Insulin-like growth factor (IGF) binding protein-related protein 1 (IGFBP-rp1), also known as IGF binding protein-7 (IGFBP-7) and Mac25 is a 31 - 37 kDa secreted glycoprotein that belongs to the IGFBP superfamily of molecules (1, 2). Members of this superfamily are characterized by the presence of 10 ‑ 12 conserved cysteines in the first third of the molecule, and the partial conservation of an xCGCCxxC octapeptide motif that exists in an N‑terminal IGFBP domain (1, 3). Mouse IGFBP-7 cDNA encodes a 281 amino acid (aa) precursor protein that contains a putative 25 aa signal peptide and a 256 aa mature region. The mature protein contains an N‑terminal 43 aa IGFBP domain that is followed by a 52 aa Kazal-type serine proteinase inhibitor domain and a 105 aa C-terminal Ig-like C2‑type domain (4, 5). The molecule is known to contain about 4 kDa of carbohydrate and believed to undergo phosphorylation (6). Mature mouse IGFBP-7 is 95% and 91% aa identical to mature rat and human IGFBP-7, respectively. Cells known to express IGFBP-7 include osteoblasts, select skeletal muscle fibers, visceral and vascular smooth muscle cells, breast epithelium, ciliated epithelium, renal tubular epithelium, astrocytes and oligodendroglia, and vascular endothelium in all tissues except brain (7). IGFBP-7 will bind both IGF-I and insulin, albeit at low affinity. When bound to IGF-I, it participates in growth promoting effects (8). Alternatively, IGFBP-7 by itself is an inhibitor of cell proliferation (6). Thus, its function is unclear. It is known to bind heparin, syndecan-1 and chemokines (8, 9). Based on human studies and aa conservation in relevant regions, mouse IGFBP-7 might be be expected to undergo proteolytic cleavage extracellularly (8). This will create an 8 kDa, 72 aa subunit (containing the IGFBP domain) that is disulfide-linked to a 25 kDa, 184 aa C-terminal subunit. Cleavage will reduce IGF‑I bonding activity and the promotion of IGF‑dependent cell proliferation.