmic IRS-1 and RFS or OS in the same group of patients. In multivariate analysis of patients receiving tamoxifen, negative nuclear IRS-1 showed a significantly reduced RFS (P = 0.046) and OS (P = 0.018). Combining both PR and nuclear IRS-1, tamoxifen-treated patients with PR+/IRS-1+ tumors had a better RFS (P = 0.0003) and OS (P < 0.0001) when compared with patients with PR-/IRS-1- tumors. In conclusion, nuclear IRS-1 may be a useful marker to predict tamoxifen response in patients with early breast cancer, particularly when assessed in combination with PR.

Molecular predictors of response to a humanized anti-insulin-like growth factor-I receptor monoclonal antibody in breast and colorectal cancer

The insulin-like growth factor-I receptor (IGF-IR) pathway is required for the maintenance of the transformed phenotype in neoplastic cells and hence has been the subject of intensive drug discovery efforts. A key aspect of successful clinical development of targeted therapies directed against IGF-IR will be identification of responsive patient populations. Toward that end, we have endeavored to identify predictive biomarkers of response to an anti-IGF-IR-targeting monoclonal antibody in preclinical models of breast and colorectal cancer. We find that levels of the IGF-IR itself may have predictive value in these tumor types and identify other gene expression predictors of in vitro response. Studies in breast cancer models suggest that IGF-IR expression is both correlated and functionally linked with estrogen receptor signaling and provide a basis for both patient stratification and rational combination therapy with antiestrogen-targeting agents. In addition, we find that levels of other components of the signaling pathway such as the adaptor proteins IRS1 and IRS2, as well as the ligand IGF-II, have predictive value and report on the development of a pathway-focused panel of diagnostic biomarkers that could be used to test these hypotheses during clinical development of IGF-IR-targeting therapies.

Insulin-like growth factor-I receptor, E-cadherin and alpha v integrin form a dynamic complex under the control of alpha-catenin

Dynamic crosstalk between cell adhesion molecules, extracellular matrix and soluble informative factors is essential for cancer cell migration and invasion. Here, we investigated the mechanisms by which the E-cadherin/catenin complex and alpha v integrin can modulate insulin-like growth factor-I (IGF-I)-induced cell migration. Human colon mucosa, human colon cancer cell lines, HT29-D4 and HCT-8 derivatives that differ in their expression of alpha-catenin, were used as models. Interactions between E-cadherin, alpha v integrin and IGF-I receptor (IGF-IR) were analyzed by coimmunoprecipitation and immunolocalization experiments. The impact of these interactions on cell mobility was determined by haptotaxis assays. We report that alpha v integrin, E-cadherin and IGF-IR form a ternary complex in both cultured cancer cells and human normal colonic mucosa. alpha-Catenin regulates the scaffolding of this complex. IGF-IR ligation by IGF-I induces the disruption of the complex and the relocalization of alpha v integrin from cell-cell contacts to focal contact sites. This perturbation is correlated with the observed increase in cell migration. These results suggest that regulation of the alpha v integrin/E-cadherin/IGF-IR scaffolding is essential for the modulation of cell mobility. Its alteration could be of major importance to sustain alterations in cell adhesion that occur during cancer cell invasion and metastasis.

Insulin receptor substrate 1 knockdown in human MCF7 ER+ breast cancer cells by nuclease-resistant IRS1 siRNA conjugated to a disulfide-bridged D-peptide analogue of insulin-like growth factor 1

IRS-1 overexpression has been associated with breast cancer development, hormone independence and antiestrogen resistance. IRS-1 is a major downstream signaling protein for insulin and IGF1 receptors, conveying signals to PI-3K/Akt and ERK1/2 pathways. In estrogen-sensitive breast cancer cell lines, the widely used antiestrogen tamoxifen treatment reduces IRS-1 expression and function, thereby inhibiting IRS-1/PI-3K signaling. IRS-1 may serve as an alternative target to overexpressed IGF1R in breast cancer. While siRNA technology has become commonplace in many laboratories for in vitro gene knockdown studies, and in vivo stability issues are largely solved, its use in vivo is limited by an inability to efficiently and specifically deliver it to the intended site of action. We previously reported reduced survival of human MCF7 estrogen receptor positive breast cancer cells treated with a normal IRS1 siRNA delivered by a cationic lipid, plus an additive effect in combination with tamoxifen. We now report enhanced cellular uptake, relative to the unconjugated serum-stabilized IRS1 siRNA, of a serum-stabilized IRS1 siRNA conjugated with our previously characterized peptide mimetic of IGF1, D-(Cys-Ser-Lys-Cys), without the use of cationic lipids or electroporation, in MCF7 cells that overexpress IGF1R. Excess native IGF1 blocked uptake. An IRS1 siRNA cholesterol conjugate, targeted universally to cell membranes, was taken up by MCF7 cells as much as the peptide mimetic conjugate. IRS1 mRNA knockdown and IRS-1 protein knockdown were comparable for the IGF1 peptide and cholesterol conjugates. The unconjugated serum-stabilized IRS1 siRNA control showed negligible effects. Viability assays showed additive effects of siRNA treatment in combination with tamoxifen. In summary, we have taken the first step in converting an siRNA into a pharmacologically active agent for breast cancer.

