Insulin/insulin-like growth factor-I and estrogen cooperate to stimulate cyclin E-Cdk2 activation and cell Cycle progression in MCF-7 breast cancer cells through differential regulation of cyclin E and p21(WAF1/Cip1)

Association between prediabetes and breast cancer: a comprehensive meta-analysis

BACKGROUND

Breast cancer accounts for up to 30% of cancer cases in women in the US. Diabetes mellitus has been recognized as a risk factor for breast cancer. Some studies have suggested that prediabetes may also be associated with breast cancer whereas other studies have shown no or an inverse association; thus, we conducted a meta-analysis to assess the risk of breast cancer in prediabetes.

METHODS

We searched PubMed/Medline, EMBASE, Google Scholar, and Scopus to identify studies that reported breast cancer risks in patients having prediabetes compared to normoglycemic patients. Binary random-effects model was used to calculate a pooled odds ratio (OR) with 95% confidence intervals. I2 statistics were used to assess heterogeneity. Leave-one-out sensitivity analysis and subgroup analyses were performed.

RESULTS

We analyzed 7 studies with 24,586 prediabetic and 224,314 normoglycemic individuals (783 and 5739 breast cancer cases, respectively). Unadjusted odds ratio (OR) for breast cancer was 1.45 (95% CI = 1.14, 1.83); adjusted OR was 1.19 (95% CI = 1.07, 1.34) in prediabetes. Subgroup analysis revealed a higher breast cancer risk in individuals aged less than 60 years (OR = 1.86, 95% CI = 1.39, 2.49) than in those aged 60 years or more (OR = 1.07, 95% CI = 0.97, 1.18). Subgroup analysis by median follow-up length indicated a higher risk of breast cancer for follow-ups of less than or equal to 2 years (OR = 2.34, 95% CI = 1.85, 2.95) than in those of over 10 years (OR = 1.1, 95% CI = 0.99, 1.23) and 6 to 10 years (OR = 1.03, 95% CI = 0.88, 1.21).

CONCLUSIONS

In conclusion, individuals with prediabetes have higher risk of developing breast cancer than those with normoglycemia, especially younger prediabetes patients. These individuals may benefit from early identification, monitoring, and interventions to reverse prediabetes.

Association of preoperative serum adipokines, insulin, and sex steroid hormones with breast cancer risk in the Indian women

BACKGROUND

Obesity-related factors such as adipokines, insulin, insulin-like growth factors, and sex steroid hormones have been reported to be involved in breast carcinogenesis. Studies across the world suggest an important, but still controversial, role of obesity in breast cancer risk. This study aims to evaluate the association of obesity-related factors such as adipokines, insulin, insulin resistance, and sex steroid hormones with breast cancer risk in the Indian population.

MATERIALS AND METHODS

Anthropometric and biochemical measurements were taken in 60 newly diagnosed and histologically confirmed breast cancer patients and 50 healthy controls. Preoperative serum levels of adiponectin, leptin, insulin, estrogen, and testosterone were measured using ELISA (enzyme-linked immunosorbent assay). The data were analyzed and compared.

RESULTS

The mean serum total cholesterol (T.CHOL) and leptin levels were significantly higher ( P = 0.047), whereas testosterone levels were significantly lower in patients than in controls. Waist circumference (WC) and leptin levels showed a significant positive association with breast cancer risk. Association of serum leptin levels with breast cancer risk persisted after adjusting for age, body mass index (BMI), and WC parameters (odds ratio [ OR ] = 1.042, P = 0.03). Leptin levels positively correlated with WC and triglycerides (TG), whereas insulin and insulin resistance positively correlated with BMI, WC, TG, and T.CHOL ( P < 0.05). Among the tumor characteristics, serum adiponectin showed a positive correlation with lymph node involvement, whereas serum estradiol levels were positively correlated with ER (estrogen receptor) and PR (progesterone receptor) status.

CONCLUSION

Together, our study supports the association of obesity (WC) with breast cancer risk and also suggests the potential role of leptin as a biomarker for breast cancer risk, independent of obesity.

Cell Cycle Status Influences Resistance to Apoptosis Induced by Oxidative Stress in Human Breast Cancer Cells, Which Is Accompanied by Modulation of Autophagy

Cancer cells are characterised by uncontrolled cell proliferation; however, some of them can temporarily arrest their cell cycle at the G0 or G1 phase, which could contribute to tumour heterogeneity and drug resistance. The cell cycle status plays a critical role in chemosensitivity; however, the influence of G0- and G1-arrest has not been elucidated. To study the cell cycle arrest-mediated resistance, we used MCF-7 cells and generated three populations of cells: (1) cells arrested in the G0-like phase, (2) cells that resumed the cell cycle after the G0-like phase and (3) cells arrested in early G1 with a history of G0-like arrest. We observed that both the G0-like- and the G1-arrested cells acquired resistance to apoptosis induced by oxidative stress, accompanied by a decreased intracellular reactive oxygen species and DNA damage. This effect was associated with increased autophagy, likely facilitating their survival at DNA damage insult. The cell cycle reinitiation restored a sensitivity to oxidative stress typical for cells with a non-modulated cell cycle, with a concomitant decrease in autophagy. Our results support the need for further research on the resistance of G0- and G1-arrested cancer cells to DNA-damaging agents and present autophagy as a candidate for targeting in anticancer treatment.

Co-expression network analysis of frontal cortex during the progression of Alzheimer's disease

Mechanisms of Alzheimer's disease (AD) and its putative prodromal stage, amnestic mild cognitive impairment (aMCI), involve the dysregulation of multiple candidate molecular pathways that drive selective cellular vulnerability in cognitive brain regions. However, the spatiotemporal overlap of markers for pathway dysregulation in different brain regions and cell types presents a challenge for pinpointing causal versus epiphenomenal changes characterizing disease progression. To approach this problem, we performed Weighted Gene Co-expression Network Analysis and STRING interactome analysis of gene expression patterns quantified in frontal cortex samples (Brodmann area 10) from subjects who died with a clinical diagnosis of no cognitive impairment, aMCI, or mild/moderate AD. Frontal cortex was chosen due to the relatively protracted involvement of this region in AD, which might reveal pathways associated with disease onset. A co-expressed network correlating with clinical diagnosis was functionally associated with insulin signaling, with insulin (INS) being the most highly connected gene within the network. Co-expressed networks correlating with neuropathological diagnostic criteria (e.g., NIA-Reagan Likelihood of AD) were associated with platelet-endothelium-leucocyte cell adhesion pathways and hypoxia-oxidative stress. Dysregulation of these functional pathways may represent incipient alterations impacting disease progression and the clinical presentation of aMCI and AD.

Neu Perspectives, Therapies, and Challenges for Metastatic HER2-Positive Breast Cancer

Even though gene amplification or protein overexpression occurs in approximately one-fifth of all breast cancers, the discovery of HER2 has, nevertheless, had profound implications for the disease. Indeed, the characterization of the receptor resulted in a number of significant advances. Structurally, unique features provided avenues for the development of numerous compounds with target-specificity; molecularly, biological constructs revealed a highly complex, internal signal transduction pathway with regulatory effects on tumor proliferation, survival, and perhaps, even resistance; and clinically, disease outcomes manifested its predictive and prognostic value. Yet despite the receptor’s utility, the beneficial effects are diminished by tumor recurrence after neo- or adjuvant therapy as well as losses resulting from the inability to cure patients with metastatic disease. What these observations suggest is that while tumor response may be partially linked to uncoupling cell surface message reception and nuclear gene expression, as well as recruitment of the innate immune system, disease progression and/or resistance may involve a reprogrammable signaling mainframe that elicits alternative growth and survival signals. This review attempts to meld current perceptions related to HER2-positive metastatic breast cancer with particular attention to current biological insights and therapeutic challenges.

Sex Hormones, Insulin, and Insulin-like Growth Factors in Recurrence of High-Stage Endometrial Cancer

BACKGROUND

The influence of sex hormone and insulin/insulin-like growth factor (IGF) axis signaling on endometrial cancer recurrence is unknown. We evaluated these pathways in a prospective cohort of Gynecologic Oncology Group (GOG)0210 trial endometrial adenocarcinoma patients.

METHODS

Stage II-IV patients (N = 816) were included in this study. Pretreatment specimens were tested for tumor mRNA and protein expression of IGF1, IGF2, IGF-binding proteins (IGFBP)-1 and -3, insulin (IR) and IGF-I receptors (IGF1R), phosphorylated IR/IGF1R (pIGF1R/pIR), and estrogen (ER) and progesterone receptors (PR) using qPCR and IHC. Serum concentrations of insulin, IGF-I, IGFBP-3, estradiol, estrone, and sex hormone binding globulin were measured. HRs and 95% confidence intervals (CI) for progression-free survival were calculated from Cox models adjusting for age, stage, and grade.

