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.
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.
Dai
Wei
W
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA.
Kamei
Hiroyasu
H
Zhao
Yang
Y
Ding
Jun
J
Du
Zhou
Z
Duan
Cunming
C
D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D019143:Evolution, Molecular; D020131:Genes, Duplicate; D017403:In Situ Hybridization; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000235:genetics* / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000378:metabolism*; D010802:Phylogeny; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015533:Transcriptional Activation; D015027:Zebrafish / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism
D018975:Insulin-Like Growth Factor Binding Protein 5; D019913:Nuclear Localization Signals; D020033:Protein Isoforms; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I