4E-binding proteins, the suppressors of eukaryotic initiation factor 4E, are down-regulated in cells with acquired or intrinsic resistance to rapamycin

Michael B. Dilling, Glen S. Germain, Lorina Dudkin, Arun L. Jayaraman, Xiongwen Zhang, Franklin C. Harwood, Peter J. Houghton

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Abstract

To determine whether inhibition of either the ribosomal p70 S6 kinase or eukaryotic initiation factor (eIF) 4E pathways downstream of the mammalian target of rapamycin, mTOR, contributes to rapamycin-induced growth arrest, clones of Rh30 rhabdomyosarcoma cells were selected for rapamycin resistance. Expression of c-Myc and anchorage-independent growth were enhanced in resistant cells. Resistance was unstable in each of three clones characterized. In resistant cells, as compared with parental cells, ∼10-fold less 4E-binding protein (4E-BP) was bound to eIF4E, and total cellular 4E-BP was markedly reduced. Levels of eIF4E were unchanged. Steady-state levels of 4E-BP transcript remained unaltered, but the rate of 4E-BP synthesis was reduced in resistant cells. In cells that reverted to rapamycin sensitivity, levels of total 4E-BP returned to those of parental cells. Compared with parental cells, resistant clones had either similar or lower levels and activity of ribosomal p70 S6 kinase, but c-Myc levels were elevated in both resistant and revertant clones. Several colon carcinoma cell lines with intrinsic rapamycin resistance were found to have low 4E-BP:eIF4E ratios. In stable clones of HCT8 carcinoma engineered to overexpress 4E-BP, rapamycin sensitivity increased markedly (>1000.fold) as 4E-BP expression increased. These results suggest that the 4E-BP:eIF4E ratio is an important determinant of rapamycin resistance and controls certain aspects of the malignant phenotype.

Original languageEnglish (US)
Pages (from-to)13907-13917
Number of pages11
JournalJournal of Biological Chemistry
Volume277
Issue number16
DOIs
StatePublished - Apr 19 2002
Externally publishedYes

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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