Autocrine production of insulin-like growth factor-I (IGF-I) affects paracellular transport across epithelial cells in vitro

Autocrine production of growth factors can have significant effects on cell activity. We report for the first time that autocrine production of insulin-like growth factor-I (IGF-I) alters paracellular transport across bovine mammary epithelial cells in vitro. Paracellular transport was assessed by measuring phenol red transport across mammary alveolar cells-large T antigen (MAC-T cells) derived from parental mammary epithelial cells, cultured on porous membranes and compared with two different transfected MAC-T cell lines that constitutively secrete IGF-I. Phenol red transport was essentially blocked in parental cell culture after six days, while IGF-I secreting cells provided essentially no barrier. Surprisingly, neither co-culture studies between parental and IGF-I-secreting cells nor addition of exogenous IGF-I or IGF-binding protein-3 reversed the phenol red transport properties. IGF-I-secreting cells did however express lower levels of the junction components occludin and E-cadherin than parental cells, suggesting that localized autocrine IGF-I activity might lead to increased permeability via changes in both the tight and adherens junction protein levels.

Not so simple: the complexity of phosphotyrosine signaling at cadherin adhesive contacts

Cadherin cell-cell adhesion critically determines tissue organization and integrity in many organs of the body. Cadherin function influences patterning and morphogenesis while cadherin dysfunction contributes to disease, notably tumor invasion and metastasis. Cell signaling events are intimately linked with cadherin function; it is increasingly apparent that not only do cellular signals regulate cadherin function, but cadherins can also, in turn, modulate cell signaling itself. In this review, we discuss the complex interrelationship between phosphotyrosine-based cell signaling and cadherin adhesion. We focus on the interplay of events that occur at the cell surface and address three issues: the diverse mechanisms that activate phosphotyrosine signaling at cadherin cell-cell contacts, the functional impact of such signaling for cadherin adhesion, and the emerging capacity for cadherins to regulate growth factor signaling.

Insulin-like growth factors control cell migration in health and disease

Insulin-like growth factors I and II (IGF-I and IGF-II) have an ancient origin and play essential roles in fundamental biological processes. Although IGFs are principally known for their roles in regulating cell growth and survival, their ability to influence cell motility is just as significant. In the past 20 years, research has provided indisputable evidence for the regulatory role of IGFs in the migration of various cell types. Cell migration is crucial for reproduction, development, and tissue regeneration; IGFs play an important role in coordinating these processes. Moreover, studies continue to uncover the IGFs' role in stimulating cancer cell migration, invasion and metastasis. This review surveys current knowledge on the cell migration-modulating properties of IGFs and the biochemical pathways by which these peptides regulate cell movement in both physiological and pathological conditions.

Insulin-like growth factor 1 differentially regulates estrogen receptor-dependent transcription at estrogen response element and AP-1 sites in breast cancer cells

