| Dickkopf related protein 2 (Dkk-2) is a member of the Dickkopf family of secreted Wnt modulators (1-3). Dkk proteins contain a signal peptide and two conserved cysteine-rich domains that are separated by a linker region. The second cysteine-rich domain mediates Dkk-2 binding activities, and its interaction with B-propeller domains of LRP-5/6 has been mapped (2-4, 7). The 226aa, 35kD mature human Dkk-2 shares 96%, 97%, 97%, 97%, 97% and 98% aa identity with mouse, rat, canine, equine, bovine and porcine Dkk-2, respectively. Mouse Dkk-2 can activate the canonical Wnt signaling pathway in Xenopus embryos, showing evolutionary conservation of function (5). Dkk proteins modify Wnt engagement of a receptor complex composed of a Frizzled protein and a low-density lipoprotein receptor-related protein, either LRP-5 or LRP-6 (3). Also, Kremen-1 and Kremen-2 are high affinity receptors for Dkk-1 and Dkk-2 (9). When LRP-6 is overexpressed, direct high-affinity binding of Dkk-2 to LRP can enhance canonical Wnt signaling (6-8). However, when Dkk-2 and LRP-6 form a ternary complex with Kremen-2, Wnt signaling is inhibited due to internalization of Dkk-2/LRP6/Krm2 complexes (9, 10). Thus, depending on the cellular context, Dkk-2 can either activate or inhibit canonical Wnt signaling (3). In contrast, binding of Dkk-1 or Dkk-4 to LRP is consistently antagonistic (3). Dkk proteins are expressed in mesenchymal tissues and control epithelial transformations. Dkk-2 expression has been studied most in bone and eye, although it is expressed as early as periimplantation in mice (11). Mouse Dkk-1 or Dkk-2 deficiencies have opposite effects on bone homeostasis, despite down-regulating Wnt antagonism in both cases (12, 13). Dkk-2 expression is induced by Wnts in bone, and is thought to enhance bone density by promoting terminal differentiation of osteoblasts and mineral deposition (12). In contrast, Dkk-1 negatively regulates late osteoblast proliferation, which limits bone density (13). Dkk-2-deficient mice are blind, exhibiting faulty differentiation of corneal epithelium and ectopic blood vessels in the periocular mesenchyme (14, 15). Recombinant protein corresponding to Met1-Ile259 from human Dkk-2 expressed in CHO cells. Molecular Weight: ~25.8kD Biological Activity: Measured in a competitive binding assay. When recombinant mouse Kremen-1 is immobilized at 4ug/ml (100ul/well), recombinant human Dkk-2 inhibits 50% binding of biotinylated recombinant human Dkk-1 (200ng/mL) at the concentration range of 1.5-6ug/ml. Storage and Stability: Lyophilized and reconstituted products are stable for 6 months after receipt at -20C. Reconstitute with sterile PBS. Aliquot to avoid repeated freezing and thawing. Store 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. |