RESULTS

Recurrence occurred in 280 (34%) cases during a median of 4.6 years of follow-up. ER positivity (HR, 0.67; 95% CI, 0.47-0.95), IR positivity (HR, 0.53; 95% CI, 0.29-0.98), and circulating IGF-I (highest vs. lowest quartile: HR, 0.66; 95% CI, 0.47-0.92) were inversely associated with recurrence risk. Circulating estradiol (highest vs. lowest tertile: HR, 1.55; 95% CI, 1.02-2.36) and pIGF1R/pIR positivity (HR, 1.40; 95% CI, 1.02-1.92) were associated with increased recurrence risk.

CONCLUSIONS

Circulating estradiol and tumor tissue phosphorylated (activated) IGR1R/IR were independently associated with higher risk of recurrence in patients with endometrial cancer.

IMPACT

This study may inform future clinical trials of endocrine-targeted adjuvant therapies in patients with endometrial cancer that could include baseline assessment of serum and tissue biomarkers of estradiol and insulin signaling pathways.

LncRNA HCP5 promotes cell proliferation and inhibits apoptosis via miR-27a-3p/IGF-1 axis in human granulosa-like tumor cell line KGN

This study aimed to reveal the potential roles of long non-coding RNA HCP5 (lncRNA HCP5) and its potential molecular mechanism in polycystic ovarian syndrome (PCOS). The human granulosa-like tumor cell line KGN was used for assessing the effects of HCP5 in the proliferation and apoptosis of granulosa cells (GCs). The results showed that downregulation of HCP5 suppressed cell proliferation through arresting cell cycle progression at G1 phase, and induced the apoptosis via activating mitochondrial pathway, while overexpression of HCP5 played the opposite effects in KGN cells. We predicted and confirmed miR-27a-3p was a directly target to HCP5 and it could directly bind with insulin-like growth factor-1 (IGF-1). Next, we performed gain- and loss-of-functions approaches by transfecting miR-27a-3p inhibitor into HCP5 knocking down cells and transfecting miR-27a-3p mimics into HCP5 overexpressing cells. The results demonstrated that downregulation and upregulation of miR-27a-3p could block the effects on the proliferation and apoptosis mediated by silencing and overexpressing HCP5 in KGN cells. Additionally, miR-27a-3p inhibitor remarkably reversed the IGF-1 decrease regulated by knocking down HCP5 and miR-27a-3p mimics inhibited the IGF-1 increase modulated by overexpressing HCP5 in KGN cells. Furthermore, we observed that the promoted cell vitality and reduced apoptosis mediated by enforced expression of HCP5 could be alleviated when the KGN cells transfected with IGF-1 siRNA. Our findings indicate that HCP5 might be a potential regulatory factor for development of PCOS through regulating the miR-27a-3p/IGF-1 axis.

Adipose Tissue, Obesity and Adiponectin: Role in Endocrine Cancer Risk

Adipose tissue has been recognized as a complex organ with endocrine and metabolic roles. The excess of fat mass, as occurs during overweight and obesity states, alters the regulation of adipose tissue, contributing to the development of obesity-related disorders. In this regard, many epidemiological studies shown an association between obesity and numerous types of malignancies, comprising those linked to the endocrine system (e.g., breast, endometrial, ovarian, thyroid and prostate cancers). Multiple factors may contribute to this phenomenon, such as hyperinsulinemia, dyslipidemia, oxidative stress, inflammation, abnormal adipokines secretion and metabolism. Among adipokines, growing interest has been placed in recent years on adiponectin (APN) and on its role in carcinogenesis. APN is secreted by adipose tissue and exerts both anti-inflammatory and anti-proliferative actions. It has been demonstrated that APN is drastically decreased in obese individuals and that it can play a crucial role in tumor growth. Although literature data on the impact of APN on carcinogenesis are sometimes conflicting, the most accredited hypothesis is that it has a protective action, preventing cancer development and progression. The aim of the present review is to summarize the currently available evidence on the involvement of APN and its signaling in the etiology of cancer, focusing on endocrine malignancies.

Physical Exercise Positively Influences Breast Cancer Evolution

Breast cancer is one of the most commonly diagnosed types of cancer in women. Its pathogenesis involves genetic, hormonal, and environmental factors. A large body of evidence indicates that physical activity has positive effects on every aspect of breast cancer evolution, including prevention, medical treatment, and aftercare clinical settings. Thus, different types of exercise can influence the prevention and progression of the disease through several common mechanisms, such as reduction of insulin resistance and improvement of immunity and cardiovascular function. Furthermore, acute and chronic symptoms of breast cancer, such as cachexia, muscle mass loss, fatigue, cardiotoxicity, weight gain, hormone alterations, bone loss, and psychologic adverse effects, may all be favorably influenced by regular exercise. We review the relation of intensity and duration of exercise with potential pathophysiologic pathways, including obesity-related hormones and sex steroid hormone production, oxidative stress, epigenetic alterations such as DNA hypomethylation, and changes in telomere length, within the context of the beneficial effects of exercise. The potential role of exercise in reducing the intensity of the adverse effects that result from breast cancer and anticancer treatment is also discussed.

Linear growth and endocrine function in children with ataxia telangiectasia

INTRODUCTION

Ataxia telangiectasia (AT) is a rare, genetic, primary immune deficiency disease characterized by immunodeficiency and neurological manifestations, with an increased tendency to infection, malignancy, and autoimmune diseases. Both growth delay and endocrine abnormalities are occasionally reported in these patients.

PATIENTS AND METHODS

We studied growth parameters height (Ht), weight, body mass index (BMI) and calculated the Ht standard deviation scores (HtSDS) of 13 patients (age 7.7 ± 3.5 years-age range: 3-14.5 years) with AT in relation to their mid-parental Ht SDS (MPHtSDS). We measured their serum calcium (Ca), phosphorus (PO4), alkaline phosphatase, alanine transferase (ALT), serum ferritin, creatinine and albumin concentrations. Endocrine investigations included the assessment of serum free thyroxine (FT4), thyrotropin (TSH), insulin-like growth factor-I (IGF-I) and morning cortisol. Complete blood count and serum immunoglobulins (IgG, IgM and IgA antibodies) were also measured. Growth data were correlated to hormonal and immune data.

RESULTS

About 31% of patients with AT had short stature (HtSDS <-2). However, their MPHtSDS denoted that their short stature was familial because four out of 13 had MPHtSDS <-2. They had low BMI, and two of them had low serum albumin and IGF-I, denoting malnutrition or disturbed growth hormone secretion. Elevated serum ALT and ferritin in some patients suggest immune-related inflammation in the liver. 30% of patients had high TSH, two of them had low FT4 diagnosing overt (15%) and sub-clinical (15%) hypothyroidism. Anti-thyroid peroxidase antibodies were high in two out of 13 patients denoting immune-related thyroid aggression. Eight out of 13 patients had Vitamin D deficiency (<20 ng/ml) however, their serum Ca and PO4 levels were in the normal range. One adolescent girl (14.5 years) had hyper-gonadotropic hypogonadism (low estradiol and high follicle stimulating hormone). All patients had normal 8 AM cortisol and renal function. None of the growth parameters were correlated with the IgG, IgM or IgA levels.

IN SUMMARY

Patients with AT had a high prevalence of growth retardation and endocrine dysfunction in the form of low IGF-I, overt and subclinical hypothyroidism and hypogonadism. Physicians should be aware of these possible endocrinopathies for an early diagnosis and proper treatment.

Synthetic retinoid fenretinide in breast cancer chemoprevention

Preclinical models suggest that retinoids inhibit mammary carcinogenesis. The induction of apoptosis is a unique feature of fenretinide, the most-studied retinoid in clinical trials of breast cancer chemoprevention, owing to its selective accumulation in breast tissue and its favorable toxicological profile. In a Phase III breast cancer prevention trial, fenretinide showed a strong trend of reduction of incidence of second breast malignancies in premenopausal women, which was confirmed by 15 years of follow-up. This warrants further research on the mechanisms of action and potential efficacy of fenretinide and provides the rationale for a Phase III primary prevention trial in young women at high risk for breast cancer. This review will highlight the role of fenretinide in breast cancer chemoprevention.