Cross-talk between insulin-like growth factor 1 (IGF-1) and estrogen receptor alpha (ER) regulates gene expression in breast cancer cells, but the underlying mechanisms remain unclear. Here, we studied how 17-beta-estradiol (E2) and IGF-1 affect ER transcriptional machinery in MCF-7 cells. E2 treatment stimulated ER loading on the estrogen response element (ERE) in the pS2 promoter and on the AP-1 motif in the cyclin D1 promoter. On ERE, similar amounts of liganded ER were found at 1-24-h time points, whereas on AP-1, ER binding fluctuated over time. At 1 h, liganded ER was recruited to ERE together with histone acetyltransferases SRC-1 and p300, ubiquitin ligase E6-AP, histone methyltransferase Carm1 (Carm), and polymerase (pol) II. This coincided with increased histone H3 acetylation and up-regulation of pS2 mRNA levels. At the same time, E2 moderately increased cyclin D1 expression, which was associated with the recruitment of liganded ER, SRC-1, p300, ubiquitin ligase E6-AP (E6L), Mdm2, and pol II, but not other regulatory proteins, to AP-1. In contrast, at 1 h, IGF-1 increased the recruitment of the ER.SRC-1.p300.E6L.Mdm2.Carm.pol II complex on AP-1, but not on ERE, and induced cyclin D1, but not pS2, mRNA expression. Notably, ER knockdown reduced the association of ER, E6L, Mdm2, Carm, and pol II with AP-1 and resulted in down-regulation of cyclin D1 expression. IGF-1 potentiated the effects of E2 on ERE but not to AP-1 and increased E2-dependent pS2, but not cyclin D1, mRNA expression. In conclusion, E2 and IGF-1 differentially regulate ER transcription at ERE and AP-1 sites.

Mammary tumorigenesis and metastasis caused by overexpression of insulin receptor substrate 1 (IRS-1) or IRS-2

Insulin receptor substrates (IRSs) are signaling adaptors that play a major role in the metabolic and mitogenic actions of insulin and insulin-like growth factors. Reports have recently noted increased levels, or activity, of IRSs in many human cancers, and some have linked this to poor patient prognosis. We found that overexpressed IRS-1 was constitutively phosphorylated in vitro and in vivo and that transgenic mice overexpressing IRS-1 or IRS-2 in the mammary gland showed progressive mammary hyperplasia, tumorigenesis, and metastasis. Tumors showed extensive squamous differentiation, a phenotype commonly seen with activation of the canonical beta-catenin signaling pathway. Consistent with this, IRSs were found to bind beta-catenin in vitro and in vivo. IRS-induced tumorigenesis is unique, given that the IRSs are signaling adaptors with no intrinsic kinase activity, and this supports a growing literature indicating a role for IRSs in cancer. This study defines IRSs as oncogene proteins in vivo and provides new models to develop inhibitors against IRSs for anticancer therapy.

Responses of human colorectal tumor cells to treatment with the anti-epidermal growth factor receptor monoclonal antibody ICR62 used alone and in combination with the EGFR tyrosine kinase inhibitor gefitinib

The anti-epidermal growth factor receptor (EGFR) monoclonal antibody cetuximab has been approved for the treatment of patients with metastatic colorectal cancer. However, there is currently no reliable marker for response to therapy with the EGFR inhibitors. In this study, we investigated the sensitivity of 10 human colorectal tumor cell lines (DiFi, CCL218, CCL221, CCL225, CCL227, CCL228, CCL231, CCL235, CCL244, and HCT-116) to treatment with our anti-EGFR monoclonal antibody, ICR62, and/or the EGFR tyrosine kinase inhibitor, gefitinib. Of the cells examined, only DiFi contained high levels of constitutively active EGFR and were highly sensitive to treatment with both ICR62 (IC(50) = 0.52 nmol/L) and gefitinib (IC(50) = 27.5 nmol/L). In contrast, the growth of other tumor cell lines, which contained low levels of the EGFR, HER-2, and pAkt but comparable or even higher basal levels of phosphorylated mitogen-activated protein kinase (pMAPK), were relatively resistant to treatment with both inhibitors. Both ICR62 and gefitinib induced EGFR down-regulation, reduced the basal levels of pEGFR at five known tyrosine residues, pMAPK, and pAkt, and increased the sub-G(1) population in DiFi cells. However, treatment with a combination of ICR62 and gefitinib neither sensitized colorectal tumor cells that were insensitive to treatment with the single agent nor enhanced the growth-inhibitory effect of the single agent in DiFi cells. These results indicate that basal levels of pMAPK and pAkt are not good indicators of response to the EGFR inhibitors in colorectal cancer cells and dual targeting of the EGFR by a combination of ICR62 and gefitinib is not superior to treatment with a single agent.

