Translational Control Antibody Sampler Kit

Background

Key steps in translational control occur at the level of eukaryotic initiation factor 4F (eIF4F) and p70 S6 kinase regulation. eIF4F is a complex whose functions include the recognition of the mRNA 5' cap structure. Several stimuli, such as insulin and various growth and survival factors, regulate the eIF4F complex and p70 S6 kinase primarily by triggering a signaling cascade dependent on sequential activation of PI3K, Akt/PKB and mTOR/FRAP kinases. Akt is activated by phosphorylation within the C-terminus at Ser473 and within the activation loop at Thr308 by phospholipid-dependent kinases. Inactivation in vivo of PI3K by the highly selective inhibitor LY294002 inhibits Akt and downstream elements of this cascade. Direct phosphorylation of mTOR/FRAP at Ser2448 by Akt is a key regulatory event controlling its kinase activity. mTOR/FRAP activity can be effectively blocked by Rapamycin, leading to inactivation of eukaryotic initiation factor 4E binding protein 1 (4E-BP1), an inhibitor of translation initiation, and activation of p70 S6 kinases. Inactivation of 4E-BP1 by sequential phosphorylation causes the release of eIF4E, which, together with eIF4G and other factors, forms a functional eIF4F cap binding complex. p70 S6 kinases phosphorylates the 40S ribosomal subunit protein S6 and stimulates the translation of 5' oligopyrimidine tract containing mRNAs. The Erk pathway is also involved in regulation at this level by regulating the eIF4E kinase, Mnk1, and activating p70 S6 kinase. Tuberin, a product of the tumor supressor gene TSG2, is directly phosphorylated atThr1462 by Akt/PKB. Tuberin inhibits the mammalian target of rapamycin, mTOR, which results in inhibition of p70 S6 kinase and activation of 4E-BP1 and, therefore, inhibition of translation.