Insulin-like growth factor II (IGF-II) mRNA expression during hepatocarcinogenesis in transgenic mice

Insulin-like growth factor II in hepatocellular carcinoma

Hepatocellular carcinoma is one of the most common malignant human tumors. Hepatocarcinogenesis is a multistep process with a multifactorial etiology. Chronic hepatitis B and hepatitis C virus infection, alcohol drinking and cirrhosis of any etiology are the major risk factors for hepatocellular carcinoma. Growth factors, their receptors and related proteins are involved in the process of malignant transformation. The IGF axis is involved in the proliferation and differentiation of normal, transformed and malignant hepatocytes. In the context of hepatocarcinogenesis, IGF-II has, in particular, been investigated thoroughly. Increased IGF-II bioavailability, protease activity of IGF-binding proteins and IGF-I receptor expression, decreased expression of IGF-II receptor and IGF-binding proteins are thought to contribute to hepatocellular carcinoma genesis. This review will first focus on the role of the IGF axis in hepatocarcinogenesis. In the second part it will emphasize circulating IGF-II levels in chronic liver disease and hepatocellular carcinoma, and diagnostic application of serum IGF-II level in both small and larger hepatocellular carcinoma.

A human monoclonal antibody against insulin-like growth factor-II blocks the growth of human hepatocellular carcinoma cell lines in vitro and in vivo

Elevated expression of insulin-like growth factor-II (IGF-II) is frequently observed in a variety of human malignancies, including breast, colon, and liver cancer. As IGF-II can deliver a mitogenic signal through both IGF-IR and an alternately spliced form of the insulin receptor (IR-A), neutralizing the biological activity of this growth factor directly is a potential alternative option to IGF-IR-directed agents. Using a Fab-displaying phage library and a biotinylated precursor form of IGF-II (1-104 amino acids) as a target, we isolated Fabs specific for the E-domain COOH-terminal extension form of IGF-II and for mature IGF-II. One of these Fabs that bound to both forms of IGF-II was reformatted into a full-length IgG, expressed, purified, and subjected to further analysis. This antibody (DX-2647) displayed a very high affinity for IGF-II/IGF-IIE (K(D) value of 49 and 10 pmol/L, respectively) compared with IGF-I (approximately 10 nmol/L) and blocked binding of IGF-II to IGF-IR, IR-A, a panel of insulin-like growth factor-binding proteins, and the mannose-6-phosphate receptor. A crystal complex of the parental Fab of DX-2647 bound to IGF-II was resolved to 2.2 A. DX-2647 inhibited IGF-II and, to a lesser extent, IGF-I-induced receptor tyrosine phosphorylation, cellular proliferation, and both anchorage-dependent and anchorage-independent colony formation in various cell lines. In addition, DX-2647 slowed tumor progression in the Hep3B xenograft model, causing decreased tumoral CD31 staining as well as reduced IGF-IIE and IGF-IR phosphorylation levels. Therefore, DX-2647 offers an alternative approach to targeting IGF-IR, blocking IGF-II signaling through both IGF-IR and IR-A.

Reactivation of the insulin-like growth factor-II signaling pathway in human hepatocellular carcinoma

Constitutive activation of the insulin-like growth factor (IGF)-signaling axis is frequently observed in human hepatocellular carcinoma (HCC). Especially the overexpression of the fetal growth factor IGF-II, IGF-Ireceptor (IGF-IR), and cytoplasmic downstream effectors such as insulin-receptor substrates (IRS) contribute to proliferation, anti-apoptosis, and invasive behavior. This review focuses on the relevant alterations in this signaling pathway and independent in vivo models that support the central role IGF-II signaling during HCC development and progression. Since this pathway has become the center of interest as a target for potential anti-cancer therapy in many types of malignancies, various experimental strategies have been developed, including neutralizing antibodies and selective receptor kinase inhibitors, with respect to the specific and efficient reduction of oncogenic IGF-II/IGF-IR-signaling.