Insulin-like growth factor-I promotes resistance of bovine preimplantation embryos to heat shock through actions independent of its anti-apoptotic actions requiring PI3K signaling

For the bovine preimplantation embryo, insulin-like growth factor-I (IGF-I) is a survival factor that blocks the induction of apoptosis and reduces the decrease in development caused by heat shock. The first objective was to determine the signaling pathways whereby IGF-I acts to increase embryo cell number while inhibiting heat-shock induced apoptosis. Exposure of embryos to heat shock reduced cell number and increased percent apoptosis, but IGF-I increased cell number and blocked induction of apoptosis caused by heat shock. Actions of IGF-I to increase cell number were blocked by treatment with the mitogen activated protein kinase kinase (MAPKK) inhibitor PD 98059 whereas the phosphatidylinositol 3-kinase (PI3K) inhibitor LY 294002 had no effect. Conversely, LY 294002 but not PD 98059 blocked actions of IGF-I to inhibit induction of apoptosis caused by heat shock. The second objective was to determine whether IGF-I blocks effects of heat shock on development to the blastocyst stage by preventing apoptosis. Culture of embryos with IGF-I was effective in blocking the reduction in blastocyst development caused by heat shock-this action occurred even in the presence of LY 294002. Addition of another inhibitor of apoptosis, the caspase-3 inhibitor z-DEVD-fmk, did not mimic the protective effects of IGF-I on blastocyst development. Surprisingly, IGF-I was not effective in blocking the reduction in blastocyst development caused by heat shock when cultured with z-DEVD-fmk. In conclusion, the anti-apoptotic actions of IGF-I require PI3K signaling while actions to promote proliferation require MAPKK signaling. Moreover, actions of IGF-I to allow heat-shocked embryos to continue development to the blastocyst stage are independent of its anti-apoptotic effects.

The relationship between the insulin-like growth factor-1 system and the oestrogen metabolising enzymes in breast cancer tissue and its adjacent non-cancerous tissue

AIMS

Previous studies have shown that oestrogen and Insulin-like Growth Factor-1 (IGF-1) act synergistically and cross-stimulatory while the oestrogen receptor (ER) and IGF-1R downstream signalling pathways interact at many levels. We investigate the relationship between the ER, and IGF-1R and their ligands in a series of human breast cancer tissue and adjacent non-cancerous tissue (ANCT).

METHODS

A series of 139 pairs of breast cancer tissue and ANCT were obtained and divided into ER positive and ER negative groups based on tumour ER alpha immunostaining. All samples were processed for real-time quantitative-PCR to measure IGF-1, IGF-1R, ER alpha, STS and Cyp-19 mRNA levels. In addition, ER positive MCF-7 and ER negative MDA-MB-231 cell lines were treated separately with IGF-1 and an IGF-1R inhibitor called Tyrphostin AG1024 to see the effects of stimulating and inhibiting the IGF-1R. MCF-7 cell line was also treated with 4-hydroxytamoxifen. The mRNA levels of IGF-1, IGF-1R, ER alpha, STS and Cyp-19 of treated cell lines were measured and compared to those of non-treated controls. Data generated was normalised to Cytokeratin-19 mRNA levels.

RESULTS

IGF-1R expression was higher in tumour tissue compared to ANCT (P = 0.038) while IGF-1 expression was marginally higher in ANCT compared to tumour tissue only in the ER positive samples (P = 0.098). ER positive tumours had a higher expression of IGF-1 compared to ER negative tumours (P = 0.001) while IGF-1R, STS and Cyp-19 expression were higher in ER negative tumours (P = 0.000, 0.000 and 0.006 respectively). There was no difference in STS or Cyp-19 expression in tumours or ANCT. Using Spearman's Correlation test, IGF-1 positively correlated with STS, Cyp-19 and ER alpha in ER positive and negative groups (Coefficient = +0.497, +0.662 and +0.651 respectively, P = 0.000 in all). IGF-1R correlated with IGF-1, STS, Cyp-19 and ER alpha only in the ER negative tumours (Coefficient = +0.620, +0.394, +0.692 and +0.662 respectively, P = 0.000, 0.012, 0.000 and 0.000 respectively). In cell lines, IGF-1 treatment led to an increase in the mean expression of IGF-1, IGF-1R, STS and Cyp-19 in both cell lines while ER alpha expression increased only in MCF-7. IGF-1R inhibition caused a decrease in expression of all five genes in MDA-MB-231 but not in the MCF-7 cell line. Treatment with 4-hydroxytamoxifen caused a decrease in expression of all five genes.