An insulin-like growth factor homologue of Singapore grouper iridovirus modulates cell proliferation, apoptosis and enhances viral replication

Insulin-like growth factors (IGFs) play crucial roles in regulating cell differentiation, proliferation and apoptosis. In this study, a novel IGF homologue gene (IGF-like) encoded by Singapore grouper iridovirus (SGIV) ORF062R (termed SGIV–IGF), was cloned and characterized. The coding region of SGIV–IGF is 771 bp in length, with a variable number of tandem repeats (VNTR) locus at the 3′-end. We cloned one isoform of this novel gene, 582 bp in length, containing the predicted IGF domain and 3.6 copy numbers of the 27 bp repeat unit. SGIV–IGF was an early transcribed gene during viral infection, and SGIV–IGF was distributed predominantly in the cytoplasm with a diffused granular appearance. Intriguingly, overexpression of SGIV–IGF was able to promote the growth of grouper embryonic cells (GP cells) by promoting G1/S phase transition, which was at least partially dependent on its 3′-end VNTR locus. Furthermore, viral titre assay and real-time quantitative PCR (RT-qPCR) analysis proved that SGIV–IGF could promote SGIV replication in grouper cells. In addition, overexpression of SGIV–IGF mildly facilitated apoptosis in SGIV-infected non-host fathead minnow (FHM) cells. Together, our study demonstrated a novel functional gene of SGIV which may regulate viral replication and cellular processes through multiple mechanisms that appear to be cell type-dependent.

Insulin and IGFs in obesity-related breast cancer

Obesity and the Metabolic Syndrome are associated with multiple factors that may cause an increased risk for cancer and cancer-related mortality. Factors involved include hyperinsulinemia, hyperglycemia, hyperlipidemia and IGFs. Insulin resistance is also associated with alterations in the levels of proinflammatory cytokines, chemokines, adipokines (leptin, adiponectin) that may also be contributing factors. The insulin family of proteins is ubiquitously expressed and has pleiotropic effects on metabolism and growth. However insulin, IGF-1 and particularly IGF-2 have been identified as tumor promoters in multiple studies. Mouse models have focused on insulin and IGF-1 and their receptors as being involved in tumor progression and metastases. The role of the insulin receptor as either mediating the effects on tumors or as compensating for the insulin-like growth factor receptor has arisen. Its role has been supported by preclinical studies and the importance of insulin resistance and hyperinsulinemia in obesity and early diabetes. Since the focus of this review is the insulin-family we will focus on insulin, IGF-1 and IGF-2.

Proteomic snapshot of breast cancer cell cycle: G1/S transition point

The biological processes that unfold during the G1-phase of the cell cycle are dependent on extracellular mitogenic factors that signal the cell to enter a state of quiescence, or commit to a cell-cycle round by passing the restriction point (R-point) and enter the S-phase. Unlike normal cells, cancer cells evolved the ability to evade the R-point and continue through the cell cycle even in the presence of extensive DNA damage or absence of mitogenic signals. The purpose of this study was to perform a quantitative proteomic evaluation of the biological processes that are responsible for driving MCF-7 breast cancer cells into division even when molecular checkpoints such as the G1/S R-point are in place. Nuclear and cytoplasmic fractions of the G1 and S cell-cycle phases were analyzed by LC-MS/MS to result in the confident identification of more than 2700 proteins. Statistical evaluation of the normalized data resulted in the selection of proteins that displayed twofold or more change in spectral counts in each cell state. Pathway mapping, functional annotation clustering, and protein interaction network analysis revealed that the top-scoring clusters that could play a role in overriding the G1/S transition point included DNA damage response, chromatin remodeling, transcription/translation regulation, and signaling proteins.

High glucose and insulin differentially modulates proliferation in MCF-7 and MDA-MB-231 cells

Various preclinical and clinical studies have linked diabetes and breast cancer, but little is known regarding the molecular mechanism involved. This study aimed to investigate the effect of high glucose and insulin in breast cancer cells (MCF-7: non-invasive, hormone dependent, and MDA-MB-231: invasive, hormone independent). In contrast to MCF-7 cells, high glucose augmented proliferation of MDA-MB-231 cells as observed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and bromodeoxyuridine assays. The high-glucose condition led to increased expression of cyclin D1, de-phosphorylation of p38, and increased phosphorylation of ERK in MDA-MB-231 cells but not in MCF-7 cells. Interestingly, we observed increased phosphorylation of GSK-3β, NF-κB, and ERα only in MCF-7 cells, highlighting their role as potential targets in prevention of progression of breast cancer under a high-glucose and insulin condition. Furthermore, insulin treatment under a high-glucose condition resulted in increased histone H3 phosphorylation and de-acetylation only in MDA-MB-231 cells. Taken together, we provide the first evidence that high glucose and insulin promotes proliferation of MDA-MB-231 cells by differential alteration of GSK-3β, NF-κB, and ERα expression and histone H3 modifications, which may directly or indirectly modulate the expression of genes involved in its proliferation.

Ligand-free estrogen receptor activity complements IGF1R to induce the proliferation of the MCF-7 breast cancer cells

Background

Ligand-dependent activation of the estrogen receptor (ER) as well as of the insulin-like growth factor type 1 (IGF1R) induces the proliferation of luminal breast cancer cells. These two pathways cooperate and are interdependent. We addressed the question of the mechanisms of crosstalk between the ER and IGF1R.

Methods

We evaluated the mitogenic effects of estradiol (E2; agonist ligand of ER) and of insulin (a ligand of IGF1R) in the MCF-7 cells by flow cytometry and by analyzing the cell levels of cell cycle-related proteins (immunoblotting) and mRNA (RT-QPCR). To verify the requirement for the kinase activity of Akt (a downstream target of IGF1R) in the mitogenic action of estradiol, we used shRNA strategy and shRNA-resistant expression vectors.

Results

The activation of the ER by E2 is unable to induce the cell cycle progression when the phosphatidyl inositol-3 kinase (PI3K)/Akt signaling is blocked by a chemical inhibitor (LY 294002) or by shRNA targeting Akt1 and Akt2. shRNA-resistant Akt wild-type constructs efficiently complemented the mitogenic signaling activity of E2 whereas constructs with inactivated kinase function did not. In growth factor-starved cells, the residual PI3K/Akt activity is sufficient to complement the mitogenic action of E2. Conversely, when ER function is blocked by the antiestrogen ICI 182780, IGF1R signaling is intact but does not lead to efficient reinitiation of the cell cycle in quiescent, growth factor-starved MCF-7 cells. The basal transcription-promoting activity of ligand-free ER in growth factor-starved cells is sufficient to complement the mitogenic action of the IGF1R-dependent signaling.

Conclusions

The basal ER activity in the absence of ligand is sufficient to allow efficient mitogenic action of IGF1R agonists and needs to be blocked to prevent the cell cycle progression.

Insulin promotes proliferation, survival, and invasion in endometrial carcinoma by activating the MEK/ERK pathway

The involvement of insulin in endometrial carcinoma (EC) was investigated using radioimmunoassay, Western blot, immunoprecipitation, MTT, and Annexin V-FITC/PI assays in tissue samples and cultured cells. Serum levels of insulin, p-p52Shc, p-p46Shc, Shc·Grb2 complexes, p-MEK, p-ERK, and cyclin D1 were elevated in patients with EC. Expression of key proteins in the MEK/ERK pathway, including p-p52Shc, Shc·Grb2 complexes, p-MEK, p-ERK, and cyclin D1, was significantly higher in patients with advanced FIGO stage, high grade, and lymph-node metastasis and correlated positively with serum insulin concentration. Insulin promotes Ishikawa 3-H-12 cell proliferation, survival, and invasion, and these effects induced by insulin were significantly blocked by MEK inhibitor PD98059. Insulin thus promotes EC cell proliferation, survival, and invasion via the MEK/ERK pathway.

Minireview: Putting physiology back into estrogens' mechanism of action

After decades of research, the mechanism by which estrogens stimulate the proliferation of epithelial cells in the endometrium and mammary gland, and in the carcinomas that arise in those tissues, is still not understood. Cells do not proliferate in response to 17β-estradiol (E2) alone, and although it is widely recognized that growth factors play a role in E2's proliferative effect, exactly how they are involved is unclear. It has long been known that the proliferation of endometrial epithelial cells is preceded by dramatic increases in blood flow and microvascular permeability, filling the subepithelial stroma with plasma and the proteins it contains, such as IGF-I, which is known to synergize with E2 in the induction of cell proliferation. The hyperpermeability is caused by vascular endothelial growth factor (VEGF), which is rapidly induced by E2, via the transcription factors hypoxia-inducible factor 1 and estrogen receptor α, in luminal epithelial cells in vivo. As we recently showed, VEGF is also strongly induced in endometrial cancer cells in vitro when excessive degradation of hypoxia-inducible factor 1α, caused by the abnormally high oxygen level to which cultured cells are exposed, is prevented. Putting these facts together, we now propose a new model of E2-induced proliferation in which VEGF-induced vascular hyperpermeability plays an essential role. E2 first induces the expression by endometrial epithelial cells of VEGF, which then acts in a paracrine manner to induce interendothelial cell gaps in subepithelial blood vessels, through which plasma and the proteins therein enter the adjacent stroma. Plasma carries even more E2, which circulates bound to proteins, and IGF-l, which together drive epithelial cells completely through the cell cycle.

