Duplicated zebrafish insulin-like growth factor binding protein-5 genes with split functional domains: evidence for evolutionarily conserved IGF binding, nuclear localization, and transactivation activity

FASEB J. 2010 Jun;24(6):2020-9. doi: 10.1096/fj.09-149435. Epub 2010 Jan 15.


Insulin-like growth factor binding protein (IGFBP)-5 is a secreted protein that binds to IGF and modulates IGF actions. IGFBP-5 is also found in the nucleus of mammalian cells and has transactivation activity. The structural basis of this transactivation activity and its role in mediating IGF-independent actions are not clear. Here we report that there are 2 igfbp-5 genes in zebrafish and other teleost fish. In zebrafish, igfbp-5a and -5b are expressed in spatially restricted, mostly nonoverlapping domains during early development. The IGF binding site is conserved in both zebrafish IGFBP-5s, and they are both secreted and capable of IGF binding. Both proteins contain a consensus bipartite nuclear localization signal and were found in the nucleus when introduced into cultured cells. Although zebrafish IGFBP-5b possesses transactivation activity, zebrafish IGFBP-5a lacks this activity. Mutational analysis demonstrated that 2 unique amino acids in positions 22 and 56 of IGFBP-5a are responsible for its lack of transactivation activity. These findings suggest that the duplicated zebrafish IGFBP-5s have evolved divergent regulatory mechanisms and distinct biological properties by partitioning of ancestral structural domains and provide new evidence for a conserved role of the IGF binding, nuclear localization, and transactivation domain of this multifunctional IGFBP.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Nucleus / metabolism*
  • Cloning, Molecular
  • Cytoplasm / metabolism
  • Evolution, Molecular
  • Genes, Duplicate*
  • In Situ Hybridization
  • Insulin-Like Growth Factor Binding Protein 5 / genetics*
  • Insulin-Like Growth Factor Binding Protein 5 / metabolism
  • Insulin-Like Growth Factor I / metabolism*
  • Molecular Sequence Data
  • Nuclear Localization Signals / metabolism*
  • Phylogeny
  • Protein Isoforms
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sequence Homology, Amino Acid
  • Transcriptional Activation
  • Zebrafish / genetics*
  • Zebrafish / growth & development
  • Zebrafish / metabolism


  • Insulin-Like Growth Factor Binding Protein 5
  • Nuclear Localization Signals
  • Protein Isoforms
  • RNA, Messenger
  • Insulin-Like Growth Factor I