Nat1 promotes translation of specific proteins that induce differentiation of mouse embryonic stem cells [expression 2]

Nat1 (also known as p97/Dap5/Eif4g2) is a ubiquitously expressed cytoplasmic protein that is homologous to the c-terminal two thirds of eukaryotic translation initiation factor 4G (also known as Eif4g1). We previously showed that Nat1-null mouse embryonic stem cells (mESCs) were resistant to differentiation. In the current study, we found that NAT1 and eIF4G1 share many binding proteins, such as eIF3, eIF4A and ribosomal proteins. However, NAT1did not bind to eIF4E or poly A binding proteins, which are critical for cap-dependent translation initiation. In contrast, compared to eIF4G1, NAT1 preferentially interacts with eIF2, FMR and related proteins, and especially PRRC2 family members. We also found that Nat1-null mESCs possess a transcriptional profile similar, though not identical, to ground state, which is established in wild-type mES cells when treated with inhibitors of the ERK and GSK3 signaling pathways. In Nat1-null mESCs, the ERK pathway is suppressed even without inhibitors. Ribosome profiling revealed that translation of Map3k3 and Sos1 is suppressed in the absence of Nat1. Forced expression of Map3k3 induced differentiation of Nat1-null mESCs. These data collectively showed that Nat1 is involved in translation of proteins that are required for cell differentiation. The effects of Map3k3 expression in Nat1-null mouse embryonic stem cells, N=15; wild-type mouse embryonic stem cells, N=3, Nat1-null mouse embryonic stem cells, N=3, tet-Map3k3-expressing Nat1-null mouse embryonic stem cells cultured with Dox, N=3, tet-Map3k3-expressing Nat1-null mouse embryonic stem cells cultured without Dox, N=3, tet-EGFP-expressing Nat1-null mouse embryonic stem cells cultured with Dox, N=3