Recombinant human FGF-18 protein

Summary

• High purity human protein (Uniprot number: O76093)
• >98%, by SDS-PAGE quantitative densitometry
• Source: Expressed in E. coli
• Size in 20.2 kDa monomer
• Animal origin-free (AOF) and carrier protein-free
• Manufactured in Cambridge, UK
• Lyophilized from Tris/NaCl
• Resuspend in water at >100 µg/mL, prepare single-use aliquots, add carrier protein if desired, and store frozen at -20°C or -80°C.

Featured applications

• Growth and proliferation of chondrocytes, fibroblasts and primary cells
• Culture of mesenchymal, embryonic and pluripotent stem cells
• Directed chondrogenic differentiation of mesenchymal stem cells
• Directed osteogenic differentiation of mesenchymal stem cells
• Stimulation of angiogenesis and vascular network development
• Induction of cell migration, proliferation and extracellular matrix production

Bioactivity

Purity

Qkine FGF-18 is as biologically active as a comparable alternative supplier protein

Quantitative luciferase reporter assay shows equivalent bioactivity of Qkine FGF-18 (Qk069, green) and alternative supplier FGF-18 (Supplier B, black). HEK293T reporter cells were treated in triplicate with a serial dilution of FGF-18 for 3 hours. Firefly luciferase activity is measured and normalized to control Renilla luciferase activity.

Protein background

Dickkopf-related protein 1 (DKK-1) is a protein integral to the regulation of the Wnt signaling pathway and plays a pivotal role in embryonic development, tissue homeostasis, and various pathological conditions, including cancer [1-4]. As a member of the DKK protein family alongside DKK-2, DKK-3, and DKK-4, DKK-1 was initially identified as a Xenopus head-forming molecule and functions as a potent antagonist of the Wnt signaling pathway  [1].

With cell culture application, DKK1 is widely used for orchestrating cell fate decisions, self-renewal, and differentiation [5-6]. Its addition to the cell culture medium facilitates the binding to LDL receptor-related proteins 5 and 6 (LRP5/6) co-receptors, thereby inhibiting the activation of the canonical Wnt/β-catenin pathway  [7-8]. This interference proves instrumental in maintaining pluripotency, particularly by finely regulating the equilibrium between self-renewal and differentiation in embryonic stem cells (ESCs) [9].

The versatile utility of DKK-1 extends to the directed differentiation of induced pluripotent stem cells (iPSCs) into specific lineages, including neural differentiation, where it serves to promote the development of neural lineages [10]. Additionally, DKK-1 guides osteogenic differentiation of mesenchymal stem cells (MSCs), offering implications for bone tissue engineering and other related applications [11].

In the context of disease modeling in vitro, DKK1 finds application in mimicking conditions associated with dysregulated Wnt signaling pathways, as seen in certain cancers exhibiting aberrant Wnt expression, such as esophageal squamous cell carcinomas and hormone-resistant breast cancers [12].

Further insights into the regulatory mechanisms of DKK1 and its familial counterpart DKK-4 underscore their significant roles in modulating the Wnt/β-catenin signaling pathway. This pathway involves the interaction of Wnt ligands with the seven-transmembrane receptor Frizzled, along with co-receptors LRP5 and LRP6. DKK-1 forms inhibitory complexes with LRP5 and LRP6, as well as another receptor, Kremen, leading to endocytosis of this complex and subsequent removal of LRP5 and LRP6 from the cell surface [13-14].

DKK1 protein exhibits a structured composition. It includes an N-terminal signal peptide directing its secretion, a conserved cysteine-rich domain (CRD) crucial for disulfide bond formation, and a linker connecting the CRD to the C-terminal region. This C-terminal region interacts with other proteins and is implicated in the overall conformation and function of DKK-1. Specific amino acid residues within the CRD and C-terminal regions are vital for DKK-1’s inhibitory effect on the Wnt signaling pathway [15].

Notably, DKK-1’s inhibition of the Wnt pathway proves indispensable for anterior development, disrupting posterior patterning in vertebrates. This is evident in mice lacking DKK1 expression, where a deficiency leads to the absence of head formation [2,16]. Collectively, these molecular and functional insights underscore DKK-1’s intricate role in cellular processes and its potential as a valuable tool in manipulating cellular behaviour in diverse experimental settings.

