Disease relevance of Eif4ebp1

• We report that the combined disruption of 4E-BP1 and 4E-BP2 in mice increased their sensitivity to diet-induced obesity [1].
• Using phospho-specific antibody against Thr(70) of 4E-BP1, rapid and persistent dephosphorylation within 30 min of exposure to rapamycin was detected in Rh18 rhabdomyosarcoma cells [2].
• RESULTS: Akt, p70 S6 kinase, and 4E-BP-1 were induced and phosphorylated in rat glomerular lysates after 12 weeks of STZ injection when mesangial and glomerular hypertrophy was observed [3].
• Under these experimental conditions, PHAS-I is apparently not required for the normal development and reproductive behavior of female mice, but is required for normal body weight in male mice; the mechanisms responsible for this phenotype remain to be determined [4].
• HIV antiretroviral agents inhibit protein synthesis and decrease ribosomal protein S6 and 4EBP1 phosphorylation in C2C12 myocytes [5].

High impact information on Eif4ebp1

• Consistent with these observations, translation of the peroxisome proliferator-activated receptor-gamma co-activator 1 (PGC1), a transcriptional co-activator implicated in mitochondrial biogenesis and adaptive thermogenesis, is increased in white adipose tissue of Eif4ebp1-/- mice [6].
• Adipose tissue reduction in mice lacking the translational inhibitor 4E-BP1 [6].
• These findings demonstrate that 4E-BP1 is a novel regulator of adipogenesis and metabolism in mammals [6].
• Pim-2-dependent maintenance of cell size and survival correlated with its ability to maintain rapamycin-resistant phosphorylation of the translational repressor 4E-BP1 and phosphorylation of the BH3 protein BAD [7].
• Elevated sensitivity to diet-induced obesity and insulin resistance in mice lacking 4E-BP1 and 4E-BP2 [1].

Biological context of Eif4ebp1

• Increased adiposity was explained at least in part by accelerated adipogenesis driven by increased expression of CCAAT/enhancer-binding protein delta (C/EBPdelta), C/EBPalpha, and PPARgamma coupled with reduced energy expenditure, reduced lipolysis, and greater fatty acid reesterification in the adipose tissue of 4E-BP1 and 4E-BP2 double KO mice [1].
• Consistent with these findings, DAMGO-stimulated phosphorylation of 4E-BP1 impairs its ability to bind the translation initiation factor eIF-4E [8].
• BACKGROUND: Augmented protein translation by insulin involves activation of eukaryotic initiation factor 4E (eIF4E) that follows release of eIF4E from a heterodimeric complex by phosphorylation of its inhibitory binding protein, 4E-BP1 [9].
• 4E-BP1 inhibited GLUT1 mRNA translation in vitro [10].
• C2C12 cells expressing either Delta91mTORrr or kinase-dead mTORrr(D2338A) could not phosphorylate 4E-BP1 in the presence of rapamycin and could not abrogate the inhibition of myogenesis [11].

Anatomical context of Eif4ebp1

• We examined insulin regulation of 4E-BP1 phosphorylation in murine proximal tubular epithelial cells [9].
• The effects of insulin on the mammalian target of rapamycin, mTOR, were investigated in 3T3-L1 adipocytes. mTOR protein kinase activity was measured in immune complex assays with recombinant PHAS-I as substrate [12].
• Our results show that Delta10mTORrr signals 4E-BP1 and permits rapamycin-treated myoblasts to differentiate, confirming the mTOR dependence of the inhibition of myogenesis by rapamycin [11].
• In contrast, in leucine-starved myotubes, there were no change in the 4E-BP1-eIF4E association or eIF2alpha phosphorylation, suggesting that these factors were not rate limiting for decreasing protein synthesis in leucine-deprived myotubes [13].
• Thus, association of eIF4E with 4E-BP1 represses mRNA translation by preventing the binding of mRNA to the ribosome [14].

