EIF2B‐epsilon is translationally regulated through a mTOR‐dependent signaling pathway

Abstract

eIF2B mediates a rate-controlling step in the initiation of mRNA translation. In previous studies we demonstrated an association between mTOR signaling and expression of the catalytic ε-subunit of eIF2B, a relationship that appeared to involve translational rather than transcriptional mechanisms. In the present study, regulation of eIF2Bε mRNA translation was further examined in Rat2 cells. Activation of mTOR in the cells specifically upregulated translation of eIF2Bε mRNA without affecting translation of mRNAs encoding the other subunits of eIF2B. Upregulated translation was prevented by rapamycin treatment suggesting a requirement for mTOR. Exogenous expression of Rheb, an upstream activator of TOR, was sufficient to upregulate eIF2Bε mRNA translation. Among the five subunits of eIF2B, the 5′-noncoding region (NCR) of eIF2Bε is unique in possessing a 5′-terminal oligopyrimidine (TOP) tract. To verify the role of the TOP sequence in mTOR-dependant eIF2Bε mRNA translation, either the 5′-NCR of the eIF2Bε or the eIF2Bγ mRNA was coupled to luciferase to generate reporter constructs. When expressed in Rat 2 cells, the eIF2Bε, but not the eIF2Bγ, construct showed a ~40% increase in luciferase activity in response to activation of mTOR signaling. Specific point mutations in the putative TOP sequence are currently being tested to verify its role in regulating eIF2Bε mRNA translation. (supported NIH grant DK15658)