Targeted knockdown of the RNA-binding protein CRD-BP promotes cell proliferation via an insulin-like growth factor II-dependent pathway in human K562 leukemia cells.
The c-myc mRNA coding region determinant-binding protein (CRD-BP) was first identified as a masking protein that stabilizes c-myc mRNA in a cell-free mRNA degradation system. Thus, CRD-BP is thought to promote cell proliferation by maintaining c-Myc at critical levels. CRD-BP also appears to be an oncofetal protein, based upon its expression during mammalian development and in some tumors. By using K562 leukemia cells as a model, we show that CRD-BP gene silencing by RNA interference significantly promoted proliferation, indicating an inhibitory effect of CRD-BP on proliferation. Unexpectedly, CRD-BP knockdown had no discernible effect on c-myc mRNA levels. CRD-BP is also known as insulin-like growth factor II (IGF-II) mRNA-binding protein-1. It has been reported to repress translation of a luciferase reporter mRNA containing an IGF-II 5'-untranslated region known as leader 3 but not one containing IGF-II leader 4. CRD-BP knockdown markedly increased IGF-II mRNA and protein levels but did not alter translation of luciferase reporter mRNAs containing 5'-untranslated regions consisting of either IGF-II leader 3 or leader 4. Addition of antibody against IGF-II to cell cultures inhibited the proliferative effect of CRD-BP knockdown, suggesting that regulation of IGF-II gene expression, rather than c-myc mRNA levels, mediates the proliferative effect of CRD-BP knockdown. Thus, we have identified a dominant function for CRD-BP in cell proliferation of human K562 cells, involving a possible IGF-II-dependent mechanism that appears independent of its ability to serve as a c-myc mRNA masking protein.
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.
Patel
Meera
M
Hu
Yan
Y
Charles
Sandy
S
Herrick
David J
DJ
Brewer
Gary
G
D020121:5' Untranslated Regions; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004396:Coloring Agents / Q000494:pharmacology; D003470:Culture Media / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D020868:Gene Silencing; D017930:Genes, Reporter; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D020014:K562 Cells; D008156:Luciferases / Q000378:metabolism; D011485:Protein Binding; D014176:Protein Biosynthesis; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014343:Trypan Blue / Q000494:pharmacology; D015854:Up-Regulation
D020121:5' Untranslated Regions; D004396:Coloring Agents; D003470:Culture Media; C406144:IGF2BP1 protein, human; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D003609:Dactinomycin; D007335:Insulin-Like Growth Factor II; D008156:Luciferases; D014343:Trypan Blue