A mathematical model of cell cycle progression applied to the MCF-7 breast cancer cell line

In this paper, we present a model of cell cycle progression and apply it to cells of the MCF-7 breast cancer cell line. We consider cells existing in the three typical cell cycle phases determined using flow cytometry: the G1, S, and G2/M phases. We further break each phase up into model phases in order to capture certain features such as cells remaining in phases for a minimum amount of time. The model is also able to capture the environmentally responsive part of the G1 phase, allowing for quantification of the number of environmentally responsive cells at each point in time. The model parameters are carefully chosen using data from various sources in the biological literature. The model is then validated against a variety of experiments, and the excellent fit with experimental results allows for insight into the mechanisms that influence observed biological phenomena. In particular, the model is used to question the common assumption that a 'slow cycling population' is necessary to explain some results. Finally, an extension is proposed, where cell death is included in order to accurately model the effects of tamoxifen, a common first line anticancer drug in breast cancer patients. We conclude that the model has strong potential to be used as an aid in future experiments to gain further insight into cell cycle progression and cell death.

Cyclin-dependent kinase-mediated phosphorylation of RBP1 and pRb promotes their dissociation to mediate release of the SAP30·mSin3·HDAC transcriptional repressor complex

Eukaryotic cell cycle progression is mediated by phosphorylation of protein substrates by cyclin-dependent kinases (CDKs). A critical substrate of CDKs is the product of the retinoblastoma tumor suppressor gene, pRb, which inhibits G(1)-S phase cell cycle progression by binding and repressing E2F transcription factors. CDK-mediated phosphorylation of pRb alleviates this inhibitory effect to promote G(1)-S phase cell cycle progression. pRb represses transcription by binding to the E2F transactivation domain and recruiting the mSin3·histone deacetylase (HDAC) transcriptional repressor complex via the retinoblastoma-binding protein 1 (RBP1). RBP1 binds to the pocket region of pRb via an LXCXE motif and to the SAP30 subunit of the mSin3·HDAC complex and, thus, acts as a bridging protein in this multisubunit complex. In the present study we identified RBP1 as a novel CDK substrate. RBP1 is phosphorylated by CDK2 on serines 864 and 1007, which are N- and C-terminal to the LXCXE motif, respectively. CDK2-mediated phosphorylation of RBP1 or pRb destabilizes their interaction in vitro, with concurrent phosphorylation of both proteins leading to their dissociation. Consistent with these findings, RBP1 phosphorylation is increased during progression from G(1) into S-phase, with a concurrent decrease in its association with pRb in MCF-7 breast cancer cells. These studies provide new mechanistic insights into CDK-mediated regulation of the pRb tumor suppressor during cell cycle progression, demonstrating that CDK-mediated phosphorylation of both RBP1 and pRb induces their dissociation to mediate release of the mSin3·HDAC transcriptional repressor complex from pRb to alleviate transcriptional repression of E2F.

Reduced expression of ubiquitin ligase FBXW7 mRNA is associated with poor prognosis in breast cancer patients

FBXW7 is a cell cycle regulatory gene that ubiquitinates positive cell cycle regulators such as c-Myc and cyclin E, allowing for cell cycle exit. Defects in the FBXW7 gene that lead to cell cycle re-entry and expedite the G1-S transition is thought to be one of the causes of cancer development. However, its clinical importance for breast cancer patients remains undetermined. This prompted us to investigate its expression level in breast cancer patients to establish its clinical significance. The expression level of FBXW7 mRNA was assessed in 186 cases of primary invasive breast cancer. Correlations between FBXW7 mRNA expression and clinicopathological factors, prognoses and immunohistochemical expression levels of Ki-67, FBXW7, c-Myc and cyclin E were analyzed. In vitro investigation of FBXW7 gene silencing in a breast cancer cell line was conducted. FBXW7 mRNA was expressed at significantly lower levels in patients with high histological grade and hormone receptor-negative tumors. Patients with lower FBXW7 mRNA expression had a poorer prognosis for breast cancer-specific survival than those with higher expression. A high Ki-67 labeling index and positive cyclin E protein expression were significantly correlated with lower FBXW7 mRNA expression. In vitro, silencing FBXW7 enhanced expression of c-Myc and cyclin E proteins and upregulated both cell proliferation and G1-S transition. In breast cancer, reduced FBXW7 mRNA expression may have independent prognostic potential through the enhanced function of cell cycle regulatory proteins.

Estrogen regulated expression of the p21 Waf1/Cip1 gene in estrogen receptor positive human breast cancer cells

The cyclin-dependent kinase inhibitor protein p21(Waf1/Cip1) is a potent tumor suppressor. Here, we demonstrate that estradiol regulates the p21(Waf1/Cip1) gene. Estradiol induces p21(Waf1/Cip1) mRNA expression within 30-60 min independent of new protein synthesis in the estrogen receptor alpha (ER alpha) positive human breast cancer cell line MCF-7. Similar to other estradiol responsive promoters, the p21(Waf1/Cip1) upstream promoter region has several estrogen response element (ERE) half-sites nestled in AP-1 binding sites, which are positioned upstream to Sp1 binding sites. Using the chromatin immunoprecipitation (ChIP) assay, we show that estradiol stimulation resulted in the recruitment of transcription factors ER alpha, Sp1, and Sp3 to the p21(Waf1/Cip1) upstream promoter element. The Sp1 inhibitor mithramycin A abrogated Sp1, and to a lesser extent Sp3 binding, and markedly reduced the estradiol stimulated p21(Waf1/Cip1) gene expression. However, ER alpha binding was not affected in the mithramycin A and estradiol treated cells. On closer examination of the half-site ERE/AP-1 sites upstream to the Sp1 sites in a separate ChIP experiment, we found a pronounced association of ER alpha upon estradiol treatment compared to almost negligible binding of Sp1 or Sp3. Together these studies provide evidence that ER alpha is recruited to the half-site ERE/AP-1 sites in the p21(Waf1/Cip1) upstream promoter element. Although Sp1/Sp3 is not involved in the recruitment of ER alpha to the promoter, Sp1 is necessary for estrogen-induced p21(Waf1/Cip1) promoter activity.

Functional analysis of familial Asp67Glu and Thr1051Ser BRCA1 mutations in breast/ovarian carcinogenesis

Estrogen is believed to be pre-initiator in the risk of breast cancer. The BRCA1 is a tumor suppressor gene associated with breast and ovarian cancer risk. This report describes functional analysis of two BRCA1 missense mutations (Asp67Glu and Thr1051Ser) observed in the familial breast/ovarian cancer patients in Thailand. Levels of luciferase activity of the two mutations were relatively lower than in the wild-type BRCA1. It is indicated that mutants may fail to promote the estrogen receptor dependent functions. It is presumed that estrogen and insulin/IGF-1 regulate c-Myc and cyclin D1 during breast cancer cell proliferation. It is also likely to affect ubiquitination mechanism. Since three affected cancer families carry the Asp67Glu mutation, it is believed that this type of mutation could have some effect on breast/ovarian cancer progression.

The aromatase inhibitor letrozole and inhibitors of insulin-like growth factor I receptor synergistically induce apoptosis in in vitro models of estrogen-dependent breast cancer

Introduction

Endocrine-dependent, estrogen receptor positive breast cancer cells proliferate in response to estrogens, synthesized by the cytochrome p450 aromatase enzyme. Letrozole is a potent nonsteroidal aromatase inhibitor that is registered for the treatment of postmenopausal women with advanced metastatic breast cancers and in the neoadjuvant, early, and extended adjuvant indications. Because crosstalk exists between estrogen receptor and insulin-like growth factor I receptor (IGF-IR), the effect of combining a selective IGF-IR inhibitor (NVP-AEW541) with letrozole was assessed in two independent in vitro models of estrogen-dependent breast cancer.

Methods

MCF7 and T47D cells stably expressing aromatase (MCF7/Aro and T47D/Aro) were used as in vitro models of aromatase-driven breast cancer. The role of the IGF-IR pathway in breast cancer cells stimulated only by 17β-estradiol or androstenedione was assessed by proliferation assays. The combination of letrozole and NVP-AEW541 was assessed for synergy in inhibiting cell proliferation using Chou-Talalay derived equations. Finally, combination or single agent effects on proliferation and apoptosis were assessed using proliferation assays, flow cytometry, and immunoblotting.

