Regulation of global gene expression in the bone marrow microenvironment by androgen: androgen ablation increases insulin-like growth factor binding protein-5 expression

Secreted insulin-like growth factor binding protein 5 functions as a tumor suppressor and chemosensitizer through inhibiting insulin-like growth factor 1 receptor/protein kinase B pathway in acute myeloid leukemia

BACKGROUND

In addition to being secreted into the intercellular spaces by exocytosis, insulin-like growth factor binding protein 5 (IGFBP5) may also remain in the cytosol or be transported to the nucleus. Depending on the different cellular context and subcellular distribution, IGFBP5 can act as a tumor suppressor or promoter through insulin-like growth factor -dependent or -independent mechanisms. Yet, little is known about the impacts of IGFBP5 on acute myeloid leukemia (AML) and its underlying mechanism.

METHODS

Here we investigated the roles of IGFBP5 in human AML by using recombinant human IGFBP5 (rhIGFBP5) protein and U937 and THP1 cell lines which stably and ectopically expressed IGFBP5 or mutant IGFBP5 (mtIGFBP5) with the lack of secretory signal peptide. Cell counting kit-8 and flow cytometry assay were conducted to assess the cell viability, cell apoptosis and cell cycle distribution. Cytotoxicity assay was used to detect the chemosensitivity. Leukemia xenograft model and hematoxylin-eosin staining were performed to evaluate AML progression and extramedullary infiltration in vivo.

RESULTS

In silico analysis demonstrated a positive association between IGFBP5 expression and overall survival of the AML patients. Both IGFBP5 overexpression and extrinsic rhIGFBP5 suppressed the growth of THP1 and U937 cells by inducing cell apoptosis and arresting G1/S transition and promoted the chemosensitivity of U937 and THP1 cells to daunorubicin and cytarabine. However, overexpression of mtIGFBP5 failed to demonstrate these properties. An in vivo xenograft mouse model of U937 cells also indicated that overexpression of IGFBP5 rather than mtIGFBP5 alleviated AML progression and extramedullary infiltration. Mechanistically, these biological consequences depended on the inactivation of insulin-like growth factor 1 receptor -mediated phosphatidylinositol-3-kinase/protein kinase B pathway.

CONCLUSIONS

Our findings revealed secreted rather than intracellular IGFBP5 as a tumor-suppressor and chemosensitizer in AML. Upregulation of serum IGFBP5 by overexpression or addition of extrinsic rhIGFBP5 may serve as a suitable therapeutic approach for AML.

Functions of Steroid Hormones in the Male Reproductive Tract as Revealed by Mouse Models

Steroid hormones are capable of diffusing through cell membranes to bind with intracellular receptors to regulate numerous physiological processes. Three classes of steroid hormones, namely androgens, estrogens and glucocorticoids, contribute to the development of the reproductive system and the maintenance of fertility. During the past 30 years, mouse models have been produced in which the expression of genes encoding steroid hormone receptors has been enhanced, partially compromised or eliminated. These mouse models have revealed many of the physiological processes regulated by androgens, estrogens and to a more limited extent glucocorticoids in the testis and male accessory organs. In this review, advances provided by mouse models that have facilitated a better understanding of the molecular regulation of testis and reproductive tract processes by steroid hormones are discussed.

Biological effects and regulation of IGFBP5 in breast cancer

The insulin-like growth factor receptor (IGF1R) pathway plays an important role in cancer progression. In breast cancer, the IGF1R pathway is linked to estrogen-dependent signaling. Regulation of IGF1R activity is complex and involves the actions of its ligands IGF1 and IGF2 and those of IGF-binding proteins (IGFBPs). Six IGFBPs are known that share the ability to form complexes with the IGFs, by which they control the bioavailability of these ligands. Besides, each of the IGFBPs have specific features. In this review, the focus lies on the biological effects and regulation of IGFBP5 in breast cancer. In breast cancer, estrogen is a critical regulator of IGFBP5 transcription. It exerts its effect through an intergenic enhancer loop that is part of the chromosomal breast cancer susceptibility region 2q35. The biological effects of IGFBP5 depend upon the cellular context. By inhibiting or promoting IGF1R signaling, IGFBP5 can either act as a tumor suppressor or promoter. Additionally, IGFBP5 possesses IGF-independent activities, which contribute to the complexity by which IGFBP5 interferes with cancer cell behavior.

