tailieunhanh - Báo cáo khóa học: The proteasome inhibitor, MG132, promotes the reprogramming of translation in C2C12 myoblasts and facilitates the association of hsp25 with the eIF4F complex

The eukaryotic translation initiation factor (eIF) 4E, is regulated by modulating both its phosphorylation and its availability to interact with the scaffold protein, eIF4G, to form the mature eIF4F complex. Here we show that treat-ment of C2C12 myoblasts with the proteasomal inhibitor, MG132 (N-carbobenzoxyl-Leu-Leu-leucinal), resulted in an early decrease inprotein synthesis rates followed by a partial recovery, reflecting the reprogramming of translation. | Eur. J. Biochem. 271 3596-3611 2004 FEBS 2004 doi The proteasome inhibitor MG132 promotes the reprogramming of translation in C2C12 myoblasts and facilitates the association of hsp25 with the eIF4F complex Joanne L. Cowan and Simon J. Morley Department of Biochemistry School of Life Sciences University of Sussex Falmer Brighton UK The eukaryotic translation initiation factor eIF 4E is regulated by modulating both its phosphorylation and its availability to interact with the scaffold protein eIF4G to form the mature eIF4F complex. Here we show that treatment of C2C12 myoblasts with the proteasomal inhibitor MG132 N-carbobenzoxyl-Leu-Leu-leucinal resulted in an early decrease in protein synthesis rates followed by a partial recovery reflecting the reprogramming of translation. The early inhibition of protein synthesis was preceded by a transient increase in eIF2a phosphorylation followed by a sustained increase in eIF4E phosphorylation. Inhibition of eIF4E phosphorylation with CGP57380 failed to prevent translational reprogramming or the moderate decrease in eIF4F complexes at later times. Prolonged incubation with MG132 resulted in the increased expression of heat shock protein hsp 25 aB-crystallin and hsp70 with a population of hsp25 associating with the eIF4F complex in a p38 mitogen-activated protein kinase-dependent manner. Under these conditions eIF4GI and to a lesser extent eIF4E re-localized from a predominantly cytoplasmic distribution to a more perinuclear and granular staining. Although MG132 had little effect on the colocalization of eIF4E and eIF4GI it promoted the SB203580-sensitive association of eIF4GI and hsp25 an effect not observed with aB-crystallin. Addition of recombinant hsp25 to an in vitro translation assay resulted in stimulation of on-going translation and a moderate decrease in de novo translation indicating that this modified eIF4F complex containing hsp25 has a role to play in recovery of mRNA translation