Possible model for CCL5-mediated mRNA translation in CD4⁺ T cells. CCL5 activates the mTOR pathway and subsequent phosphorylation of p70 S6K1 and 4E-BP1. Hyperphosphorylation of 4E-BP1 leads to its release from eIF4E where it binds to eIF4G to form the eIF4F initiation complex. Through eIF4E, eIF4F binds to the mRNA 5′-cap structure and facilitates ribosome binding and unwinding secondary structure in the 5′-UTR. Translation initiation leads to a rapid up-regulation of cyclin D1 and MMP-9 protein levels to “prime” T cells for directed cell migration. S6K1 has been shown to phosphorylate eIF4B (RNA-binding protein that enhances activity of the eIF4A helicase) in response to insulin ().