Insulin-like growth factor binding protein 5 (IGFBP5) functions as a tumor suppressor in human melanoma cells

The insulin-like growth factor binding protein 5 (IGFBP5), which is often dysregulated in human cancers, plays a crucial role in carcinogenesis and cancer development. However, the function and underlying mechanism of IGFBP5 in tumor growth and metastasis has been elusive, particularly in malignant human melanoma. Here, we reported that IGFBP5 acts as an important tumor suppressor in melanoma tumorigenicity and metastasis by a series of experiments including transwell assay, xenograft model, in vivo tumor metastasis experiment, and RNA-Seq. Overexpression of IGFBP5 in A375, a typical human melanoma cell line, inhibited cell malignant behaviors significantly, including in vitro proliferation, anchorage-independent growth, migration and invasion, as well as in vivo tumor growth and pulmonary metastasis. In addition, overexpression of IGFBP5 suppressed epithelial-mesenchymal transition (EMT), and decreased the expression of E-cadherin and the key stem cell markers NANOG, SOX2, OCT4, KLF4, and CD133. Furthermore, IGFBP5 exerts its inhibitory activities by reducing the phosphorylation of IGF1R, ERK1/2, and p38-MAPK kinases and abating the expression of HIF1α and its target genes, VEGF and MMP9. All these findings were confirmed by IGFBP5 knockdown in human melanoma cell line A2058. Taken together, these results shed light on the mechanism of IGFBP5 as a potential tumor-suppressor in melanoma progression, indicating that IGFBP5 might be a novel therapeutic target for human melanoma.

Cell kinetic studies fail to identify sequentially proliferating progenitors as the major source of epithelial renewal in the adult murine prostate

There is evidence that stem cells and their progeny play a role in the development of the prostate. Although stem cells are also considered to give rise to differentiated progeny in the adult prostate epithelium ex vivo, the cohort of adult prostate stem cells in vivo as well as the mechanisms by which the adult prostate epithelium is maintained and regenerated remain highly controversial. We have attempted to resolve this conundrum by performing in vivo tracing of serially replicating cells after the sequential administration of two thymidine analogues to mice. Our results show that, during normal prostate homeostasis, sequentially proliferating cells are detected at a rate that is consistent with a stochastic process. These findings indicate that in vivo, under steady-state conditions, most adult prostate epithelial cells do not represent the progeny of a small number of specialized progenitors that generate sequentially replicating transit-amplifying (TA) cells but are formed by stochastic cell division. Similarly, no rapidly cycling TA cells were detected during regeneration following one cycle of androgen-mediated involution/regeneration of the prostate epithelium. These findings greatly enhance our understanding of the mechanisms regulating prostate epithelial cell renewal and may have significant implications in defining the cell of origin of proliferative prostatic diseases.

IRX1 hypomethylation promotes osteosarcoma metastasis via induction of CXCL14/NF-κB signaling

Osteosarcoma is a common malignant bone tumor with a propensity to metastasize to the lungs. Epigenetic abnormalities have been demonstrated to underlie osteosarcoma development; however, the epigenetic mechanisms that are involved in metastasis are not yet clear. Here, we analyzed 2 syngeneic primary human osteosarcoma cell lines that exhibit disparate metastatic potential for differences in epigenetic modifications and expression. Using methylated DNA immunoprecipitation (MeDIP) and microarray expression analysis to screen for metastasis-associated genes, we identified Iroquois homeobox 1 (IRX1). In both human osteosarcoma cell lines and clinical osteosarcoma tissues, IRX1 overexpression was strongly associated with hypomethylation of its own promoter. Furthermore, experimental modulation of IRX1 in osteosarcoma cell lines profoundly altered metastatic activity, including migration, invasion, and resistance to anoikis in vitro, and influenced lung metastasis in murine models. These prometastatic effects of IRX1 were mediated by upregulation of CXCL14/NF-κB signaling. In serum from osteosarcoma patients, the presence of IRX1 hypomethylation in circulating tumor DNA reduced lung metastasis-free survival. Together, these results identify IRX1 as a prometastatic gene, implicate IRX1 hypomethylation as a potential molecular marker for lung metastasis, and suggest that epigenetic reversion of IRX1 activation may be beneficial for controlling osteosarcoma metastasis.