Background references

1. Glinka, A. et al.Dickkopf-1 is a member of a new family of secreted proteins and functions in head induction. Nature 391, 357–362 (1998). https://doi.org/10.1038/34848
2. Grotewold, L., Theil, T. & Rüther, U. Expression pattern of Dkk-1 during mouse limb development. Mechanisms of Development 89, 151–153 (1999). https://doi.org/10.1016/s0925-4773(99)00194-x
3. Yuan, S., Hoggard, N. K., Kantake, N., Hildreth, B. E. & Rosol, T. J. Effects of Dickkopf-1 (DKK-1) on Prostate Cancer Growth and Bone Metastasis. Cells 12, 2695 (2023). doi: 10.3390/cells12232695
4. Fedi, P. et al.Isolation and Biochemical Characterization of the Human Dkk-1 Homologue, a Novel Inhibitor of Mammalian Wnt Signaling. Journal of Biological Chemistry 274, 19465–19472 (1999). doi: 10.1074/jbc.274.27.19465
5. Zhang, J., Kang, N., Yu, X., Ma, Y. & Pang, X. Radial Extracorporeal Shock Wave Therapy Enhances the Proliferation and Differentiation of Neural Stem Cells by Notch, PI3K/AKT, and Wnt/β-catenin Signaling. Sci Rep 7, 15321 (2017). https://doi.org/10.1038/s41598-017-15662-5
6. Li, M. et al.Perichondrium mesenchymal stem cells inhibit the growth of breast cancer cells via the DKK-1/Wnt/β-catenin signaling pathway. Oncology Reports 36, 936–944 (2016). doi: 10.3892/or.2016.4853
7. Bafico, A., Liu, G., Yaniv, A., Gazit, A. & Aaronson, S. A. Novel mechanism of Wnt signalling inhibition mediated by Dickkopf-1 interaction with LRP6/Arrow. Nat Cell Biol 3, 683–686 (2001). doi: 10.1038/35083081
8. Kulkarni, N. H. et al. Effects of parathyroid hormone on Wnt signaling pathway in bone. J of Cellular Biochemistry 95, 1178–1190 (2005). doi: 10.1002/jcb.20506
9. Zovoilis, A., Smorag, L., Pantazi, A. & Engel, W. Members of the miR-290 cluster modulate in vitro differentiation of mouse embryonic stem cells. Differentiation 78, 69–78 (2009). doi: 10.1016/j.diff.2009.06.003
10. Kong, X. B. & Zhang, C. Dickkopf (Dkk) 1 promotes the differentiation of mouse embryonic stem cells toward neuroectoderm. In Vitro Cell.Dev.Biol.-Animal 45, 185–193 (2009). doi: 10.1007/s11626-008-9157-2
11. Liu, N. et al.High levels of β‐catenin signaling reduce osteogenic differentiation of stem cells in inflammatory microenvironments through inhibition of the noncanonical Wnt pathway. J of Bone & Mineral Res 26, 2082–2095 (2011). https://doi.org/10.1002/jbmr.440
12. Browne, A. J. et al.p38 MAPK regulates the Wnt inhibitor Dickkopf-1 in osteotropic prostate cancer cells. Cell Death Dis 7, e2119–e2119 (2016). https://doi.org/10.1038/cddis.2016.32
13. Internalization of REIC/Dkk-3 protein by induced pluripotent stem cell-derived embryoid bodies and extra-embryonic tissues. Int J Mol Med 26, (2010). doi: 10.3892/ijmm_00000534
14. González-Sancho, J. M. et al.The Wnt antagonist DICKKOPF-1 gene is a downstream target of β-catenin/TCF and is downregulated in human colon cancer. Oncogene 24, 1098–1103 (2005). https://doi.org/10.1038/sj.onc.1208303
15. Krupnik, V. E. et al.Functional and structural diversity of the human Dickkopf gene family. Gene 238, 301–313 (1999). doi: 10.1016/s0378-1119(99)00365-0
16. Semënov, M. V. et al.Head inducer Dickkopf-1 is a ligand for Wnt coreceptor LRP6. Current Biology 11, 951–961 (2001). doi: 10.1016/s0960-9822(01)00290-1