Insulin-like growth factor binding protein-1 over-expression in transgenic mice inhibits hepatic preneoplasia

Growth Hormone's Links to Cancer

Several components of the GH axis are involved in tumor progression, and GH-induced intracellular signaling has been strongly associated with breast cancer susceptibility in genome-wide association studies. In the general population, high IGF-I levels and low IGF-binding protein-3 levels within the normal range are associated with the development of common malignancies, and components of the GH-IGF signaling system exhibit correlations with clinical, histopathological, and therapeutic parameters in cancer patients. Despite promising findings in preclinical studies, anticancer therapies targeting the GH-IGF signaling system have led to disappointing results in clinical trials. There is substantial evidence for some degree of protection against tumor development in several animal models and in patients with genetic defects associated with GH deficiency or resistance. In contrast, the link between GH excess and cancer risk in acromegaly patients is much less clear, and cancer screening in acromegaly has been a highly controversial issue. Recent studies have shown that increased life expectancy in acromegaly patients who attain normal GH and IGF-I levels is associated with more deaths due to age-related cancers. Replacement GH therapy in GH deficiency hypopituitary adults and short children has been shown to be safe when no other risk factors for malignancy are present. Nevertheless, the use of GH in cancer survivors and in short children with RASopathies, chromosomal breakage syndromes, or DNA-repair disorders should be carefully evaluated owing to an increased risk of recurrence, primary cancer, or second neoplasia in these individuals.

Systemic Complications of Acromegaly and the Impact of the Current Treatment Landscape: An Update

Acromegaly is a chronic systemic disease with many complications and is associated with increased mortality when not adequately treated. Substantial advances in acromegaly treatment, as well as in the treatment of many of its complications, mainly diabetes mellitus, heart failure, and arterial hypertension, were achieved in the last decades. These developments allowed change in both prevalence and severity of some acromegaly complications and furthermore resulted in a reduction of mortality. Currently, mortality seems to be similar to the general population in adequately treated patients with acromegaly. In this review, we update the knowledge in complications of acromegaly and detail the effects of different acromegaly treatment options on these complications. Incidence of mortality, its correlation with GH (cumulative exposure vs last value), and IGF-I levels and the shift in the main cause of mortality in patients with acromegaly are also addressed.

Endoplasmic reticulum heat shock protein gp96 maintains liver homeostasis and promotes hepatocellular carcinogenesis

BACKGROUND & AIMS

gp96, or grp94, is an endoplasmic reticulum (ER)-localized heat shock protein 90 paralog that acts as a protein chaperone and plays an important role for example in ER homeostasis, ER stress, Wnt and integrin signaling, and calcium homeostasis, which are vital processes in oncogenesis. However, the cancer-intrinsic function of gp96 remains controversial.

METHODS

We studied the roles of gp96 in liver biology in mice via an Albumin promoter-driven Cre recombinase-mediated disruption of gp96 gene, hsp90b1. The impact of gp96 status on hepatic carcinogenesis in response to diethyl-nitrosoamine (DENA) was probed. The roles of gp96 on human hepatocellular carcinoma cells (HCC) were also examined pharmacologically with a targeted gp96 inhibitor.

RESULTS

We demonstrated that gp96 maintains liver development and hepatocyte function in vivo, and its loss genetically promotes adaptive accumulation of long chain ceramides, accompanied by steatotic regeneration of residual gp96+ hepatocytes. The need for compensatory expansion of gp96+ cells in the gp96- background predisposes mice to develop carcinogen-induced hepatic hyperplasia and cancer from gp96+ but not gp96- hepatocytes. We also found that genetic and pharmacological inhibition of gp96 in human HCCs perturbed multiple growth signals, and attenuated proliferation and expansion.

CONCLUSIONS

gp96 is a pro-oncogenic chaperone and an attractive therapeutic target for HCC.

Growth hormone, the insulin-like growth factor axis, insulin and cancer risk

Growth hormone (GH), insulin-like growth factor (IGF)-I and insulin have potent growth-promoting and anabolic actions. Their potential involvement in tumor promotion and progression has been of concern for several decades. The evidence that GH, IGF-I and insulin can promote and contribute to cancer progression comes from various sources, including transgenic and knockout mouse models and animal and human cell lines derived from cancers. Assessments of the GH-IGF axis in healthy individuals followed up to assess cancer incidence provide direct evidence of this risk; raised IGF-I levels in blood are associated with a slightly increased risk of some cancers. Studies of human diseases characterized by excess growth factor secretion or treated with growth factors have produced reassuring data, with no notable increases in de novo cancers in children treated with GH. Although follow-up for the vast majority of these children does not yet extend beyond young adulthood, a slight increase in cancers in those with long-standing excess GH secretion (as seen in patients with acromegaly) and no overall increase in cancer with insulin treatment, have been observed. Nevertheless, long-term surveillance for cancer incidence in all populations exposed to increased levels of GH is vitally important.