CONCLUSIONS

IGF-1R is over-expressed in malignant tissue. IGF-1 is expressed at higher levels in ER positive tumours probably as a result of oestrogen stimulation while IGF-1R expression is higher in ER negative samples as an adaptation to lower local IGF-1 levels. An IGF-1 paracrine relationship may exist between tumour and ANCT but for STS and Cyp-19, there may be an autocrine-paracrine relationship. The IGF-1 ligand-receptor system is an important regulator of oestrogen production while oestrogen may be involved in stimulating IGF-1 expression. The expression of oestrogen synthesising enzymes is higher in ER negative breast cancers which may be due to the lack of oestrogen negative feedback or contribution from the overexpression of IGF-1R.

Activation Function-1 Domain of Estrogen Receptor Regulates the Agonistic and Antagonistic Actions of Tamoxifen

The antiestrogen tamoxifen has been widely used for decades as selective estrogen receptor (ER) modulator for ERalpha-positive breast tumors. Tamoxifen significantly reduces tumor recurrence by binding to the activation function-2 (AF-2) domain of the ER. Acquired resistance to tamoxifen in breast cancer patients is a serious therapeutic problem. Antiestrogen-resistant breast cancer often shows increased expression of the epidermal growth factor receptor (EGFR) family members, EGFR and ErbB2. In this report we now show that overexpression of EGFR or activated AKT-2 in MCF-7 cells leads to phosphorylation of Ser167 in the AF-1 domain of ERalpha, enhanced ER-amplified in breast cancer 1 (ER:AIB1) interaction in the presence of tamoxifen, and resistance to tamoxifen. In contrast, transfection of activated MAPK kinase, an immediate upstream activator of MAPK (ERK 1 and 2) into MCF-7 cells leads to phosphorylation of Ser118 in the AF-1 domain of ERalpha, inhibition of ER-amplified in breast cancer 1 (ER:AIB1) interaction in the presence of Tam, and maintenance of sensitivity to tamoxifen. Inhibition of AKT by short inhibitory RNA blocked Ser167 phosphorylation in ER and restored tamoxifen sensitivity. However, maximum sensitivity to tamoxifen was observed when both AKT and MAPK were inhibited. Taken together, these data demonstrate that different phosphorylation sites in the AF-1 domain of ERalpha regulate the agonistic and antagonistic actions of tamoxifen in human breast cancer cells.

Type I insulin-like growth factor receptor over-expression induces proliferation and anti-apoptotic signaling in a three-dimensional culture model of breast epithelial cells

Introduction

Activation of the type I insulin-like growth factor receptor (IGFIR) promotes proliferation and inhibits apoptosis in a variety of cell types. Transgenic mice expressing a constitutively active IGFIR or IGF-I develop mammary tumors and increased levels of IGFIR have been detected in primary breast cancers. However, the contribution of IGFIR activation in promoting breast cancer progression remains unknown. Mammary epithelial cell lines grown in three-dimensional cultures form acinar structures that mimic the round, polarized, hollow and growth-arrested features of mammary alveoli. We used this system to determine how proliferation and survival signaling by IGFIR activation affects breast epithelial cell biology and contributes to breast cancer progression.

Methods

Pooled, stable MCF-10A breast epithelial cells expressing wild-type IGFIR or kinase-dead IGFIR (K1003A) were generated using retroviral-mediated gene transfer. The effects of over-expression of wild-type or kinase-dead IGFIR on breast epithelial cell biology were analyzed by confocal microscopy of three-dimensional cultures. The contribution of signaling pathways downstream of IGFIR activation to proliferation and apoptosis were determined by pharmacological inhibition of phosphatidylinositol 3' kinase (PI3K) with LY294002, MAP kinase kinase (MEK) with UO126 and mammalian target of rapamycin (mTOR) with rapamycin.

Results

We found that MCF-10A cells over-expressing the IGFIR formed large, misshapen acinar structures with filled lumina and disrupted apico-basal polarization. This phenotype was ligand-dependent, occurring with IGF-I or supraphysiological doses of insulin, and did not occur in cells over-expressing the kinase-dead receptor. We observed increased proliferation, decreased apoptosis and increased phosphorylation of Ser⁴⁷³ of Akt and Ser²⁴⁴⁸ of mTOR throughout IGFIR structures. Inhibition of PI3K with LY294002 or MEK with UO126 prevented the development of acinar structures from IGFIR-expressing but not control cells. The mTOR inhibitor rapamycin failed to prevent IGFIR-induced hyperproliferation and survival signaling.

