The RNA-binding protein IMP-3 is a translational activator of insulin-like growth factor II leader-3 mRNA during proliferation of human K562 leukemia cells.
IMP-3, a member of the insulin-like growth factor-II (IGF-II) mRNA-binding protein (IMP) family, is expressed mainly during embryonic development and in some tumors. Thus, IMP-3 is considered to be an oncofetal protein. The functional significance of IMP-3 is not clear. To identify the functions of IMP-3 in target gene expression and cell proliferation, RNA interference was employed to knock down IMP-3 expression. Using human K562 leukemia cells as a model, we show that IMP-3 protein associates with IGF-II leader-3 and leader-4 mRNAs and H19 RNA but not c-myc and beta-actin mRNAs in vivo by messenger ribonucleoprotein immunoprecipitation analyses. IMP-3 knock down significantly decreased levels of intracellular and secreted IGF-II without affecting IGF-II leader-3, leader-4, c-myc, or beta-actin mRNA levels and H19 RNA levels compared with the negative control siRNA treatment. Moreover, IMP-3 knock down specifically suppressed translation of chimeric IGF-II leader-3/luciferase mRNA without altering reporter mRNA levels. Together, these results suggest that IMP-3 knock down reduced IGF-II expression by inhibiting translation of IGF-II mRNA. IMP-3 knock down also markedly inhibited cell proliferation. The addition of recombinant human IGF-II peptide to these cells restored cell proliferation rates to normal. IMP-3 and IMP-1, two members of the IMP family with significant structural similarity, appear to have some distinct RNA targets and functions in K562 cells. Thus, we have identified IMP-3 as a translational activator of IGF-II leader-3 mRNA. IMP-3 plays a critical role in regulation of cell proliferation via an IGF-II-dependent pathway in K562 leukemia cells.
Liao
Baisong
B
Department of Molecular Genetics, Microbiology, and Immunology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA.
Hu
Yan
Y
Herrick
David J
DJ
Brewer
Gary
G
D020121:5' Untranslated Regions / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism*; D020014:K562 Cells; D007938:Leukemia / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*
D020121:5' Untranslated Regions; D016601:RNA-Binding Proteins; D015534:Trans-Activators; D007335:Insulin-Like Growth Factor II