Results

Both MCF7 and T47D cells, as well as MCF7/Aro and T47D/Aro, exhibited sensitivity to inhibition of 17β-estradiol dependent proliferation by NVP-AEW541. Letrozole combined with NVP-AEW541 synergistically inhibited androstenedione-dependent proliferation in aromatase-expressing cells with combination index values of 0.6 or less. Synergistic combination effects correlated with higher levels of apoptosis as compared with cells treated with the single agent alone. Treatment with either agent also appeared to inhibit IGF-IR signalling via phosphoinositide 3-kinase. Notably, IGF-IR inhibition had limited effect on estrogen-dependent proliferation in the cell lines, but was clearly required for survival, suggesting that the combination of letrozole and IGF-IR inhibition sensitizes cells to apoptosis.

Conclusion

Inhibition of the IGF-IR pathway and aromatase was synergistic in two independent estrogen-dependent in vitro models of breast cancer. Moreover, synergism of NVP-AEW541 and letrozole correlated with induction of apoptosis, but not cell cycle arrest, in the cell lines tested. Combination of IGF-IR inhibitors and letrozole may hold promise for the treatment of patients with estrogen-dependent breast cancers.

Identification of breast cancer peptide epitopes presented by HLA-A*0201

Cellular immune mechanisms detect and destroy cancerous and infected cells via the human leukocyte antigen (HLA) class I molecules that present peptides of intracellular origin on the surface of all nucleated cells. The identification of novel, tumor-specific epitopes is a critical step in the development of immunotherapeutics for breast cancer. To directly identify peptide epitopes unique to cancerous cells, secreted human class I HLA molecules (sHLA) were constructed by deletion of the transmembrane and cytoplasmic domain of HLA A*0201. The resulting sHLA-A*0201 was transferred and expressed in breast cancer cell lines MCF-7, MDA-MB-231, and BT-20 as well as in the immortal, nontumorigenic cell line MCF10A. Stable transfectants were seeded into bioreactors for production of > 25 mg of sHLA-A*0201. Peptides eluted from affinity purified sHLA were analyzed by mass spectroscopy. Comparative analysis of HLA-A*0201 peptides revealed 5 previously uncharacterized epitopes uniquely presented on breast cancer cells. These peptides were derived from intracellular proteins with either well-defined or putative roles in breast cancer development and progression: Cyclin Dependent Kinase 2 (Cdk2), Ornithine Decarboxylase (ODC1), Kinetochore Associated 2 (KNTC2 or HEC1), Macrophage Migration Inhibitory Factor (MIF), and Exosome Component 6 (EXOSC6). Cellular recognition of the MIF, KNTC2, EXOSC6, and Cdk2 peptides by circulating CD8+ cells was demonstrated by tetramer staining and IFN-gamma ELISPOT. The identification and characterization of peptides unique to the class I of breast cancer cells provide putative targets for the development of immune diagnostic tools and therapeutics.

IGF-I plus E2 induces proliferation via activation of ROS-dependent ERKs and JNKs in human breast carcinoma cells

Induction of 17beta-estradiol (E2) and insulin-like growth factor-I (IGF-I) has been detected in breast carcinoma, however the interaction between E2 and IGF-I in the proliferation of breast carcinoma cells is still unclear. In the present study, we found that IGF-I enhances the E2-induced proliferation in MCF-7 human breast carcinoma cells in accordance with stimulation of colony formation via a soft agar assay. Activation of insulin receptor substrate-1 (IRS-1) protein and extracellular signal-related kinases (ERKs) and c-Jun N-terminal kinases (JNKs), but not p38 mitogen-activated protein kinase (MAPK), via phosphorylation induction was detected in MCF-7 cells treated with IGF-I plus E2 (E2/IGF-I). E2/IGF-I-induced proliferation was blocked by chemical inhibitors of ERKs (PD98059) and JNKs (SP600125). An increase in the expression of c-Jun protein was detected in E2/IGF-I-treated MCF-7 cells, and this was inhibited by PD98059 and SP600125. Transfection of the dominant negative MEKK and JNK plasmids significantly reduced E2/IGF-I-induced proliferation with suppression of c-Jun protein expression. An increase in peroxide production was detected in E2/IGF-I-treated cells, and N-acetyl-L-cysteine (NAC) and Tiron (TIR) addition significantly inhibited E2/IGF-I-induced cell proliferation with blocking of the phosphorylation of ERKs and JNKs, and the expression of c-Jun protein. Additionally, 3-OH flavone, baicalein, and quercetin showed effective inhibitory activities against E2/IGF-I-induced proliferation through suppressing proliferative events such as phosphorylation of IRS-1, ERKs, and JNKs proteins, and induction of c-Jun protein and colony formation. These results indicate that IGF-I interacts with E2 to promote the proliferation of breast carcinoma cells via ROS-dependent MAPK activation and c-Jun protein expression. The structure-related inhibition of E2/IGF-I-induced proliferative events by flavonoids is elucidated.

Breast cancer cell proliferation is inhibited by BAD: regulation of cyclin D1

Recent investigations suggest that functions of the proapoptotic BCL2 family members, including BAD, are not limited to regulation of apoptosis. Here we demonstrate that BAD inhibits G(1) to S phase transition in MCF7 breast cancer cells independent of apoptosis. BAD overexpression inhibited G(1) transit and cell growth as well as cyclin D1 expression. Inhibition of cyclin D1 expression was mediated through inhibition of transcription activated by AP1. Chromatin immunoprecipitation assays indicated that BAD is localized at the 12-O-tetradecanoylphorbol-13-acetate-response element (TRE) and cAMP-response element (CRE) in the cyclin D1 promoter. This was shown to reflect direct binding interactions of BAD with c-Jun, and this interaction inhibited the activity of AP1 complexes at TRE. BAD did not interact with phosphorylated forms of c-Jun. Our data suggest that inhibitory TRE/CRE-c-Jun-BAD complexes are present at the cyclin D1 promoter in quiescent cells. Estrogen stimulation displaced BAD from TRE/CRE elements in MCF7 cells, whereas BAD overexpression inhibited estrogen-induced cyclin D1 synthesis and cell proliferation. Inhibition of endogenous BAD in MCF7 cells markedly increased the proliferative fraction and DNA synthesis, activated Cdks, and increased cyclin D1 protein levels. This action of BAD required serine residues Ser(75) and Ser(99). Both phosphorylated and unphosphorylated forms of BAD localized to the nuclei of human breast epithelial cells. Thus, we demonstrate a novel role for BAD in cell cycle regulation dependent upon its phosphorylation state and independent of the BAD/BCL2 interaction and apoptosis.

Effects of a Low-Fat, High-Fiber Diet and Exercise Program on Breast Cancer Risk Factors In Vivo and Tumor Cell Growth and Apoptosis In Vitro

The present study investigated the effects of a diet and exercise intervention on known breast cancer (BCa) risk factors, including estrogen, obesity, insulin, and insulin-like growth factor-I (IGF-I), in overweight/obese, postmenopausal women. In addition, using the subjects' pre- and postintervention serum in vitro, serum-stimulated growth and apoptosis of three estrogen receptor-positive BCa cell lines were studied. The women where placed on a low-fat (10-15% kcal), high-fiber (30-40 g per 1,000 kcal/day) diet and attended daily exercise classes for 2 wk. Serum estradiol was reduced in the women on hormone treatment (HT; n = 28) as well as those not on HT (n = 10). Serum insulin and IGF-I were significantly reduced in all women, whereas IGF binding protein-1 was increased significantly. In vitro growth of the BCa cell lines was reduced by 6.6% for the MCF-7 cells, 9.9% for the ZR-75-1 cells, and 18.5% for the T-47D cells. Apoptosis was increased by 20% in the ZR-75-1 cells, 23% in the MCF-7 cells, and 30% in the T-47D cells (n = 12). These results show that a very-low-fat, high-fiber diet combined with daily exercise results in major reductions in risk factors for BCa while subjects remained overweight/obese. These in vivo serum changes slowed the growth and induced apoptosis in serum-stimulated BCa cell lines in vitro.

