| ROBO4, also called magic roundabout, is a ~150kD glycoprotein belonging to the ROBO family (1). ROBOs are molecular guidance receptors that typically interact with Slit ligands to regulate axon guidance and neuronal migration (2). Unlike other family members, ROBO4 is mainly restricted to the vascular endothelium (1, 2). Expression in early hematopoietic progenitors is also reported (3). The human ROBO4 cDNA encodes 1012 amino acids (aa), including a 27 aa signal sequence, a 440 aa extracellular domain (ECD) containing two C2 type Ig domains and two fibronectin type III (FNIII) domains, a transmembrane domain and an intracellular domain. ROBO4 diverges from other ROBOs in the number of Ig, FNIII and cytoplasmic CC domains (1, 4). Within the ECD, human ROBO4 shares 80%, 80%, 87% and 88% aa identity with mouse, rat, bovine and canine ROBO4, respectively. Vascular endothelial ROBO4 is expressed at highest levels in during development and vascular remodeling, including tumor angiogenesis (1, 2, 4 6). It is proposed to contribute to vascular stability. Consistent with this, endogenous ROBO4 is concentrated in the vascular stalk and sprouts rather than tip cells and appears to protect newly formed blood vessels against VEGFinduced vascular leak (6 9). ROBO4 binding of Slit proteins has been variably reported, and when detected may be mediated by ROBO4/ROBO1 heterodimers (2, 4 7, 9 13). ROBO4 is also variably reported to stimulate or inhibit cell migration or filopodia formation (2, 4 13). Effects on cell movement may be mediated through intracellular binding of WASP, Ras/Rac/Rho, Mena, Srcor Paxillin related proteins, all of which affect the cytoskeleton (5 7, 10 12). Recombinant soluble ROBO4 ECD can antagonize endothelial cell migration and in vivo angiogenesis (13). Source: Recombinant corresponding to human ROBO4 expressed in NS0 cells. Molecular Weight: ~74kD Biological Activity: Measured by its binding ability in a functional ELISA. When recombinant human ROBO4 Fc Chimera is immobilized at 5ug/ml, biotinylated recombinant rat UNC5H2/Fc Chimera binds with an apparent KD < 20nM. Endotoxin Level: <1EU/ug (LAL method) Storage and Stability: Lyophilized powder may be stored at -20C. Stable for 12 months at -20C. Reconstitute with sterile buffer. Aliquot to avoid repeated freezing and thawing. Store at -20C. Reconstituted product is stable for 6 months at -20C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer. |