Conclusion

Increased proliferation and survival signaling as well as loss of apico-basal polarity by IGFIR activation in mammary epithelial cells may promote early lesions of breast cancer. Three-dimensional cultures of MCF-10A cells over-expressing the IGFIR are a useful model with which to study the role of IGFIR signaling in breast cancer progression and for characterizing the effects of chemotherapeutics targeted to IGFIR signaling.

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.

Insulin-like growth factor I controls adhesion strength mediated by alpha5beta1 integrins in motile carcinoma cells

One of the intriguing questions regarding cell motility concerns the mechanism that makes stationary cells move. Here, we provide the first physical evidence that the onset of breast cancer cell motility in response to insulin-like growth factor I (IGF-I) correlates with lowering of adhesion strength from 2.52 +/- 0.20 to 1.52 +/- 0.13 microdynes/microm2 in cells attached to fibronectin via alpha5beta1 integrin. The adhesion strength depends on the dose of IGF-I and time of IGF-I treatment. Weakening of cell-matrix adhesion is blocked significantly (p < 0.01) by the catalytically inactive IGF-I receptor (IGF-IR) and the phosphoinositide 3-kinase (PI-3 kinase) inhibitor LY-294002, but it is unaffected by mitogen-activated protein kinase kinase inhibitor UO-126 and Src kinase inhibitor PP2. Sustained blockade of Rho-associated kinase (ROCK) with Y-27632 down-regulates adhesion strength in stationary, but not in IGF-I-treated, cells. Jasplakinolide, a drug that prevents actin filament disassembly, counteracts the effect of IGF-I on integrin-mediated cell adhesion. In the absence of growth factor signaling, ROCK supports a strong adhesion via alpha5beta1 integrin, whereas activation of the IGF-IR kinase reduces cell-matrix adhesion through a PI-3K-dependent, but ROCK-independent, mechanism. We propose that disassembly of the actin filaments via PI-3 kinase pathway contributes to weakening of adhesion strength and induction of cell movement. Understanding how cell adhesion and migration are coordinated has an important application in cancer research, developmental biology, and tissue bioengineering.

Imaging oncogene expression

In 2003, approximately 39,800 women in the US will die from breast cancer. Mammography and physical examination miss up to 40% of early breast cancers. Moreover, if an abnormality is found, an invasive diagnostic procedure must still be performed to determine if the breast contains atypia or cancer, even though approximately 85% of abnormalities are benign. Scintigraphic imaging of gene expression in vivo by noninvasive means could direct physicians to appropriate targets for intervention at the onset of disease and thereby significantly impact patient management. Until now, no method has been available to image specific overexpressed oncogene mRNAs in vivo by scintigraphic imaging. We hypothesize that gamma-emitting Tc-99m-PNA-peptides can be taken up by human ER+ and ER- breast cancer xenografts, hybridize to complementary mRNA targets in those cells, and concentrate sufficiently in tumor tissue to allow noninvasive imaging of oncogene overexpression. To prepare the probes, peptide analogs of insulin-like growth factor 1 (IGF1) were extended from a solid support by Fmoc coupling. Peptide nucleic acid (PNA) dodecamers antisense to CCND1 and MYC mRNAs were then extended from the N-terminus of IGF1, followed by a chelator peptide, using Fmoc coupling for all residues. The cysteine thiols were cyclized on the solid support, either before or after PNA extension. This simplified synthetic approach allows preparation of a variety of multipeptide disulfide-bridged PNA chimeras. A chelating peptide-PNA chimera antisense to MYC mRNA was then labeled efficiently with Tc-99m, yielding a single product. Tissue distribution studies of antisense and mismatch chimeras at 4 h and 24 h after administration displayed modest accumulation in the liver and kidneys, with appreciable levels in tumors. This result enables testing of Tc-99m-peptide-PNA probes to image gene expression in tumors.