In vivo passage of human prostate cancer cells in mice results in stable gene expression changes affecting numerous cancer-associated biological processes

BACKGROUND

While therapeutic resistance is difficult to model in vitro in its entirety, in vivo passage and re-derivation of treatment resistant prostate cancer cell variants is a strategy to study therapeutic resistance more comprehensively. However, the process of in vivo passage itself may result in gene expression changes that could confound the analysis of such resistant cell variants compared to their parental cell lines.

METHODS

We compared the expression profiles of parental PC-3 human prostate cancer cells and PC-3 cells re-derived after in vivo passage in athymic nude mice. Whole transcriptome information was obtained using the SOLiD 4 system (Applied Biosystems). Differentially expressed genes were mapped to genes in the Database for Annotation, Visualization and Integrated Discovery for gene enrichment and functional annotation analysis. The expression of a panel of these genes was validated using quantitative RT-PCR.

RESULTS

Altogether, 21,032 distinct transcripts were found in PC-3 and/or NS1.1. Of these, 906 were differentially regulated (≥2-fold) in NS1.1 versus PC-3. 337 transcripts were upregulated, and 569 were downregulated, including genes previously associated with various aspects of prostate carcinogenesis such as TLR4 and IGFBP5, respectively. Gene ontology analysis of the differentially expressed transcripts revealed enrichment for biological processes such as cell adhesion, migration, and angiogenesis.

CONCLUSIONS

When using in vivo as opposed to in vitro derived prostate cancer cell variants for comparative genetic studies of complex traits such as therapeutic resistance, one may be better served to use similarly in vivo passaged control cell variants instead of parental cell lines.

Elevated insulin-like growth factor binding protein-1 (IGFBP-1) in men with metastatic prostate cancer starting androgen deprivation therapy (ADT) is associated with shorter time to castration resistance and overall survival

BACKGROUND

Insulin-like growth factor (IGF) and adipokines have been implicated in prostate cancer carcinogenesis.

METHOD

Data from 122 men with serum samples drawn within 3 months of starting ADT for metastatic prostate cancer was accessed retrospectively. IGF-1, IGF binding protein (BP)-1, leptin, and adiponectin levels were measured by multiplex electrochemiluminescence assays. A multivariable Cox model assessed the association of time to castration resistant prostate cancer (CRPC) and overall survival by the protein levels, adjusted for clinical variables, age and prostate specific antigen (PSA) levels at start of ADT, race, ECOG status, extent of metastases and were reported as hazard ratio (HR) with 95% confidence interval (CI).

RESULTS

Median follow-up and overall survival were 44 and 42.2 months, respectively. ECOG performance status (≥ 1 vs. 0) was negatively associated with overall survival [H  = 2.8 (1.1-7.0), P = 0.03], and PSA nadir <0.2 was predictive of longer time to CRPC [HR = 0.3 (0.2-0.5), P < 0.0001]. The median time to CRPC by low, middle, and top IGFBP-1 tertile distribution was 20.7, 18.1, and 12.4 months, respectively, with HR for middle versus low tertile levels 3.1 (1.7-5), P = 0.0003, and for top versus low tertile levels was 2.4 (1.3-4.2), P = 0.003. The median overall survival by low, middle and top tertile IGFBP-1 level was 48.5, 46.4, and 32.8 months, respectively, with HR for top versus low tertile 2.5 (1.2-5.1), P = 0.01. There was no association with IGF-1, adiponectin and leptin.

