Insulin-like growth factor-binding protein family 1-6, chordata <p> Insulin-like growth factors (IGFs)-I and -II are small secreted peptides that stimulate the survival, and promote the proliferation and differentiation, of many cell types [<cite idref="PUB00053602"/>]. In biological fluids, these growth factors are usually bound to IGF-binding proteins (IGFBPs), which regulate their availability and activity by prolonging their half-life and modulating their receptor interactions. </p> <p> To date, six IGFBP family members have been identified (termed IGFBP1-6) [<cite idref="PUB00053603"/>]. They share a conserved gene (intron-exon) organisation and high IGF-binding affinity. Structurally, the proteins also share a common domain architecture, possessing a conserved N-terminal IGFBP domain, a highly variable mid-section, and a thyroglobulin type-1 (Tg1) domain in their C-terminal regions. </p> <p> In addition to their role in the regulation of IGF activity, there is evidence for the direct association of IGFBPs with a variety of extracellular and cell surface molecules [<cite idref="PUB00053604"/>, <cite idref="PUB00053605"/>], with consequent effects upon important biological processes. These include modulation of bone cell proliferation [<cite idref="PUB00053606"/>], and growth arrest of breast and prostate cancer cells [<cite idref="PUB00053604"/>, <cite idref="PUB00053607"/>]. </p>