The proliferating role of insulin and insulin-like growth factors in cancer

Epidemiological studies have reported an increased risk of cancer in people with type 2 diabetes (T2DM) and obesity, related in part to hyperinsulinemia, secondary to insulin resistance. Hyperinsulinemia leads to increased expression of insulin-like growth factor (IGF)-I expression. In fact, increased insulin, IGF-I and IGF-II levels are associated with tumor growth in vitro, in animal models, and in epidemiological studies in humans. In this paper, we discuss the roles of insulin, IGF-I and IGF-II, their interaction with the insulin receptor (IR) and IGF-I receptor (IGF-IR), and their signaling pathways and regulation as these pertain to tumor growth. We explain how these pathways have been deciphered by in vitro and in vivo studies, and how they are being exploited in the development of targeted cancer therapies.

The insulin-like growth factor system and its receptors: A potential novel anticancer target

The current generation of novel anticancer therapies that are in preclinical and clinical development are based on exploiting our increasing understanding of the molecular and cellular basis of cancer development and progression. Accelerated rates of cell division and proliferation have been postulated to predispose to the development of malignant disease. The insulin-like growth factor (IGF) signaling system has an important physiological role in regulating cellular proliferation and apoptosis. This function has led to considerable interest in its relevance to neoplasia over the last decade. In this review, we give an overview of the IGF system physiology, discuss the epidemiological significance of IGF signaling and neoplasia, and review the preclinical and clinical studies in targeting IGF receptors as cancer therapies.

Hepatic IGFBP1 is a prosurvival factor that binds to BAK, protects the liver from apoptosis, and antagonizes the proapoptotic actions of p53 at mitochondria

Liver is generally refractory to apoptosis induced by the p53 tumor suppressor protein, but the molecular basis remains poorly understood. Here we show that p53 transcriptional activation leads to enhanced expression of hepatic IGFBP1 (insulin-like growth factor-binding protein-1). Exhibiting a previously unanticipated role, a portion of intracellular IGFBP1 protein localizes to mitochondria where it binds to the proapoptotic protein BAK and hinders BAK activation and apoptosis induction. Interestingly, in many cells and tissues p53 also has a direct apoptotic function at mitochondria that includes BAK binding and activation. When IGFBP1 is in a complex with BAK, formation of a proapoptotic p53/BAK complex and apoptosis induction are impaired, both in cultured cells and in liver. In contrast, livers of IGFBP1-deficient mice exhibit spontaneous apoptosis that is accompanied by p53 mitochondrial accumulation and evidence of BAK oligomerization. These data support the importance of BAK as a mediator of p53's mitochondrial function. The results also identify IGFBP1 as a negative regulator of the BAK-dependent pathway of apoptosis, whose expression integrates the transcriptional and mitochondrial functions of the p53 tumor suppressor protein.

The role of the IGF system in cancer growth and metastasis: overview and recent insights

IGF-I receptor (IGF-IR) signaling and functions are mediated through the activities of a complex molecular network of positive (e.g., type I IGF) and negative (e.g., the type II IGF receptor, IGF-IIR) effectors. Under normal physiological conditions, the balance between the expression and activities of these molecules is tightly controlled. Changes in this delicate balance (e.g., overexpression of one effector) may trigger a cascade of molecular events that can ultimately lead to malignancy. In recent years, evidence has been mounting that the IGF axis may be involved in human cancer progression and can be targeted for therapeutic intervention. Here we review old and more recent evidence on the role the IGF system in malignancy and highlight experimental and clinical studies that provide novel insights into the complex mechanisms that contribute to its oncogenic potential. Controversies arising from conflicting evidence on the relevance of IGF-IR and its ligands to human cancer are discussed. Our review highlights the importance of viewing the IGF axis as a complex multifactorial system and shows that changes in the expression levels of any one component of the axis, in a given malignancy, should be interpreted with caution and viewed in a wider context that takes into account the expression levels, state of activation, accessibility, and functionality of other interacting components. Because IGF targeting for anticancer therapy is rapidly becoming a clinical reality, an understanding of this complexity is timely because it is likely to have an impact on the design, mode of action, and clinical outcomes of newly developed drugs.

