The insulin-like growth factor 1 (IGF1) signalling pathway has important roles in regulating cellular proliferation and apoptosis. Converging results from epidemiological research and in vivo carcinogenesis models indicate that high levels of circulating IGF1 are associated with increased risk of several common cancers. Ongoing research seeks to clarify the mechanisms underlying these observations and to determine the extent to which IGF physiology influences patterns of cancer incidence. Various therapeutic strategies that target the IGF1 receptor have demonstrated impressive antineoplastic activity in laboratory models, and clinical trials of several novel drug candidates are planned.

Insulin-like growth factors and neoplasia.

I. Introduction THE insulin-like growth factors (IGFs) and their receptors and binding proteins constitute a family of cellular modulators that play essential roles in the regulation of growth and development. The IGF ligands include three structurally related peptides: insulin, IGF-I, and IGF-II. Unlike insulin, IGF-I and IGF-II are expressed ubiquitously, albeit in a highly regulated manner (see reviews in Refs. 1-5). The biological functions of the IGFs are mediated by a family of transmembrane receptors, which includes the insulin, IGF-I, and IGF-II/mannose-6-phosphate (M-6-P) receptors. While the IGF-I receptor is the primary mediator of IGF action, the insulin and IGF-II/M-6-P receptors may also mediate some of these functions (Fig. 1) (6, 7). The biological actions of the IGFs are modulated by a family of at least six IGF-binding proteins (IGFBPs) that are found in the circulation and in extracellular compartments and are produced by most tissues. The IGFBPs are capable of inhibiting or enhancing I...

Molecular and cellular aspects of the insulin-like growth factor I receptor

The molecular basis of lung morphogenesis

Hypoxia-inducible factor 1 (HIF-1) activates transcription of genes encoding glucose transporters, glycolytic enzymes, vascular endothelial growth factor, and other proteins involved in O 2 homeostasis and tumor progression. The expression and transcriptional activity of the HIF-1α subunit is regulated by the cellular O 2 concentration. We demonstrate that insulin, insulin-like growth factor (IGF)-1, and IGF-2 induce expression of HIF-1α, which is required for expression of genes encoding IGF-2, IGF-binding protein (IGFBP)-2 and IGFBP-3. These data provide a novel mechanism by which HIF-1α overexpression may occur in tumor cells and contribute to an autocrine growth factor loop.

https://cancerres.aacrjournals.org/content/canres/59/16/3915.full.pdf

Reciprocal Positive Regulation of Hypoxia-inducible Factor 1α and Insulin-like Growth Factor 2

The insulin-like growth factor (IGF) family of peptides, binding proteins, and receptors are important for normal human growth and development and are involved in the specialized functions of most physiologic systems. Most members of the IGF system are expressed by different cancer cells and may play an important role in the propagation of these malignancies. New therapies aimed at modulating various components of the IGF system could affect the progression and metastasis of cancer.

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Insulin-like Growth Factors and Cancer

Fibroblast cell lines, designated R- and W cells, were generated, respectively, from mouse embryos homozygous for a targeted disruption of the Igf1r gene, encoding the type 1 insulin-like growth factor receptor, and from their wild-type littermates. W cells grow normally in serum-free medium supplemented with various combinations of purified growth factors, while pre- and postcrisis R- cells cannot grow, as they are arrested before entering the S phase. R- cells are able to grow in 10% serum, albeit more slowly than W cells, and with all phases of the cell cycle being elongated. An activated Ha-ras expressed from a stably transfected plasmid is unable to overcome the inability of R- cells to grow in serum-free medium supplemented with purified clones. Nevertheless, even in the presence of serum, R- cells stably transfected with Ha-ras, alone or in combination with simian virus 40 large T antigen, fail to form colonies in soft agar. Reintroduction into R- cells (or their derivatives) of a plasmid expressing the human insulin-like growth factor I receptor RNA and protein restores their ability to grow with purified growth factors or in soft agar. The signaling pathways participating in cell growth and transformation are discussed on the basis of these results.

Effect of a null mutation of the insulin-like growth factor I receptor gene on growth and transformation of mouse embryo fibroblasts.

When wild-type mouse embryo cells are stably transfected with a plasmid constitutively overexpressing the epidermal growth factor (EGF) receptor (EGFR), the resulting cells can grow in serum-free medium supplemented solely with EGF. Supplementation with EGF also induces in these cells the transformed phenotype (growth in soft agar). However, when the same EGFR expression plasmid is introduced and overexpressed in cells derived from littermate embryos in which the insulin-like growth factor I (IGF-I) receptor genes have been disrupted by homologous recombination, the resulting cells are unable to grow or to be transformed by the addition of EGF. Reintroduction into these cells (null for the IGF-I receptor) of a wild-type (but not of a mutant) IGF-I receptor restores EGF-mediated growth and transformation. Our results indicate that at least in mouse embryo fibroblasts, the EGFR requires the presence of a functional IGF-I receptor for its mitogenic and transforming activities.

D Coppola

Papers

Effect of a null mutation of the insulin-like growth factor I receptor gene on growth and transformation of mouse embryo fibroblasts.

A functional insulin-like growth factor i receptor is required for the mitogenic and transforming activities of the epidermal growth factor receptor