GIGYF1/2 proteins use auxiliary sequences to selectively bind to 4EHP and repress target mRNA expression

Abstract

The eIF4E homologous protein (4EHP) is thought to repress translation by competing with eIF4E for binding to the 5 ′ cap structure of specific mRNAs to which it is recruited through interactions with various proteins, including the GRB10-interacting GYF (glycine-tyrosine-phenylalanine domain) proteins 1 and 2 (GIGYF1/2). Despite its similarity to eIF4E, 4EHP does not interact with eIF4G and therefore fails to initiate translation. In contrast to eIF4G, GIGYF1/2 bind selectively to 4EHP but not eIF4E. Here, we present crystal structures of the 4EHP-binding regions of GIGYF1 and GIGYF2 in complex with 4EHP, which reveal the molecular basis for the selectivity of the GIGYF1/2 proteins for 4EHP. Complementation assays in a GIGYF1/2-null cell line using structure-based mutants indicate that 4EHP requires interactions with GIGYF1/2 to down-regulate target mRNA expression. Our studies provide structural insights into the assembly of 4EHP-GIGYF1/2 repressor complexes and reveal that rather than merely facilitating 4EHP recruitment to transcripts, GIGYF1/2 proteins are required for repressive activity.

GIGYF2 and 4EHP Inhibit Translation Initiation of Defective Messenger RNAs to Assist Ribosome-Associated Quality Control

“…GIGYF2 and 4EHP enable the cell to break this cycle by allowing a failed translation event to initiate a specific negative feedback loop which shuts down further translation of the message. Although GIGYF2 and 4EHP have been implicated in translational control in a number of different settings (14,15,19,26,27), our data argue that faulty mRNAs that cause ribosome stalling comprise an important subset of endogenous substrates for GIGYF2 and 4EHP mediated repression. Indeed, we see loss of GIGYF2 stabilizes two distinct classes of stalling reporters.…”

“…We focused our attention on the second factor, GIGYF2, which has not been previously implicated in the cellular response to damaged messages. Overexpression studies of tagged GIGYF2 have shown that it interacts with the inhibitory cap-binding protein 4EHP (14) and the ubiquitin ligase ZNF598 (15), which is responsible for detecting ribosome collisions and targeting stalled ribosomes to RQC (16,17).…”

The suppressive cap-binding-complex factor 4EIP is required for normal differentiation

“…Mammalian and Drosophila 4EHPs are required for correct translation control during development (18)(19)(20)(21). Interactions with partner proteins such as Bicoid (16) or GIGYF2 (=GIF2) (22)(23)(24), and with the RISC complex (25,26), have been implicated in induction of mRNA decay and/or translation suppression by 4EHPs. GIGYF2 appears to be able to act both in conjunction with (24), and independently of, 4EHP (27), and interactions with both Ago2 (28) and the CAF1/NOT complex (27) have been documented.…”

capCLIP: a new tool to probe protein synthesis in human cells through capture and identification of the eIF4E-mRNA interactome

“…For example, capCLIP may be especially valuable for elucidating the specific biological role(s) of other cellular cap-binding proteins, particularly the eIF4E2 (4EHP) and eIF4E3, the other two cytoplasmic cap-binding proteins in mammals. While eIF4E2 is generally thought to play a role in translational repression (see, for example (59,60)), other work suggests eIF4E2 promotes mRNA translation in certain cellular contexts (61). As capCLIP makes no assumptions about the cellular role of a cap-binding protein, it is an ideal method for elucidating eIF4E2 function.…”