The Insulin-like Growth Factor-binding Protein 1 Gene Is a Primary Target of Peroxisome Proliferator-activated Receptors

Insulin-like growth factor-binding protein 1 (IGFBP-1) is a biomarker for metabolic and hyperproliferative diseases. At the same time, the nuclear receptors peroxisome proliferator-activated receptors (PPARs) are known for their critical role in the development of both the metabolic syndrome and various cancers. Here we demonstrate, in human hepatocellular carcinoma cells and in normal mouse liver, that IGFBP-1 mRNA expression is under the primary control of PPAR ligands. We applied an improved in silico screening approach for PPAR response elements (PPREs) and identified five candidate PPREs located within 10 kb of the transcription start site (TSS) of the IGFBP-1 gene. Chromatin immunoprecipitation assays showed that, in living cells, the genomic region containing the most proximal PPRE, at position -1200 (relative to the TSS), preferentially associates with multiple PPAR subtypes and various other components of the transcriptional apparatus, which include their heterodimerizing partner, retinoid X receptor, as well as phosphorylated RNA polymerase II, co-repressor, co-activator, and mediator proteins. Moreover, further chromatin immunoprecipitation assays demonstrated that the TSS regions of the IGFBP-1 gene and those of the related IGFBP-2, -5, and -6, but not of IGFBP-3 and -4 genes, bind PPARs as well. We also show that these additional PPAR binding genes contain a number of candidate PPREs and that their mRNA levels respond quickly to the presence of PPAR ligands, indicating that they are also primary PPAR target genes.

Chemical Genetic Identification of the IGF-Linked Pathway that Is Mediated by STAT6 and MFP2

Insulin-like growth factor 2 (IGF2) is a potent mitogen whose deregulation plays a role in developing liver, breast, and prostate cancers. Here, we take a small-molecule approach to investigate molecular pathways that modulate IGF2 signaling, by using chromeceptin, a synthetic molecule that selectively impairs the viability and growth of IGF2-overexpressing hepatocellular carcinoma cells. Affinity purification revealed that chromeceptin binds to multifunctional protein 2 (MFP-2), a seemingly multifunctional enzyme implicated in peroxisomal beta-oxidation. The small molecule-protein interaction stimulates the expression of IGF binding protein 1 (IGFBP-1) and suppressor of cytokine signaling-3 (SOCS-3), two cellular attenuators of the IGF signals, through activation of signal transducers and activators of transcription 6 (STAT6). The results underline the importance of STATs in IGF/insulin regulation, and they implicate a new pathway for STAT6 activation that is amenable to small-molecule intervention.

Altered proteolysis and global gene expression in hepatitis B virus X transgenic mouse liver

Hepatitis B virus X (HBX) is essential for the productive infection of hepatitis B virus (HBV) in vivo and has a pleiotropic effect on host cells. We have previously demonstrated that the proteasome complex is a cellular target of HBX, that HBX alters the proteolytic activity of proteasome in vitro, and that inhibition of proteasome leads to enhanced viral replication, suggesting that HBX and proteasome interaction plays a crucial role in the life cycle and pathogenesis of HBV. In the present study, we tested the effect of HBX on the proteasome activities in vivo in a transgenic mouse model in which HBX expression is developmentally regulated by the mouse major urinary promoter in the liver. In addition, microarray analysis was performed to examine the effect of HBX expression on the global gene expression profile of the liver. The results showed that the peptidase activities of the proteasome were reduced in the HBX transgenic mouse liver, whereas the activity of another cellular protease was elevated, suggesting a compensatory mechanism in protein degradation. In the microarray analysis, diverse genes were altered in the HBX mouse livers and the number of genes with significant changes increased progressively with age. Functional clustering showed that a number of genes involved in transcription and cell growth were significantly affected in the HBX mice, possibly accounting for the observed pleiotropic effect of HBX. In particular, insulin-like growth factor-binding protein 1 was down-regulated in the HBX mouse liver. The down-regulation was similarly observed during acute woodchuck hepatitis virus infection. Other changes including up-regulation of proteolysis-related genes may also contribute to the profound alterations of liver functions in HBV infection.

The biological actions of dehydroepiandrosterone involves multiple receptors

Dehydroepiandrosterone has been thought to have physiological functions other than as an androgen precursor. The previous studies performed have demonstrated a number of biological effects in rodents, such as amelioration of disease in diabetic, chemical carcinogenesis, and obesity models. To date, activation of the peroxisome proliferators activated receptor alpha, pregnane X receptor, and estrogen receptor by DHEA and its metabolites have been demonstrated. Several membrane-associated receptors have also been elucidated leading to additional mechanisms by which DHEA may exert its biological effects. This review will provide an overview of the receptor multiplicity involved in the biological activity of this sterol.

Insulin-like growth factor binding proteins in development

IGFBPs regulate growth and development by regulating IGF transport to tissues and IGF bioavailability to IGF receptors at cell membrane level. IGFBP excess leads predominantly to inhibition of IGF action and growth retardation with impaired organogenesis. Absence of human and also mouse ALS leads to decreased IGF-I levels in circulation and causes mild growth retardation. Although IGFBP KO mice demonstrate relatively minor phenotypes, the possibility of compensatory mechanisms that mask the phenotypic manifestation of lack of individual binding proteins needs to be further investigated. Recent studies of hepatic regeneration in IGFBP-1 KO mice and also with mutant IGFBP-3 Tg mice provide some limited support for the existence of IGF-independent mechanism of action in vivo.