Cadherins in cancer

The presence of a functional E-cadherin/catenin cell-cell adhesion complex is a prerequisite for normal development and maintenance of epithelial structures in the mammalian body. This implies that the acquisition of molecular abnormalities that disturb the expression or function of this complex is related to the development and progression of most, if not all, epithelial cell-derived tumors, i.e. carcinomas. E-cadherin downregulation is indeed correlated with malignancy parameters such as tumor progression, loss of differentiation, invasion and metastasis, and hence poor prognosis. Moreover, E-cadherin has been shown to be a potent invasion suppressor as well as a tumor suppressor. Disturbed expression profiles of the E-cadherin/catenin complex have been demonstrated in histological sections of many human tumor types. In different kinds of carcinomas, biallelic downregulation of the E-cadherin gene, resulting in tumor-restricted decrease or even complete loss of E-cadherin expression, appears to be caused by a variety of inactivation mechanisms. Gene deletion due to loss of heterozygosity of the CDH1 locus on 16q22.1 frequently occurs in many carcinoma types. However, somatic inactivating mutations resulting in aberrant E-cadherin expression by loss of both wild-type alleles is rare and restricted to only a few cancer types. A majority of carcinomas thus seems to show deregulated E-cadherin expression by other mechanisms. The present evidence proposes transcriptional repression as a powerful and recurrent molecular mechanism for silencing E-cadherin expression. The predominant mechanisms emerging in most carcinomas are hypermethylation of the E-cadherin promoter and expression of transrepressor molecules such as SIP1, Snail, and Slug that bind sequence elements in the proximal E-cadherin promoter. Interestingly, complex differential expression of other cadherins seems to be associated with loss of E-cadherin and to reinforce effects of this loss on tumor progression. Multiple agents can upregulate and stabilize the E-cadherin/catenin complex. Especially for those tumors with transcriptional and thus reversible downregulation of E-cadherin expression, these drug agents offer important therapeutic opportunities.

Nonendocrine Pathways and Endocrine Resistance

An increasing body of evidence demonstrates that growth factor networks are highly interactive with estrogen receptor signaling in the control of breast cancer growth. As such, tumor responses to antiestrogens are likely to be a composite of the estrogen receptor and growth factor-inhibitory activity of these agents, with alterations/aberrations in growth factor signaling providing a mechanism for the development of antiestrogen resistance. In this light, the current article focuses on illustrating the relationship between growth factor signaling and antiestrogen failure in our in-house tumor models of breast cancer and describing how we are now beginning to successfully target growth factor activity to improve the effects of antiestrogen drugs and to block aggressive disease progression.

Insulin-like Growth Factor-II Regulates PTEN Expression in the Mammary Gland

The tumor suppressor PTEN is altered in many cancers, including breast cancer, but only a handful of factors are known to control its expression. PTEN plays a vital role in cell survival and proliferation by regulating Akt phosphorylation, a key component of the phosphatidylinositol 3 kinase (PI3K) pathway. Here we show that insulin-like growth factor-II (IGF-II), which signals through PI3K, regulates PTEN expression in the mammary gland. IGF-II injection into mouse mammary gland significantly increased PTEN expression. Transgenic IGF-II expression also increased mammary PTEN protein, leading to reductions in Akt phosphorylation, epithelial proliferation, and mammary morphogenesis. IGF-II induced PTEN promoter activity and protein levels and this involved the immediate early gene egr-1. Thus, we have identified a novel negative feedback loop within the PI3K pathway where IGF-II induces PTEN expression to modulate its physiologic effects.

99mTc-peptide-peptide nucleic acid probes for imaging oncogene mRNAs in tumours

Imaging oncogene mRNA in tumours would provide a powerful tool for the early detection of occult malignant lesions. The goal was to prepare a chimera consisting of a dodecamer antisense peptide nucleic acid (PNA) specific for c-MYC oncogene overexpressed in human breast cancer cells and a chelating moiety that facilitates quantitative radiolabelling with 99mTc and evaluate it for hybridization and tissue distribution in laboratory animals. The pentapeptide chelator-PNA dodecamer specific for c-MYC mRNA was extended from a solid support by 9-fluorenylmethyloxycarbonyl (Fmoc) coupling. Similarly, a chelator-PNA chimera with four central mismatches was also prepared which served as a control. The chimeras were purified, characterized and evaluated for hybridization to c-MYC mRNA by fluorescent, real-time polymerase chain reaction (RT-PCR). The chimeras were labelled with 99mTc and their tissue distribution was examined in athymic nude mice bearing experimental human breast tumours. 99mTc radiolabelling was quantitative and presented a single peak in reversed phase liquid chromatography. Fluorescent real-time polymerase chain reactions using primer and fluorescent probe sets previously calculated for c-MYC mRNA demonstrated inhibition of reverse transcription by the c-MYC specific chimera as compared to that of the control. Tissue distribution studies of antisense and mismatch chimeras at 4 h and 24 h after administration displayed modest accumulation in the liver, and appreciable levels in tumours. These observations suggest that 99mTc-peptide-PNA probes might be useful for imaging gene expression in tumours, and the approach is worthy of further investigation.