Comparison of basal gene expression profiles and effects of hepatocarcinogens on gene expression in cultured primary human hepatocytes and HepG2 cells

Toxicogenomics is a relatively new discipline of toxicology. Microarrays and bioinformatics tools are being used successfully to understand the effects of toxicants on in vivo and in vitro model systems, and to gain a better understanding of the relevance of in vitro models commonly used in toxicological studies. In this study, cDNA filter arrays were used to determine the basal expression patterns of human cultured primary hepatocytes from different male donors; compare the gene expression profile of HepG2 to that of primary hepatocytes; and analyze the effects of three genotoxic hepatocarcinogens; aflatoxin B(1) (AFB(1)), 2-acetylaminofluorene (2AAF), and dimethylnitrosamine (DMN), as well as one non-gentoxic hepatotoxin, acetaminophen (APAP) on gene expression in both in vitro systems. Real-time PCR was used to verify differential gene expression for selected genes. Of the approximately 31,000 genes screened, 3-6% were expressed in primary hepatocytes cultured on matrigel for 16 h. Of these genes, 867 were expressed in cultured hepatocytes from all donors. HepG2 cells expressed about 98% of the genes detectable in cultured primary hepatocytes, however, 31% of the HepG2 transcriptome was unique to the cell line. A number of these genes are expressed in human liver but expression is apparently lost during culture. There was considerable variability in the response to chemical carcinogen exposure in primary hepatocytes from different donors. The transcription factors, E2F1 and ID1 mRNA were increased three-fold and six-fold (P < 0.05, P < 0.01), respectively, in AFB(1) treated primary human hepatocytes but were not altered in HepG2. ID1 expression was also increased by dimethylnitrosamine, acetylaminofluorene and acetaminophen in both primary hepatocytes and HepG2. Identification of genes that are expressed in primary hepatocytes from most donors, as well as those genes with variable expression, will aid in understanding the variability in human reactions to drugs and chemicals. This study suggests that identification of biomarkers of exposure to some chemicals may be possible in the human through microarray analysis, despite the variability in responses.

Diethylnitrosamine induces long-lasting re-expression of insulin-like growth factor II during early stages of liver carcinogenesis in mice

The expression of the insulin-like growth factor II (IGF-II) gene (Igf2) in rodents is completely abrogated in almost all adult tissues. A prominent exception are neoplasms in which IGF-II frequently serves as an autocrine growth factor. We have investigated the potential role of Igf2 expression during liver carcinogenesis. After application of diethylnitrosamine (DEN) preneoplastic foci and adenomas emerged in liver tissue of wild-type and phosphoenolpyruvate carboxykinase (PEPCK)-IGF-II transgenic mice. Surprisingly, number and size of preneoplastic foci were not significantly increased in PEPCK-IGF-II mice as compared with wild-type animals. In situ preparation showed that early adenomas expressed Igf2 transcripts. Reverse transcriptase polymerase chain reaction (RT-PCR) and restriction enzyme analysis confirmed that DEN treatment had indeed reactivated the hepatic expression of murine Igf2 in control mice in a dose-dependent manner. This re-expression of Igf2 persisted for at least 18 months. Species-specific RT-PCR analyses also revealed the presence of murine Igf2 mRNAs in some PEPCK-IGF-II mice. A similar reactivation of Igf2 was detected in bovine growth hormone transgenic mice which develop hepatocellular neoplasms with high frequency. Our results suggest that reactivation of Igf2 is an early event during hepatocarcinogenesis in mice. Its appearance in two independent animal models suggests that Igf2 may be important at pivotal checkpoints of hepatocarcinogenesis.

Cytokines in the liver

Cytokines comprise a group of small proteins released from cells in order to influence the function of other cells. By binding to highly specific cell-surface receptors, they trigger a vast array of intracellular signalling cascades. Cytokines have been described as interleukins, growth factors, interferons and chemokines. Unlike hormones, which act in a similar way, cytokines are produced by many different types of cell and act on many other types. Most of them are produced only after certain stimuli. The most intense field of cytokine activity is without doubt host defence. The liver resembles a central organ of cytokine activity due to the fact that it hosts hepatocytes, which are highly susceptible to the activity of cytokines in a variety of physiological and pathophysiological processes. Moreover, the non-parenchymal cells of the liver, in particular Kupffer cells (KCs), the resident tissue macrophages of the liver, are able to synthesize a variety of cytokines that may act systemically on any other organ of the body, or in a paracrine manner on hepatocytes and other non-parenchymal liver cells. A classic example of how cytokines act can be observed during the acute phase reaction discussed in this article. The role of cytokines in liver development, acute liver injury, liver regeneration, liver fibrosis and liver metastasis is also discussed.