Associations of Eif4ebp1 with chemical compounds

• Finally, rapamycin (0.75 mg/kg) administered to rats 2 h before leucine gavage inhibited the phosphorylation of S6 and 4E-BP1 induced by leucine [15].
• Both LY294002 and rapamycin blocked the insulin and IGF-I-induced increases in 4EBP1 phosphorylation [16].
• NAC and DPI also blocked Akt activation which is required for 4E-BP1 phosphorylation [17].
• The camostat-induced increases in protein synthesis and 4E-BP1 and S6 phosphorylation were almost totally abolished by administration of the mTOR inhibitor rapamycin 1 h prior to camostat feeding [18].
• Difluoromethylornithine-induced polyamine depletion produced a significant fall in the rate of 4E-BP1 gene transcription in IEC-6 cells, without a change in stability of the 4E-BP1 message [19].

Enzymatic interactions of Eif4ebp1

• Strikingly, upon induction of eIF4E, 4E-BP1 became dephosphorylated and the extent of dephosphorylation was proportional to the expression level of eIF4E [20].

Regulatory relationships of Eif4ebp1

• Moreover, p53 activation inhibits rapamycin-insensitive protein kinase activity against 4E-BP1 [21].
• Insulin also increased the phosphorylation of PHAS-I and promoted dissociation of the PHAS-I eukaryotic initiation factor-4E (eIF-4E) complex, effects that were maximal within 10 min [22].
• Prolactin and insulin synergize to regulate the translation modulator PHAS-I via mitogen-activated protein kinase-independent but wortmannin- and rapamycin-sensitive pathway [23].
• This conditionally active Akt was also found to rapidly stimulate in these cells the phosphorylation of properties of PHAS-I, a key protein in the regulation of protein synthesis [24].
• Incubating 3T3-L1 adipocytes with rapamycin and wortmannin inhibited insulin-stimulated phosphorylation of PHAS-I at concentrations similar to those that inhibited activation of p70S6K [25].

Other interactions of Eif4ebp1

• Activation of a temperature-sensitive form of mouse p53 in murine erythroleukaemia cells rapidly inhibits protein synthesis and causes early dephosphorylation and cleavage of protein synthesis initiation factor eIF4GI and the eIF4E-binding protein 4E-BP1 [21].
• Regulation of the phosphorylation and integrity of protein synthesis initiation factor eIF4GI and the translational repressor 4E-BP1 by p53 [21].
• The considerable residual differentiation in the presence of rapamycin, despite the complete blockade of p70 S6K activation, prompted us to measure the phosphorylation of another rapamycin-sensitive protein, eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1) [26].
• CONCLUSIONS: In proximal tubular epithelial cells, insulin augments 4E-BP1 phosphorylation, which is PI 3-kinase and mTOR dependent [9].
• Cleavage of 4E-BP1 was inhibited by treatment of the cells with Z-VAD.FMK, indicating it is caspase-dependent [27].

Analytical, diagnostic and therapeutic context of Eif4ebp1

• Phosphorylation of PHAS-I was monitored by immunoblotting after subjecting extracts to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate [25].
• We now demonstrate that CCI-779 rapidly inhibits mTOR activity, as indicated by S6 reduction and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) phosphorylation in two xenograft models of RMS within 24 hours of treatment [28].
• With the exception of the downregulation of extracellular matrix genes, serine protease inhibitor genes, and the upregulation of the translation initiation factor PHAS-I, this model of atrophy in cell culture has a transcriptional profile quite distinct from any study published to date with atrophy in whole muscle [29].
• Four PCR fragments containing regions with considerable homology (78%) to the human PRE were generated from the 5'-flanking sequence of the mouse 4E-BP1 gene and the fragments were used in electrophoretic gel mobility shift and supershift assays [30].
• In both cell lines, prolactin activated phosphorylation of the signal transducer and activator of transcription, Stat5-a regulator of milk protein gene transcription, and of PHAS-I-an inhibitor of translation initiation in its nonphosphorylated form [31].

References