MicroRNAs 221 and 222 inhibit normal erythropoiesis and erythroleukemic cell growth via kit receptor down-modulation

Proc Natl Acad Sci U S A. 2005 Dec 13;102(50):18081-6. doi: 10.1073/pnas.0506216102. Epub 2005 Dec 5.


MicroRNAs (miRs) are small noncoding RNAs that regulate gene expression primarily through translational repression. In erythropoietic (E) culture of cord blood CD34+ progenitor cells, the level of miR 221 and 222 is gradually and sharply down-modulated. Hypothetically, this decline could promote erythropoiesis by unblocking expression of key functional proteins. Indeed, (i) bioinformatic analysis suggested that miR 221 and 222 target the 3' UTR of kit mRNA; (ii) the luciferase assay confirmed that both miRs directly interact with the kit mRNA target site; and (iii) in E culture undergoing exponential cell growth, miR down-modulation is inversely related to increasing kit protein expression, whereas the kit mRNA level is relatively stable. Functional studies show that treatment of CD34+ progenitors with miR 221 and 222, via oligonucleotide transfection or lentiviral vector infection, causes impaired proliferation and accelerated differentiation of E cells, coupled with down-modulation of kit protein: this phenomenon, observed in E culture releasing endogenous kit ligand, is magnified in E culture supplemented with kit ligand. Furthermore, transplantation experiments in NOD-SCID mice reveal that miR 221 and 222 treatment of CD34+ cells impairs their engraftment capacity and stem cell activity. Finally, miR 221 and 222 gene transfer impairs proliferation of the kit+ TF-1 erythroleukemic cell line. Altogether, our studies indicate that the decline of miR 221 and 222 during exponential E growth unblocks kit protein production at mRNA level, thus leading to expansion of early erythroblasts. Furthermore, the results on kit+ erythroleukemic cells suggest a potential role of these miRs in cancer therapy.

Publication types

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

MeSH terms

  • Animals
  • Antigens, CD34 / metabolism
  • Cell Differentiation / genetics
  • Cell Proliferation
  • Computational Biology
  • Erythropoiesis / genetics
  • Erythropoiesis / physiology*
  • Fetal Blood / cytology
  • Gene Expression Profiling
  • Gene Expression Regulation / genetics*
  • Hematopoietic Stem Cells / metabolism*
  • Humans
  • Luciferases
  • Mice
  • Mice, Inbred NOD
  • Mice, SCID
  • MicroRNAs / genetics*
  • MicroRNAs / metabolism*
  • Proto-Oncogene Proteins c-kit / metabolism*


  • Antigens, CD34
  • MicroRNAs
  • Luciferases
  • Proto-Oncogene Proteins c-kit