Molecular analyses of liver tumors in c-myc transgenic mice and c-myc and TGF-alpha double transgenic mice

It has been demonstrated that co-expression of c-myc and transforming growth factor alpha (TGF-alpha) as transgenes in the mouse liver results in a tremendous acceleration of neoplastic development in this organ as compared to expression of either transgene alone [Murakami, H., et al. (1993) Cancer Res., 53, 1719-1723]. In order to clarify the roles of transgenes and additional other genetic alterations during hepatocarcinogenesis, we analyzed liver tumors developed in albumin/c-myc transgenic mice and albumin/c-myc and MT-1/TGF-alpha double transgenic mice. High expression of TGF-alpha transgene was found in nine of 14 (64%) liver tumors in double transgenic mice, suggesting that TGF-alpha overexpression confers growth advantage during hepatocarcinogenesis. Only one of 14 (7%) liver tumors in double transgenic mice and none of 13 liver tumors in c-myc transgenic mice showed overexpression of insulin-like growth factor II (IGF-II). This result was in contrast to the report by Takagi et al. [Takagi, H., et al. (1992) Cancer Res., 52, 5171-5177] which showed overexpression of IGF-II in 75% of liver tumors in TGF-alpha transgenic mice and suggested that the presence of c-myc transgenes together with TGF-alpha from an early stage of hepatocarcinogenesis may lead to different carcinogenic pathways which are independent of IGF-II overexpression. Expression of c-myc transgene was found in most of the liver tumors, but at lower levels than non-tumorous parts of the liver in c-myc and double transgenic mice. These results suggest that c-myc transgene expression cooperates with TGF-alpha in the early stages of hepatocarcinogenesis but has growth disadvantage in later stages of hepatocarcinogenesis. There was no evidence of mutational activation of the H-ras gene or mutational inactivation of the p53 gene in any liver tumors developed in c-myc or double transgenic mice.

Gene-targeting and transgenic approaches to IGF and IGF binding protein function

The ability to manipulate genetic information in the germ line of mice has provided powerful approaches to study gene function in vivo. These approaches have included the establishment of mouse lines in which a specified gene or genes are overexpressed, ectopically expressed, or deleted. Transgenic and gene-targeted mouse lines have been used extensively to study the function of the insulin-like growth factors (IGF), IGF-I and IGF-II, and their receptors and binding proteins. In the IGF system, these technologies have elucidated the roles of the IGFs in fetal and somatic growth and have demonstrated a critical role for this system in transformation and tumorigenesis. Analysis of combinatorial crosses of gene-targeted mouse lines also has suggested the existence of an as yet unidentified IGF receptor that regulates fetal growth. Similar approaches using transgenic and gene-targeted mouse models have been initiated to study the in vivo functions of the IGF binding proteins. These mouse models provide important tools to test specific functional questions in vivo as well as to study the long-term physiological consequences of chronic gene alterations.

The molecular pathogenesis of hepatocellular carcinoma

Some of the multiple factors involved in the molecular pathogenesis of hepatocellular carcinoma have been elucidated in recent years but no clear picture of how and in what sequence these factors interact at the molecular level has emerged yet. Transformation of hepatocytes to the malignant phenotype may occur irrespective of the aetiological agent through a pathway of chronic liver injury, regeneration and cirrhosis. The activation of cellular oncogenes, the inactivation of tumour suppressor genes and overexpression of certain growth factors contribute to the development of HCC. There is increasing evidence that the hepatitis B virus may play a direct role in the molecular pathogenesis of HCC. Aflatoxins have been shown to induce specific mutations of the p53 tumour suppressor gene thus providing a clue to how an environmental factor may contribute to tumour development at the molecular level.