Functional consequences of IGFBP excess-lessons from transgenic mice

The functions of insulin-like growth factor-binding proteins (IGFBPs) have been studied extensively in vitro, revealing IGF-dependent and also IGF-independent effects on cell growth, differentiation, and survival. In contrast, the biological relevance of IGFBPs in vivo is only partially understood. In the past decade, mouse models lacking or overexpressing specific IGFBPs have been generated by transgenic technology. Phenotypic analysis revealed features that are common for most IGFBPs (growth inhibition), but also effects that appear to be specific for some but not all IGFBPs, such as disturbed glucose homeostasis (IGFBP-1 and -3) or impaired fertility (IGFBP-1, -5, and -6). Future systematic comparison of IGFBP functions in transgenic mice will be facilitated by targeted insertion of IGFBP expression vectors and by standardized phenotype assessment. Furthermore, analysis of IGFBP expression in growth-selected mouse lines or pedigrees segregating for growth phenotypes will be important to understand the roles of IGFBPs in multigenic growth regulation.

Insulin-like growth factor I gene microsatellite repeat, collagen type Ialpha1 gene Sp1 polymorphism, and bone disease in primary biliary cirrhosis

BACKGROUND

Genetic factors have been implicated in the pathogenesis of osteoporosis, a common disorder in primary biliary cirrhosis. Insulin-like growth factor I (IGF-I) gene microsatellite repeat polymorphism was found to be associated with osteoporosis in some studies, and collagen-Ialpha1 (COLIA1) Sp1 s allele was associated with lower bone mineral density in primary biliary cirrhosis. IGF-I treatment restored osteopenia and reduced fibrogenesis in experimental cirrhosis. We investigated IGF-I and COLIA1 gene polymorphisms and bone mineral density in Hungarian primary biliary cirrhosis patients.

PATIENTS AND METHODS

Seventy female patients with primary biliary cirrhosis were enrolled (mean age 57.6 years, range 37-76 years; all anti-mitochondrial antibody M2-positive; stage II-IV). One hundred and thirty-nine age-matched female subjects served as controls (mean age 55.9 years, range 43-72 years). COLIA1 and IGF-I polymorphisms were determined by polymerase chain reaction. Bone mineral density was measured by dual-energy X-ray absorptiometry in the lumbar spine and femoral neck.

RESULTS

The IGF-I was not different between primary biliary cirrhosis patients and controls. The genotype frequency of COLIA1 polymorphism was also not different between primary biliary cirrhosis patients and controls. However, the s allele was significantly less frequent in patients with primary biliary cirrhosis. Osteoporosis was detected in 22 patients. The IGF-I 192/192 genotype was associated with higher femoral-neck z-scores compared with other genotypes.

CONCLUSION

In contrast to previous studies, the s allele was less frequent in patients with primary biliary cirrhosis, and its presence was not associated with bone mineral density. Since IGF-I polymorphism was associated with bone mineral density, it may be hypothesised that not COLIA1 but IGF-I together with other genetic and environmental factors may be involved in the complex regulation of bone mineral density in primary biliary cirrhosis.

Screening and cloning of genes differential expressed in HepG2 cells treated with bicyclol by suppression subtractive hybridization

AIM: To construct a subtractive cDNA library of genes differential expressed in human hepatocarcinoma cell line HepG2 cells treated with bicyclol using suppression subtractive hybridization (SSH) technique and to clone genes associated with its regulation effects.

METHODS: The mRNA was isolated from HepG2 cells treated with bicyclol and dimathyl sulfoxide (DMSO), respectively, and then cDNA was synthesized. After restriction enzyme RsaI digestion, small sizes cDNA were obtained. Tester cDNA was subdivided into two portions and each was ligated with different cDNA adaptor. After tester cDNA was hybridized with driver cDNA twice and underwent nested polymerase chain reaction (PCR) twice, the DNA fragment was subcloned into T/A plasmid vectors to set up the subtractive cDNA library. Amplification of the library was carried out with E. coli strain JM109. The cDNA was sequenced and analyzed in GenBank with Blast search after colony PCR.

RESULTS: The subtractive cDNA library of genes differentially expressed in HepG2 cells treated with bicyclol was constructed successfully. The amplified library contained 46 positive clones. Colony PCR showed that these clones contained 200-1 000 bp inserts. Thirty clones were analyzed by sequencing and bioinformatics. fourteen known genes were obtained.

CONCLUSION: A subtractive cDNA library of genes differential expressed in HepG2 cells treated with bicyclol using SSH technique is constructed successfully, which brings some new clues for studying the regulation mechanism of bicyclol in vivo.