A Prospective Study of Hemoglobin A1c Concentrations and Risk of Breast Cancer in Women

Impaired glucose metabolism and hyperinsulinemia have been hypothesized to increase breast cancer risk. However, findings from observational studies relating blood concentrations of hyperinsulinemia markers to breast cancer risk have been inconsistent. We prospectively evaluated whether hemoglobin A1c (HbA1c) concentrations predict breast cancer risk in a large female cohort. We included 27,110 female participants of the Women's Health Study who were, at baseline, free of cancer and had usable blood specimens as well as sufficient information on potential risk factors for breast cancer. Relative risks (RR) and 95% confidence intervals (95% CI) were estimated from Cox proportional hazards regression models. All Ps were two sided. During an average of 10 years of follow-up, 790 incident cases of invasive breast cancer were confirmed. Higher baseline HbA1c levels were not associated with an increased risk of breast cancer. The multivariate RR for the highest relative to the lowest quintile of HbA1c levels was 0.87 (95% CI, 0.69-1.10; Ptrend = 0.22). Higher HbA1c levels were also not associated with an increased risk of breast cancer according to alternative clinical cutoff points for HbA1c or in the analyses stratified by body mass index or according to certain tumor characteristics. However, a weakly inverse association was noted among postmenopausal women, especially among those who had never used hormone therapy. There was also a weakly inverse association between HbA1c levels and estrogen receptor–negative breast tumors. These data suggest that higher HbA1c concentrations do not seem to increase risk of breast cancer among apparently healthy women. (Cancer Res 2006; 66(5): 2869-75)

Posttranslational modifications of decidual IGFBP-1 by steroid hormones in vitro

Insulin-like growth factor binding protein-1 (IGFBP-1) appears to regulate insulin-like growth factors (IGFs; IGF-I and IGF-II) biological activity within the local environment of human placenta by modulating IGFs interaction with their receptors. Considering that posttranslational modifications of IGFBP-1 such as phosphorylation and proteolysis affect its affinity for IGFs, this study was undertaken to identify the role of estrogen and progesterone in this regard. The conditioned media of steroid hormone-treated decidual cells were evaluated using different approaches using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and non-denaturing PAGE following immunoblotting as well as zymographys that contained gelatin and IGFBP-1 as substrates. Our results demonstrated that medroxy progesterone acetate (MPA) treatment increased both phosphorylated and non-phosphorylated decidual-secreted IGFBP-1, whereas 17beta-estradiol (E2) treatment attenuated its phosphorylated forms. Furthermore, the results of zymography revealed that steroid hormones regulated the activity of decidual-secreted matrix metalloproteinases (MMP)-2 and -9, in which E2 treatment up-regulated the MMP-9 activity. Finally, it was demonstrated in our study that decidual-secreted MMP-9 was capable of degrading human amniotic fluid-derived IGFBP-1. In conclusion, our data implicate steroid hormones in the control of IGF system activities at the embryo-maternal interface, at least in part, through their effects on the post-translation changes of decidual-secreted IGFBP-1 such as its phosphorylation and/or proteolysis.

Progesterone Inhibits the Estrogen-Induced Phosphoinositide 3-Kinase→AKT→GSK-3β→Cyclin D1→pRB Pathway to Block Uterine Epithelial Cell Proliferation

The mammalian cell cycle is regulated by the cyclin/cyclin-dependent kinase (CDK) phosphorylation of the retinoblastoma (pRB) family of proteins. Cyclin D1 with its CDK4/6 partners initiates the cell cycle and acts as the link between extracellular signals and the cell cycle machinery. Estradiol-17β (E2) stimulates uterine epithelial cell proliferation, a process that is completely inhibited by pretreatment with progesterone (P4). Previously, we identified cyclin D1 localization as a key point of regulation in these cells with E2 causing its nuclear accumulation and P4 retaining it in the cytoplasm with the resultant inhibition of pRB phosphorylation. Here we show that E2 stimulates phosphoinositide 3-kinase to activate phosphokinase B/AKT to effect an inhibitory phosphorylation of glycogen synthase kinase (GSK-3β). This pathway is suppressed by P4. Inhibition of the GSK-3β activity in P4-treated uteri by the specific inhibitor, LiCl, reversed the nuclear accumulation of cyclin D1 and in doing so, caused pRB phosphorylation and the induction of downstream genes, proliferating cell nuclear antigen and Ki67. Conversely, inhibition of phosphoinositide 3 kinase by LY294002 or Wortmanin reversed the E2-induced GSK-3β Ser9 inhibitory phosphorylation and blocked nuclear accumulation of cyclin D1. These data show the reciprocal actions of E2 and P4 on the phosphoinositide 3-kinase through to the GSK-3β pathway that in turn regulates cyclin D1 localization and cell cycle progression. These data reveal a novel signaling pathway that links E2 and P4 action to growth factor-mediated signaling in the uterus.

Hormonal regulation of the Grb14 signal modulator and its role in cell cycle progression of MCF-7 human breast cancer cells

Growth factor receptor bound (Grb)14 is a member of the Grb7 family of src homology (SH)2 domain-containing proteins. These proteins perform both adaptor and modulatory roles in receptor tyrosine kinase (RTK) signaling, although their regulation is poorly understood. In this study, a positive correlation between Grb14 protein expression and ER alpha status in breast cancer cell lines led us to investigate regulation of Grb14 by estradiol and insulin, which synergize in the regulation of breast cancer cell proliferation. In MCF-7 cells maintained in charcoal-stripped serum, Grb14 expression was downregulated by estradiol and increased by the pure anti-estrogen ICI 182780. Under serum-free conditions, insulin enhanced Grb14 expression but this effect was repressed by estradiol when both hormones were used in combination. Using a system in which c-Myc induction drives cell cycle progression independently of estradiol, we demonstrated that Grb14 regulation was specific to estradiol treatment. Finally, we demonstrated a novel functional role for Grb14 whereby its overexpression inhibited not only insulin- but also estrogen-induced cell cycle progression. This was associated with decreased extracellular signal-regulated kinase (Erk)1/2 activation in insulin-stimulated Grb14-overexpressing cells. These data represent the first demonstration of regulation of Grb14 expression levels in response to hormonal stimuli, and are consistent with its role as a repressor of insulin signaling where it is induced as a negative feedback mechanism. A role for Grb14 is also shown in estrogen/insulin crosstalk since estradiol blocks the insulin-induced induction of this protein.

Progesterone stimulates mammary gland ductal morphogenesis by synergizing with and enhancing insulin-like growth factor-I action

Progestins have been implicated in breast cancer development, yet a role for progesterone (Pg) in ductal morphogenesis (DM) has not been established. To determine whether Pg could cause DM, we compared relative effects of Pg, estradiol (E2) and IGF-I on anatomical and molecular biological parameters of IGF-I-related DM in oophorectomized female IGF-I(-/-) mice. Pg had little independent effect on mammary development, but together with IGF-I, in the absence of E2, Pg stimulated an extensive network of branching ducts, occupying 92% of the gland vs. 28.3% with IGF-I alone, resembling pubertal development (P < 0.002). Its major effect was on enhancing duct length and branching (P < 0.002). Additionally, Pg enhanced phosphorylation of IRS-1, increased cell division, and increased the antiapoptotic effect of IGF-I. Pg action was inhibited by RU486 (P < 0.01). E2 also stimulated DM by enhancing IGF-I action but had a greater effect on terminal end bud formation and side branching (P < 0.002). In contrast to previous findings, long-term exposure to E2 alone, without IGF-I, caused formation of ducts and side branches, a novel finding. Both IGF-I and E2 were found necessary for Pg-induced alveolar development. In conclusion, Pg, through Pg receptor can enhance IGF-I action in DM, and E2 acts through a similar mechanism; E2 alone caused formation of ducts and side branches; there were differences in the actions of Pg and E2, the former largely affecting duct formation and extension, and the latter side branching; and both IGF-I and E2 were necessary for Pg to form mature alveoli.

Factors associated with circulating levels of insulin-like growth factor-I and insulin-like growth factor binding protein-3 in 740 women at risk for breast cancer

Prospective studies have shown an association between elevated plasma levels of insulin-like growth factor-I (IGF-I) and/or decreased levels of its major circulating carrier protein insulin-like growth factor binding protein-3 (IGFBP-3) and increased risk of major cancers. Identifying the factors which affect these biomarkers is of particular interest as subjects at increased risk could benefit from lifestyle changes, and/or chemoprevention intervention. We evaluated the association between constitutional, hormonal and clinical factors and IGF-I and IGFBP-3 in 740 women, including 376 unaffected women and 364 women with intraepithelial neoplasia (IEN) or early invasive breast cancer enrolled in breast cancer chemoprevention trials, conducted at a single institution. Age, body mass index (BMI), height, waist to hip girth ratio (WHR), parity, menopausal status, age at menarche, number of affected first degree relatives, number of biopsies and breast cancer status were considered in the analysis. Women with early breast cancer had 21% higher IGF-I levels (p = 0.033) and 19% higher IGF-I/IGFBP-3 molar ratio (p = 0.047) than unaffected women. In unaffected women, age was negatively associated with IGF-I (p = 0.002) and IGF-I/IGFBP-3 (p = 0.001), while age at menarche was negatively associated with IGFBP-3 levels (p = 0.043). In women with IEN or early breast cancer, IGF-I levels were negatively associated with age (p < 0.001), and positively associated with prior biopsies for benign disease (p = 0.013), while age, parity and menopausal status were significant predictors of IGF-I/IGFBP-3 molar ratio. We conclude that circulating IGF-I levels are higher in women with prior breast cancer compared to unaffected women, and that IGF-I and/or IGFBP-3 levels are influenced by age and by reproductive and hormonal factors. These findings support their putative role as breast cancer risk biomarker.