Expression of insulin-like growth factor II (IGF-II) in human hepatocellular carcinomas: an immunohistochemical study

Recent results obtained using molecular biology techniques have suggested a possible role for insulin-like growth factor II (IGF-II) in the pathogenesis of hepatocellular carcinoma (HCC). To investigate this phenomenon, a monoclonal antibody was used against IGF-II to study 54 patients with HCC. The presence of HBsAg was also tested both in serum and liver tissue. A positive immunoreaction was found in 9/15 (60%) of the HCC arising in cirrhotic livers of patients who had serum markers for HBV (HBV + positive patients). These results provide further evidence that HBV might play a role in the expression of IGF-II. In HCC of patients without any markers of HBV infection (HBV- negative patients), IGF-II was detected in 10/39 (25.6%) of the tumors, and in some benign neoplastic lesions. It was found not only in neoplastic cells but also in some dysplastic nodules. The speculation arises that IGF-II expression may play a role in some steps of hepato-carcinogenesis.

Transforming growth factor alpha dramatically enhances oncogene-induced carcinogenesis in transgenic mouse pancreas and liver

To characterize the effect(s) of transforming growth factor alpha (TGF alpha) during multistage carcinogenesis, we examined tumor development in pancreas and liver of transgenic mice that coexpressed TGF alpha with either viral (simian virus 40 T antigens [TAg]) or cellular (c-myc) oncogenes. In pancreas, TGF alpha itself was not oncogenic, but it nevertheless dramatically accelerated growth of tumors induced by either oncogene alone, thereby reducing the host life span up to 60%. Coexpression of TGF alpha and TAg produced an early synergistic growth response in the entire pancreas together with the more rapid appearance of preneoplastic foci. Coexpression of TGF alpha and c-myc also accelerated tumor growth in situ and produced transplantable acinar cell carcinomas whose rate of growth was TGF alpha dependent. In liver, expression of TGF alpha alone increased the incidence of hepatic cancer in aged mice. However, coexpression of TGF alpha with c-myc or TAg markedly reduced tumor latency and accelerated tumor growth. Significantly, expression of the TGF alpha and myc transgenes in hepatic tumors was induced up to 20-fold relative to expression in surrounding nonneoplastic liver, suggesting that high-level overexpression of these proteins acts as a major stimulus for tumor development. Finally, in both pancreas and liver, combined expression of TGF alpha and c-myc produced tumors with a more malignant (less differentiated) appearance than did expression of c-myc alone, consistent with an influence of TGF alpha upon the morphological character of c-myc-induced tumor progression. These findings demonstrate the importance of TGF alpha expression during multistage carcinogenesis in vivo and point to a major role for this growth factor as a potent stimulator of tumor growth.

Transforming growth factor alpha dramatically enhances oncogene-induced carcinogenesis in transgenic mouse pancreas and liver

To characterize the effect(s) of transforming growth factor alpha (TGF alpha) during multistage carcinogenesis, we examined tumor development in pancreas and liver of transgenic mice that coexpressed TGF alpha with either viral (simian virus 40 T antigens [TAg]) or cellular (c-myc) oncogenes. In pancreas, TGF alpha itself was not oncogenic, but it nevertheless dramatically accelerated growth of tumors induced by either oncogene alone, thereby reducing the host life span up to 60%. Coexpression of TGF alpha and TAg produced an early synergistic growth response in the entire pancreas together with the more rapid appearance of preneoplastic foci. Coexpression of TGF alpha and c-myc also accelerated tumor growth in situ and produced transplantable acinar cell carcinomas whose rate of growth was TGF alpha dependent. In liver, expression of TGF alpha alone increased the incidence of hepatic cancer in aged mice. However, coexpression of TGF alpha with c-myc or TAg markedly reduced tumor latency and accelerated tumor growth. Significantly, expression of the TGF alpha and myc transgenes in hepatic tumors was induced up to 20-fold relative to expression in surrounding nonneoplastic liver, suggesting that high-level overexpression of these proteins acts as a major stimulus for tumor development. Finally, in both pancreas and liver, combined expression of TGF alpha and c-myc produced tumors with a more malignant (less differentiated) appearance than did expression of c-myc alone, consistent with an influence of TGF alpha upon the morphological character of c-myc-induced tumor progression. These findings demonstrate the importance of TGF alpha expression during multistage carcinogenesis in vivo and point to a major role for this growth factor as a potent stimulator of tumor growth.