Detection of Human Angiopoietin‑2 by Western Blot. Western blot shows lysates of HepG2 human hepatocellular carcinoma cell line and Hep3B human hepatocellular carcinoma cell line. PVDF membrane was probed with 2 µg/mL of Goat Anti-Human Angiopoietin‑2 Polyclonal Antibody |
(Catalog # AB623) followed by HRP-conjugated Anti-Goat IgG Secondary Antibody (Catalog # HAF017). A specific band was detected for Angiopoietin‑2 at approximately 65 kDa (as indicated). This experiment was conducted under reducing conditions and using Immunoblot Buffer Group 1.
Angiopoietin-2 (Ang-2; also ANGPT2) is a secreted glycoprotein that plays a complex role in angiogenesis and inflammation (1, 2). Mature Ang-2 is 478 amino acids (aa) in length. It contains one coiled-coil domain (aa 166‑248) that mediates multimerization, and a C‑terminal fibrinogen-like domain (aa 275‑495) that mediates receptor binding. Under reducing conditions, secreted monomeric Ang-2 is 65‑66 kDa in size. Under nonreducing conditions, both natural and recombinant Ang-2 form 140 kDa dimers, 200 kDa trimers, and 250‑300 kDa tetramers and pentamers (3‑6). Alternate splicing generates a short isoform that lacks 52 amino acids (aa) preceding the coiled-coil domain (4). Mature human Ang-2 shares 86% aa sequence identity with mouse and rat Ang-2. Ang-2 is widely expressed during development, but it is restricted postnatally to highly angiogenic tissues such as the placenta, ovaries, and uterus (3). It is particularly abundant in vascular endothelial cells (EC) where it is stored in intracellular Weibel-Palade bodies (1, 3, 7). Both Ang-2 and the related Angiopoietin-1 (Ang-1) are ligands for the receptor tyrosine kinase Tie-2 (2). While Ang-1 is a potent Tie-2 agonist, Ang-2 may act as either a Tie-2 antagonist or agonist, depending upon its state of multimerization. The higher the order of oligomer, the more effective Ang-2 becomes as a Tie-2 agonist (3, 8‑11). The short isoform appears to block the binding of either Ang-1 or full-length Ang-2 to Tie-2 (4). Ang-2 functions as a pro-angiogenic factor, although it can also induce EC death and vessel regression (12, 13). Upon its release from quiescent EC, it regulates vascular remodeling by promoting EC survival, proliferation, and migration and destabilizing the interaction between EC and perivascular cells (8, 13, 14). Ang-2 is required for postnatal vascular remodeling, and it cooperates with Ang-1 during lymphatic vessel development (7, 15). It mediates the upregulation of ICAM-1 and VCAM-1 on EC, which facilitates the adhesion of leukocytes during inflammation (16). Ang-2 is upregulated in both the endothelium and tumor cells of several cancers as well as in ischemic tissue (17‑20). Its direct interaction with Integrins promotes tumor cell invasion (21, 22). Ang-2 also promotes the neuronal differentiation and migration of subventricular zone progenitor cells (20).