CONCLUSION

Elevated IGFBP-1 appears to be associated with shorter time to CRPC and lower overall survival in men with metastatic prostate cancer.

Tissue-selective regulation of androgen-responsive genes

INTRODUCTION

Androgens regulate a wide array of physiological processes, including male sexual development, bone and muscle growth, and behavior and cognition. Because androgens play a vital role in so many tissues, changes in androgen signaling are associated with a plethora of diseases. How such varied responses are achieved by a single stimulus is not well understood. Androgens act primarily through the androgen receptor (AR), a hormone nuclear receptor that is expressed in a select variety of tissues.

METHODS

In order to gain a better understanding of how the tissue-selective effects of androgens are achieved, we performed a comparison of microarray data, using previously published datasets and several of our own microarray datasets. These datasets were derived from clinically relevant, AR-expressing tissues dissected from rodents treated with the full androgen dihydrotestosterone (DHT).

RESULTS

We found that there is a diverse response to DHT, with very little overlap of androgen regulated genes in each tissue. Gene ontology analyses also indicated that, while several tissues regulate similar biological processes in response to DHT, most androgen regulated processes are specific to one or a few tissues. Thus, it appears that the disparate physiological effects mediated by androgens begin with widely varying effects on gene expression in different androgen-sensitive tissues.

CONCLUSION

The analysis completed in this study will lead to an improved understanding of how androgens mediate diverse, tissue-specific processes and better ways to assess the tissue-selective effects of AR modulators during drug development.

Insulin-like growth factor pathway: a link between androgen deprivation therapy (ADT), insulin resistance, and disease progression in patients with prostate cancer?

Androgen deprivation therapy (ADT) is standard of care for patients with metastatic hormone-sensitive prostate cancer (HSPC), yet through its induction of a hypogonadal state leads to metabolic perturbations, including insulin resistance (IR) and obesity. IR and obesity have been associated with an increased risk of progression to castrate-resistant prostate cancer (CRPC) and ultimately increased prostate cancer-specific mortality. On a molecular level, this association between obesity/IR and prostate cancer progression may be mediated by alterations in the insulin-like growth factor (IGF) axis, which has been shown to be up-regulated upon disease progression to CRPC. Targeting the IGF axis, either by anti-IGF therapy or via enhancement of peripheral insulin sensitivity, represents a viable therapeutic target in patients with prostate cancer. Using the development of IR and/or obesity may represent a clinically available biomarker that may predict those patients most likely to respond to such therapy, and warrants testing in future prospective clinical trials.

NANOG promotes cancer stem cell characteristics and prostate cancer resistance to androgen deprivation

Cancer cell molecular mimicry of stem cells (SC) imbues neoplastic cells with enhanced proliferative and renewal capacities. In support, numerous mediators of SC self-renewal have been evinced to exhibit oncogenic potential. We have recently reported that shRNA-mediated knockdown of the embryonic stem cell (ESC) self-renewal gene NANOG significantly reduced the clonogenic and tumorigenic capabilities of various cancer cells. In this study, we sought to test the potential pro-tumorigenic functions of NANOG, particularly, in prostate cancer (PCa). Using quantitative RT-PCR, we first confirmed that PCa cells expressed NANOG mRNA primarily from the NANOGP8 locus on chromosome 15q14. We then constructed a lentiviral promoter reporter in which the -3.8 kb NANOGP8 genomic fragment was used to drive the expression of green fluorescence protein (GFP). We observed that NANOGP8-GFP⁺ PCa cells exhibited cancer stem cell (CSC) characteristics such as enhanced clonal growth and tumor regenerative capacity. To further investigate the functions and mechanisms of NANOG in tumorigenesis, we established tetracycline-inducible NANOG overexpressing cancer cell lines, including both prostate (Du145 and LNCaP) and breast (MCF-7) cancer cells. NANOG induction promoted drug-resistance in MCF-7 cells, tumor regeneration in Du145 cells, and, most importantly, castration-resistant tumor development in LNCaP cells. These pro-tumorigenic effects of NANOG were associated with key molecular changes, including an upregulation of molecules such as CXCR4, IGFBP5, CD133 and ALDH1. The present gain-of-function studies, coupled with our recent loss-of-function work, establish the integral role for NANOG in neoplastic processes and shed light on its mechanisms of action.

