c‐myc‐induced hepatocarcinogenesis in the absence of IGF‐I receptor

Abstract

Numerous tumours, including hepatocarcinomas, produce IGFs, and some depend on these growth factors in a paracrine or autocrine fashion. We have shown that c-myc-induced experimental hepatocarcinogenesis is associated with enhanced production of IGF-II. To assess the role of the IGF-I receptor (IGF-IR) in hepatocarcinogenesis, we generated conditional mutant mice that overexpressed c-myc and were knocked out for IGF-IR specifically in the liver. We compared these mice with littermate controls that also overexpressed c-myc but had wild-type IGF-IR alleles. We found that the pretumoral phase, induced by early c-myc expression and characterised by increased cell proliferation, was largely unaffected by the lack of IGF-IR. To our further surprise, hepatocellular carcinomas (HCCs) lacking IGF-IR readily developed and progressed at the same rate as control HCCs. Key words: hepatocellular carcinoma; IGF-I receptor; transgenic mouse; tumour growth; liver IGF-IR, the major receptor for both IGF-I and IGF-II, plays an important role in normal cell growth and development. It consists of 2 extracellular ␣ subunits, containing the ligand-binding domain, and 2 transmembrane ␤ subunits with TK activity. IGF binding causes receptor autophosphorylation and activates TK activity, which subsequently phosphorylates a multitude of intracellular substrates, including IRSs and Shc. This leads to the downstream regulation of multiple signalling cascades, such as the MAPK and PI3K/Akt pathways. IGF-IR levels are constitutively very low in normal adult murine or human livers. Abnormal IGF-IR signalling is implicated in the development of different types of tumour, including HCC. Increased IGF-II levels have been observed in human HCC 1,2 and in tumoral liver tissue from several transgenic cancer models. 3,4 IGF-IR is overproduced in many HCC cell lines, allowing IGF-II to exert its mitogenic activity. 5 Moreover, IRS-1 is upregulated in human liver tumours and HCC cell lines. 6 Several authors have designed strategies to inhibit the IGF axis with the aim of preventing or treating HCC. Antisense therapy against IGF-I suppressed the tumorigenicity of a rat hepatoma cell line and caused regression of established tumours. 7 Injection of mice implanted with HCC with a methylated oligonucleotide downregulated IGF-II and prolonged survival. 8 Furthermore, transgenic mice that overproduce the SV40 large T antigen and that are null for IGF-II (secondarily to the disruption of the paternal Igf2 allele) develop fewer and smaller liver tumours than those carrying the normal Igf2 allele. 9 By targeting the IGF ligands, these studies highlight the importance of IGF signalling in hepatocarcinogenesis. However, they do not show whether blockade of the cognate receptor can produce similar effects. Here, we evaluated the outcome of nonreversible, Cre-lox-mediated and liver-specific IGF-IR knockout on hepatocellular tumorigenesis. Material and methods MicePK-myc transgenic mice (backcrossed with the 129/Sv genetic background for this study) express the c-m...

IGF-1R Contributes to Stress-Induced Hepatocellular Damage in Experimental Cholestasis

“…The absence of a functional Igf1r gene does not affect postnatal hepatic development or adult liver morphology. 18,21 Igf1r flox/flox littermates that had not inherited AlfpCre served as controls.…”

“…Genotyping was performed by PCR from skin biopsy samples, as described. 21 Cre-lox deletion of exon 3 in the liver was detected by triplex PCR using primers 5Ј-CCATGGGTGTTAAATGTAATGGC-3Ј, 5Ј-ATGAATGCTGGTGAGGGTTGTCTT-3Ј and 5Ј-ATCTT-GGAGTGGTGGGTCTGTTTC-3Ј, as described. 21 …”

“…Hepatocellular injury is the major triggering event of the wound healing response that leads to liver fibrosis and cancer, so we investigated whether IGF-1R influences the hepatocellular stress response in the liver. We used a mouse model of liver-specific Igf1r gene inactivation that we established previously, 18,21 and examined cellular stress and fibrogenic responses induced by cholestasis in these animals. We found that IGF-1R deletion confers protection against ER stress and cellular injury induced by cholestasis in the liver.…”

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

“…In a more indirect approach, TIMP1 overexpression reduced IGF-Ⅱ-driven HCC development in SV40T-Ag transgenic animals based on reduced tumor cell proliferation and vascularization [41,78,79] . However, it is also noteworthy that mice expressing the c-MYC oncogene and which are deficient for IGF-IR only showed a marginally reduced HCC incidence compared to animals expressing the oncogene alone [74] .…”

“…Both mice with liver-directed expression of SV40T-Ag or HBV presurface gene products (preS1 and preS2) developed HCCs, which is associated with a high level of IGF-Ⅱ expression [72] . Moreover, transgenic mice overexpressing the woodchuck hepatitis virus/c-MYC [73] , c-MYC [74] , and TGFα [75] developed HCCs accompanied by elevated IGF-Ⅱ expression in the tumors. Equally, liver tumors in p53-null animals exhibited increased amounts of IGF-Ⅱ as compared to normal littermates after delivery of polyoma virus middle T antigen (PyMT) [76] .…”