Diabetes mellitus and breast cancer

Type 2 diabetes is a serious health problem that affects more than 7% of adults in developed countries. Up to 16% of patients with breast cancer have diabetes, and two major risk factors for type 2 diabetes-old age and obesity-are also associated with breast cancer. Three mechanisms have been postulated to associate diabetes with breast cancer: activation of the insulin pathway, activation of the insulin-like-growth-factor pathway, and regulation of endogenous sex hormones. Comparative cohort studies and case-control studies suggest that type 2 diabetes may be associated with 10-20% excess relative risk of breast cancer. Gestational diabetes mellitus, but not type 1 diabetes, might also be associated with excess risk of breast cancer. Moreover, diabetes and its complications can adversely affect cancer therapy and the use of screening, which will thus affect the outcome of patients with breast cancer.

A two-by-two factorial trial comparing oral with transdermal estrogen therapy and fenretinide with placebo on breast cancer biomarkers

PURPOSE

Oral conjugated equine estrogen (CEE) and medroxyprogesterone acetate (MPA) increase breast cancer risk, whereas the effect of transdermal estradiol (E2) and MPA is less known. Fenretinide may decrease second breast malignancies in premenopausal women but not in postmenopausal women, suggesting a hormone-sensitizing effect. We compared the 6 and 12-month changes in insulin-like growth factor-I (IGF-I), IGF-binding protein-3 (IGFBP-3), IGF-I:IGFBP-3 ratio, sex-hormone binding-globulin, and computerized mammographic percent density during oral CEE or transdermal E2 with sequential MPA and fenretinide or placebo.

EXPERIMENTAL DESIGN

A total of 226 recent postmenopausal healthy women were randomly assigned in a two-by-two factorial design to either oral CEE 0.625 mg/day (n = 111) or transdermal E2, 50 microg/day (n = 115) and to fenretinide 100 mg/twice a day (n = 112) or placebo (n = 114) for 12 months. Treatment effects were investigated by the Kruskall-Wallis test and analysis of covariance. P values were two-sided.

RESULTS

After 12 months, oral CEE decreased IGF-I by 26% [95% confidence interval (CI), 22-30%] and increased sex-hormone binding-globulin by 96% (95% CI, 79-112%) relative to baseline, whereas no change occurred with transdermal E2 (P < 0.001 between groups). Fenretinide decreased IGFBP-3 relative to placebo (P = 0.04). Percentage of breast density showed an absolute increase of 3.5% (95% CI, 2.5-4.6%) during hormone therapy without differences between groups (P = 0.39).

CONCLUSIONS

Oral CEE has more favorable changes than transdermal E2 on circulating breast cancer risk biomarkers but gives similar effects on mammographic density. Fenretinide exerted little modulation on most biomarkers. The clinical implications of these findings require additional studies.

Estrogen and insulin/IGF-1 cooperatively stimulate cell cycle progression in MCF-7 breast cancer cells through differential regulation of c-Myc and cyclin D1

Estrogen and insulin/insulin-like growth factor-I (IGF-I) are major mitogens for breast epithelial cells and when co-administered, synergistically induce G(1)-S phase cell cycle progression. We investigated this cooperativity by evaluating if the key cell cycle regulators, c-Myc and cyclin D1, represent points of convergence in the action of these mitogens in MCF-7 breast cancer cells. These studies demonstrated that estrogen significantly increased both c-Myc and cyclin D1 protein, while insulin predominantly increased cyclin D1 levels. This cumulative increase in c-Myc and cyclin D1 contributes to the cooperativity of these mitogens, since ectopic expression of c-Myc or cyclin D1 cooperates with either the estrogen or insulin signaling pathways to increase cell cycle progression. Inhibition of the MAPK or PI3-kinase pathways significantly reduced c-Myc and cyclin D1 protein levels and cell cycle progression. Ectopic expression of cyclin D1 partially overcame this inhibition, while ectopic expression of c-Myc partially overcame MAPK but not PI3-kinase inhibition. Therefore, estrogen and insulin/IGF-1 differentially regulate c-Myc and cyclin D1 to cooperatively stimulate breast cancer cell proliferation.

Proapoptotic Potentials of Genistein Under Growth Stimulation by Estrogen

In mammary carcinogenesis, hormonal effects have been reported to be important factors. Estrogens are known to regulate the proliferation of breast cancer cells, whereas genistein has been shown to induce apoptosis in mammary tumor cells. This study examined genistein-induced apoptosis through the regulation of bcl-2 and bax expression in the presence of estrogen. MCF-7 cells were treated with either genistein (25, 50, and 100 microM) or in the presence of 17beta-estradiol (12.5, 25, and 50 nM) for 48 h. DNA ladder analysis and Western blot analysis of bcl-2, bax, cyclin B(1), p21, and p53 were carried out. For comparison, the in vivo system was employed using estrogen-deficient and estrogen-sufficient female rats at two different concentrations of genistein. In MCF-7 cells, DNA fragmentation was evident by the treatment of genistein in the absence and presence of estrogen. Downregulation of bcl-2 and upregulation of bax by genistein were observed. However, genistein showed no proapoptotic properties in the presence of estrogen except with the lowest concentration of estrogen. In the presence of estrogen, p21 and p53 protein expression were upregulated by high concentrations of genistein. Bcl-2/bax ratios were decreased by genistein treatment in the presence or absence of estrogen in female rats. These results demonstrate that the proapoptotic property of genistein might be influenced greatly by the concentration of estrogen in vitro, but that this influence by estrogen is not evident in vivo.

ICI182,780 induces p21Waf1 gene transcription through releasing histone deacetylase 1 and estrogen receptor alpha from Sp1 sites to induce cell cycle arrest in MCF-7 breast cancer cell line

We used the estrogen-responsive MCF-7 breast cancer cell line as a relevant model to study the anti-proliferative effects of ICI182,780 and identified the negative cell cycle regulator p21Waf1 as a specific target of ICI182,780. Furthermore, silencing of the p21Waf1 expression by small interfering RNA overcame the G0/G1 cell cycle arrest induced by ICI182,780, suggesting that the induction of p21Waf1 expression has a direct role in mediating the ICI182,780-induced G0/G1 arrest. We further demonstrated that the induction of p21Waf1 by ICI182,780 is mediated at transcriptional and gene promoter levels through the proximal Sp1 sites located near the transcription start site. Co-immunoprecipitation, DNA "pull-down," and chromatin immunoprecipitation experiments together showed that in cycling cells, estrogen receptor alpha and histone deacetylase 1 (HDAC1) are recruited to the proximal Sp1 sites of the promoter to repress p21Waf1 expression. In the presence of ICI182,780, estrogen receptor alpha and HDACs are dissociated from Sp1, resulting in increased histone acetylation and de-repression of the p21Waf1 promoter and induction of p21Waf1 expression. The fact that p21Waf1 expression is normally repressed by HDAC activity in cycling cells is further demonstrated by the finding that p21Waf1 transcription can be induced by the silencing of HDACs with small interfering RNA or treatment with HDAC inhibitors.

14-3-3σ Mediation of Cell Cycle Progression Is p53-independent in Response to Insulin-like Growth Factor-I Receptor Activation

We investigated the role of 14-3-3sigma protein in insulin-like growth factor-I (IGF-I) receptor signaling. It has been previously shown that 14-3-3sigma negatively regulates cell cycle especially in response to p53-sensitive DNA damage. In this study we demonstrated that 14-3-3sigma is a positive mediator of IGF-I receptor-induced cell proliferation. Treatment with IGF-I increased 14-3-3sigma mRNA and protein levels about 4-fold, in a time-dependent manner in MCF-7 breast cancer cells. Preincubation with the phosphoinositide 3'-kinase inhibitor LY294002 significantly reduced the effects of IGF-I on 14-3-3sigma gene expression in these cells, suggesting that this effect of IGF-I occurs via the phosphoinositide 3'-kinase pathway. 14-3-3sigma is induced by IGF-I in MCF-7 cells, which express wild-type p53, as well as in MCF-7 cells transfected with a small interference RNA targeting duplex that reduced p53 expression levels. These results suggest that IGF-I induces 14-3-3sigma expression in a manner that is independent of p53. Using the small interference RNA strategy, we demonstrated that a 70-75% reduction of 14-3-3sigma mRNA levels resulted in a similar decrease in the effects of IGF-I on cell cycle progression and proliferation in MCF-7 cells. This effect was also associated with a reduction in IGF-I-induced cyclin D1 expression. Taken together, these results suggest that 14-3-3sigma positively mediates IGF-I-induced cell cycle progression.