Insulin-like growth factor binding protein 5 suppresses tumor growth and metastasis of human osteosarcoma

Osteosarcoma (OS) is the most common primary malignancy of bone. There is a critical need to identify the events that lead to the poorly understood mechanism of OS development and metastasis. The goal of this investigation is to identify and characterize a novel marker of OS progression. We have established and characterized a highly metastatic OS subline that is derived from the less metastatic human MG63 line through serial passages in nude mice via intratibial injections. Microarray analysis of the parental MG63, the highly metastatic MG63.2 subline, as well as the corresponding primary tumors and pulmonary metastases revealed insulin-like growth factor binding protein 5 (IGFBP5) to be one of the significantly downregulated genes in the metastatic subline. Confirmatory quantitative RT-PCR on 20 genes of interest demonstrated IGFBP5 to be the most differentially expressed and was therefore chosen to be one of the genes for further investigation. Adenoviral mediated overexpression and knockdown of IGFBP5 in the MG63 and MG63.2 cell lines, as well as other OS lines (143B and MNNG/HOS) that are independent of our MG63 lines, were employed to examine the role of IGFBP5. We found that overexpression of IGFBP5 inhibited in vitro cell proliferation, migration and invasion of OS cells. Additionally, IGFBP5 overexpression promoted apoptosis and cell cycle arrest in the G1 phase. In an orthotopic xenograft animal model, overexpression of IGFBP5 inhibited OS tumor growth and pulmonary metastases. Conversely, siRNA-mediated knockdown of IGFBP5 promoted OS tumor growth and pulmonary metastases in vivo. Immunohistochemical staining of patient-matched primary and metastatic OS samples demonstrated decreased IGFBP5 expression in the metastases. These results suggest 1) a role for IGFBP5 as a novel marker that has an important role in the pathogenesis of OS, and 2) that the loss of IGFBP5 function may contribute to more metastatic phenotypes in OS.

Multifunctional roles of insulin-like growth factor binding protein 5 in breast cancer

The insulin-like growth factor axis, which has been shown to protect cells from apoptosis, plays an essential role in normal cell physiology and in cancer development. The family of insulin-like growth factor binding proteins (IGFBPs) has been shown to have a diverse spectrum of functions in cell growth, death, motility, and tissue remodeling. Among the six IGFBP family members, IGFBP-5 has recently been shown to play an important role in the biology of breast cancer, especially in breast cancer metastasis; however, the exact mechanisms of action remain obscure and sometimes paradoxical. An in-depth understanding of IGFBP-5 would shed light on its potential role as a target for breast cancer therapeutics.

Gene targeting to the stroma of the prostate and bone

Stromal-epithelial interactions mediated by paracrine signaling mechanisms dictate prostate development and progression of prostate cancer. The regulatory role of androgens in both the prostate stromal and epithelial compartments set the prostate apart from many other organs and tissues with regard to gene targeting. The identification of androgen-dependent prostate epithelial promoters has allowed successful gene targeting to the prostate epithelial compartment. Currently, there are no transgenic mouse models available to specifically alter gene expression within the prostate stromal compartment. As a primary metastatic site for prostate cancer is bone, the functional dissection of the bone stromal compartment is important for understanding stromal-epithelial interactions associated with metastatic tumor growth. Use of currently available methodologies for the expression or deletion of gene expression in recent research studies has advanced our understanding of the stroma. However, the complexity of stromal heterogeneity within the prostate remains a challenge to obtaining compartment or cell-lineage-specific in vivo models necessary for furthering our understanding of prostatic developmental, benign, tumorigenic, and metastatic growth.