A C-term truncated EIF2Bγ protein encoded by an intronically polyadenylated isoform introduces unfavorable EIF2Bγ-EIF2γ interactions.


Circir A., Bicakci G. K. , Savas B., Doken D. N. , Henden O., Can T. , ...More

Proteins, vol.90, no.3, pp.889-897, 2022 (Journal Indexed in SCI Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 90 Issue: 3
  • Publication Date: 2022
  • Doi Number: 10.1002/prot.26284
  • Title of Journal : Proteins
  • Page Numbers: pp.889-897
  • Keywords: EIF2, EIF2B, HADDOCK, intronic polyadenylation, ISR, protein interactions, structural modeling, GUANINE-NUCLEOTIDE EXCHANGE, EIF2B, ELECTROSTATICS, INHIBITION, SUBUNITS, BINDING, PCR

Abstract

Eukaryotic translation initiates upon recruitment of the EIF2-GTP center dot Met-tRNA(i) ternary complex (TC) to the ribosomes. EIF2 (alpha, beta, gamma subunits) is a GTPase. The GDP to GTP exchange within EIF2 is facilitated by the guanine nucleotide exchange factor EIF2B (alpha-epsilon subunits). During stress-induced conditions, phosphorylation of the alpha-subunit of EIF2 turns EIF2 into an inhibitor of EIF2B. In turn, inhibition of EIF2B decreases TC formation and triggers the internal stress response (ISR), which determines the cell fate. Deregulated ISR has been linked to neurodegenerative disorders and cancer, positioning EIF2B as a promising therapeutic target. Hence, a better understanding of the mechanisms/factors that regulate EIF2B activity is required. Here, combining transcript and protein level analyses, we describe an intronically polyadenylated (IPA) transcript of EIF2B's gamma-subunit. We show that the IPA mRNA isoform is translated into a C-terminus truncated protein. Using structural modeling, we predict that the truncated EIF2B gamma protein has unfavorable interactions with EIF2 gamma, leading to a potential decrease in the stability of the nonproductive EIF2:EIF2B complex. While we discovered and confirmed the IPA mRNA isoform in breast cancer cells, the expression of this isoform is not cancer-specific and is widely present in normal tissues. Overall, our data show that a truncated EIF2B gamma protein co-exists with the canonical protein and is an additional player to regulate the equilibrium between productive and nonproductive states of the EIF2:EIF2B complex. These results may have implications in stress-induced translation control in normal and disease states. Our combinatorial approach demonstrates the need to study noncanonical mRNA and protein isoforms to understand protein interactions and intricate molecular mechanisms.