Plasma membrane estrogen receptors exist and functions as dimers

A small pool of estrogen receptors (ERalpha and -beta) localize at the plasma membrane and rapidly signal to affect cellular physiology. Although nuclear ERs function mainly as homodimers, it is unknown whether membrane-localized ER exists or functions with similar requirements. We report that the endogenous ER isoforms at the plasma membrane of breast cancer or endothelial cells exist predominantly as homodimers in the presence of 17beta-estradiol (E2). Interestingly, in endothelial cells made from ERalpha /ERbeta homozygous double-knockout mice, membrane ERalpha or ERbeta are absent, indicating that the endogenous membrane receptors derive from the same gene(s) as the nuclear receptors. In ER-negative breast cancer cells or Chinese hamster ovary cells, we expressed and compared wild-type and dimer mutant mouse ERalpha. Only wild-type ERalpha supported the ability of E2 to rapidly activate ERK, cAMP, and phosphatidylinositol 3-kinase signaling. This resulted from E2 activating Gsalpha and Gqalpha at the membrane in cells expressing the wild-type, but not the dimer mutant, ERalpha. Intact, but not dimer mutant, ERalpha also supported E2-induced epidermal growth factor receptor transactivation and cell survival. We also confirmed the requirement of dimerization for membrane ER function using a second, less extensively mutated, human ERalpha. In summary, endogenous membrane ERs exist as dimers, a structural requirement that supports rapid signal transduction and affects cell physiology.

Concentration-dependent mitogenic and antiproliferative actions of 2-methoxyestradiol in estrogen receptor-positive human breast cancer cells

We compared in this study the effects of 2-methoxyestradiol (2-MeO-E(2)) on the growth of two estrogen receptor (ER)-negative human breast cancer cell lines (MDA-MB-231 and MDA-MB-435s) and two ER-positive human breast cancer cell lines (MCF-7 and T-47D). 2-MeO-E(2) exerted a concentration-dependent antiproliferative action in the ER-negative MDA-MB-231 and MDA-MB-435s cells. The presence or absence of exogenous 17beta-estradiol (E(2)) in the culture medium did not affect the potency and efficacy of 2-MeO-E(2)'s antiproliferative action in these ER-negative cells. When the ER-positive MCF-7 and T-47D cells were cultured in a medium supplemented with 10nM of exogenous E(2), 2-MeO-E(2) at 750 nM to 2 microM concentrations exerted a similar antiproliferative effect. However, when the ER-positive cell lines were cultured in the absence of exogenous E(2), 2-MeO-E(2) at relatively low concentrations (10-750 nM) had a moderate mitogenic effect, with its apparent efficacy 75-80% of that of E(2). This mitogenic effect of 2-MeO-E(2) was ER-mediated and largely attributable to 2-MeO-E(2)'s residual estrogenic activity on the basis of our following findings: (i) its effect was only manifested in the ER-positive cells but not in the ER-negative cells; (ii) its effect in the ER-positive cells was partially or fully abolished when exogenous E(2) was concomitantly present in the culture medium; (iii) 2-MeO-E(2) retained 1-2% of E(2)'s binding affinity for the human ERalpha and ERbeta, and its mitogenic effect was inhibited in a concentration-dependent manner by ICI-182,780, a pure ER antagonist; and (iv) its effect was not due to its metabolic conversion to 2-hydroxyestradiol. Our timely findings are of importance to the on-going clinical trials designed to evaluate 2-MeO-E(2)'s effectiveness for the treatment of different types (ER-positive or ER-negative) of human breast cancer. This knowledge will improve the design of clinical trials as well as the interpretation of clinical outcomes when 2-MeO-E(2) is used as a single agent therapy or as part of a combination therapy for human breast cancer.

Elevated expression of the estrogen receptor prevents the down-regulation of p21Waf1/Cip1 in hormone dependent breast cancer cells

Expression of an estrogen receptor alpha (ER) transgene in hormone independent breast cancer and normal breast epithelial cells arrests cell cycling when estradiol is added. Although endogenously expressed ER does not typically affect estradiol-induced cell cycling of hormone dependent breast cancer cells, we observed that elevated expression of a green fluorescent protein fused to ER (GFP-ER) hindered entry of estrogen treated MCF-7 cells into S phase of the cell cycle. In analyses of key cell-cycle regulating proteins, we observed that GFP-ER expression had no affect on the protein levels of cyclin D1, cyclin E, or p27, a cyclin dependent kinase (Cdk) inhibitor. However, at 24 h, p21 (Waf1, Cip1; a Cdk2 inhibitor) protein remained elevated in the high GFP-ER expressing cells but not in non-GFP-ER expressing cells. Elevated expression of p21 inhibited Cdk2 activity, preventing cells from entering S phase. The results show that elevated levels of ER prevented the down-regulation of p21 protein expression, which is required for hormone responsive cells to enter S phase.

Growth factor regulation of cell cycle progression in mammary epithelial cells

Growth factors are among the critical positive and negative regulators of cell proliferation for normal mammary/breast epithelial cells and for breast cancer cells. The mechanisms by which specific growth factors regulate the cell cycle in mammary/breast epithelial cells is beginning to be understood for several growth factor families, including the epidermal growth factor, insulin-like growth factor, and transforming growth factor-beta families. A critical issue for understanding how growth factors regulate the cell cycle in vivo is how individual factors interact with other growth factors or hormones to enhance or inhibit specific molecular targets in the cell cycle machinery. This review addresses what is currently known about how growth factors regulate the cell cycle in mammary/breast epithelial cells both individually and in coordination with other growth regulators.

Additive effects of tamoxifen and the farnesyl transferase inhibitor FTI-277 on inhibition of MCF-7 breast cancer cell-cycle progression

The efficacy of tamoxifen in the hormonal therapy of breast cancer is well established, but therapeutic resistance is inevitable. FTIs are a new class of anticancer drugs that are in phase III clinical evaluation. Since the mechanisms of action of these 2 classes of drugs are different, we tested the combination of tamoxifen and FTI-277 on inhibiting proliferation of hormone-dependent MCF-7 human breast cancer cells. An additive effect on cell proliferation was demonstrated, accompanied by an additive G(0)/G(1) arrest. The major effect of the combination of the 2 drugs was to maintain p21(waf/cip1) at an intermediate level, higher than that observed in the presence of tamoxifen alone. This was associated with an additive effect on inactivation of cyclin E-Cdk2 complexes and decreased phosphorylation of pRb and p130 pocket proteins. These effects were accompanied by increased association of 2 CDIs, p27(kip1) and p21(waf/cip1), with cyclin E-Cdk2 complexes. These data demonstrate that the additive effect is likely predominantly due to the recruitment of p27(kip1) and, to a lesser extent, p21(waf/cip1) into the cyclin E-Cdk2 complexes. Together, these results suggest that the combination of FTI and tamoxifen may increase the antitumor effect of either drug alone in breast cancer.

Estrogen-induced genes, WISP-2 and pS2, respond divergently to protein kinase pathway

Recently, we identified WISP-2 (Wnt-1 inducible signaling pathway protein 2) as a novel estrogen-inducible gene in the MCF-7 human breast cancer cell line. In this study, we examined whether WISP-2 expression is modulated by PK activators. Treatment with protein kinase A (PKA) activators [cholera toxin plus 3-isobutyl-1-methylxanthine (CT/IBMX)] induced WISP-2 expression. CT/IBMX induced expression of the other estrogen-responsive gene, pS2, more dramatically than maximum stimulation by 17beta-estradiol (E2). Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA), which directly stimulates protein kinase C (PKC) activity, completely prevented WISP-2 mRNA induction by E2, whereas it increased pS2 mRNA expression more dramatically than maximum stimulation by E2. Results of treatments with the protein synthesis inhibitor cycloheximide and the pure antiestrogen ICI182,780 suggest that these PK pathways modulate WISP-2 gene expression via different molecular mechanisms than those for pS2. Because TPA inhibits cell proliferation, we investigated whether WISP-2 induction was dependent on cell growth. Cells were treated with insulin-like growth factor-1 (IGF-1) or interleukin-1alpha (IL-1alpha) to stimulate or inhibit cell growth, respectively. These treatments had no effect on WISP-2 mRNA expression either alone or in combination with E2, suggesting that WISP-2 induction is independent of cell growth.