Retinoic acid-induced growth arrest of MCF-7 cells involves the selective regulation of the IRS-1/PI 3-kinase/AKT pathway

In the MCF-7 breast cancer cell line, insulin-like growth factors (IGFs) are known to elicit antiproliferative actions via the insulin receptor substrate-1 (IRS-1)/PI 3-kinase/AKT pathway. All-trans retinoic acid (RA) is a potent inhibitor of MCF-7 cell proliferation, but the mechanism by which growth regulation is achieved remains unclear. We investigated the effects of RA on the regulation of the IGF-IR and its key signaling elements: IRS-1, IRS-2, and SHC. Treatment of MCF-7 cells with RA caused a significant reduction in IRS-1 protein and tyrosine phosphorylation levels at a concentration and time consistent with RA-mediated growth inhibition. IRS-1 regulation is selective, as RA did not influence IRS-2 or SHC levels. Downstream signaling events were also selectively reduced, as RA abrogated IGF-I-stimulated AKT activation but did not alter erk1/2 activation. To confirm the importance of IRS-1 regulation by RA, we examined the response to RA in MCF-7 cells overexpressing IGF-IR and IRS-1. RA resistance was observed in MCF-7 cells overexpressing IRS-1 but not IGF-IR. This suggests that RA-mediated growth inhibition requires the selective downregulation of IRS-1 and AKT. Therapeutic agents targeting the IRS-1/PI 3-kinase/AKT pathway may enhance the cytostatic effects of RA in breast cancer, since overexpression of IRS-1 and AKT have been reported in primary breast tumors.

Overexpression of insulin-like growth factor II (IGFII) in ZR-75-1 human breast cancer cells: higher threshold levels of receptor (IGFIR) are required for a proliferative response than for effects on specific gene expression

Previous transfection experiments using a zinc-inducible expression vector have shown that overexpression of insulin-like growth factor II (IGFII) in MCF7 human breast cancer cells can reduce dependence on oestrogen for cell growth in vitro (DALY RJ, HARRIS WH, WANG DY, DARBRE PD. (1991) Cell Growth Differentiation 2, 457-464.). Parallel transfections now performed into another oestrogen-dependent human breast cancer cell line (ZR-75-1) yielded three clones of transfected ZR-75-1 cells that produced levels of zinc-inducible IGFII mRNA and secreted mature IGFII protein similar to those found in the transfected MCF7 cells. However, unlike in MCF7 cells, no resulting effects were found on cell growth in the ZR-75-1 clones, even though the ZR-75-1 clones possessed receptors capable of binding 125I-IGFI and showed a growth response to exogenously added IGFII. Medium conditioned by the ZR-75-1 clones could stimulate growth of untransfected MCF7 cells, indicating that the secreted IGFII protein was bioactive. Furthermore, zinc-induced IGFII was capable of increasing both pS2 mRNA levels and CAT activity from a transiently transfected AP1-CAT gene in the ZR-75-1 clones. Constitutive co-overexpression of the protein processing enzyme PC2 resulted in reduced levels of large forms of zinc-inducible IGFII, but zinc treatment still produced no effect on cell growth rate. Finally, however, constitutive co-overexpression of the type I IGF receptor (IGFIR) did result in zinc-inducible increased basal cell growth and reduced dependence on oestrogen for cell growth. These results demonstrate that while overexpression of IGFII per se was sufficient to deregulate MCF7 cell growth, the ZR-75-1 cells are limited in their proliferative response by their intrinsic receptor levels. However, although the proliferative response was limited, molecular responses (expression of pS2 and AP1-CAT) were not limited, indicating that different cellular responses can have different threshold receptor level requirements.

Insulin-like growth factor-I and estrogen interactions in breast cancer

There is increasing evidence that estradiol and insulin-like growth factor-I (IGF-I) act through a complex cross-talk mechanism to stimulate the proliferation of normal mammary epithelium to increase the risk of breast cancer. The emerging model of cross-talk suggests that estradiol regulates the expression of IGF-I and the IGF receptor I. The subsequent binding of IGF-I to its receptor initiates an intracellular signal transduction pathway that activates transcription factors, including the estrogen receptor. Recent studies show that the effects of IGF-I on estrogen receptor activity are mediated in part by the protein kinase A and phosphatidylinositol-3-kinase/Akt pathways.