The insulin-like growth factors (IGFs) are polypeptides with high sequence similarity to insulin. The IGF system (also known as IGF axis consists of two ligands (IGF-1 and IGF-2), two cell-surface receptors (IGF1R and IGF2R), a family of six high-affinity IGF binding proteins (IGFBP 1-6), at least four additional low-affinity binding proteins referred to as IGFBP related proteins (IGFBP-rP), as well as a group of enzymes involved in IGFBP degradation. The insulin-like growth factor system plays critical roles in somatic growth in an endocrine fashion (somatomedin hypothesis) as well as proliferation and differentiation of normal and malignant cells in a paracrine/autocrine fashion. Insulin-like growth factor 2 (IGF-2) is thought to be a primary growth factor required for early development while expression of insulin-like growth factor 1 (IGF-1) is required for achieving maximal growth. Insulin-like growth factors act through biding the cell-surface receptors, including IGF1R, IGF2R, the insulin receptor, the insulin-related receptor and possibly other receptors. IGF binding proteins help to modulate IGF action in complex ways that involve both inhibiting IGF action by preventing binding to the IGF-1 receptor as well as promoting IGF action possibly through aiding in delivery to the receptor and increasing IGF half-life. Recent studies have revealed important roles of the insulin-like growth factor system in diseases such as cancer, diabetes and malnutrition.
Insulin-like Growth Factor (IGF) References
Cohen P, et al. (1991) Insulin-like growth factors (IGFs), IGF receptors, and IGF-binding proteins in primary cultures of prostate epithelial cells. Journal of Clinical Endocrinology and Metabolism. 73(2): 401-7.
Kawai M, et al. (2008) Insulin-like growth factor-I and bone: lessons from mice and men. Pediatr Nephrol. 24(7): 1277-85.
Lann D, et al. (2008) The role of endocrine insulin-like growth factor-I and insulin in breast cancer. J Mammary Gland Biol Neoplasia. 13(4): 371-9.
Randhawa RS. (2008) The insulin-like growth factor system and fetal growth restrictionn. Pediatr Endocrinol Rev. 6(2): 235-40.
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