Rapamycin blocks the phosphorylation of 4E-BP1 and inhibits cap-dependent initiation of translation.

Abstract

The immunosuppressant drug rapamycin blocks progression of the cell cycle at the G1 phase in mammalian cells and yeast. Here we show that rapamycin inhibits cap‐dependent, but not cap‐independent, translation in NIH 3T3 cells. Cap‐dependent translation is also specifically reduced in extracts from rapamycin‐treated cells, as determined by in vitro translation experiments. This inhibition is causally related to the dephosphorylation and consequent activation of 4E‐BP1, a protein recently identified as a repressor of the cap‐binding protein, eIF‐4E, function. These effects of rapamycin are specific as FK506, a structural analogue of rapamycin, had no effect on either cap‐dependent translation or 4E‐BP1 phosphorylation. The rapamycin‐FK506 binding protein complex is the effector of the inhibition of 4E‐BP1 phosphorylation as excess of FK506 over rapamycin reversed the rapamycin‐mediated inhibition of 4E‐BP1 phosphorylation. Thus, inactivation of eIF‐4E is, at least in part, responsible for inhibition of cap‐dependent translation in rapamycin‐treated cells. Furthermore, these results suggest that 4E‐BP1 phosphorylation is mediated by the FRAP/TOR signalling pathway.

DNA-damaging agents cause inactivation of translational regulators linked to mTOR signalling

“…However, the magnitude of the decrease in response to etoposide was greater than that caused by rapamycin, which, like etoposide, causes inhibition of p70 S6 kinase and dephosphorylation of 4E-BP1. These data are in line with those for other cells, where treatment of serum-fed cells with rapamycin generally only causes a modest inhibition of total protein synthesis, especially at early times (see, e.g., (Beretta et al, 1996;Morley et al, 1998)). It thus seemed likely that etoposide interfered with other steps in mRNA translation in addition to those regulated through mTOR, and we therefore extended our analysis to include two proteins which are known to play key roles in regulating overall protein synthesis, eIF2 and eIF2B.…”

Metformin Induces G1 Cell Cycle Arrest and Inhibits Cell Proliferation in Nasopharyngeal Carcinoma Cells

“…5D). Inhibition of mTOR signaling often induces a G1 cell cycle arrest that correlates with down-regulation of cyclin D1 levels in some cell types (Beretta et al, 1996). We found that metformin induced G1 cell cycle arrest and decreased levels of cyclin D1.…”

“…Hypophosphorylated 4E-BP1 inhibits translation initiation by binding to eIF4E with high affinity. The binding of 4E-BP1 to eIF4E prevents the formation of the eIF4F complex, which is the rate-limiting step in translation initiation (Beretta et al, 1996). Metformin also induced phosphorylation of AMPK (T172) (Fig.…”

Degradation of eukaryotic polypeptide chain initiation factor (eIF) 4G in response to induction of apoptosis in human lymphoma cell lines

“…The experiment was carried out three times and the error bars represent standard errors of the mean dissociation of their complexes with eIF4E (Sonenberg, 1996; Lawrence and . The pathway leading to these events is inhibited by rapamycin, due to impairment of the phosphorylation of the 4E-BPs Beretta et al, 1996a). In BJAB cells overall protein synthesis is particularly sensitive to rapamycin (Kay et al, 1996), suggesting that the e ects of the drug are not limited to the translation of mRNAs with 5' terminal oligopyrimidine tracts (Je eries et al, 1994; in this system.…”

“…The extent of complex formation between the best studied of these proteins, 4E-BP1 (also known as PHAS-I) (Lawrence and , and eIF4E is regulated by the phosphorylation of 4E-BP1 (Graves et al, 1995;Von Manteu el et al, 1996;Brunn et al, 1997). This phosphorylation is activated by a pathway which can be inhibited by the macrolide immunosuppressant, rapamycin Von Manteu el et al, 1996;Beretta et al, 1996a;Fadden et al, 1997;Brunn et al, 1997). As a result rapamycin inhibits cap-dependent initiation (Beretta et al, 1996a,b), as well as antagonizing increases in protein synthesis brought about by mitogenic stimuli .…”