During chemical stress, this 5-m7G-dependent translation initiation is inhibited

During chemical stress, this 5-m7G-dependent translation initiation is inhibited. against tissue injury, our data have revealed a novel mechanism of cellular defense involvingde novoNRF2 protein translation governed by Gonadorelin acetate the EF1a interaction with the G-quadruplex in the NRF2 5 UTR during oxidative stress. KEYWORDS: RNA binding proteins, RNA structure, antioxidant genes, protein translation, proteomics == INTRODUCTION == Increasing evidence suggests that low to moderate levels of chemical stress trigger cellular defense systems. A centerpiece of such defense systems involves the expression of antioxidant and detoxification genes, many of which contain the antioxidant response element in the promoters where the NRF2 transcription factor binds. Examples of such genes include the genes for hemeoxygenase 1, NAD(P)H: quinone oxidoreductase 1, glutamate-cysteine ligase, glutathioneS-transferases, thioredoxin, and UDP-glucuronosyltransferase (14). Works from our laboratory and others have shown that the induction of the NRF2 protein contributes to elevated expression levels of these genes (58). Gene knockout studies have demonstrated that NRF2 functions as a cytoprotective gene in multiple organ systems, including the brain, cardiovascular system, airway, lung, liver, stomach, gastrointestinal tract, kidney, and bladder (3, 911). These lines of evidence support the importance of understanding the molecular pathways regulating NRF2 protein expression. Various chemical stressors, including those inducing oxidative stress, cause an accumulation of the NRF2 protein at the cellular level. The human NRF2 gene encodes an mRNA species of 2, 859 nucleotides (nt) (NCBI RefSeq accession numberNM_006164. 4) and a protein of 605 amino acids (1215). The N-terminal hydrophilic domain of the NRF2 protein interacts with KEAP1, which regulates the stability of the NRF2 protein by ubiquitination and proteasome-mediated degradation (13, 15). The C-terminal half of the NRF2 protein contains a cap-and-collar domain, a Mouse monoclonal to SKP2 basic amino acid region for DNA binding, and a leucine zipper intended for heterodimerization with a cotranscription factor, such as the small musculoaponeurotic factor (1216). Although the NRF2 protein can be stabilized due to chemically induced dissociation from KEAP1, we have found that oxidative stress inducesde novoNRF2 protein translationin vitroandin vivo(7, 8, 17). The process of protein translation is divided into three sequential stages, initiation, elongation, and termination, with initiation being the rate-limiting step. Under normal physiological conditions, translation Gonadorelin acetate Gonadorelin acetate initiation requires a 7-methyl-guanine (m7G) cap structure at the 5 end of mRNA intended for recognition by eukaryotic translation initiation factor 4E (eIF4E) (1820). eIF4E is a component of the eIF4F complex, which contains the scaffold eIF4G and the ATP-dependent helicase eIF4A. Binding of the eIF4F complex to the 5 m7G cap is catalyzed by eIF4A in an ATP-dependent manner, triggering the joining of eIF4B, an enhancer of the eIF4A helicase that removes inhibitory RNA structures. The poly(A) binding protein interacts with eIF4G to circularize mRNA and with eIF4B to stabilize the complex. In parallel to the process of mRNA recognition, the 43 Svedberg (43S) preinitiation complex (PIC) is formed, that contains eIF1, eIF1A, eIF3, eIF5, the eIF2/GTP/tRNAiMetternary complex, and the 40S subunit of the ribosome. Binding of the 43S PIC to mRNA prebound with the eIF4F complex results in the 48S initiation complex. During chemical stress, this 5-m7G-dependent translation initiation is inhibited. It is estimated that a few to 5% of genes encode mRNA species that contains an internal ribosomal entry site (IRES) in the 5 untranslated region (UTR) and can undergo translation initiation in a 5-m7G cap-independent manner (2125). However , previously reported IRESs are diverse in sequence and conformation, adding to the mystery about the identity of IRESs and how they coordinate the process of translation initiation. How certain proteins such as NRF2 can Gonadorelin acetate escape general suppression by translational machinery and be selectively translated under stress conditions remains unknown. Human NRF2 mRNA contains a 555-nucleotide 5 UTR, with 70% of the sequence being G’s or C’s. Four guanine bases can form a G-tetrad due to Hoogsteen hydrogen bonds between each guanine base (2628). Two to four G-tetrads can stack up to form a stable three-dimensional (3-D) structure, i. e., the G-quadruplex. The G-quadruplex is a four-stranded nucleic acid secondary structure typically consisting of three stacks of G-tetrads. A DNA or RNA strand containing 4 or more blocks of 2 to 4 consecutive guanines can form a stable G-quadruplex structure (26, 27, 29). Although the G-quadruplex has.