N 6-methyladenosine (m6A) is the most prevalent modification in eukaryotic messenger RNAs (mRNAs) and is interpreted by its readers, such as YTH domain-containing proteins, to regulate mRNA fate. Here we report the insulin-like growth factor 2 mRNA-binding proteins (IGF2BPs; including IGF2BP1/2/3) as a distinct family of m6A readers that target thousands of mRNA transcripts through recognizing the consensus GG(m6A)C sequence. In contrast to the mRNA-decay-promoting function of YTHDF2, IGF2BPs promote the stability and storage of their target mRNAs (e.g., MYC) in an m6A-depedent manner under normal and stress conditions and thus affect gene expression output. Moreover, the K homology (KH) domains of IGF2BPs are required for their recognition of m6A and are critical for their oncogenic functions. Our work therefore reveals a different facet of the m6A-reading process that promotes mRNA stability and translation, and highlights the functional importance of IGF2BPs as m6A readers in post-transcriptional gene regulation and cancer biology.

Protein misfolding in the endoplasmic reticulum (ER) leads to cell death through PERK-mediated phosphorylation of eIF2α, although the mechanism is not understood. ChIP-seq and mRNA-seq of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP), key transcription factors downstream of p-eIF2α, demonstrated that they interact to directly induce genes encoding protein synthesis and the unfolded protein response, but not apoptosis. Forced expression of ATF4 and CHOP increased protein synthesis and caused ATP depletion, oxidative stress and cell death. The increased protein synthesis and oxidative stress were necessary signals for cell death. We show that eIF2α-phosphorylation-attenuated protein synthesis, and not Atf4 mRNA translation, promotes cell survival. These results show that transcriptional induction through ATF4 and CHOP increases protein synthesis leading to oxidative stress and cell death. The findings suggest that limiting protein synthesis will be therapeutic for diseases caused by protein misfolding in the ER.

DNA and histone modifications exhibit noticeable impacts on gene expression 1 . Being the most prevalent internal modification in mRNA, N 6 -Methyladenosine (m 6 A) mRNA modification emerges as an important post-transcriptional mechanism of gene regulation 2 - 4 and plays critical roles in various normal and pathological bioprocesses 5 - 12 . However, how m 6 A is precisely and dynamically deposited in the transcriptome remains elusive. Here we report that H3K36me3 histone modification, a marker for transcription elongation, globally guides m 6 A modification. We found that m 6 A modifications enrich in the vicinity of H3K36me3 peaks, and are reduced globally when cellular H3K36me3 is depleted. Mechanistically, H3K36me3 is recognized and bound directly by METTL14, a critical component of the m 6 A methyltransferase complex (MTC), which in turn facilitates the binding of the m 6 A MTC to adjacent RNA polymerase II, and thereby delivering the m 6 A MTC to actively transcribed nascent RNAs to deposit m 6 A co-transcriptionally. In mouse embryonic stem cells, phenocopying Mettl14 silencing, H3K36me3 depletion also induces m 6 A reduction transcriptome-wide and in pluripotency transcripts, resulting in increased cell stemness. Collectively, our studies reveal the critical roles of H3K36me3 and METTL14 in determining precise and dynamic m 6 A deposition in mRNA, and uncover another layer of gene expression regulation involving crosstalk between histone modification and RNA methylation.

Background: Protein synthesis control is important for ␤-cell fate during ER stress. Results: Increased protein synthesis during chronic ER stress in ␤-cells involves the transcriptional induction of an amino acid transporter network. Conclusion: Increased amino acid uptake in ␤-cells during ER stress promotes apoptosis. Significance: Induced expression of a network of amino acid transporters in islets can contribute to chronic ER stress-induced diabetes.

Regulation of cell volume is of great importance because persistent swelling or shrinkage leads to cell death. Tissues experience hypertonicity in both physiological (kidney medullar cells) and pathological states (hypernatremia). Hypertonicity induces an adaptive gene expression program that leads to cell volume recovery or apoptosis under persistent stress. We show that the commitment to apoptosis is controlled by phosphorylation of the translation initiation factor eIF2␣, the master regulator of the stress response. Studies with cultured mouse fibroblasts and cortical neurons show that mutants deficient in eIF2␣ phosphorylation are protected from hypertonicity-induced apoptosis. A novel link is revealed between eIF2␣ phosphorylation and the subcellular distribution of the RNA-binding protein heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1). Stress-induced phosphorylation of eIF2␣ promotes apoptosis by inducing the cytoplasmic accumulation of hnRNP A1, which attenuates internal ribosome entry site-mediated translation of anti-apoptotic mRNAs, including Bcl-xL that was studied here. Hypertonic stress induced the eIF2␣ phosphorylation-independent formation of cytoplasmic stress granules (SGs, structures that harbor translationally arrested mRNAs) and the eIF2␣ phosphorylation-dependent accumulation of hnRNP A1 in SGs. The importance of hnRNP A1 was demonstrated by induction of apoptosis in eIF2␣ phosphorylation-deficient cells that express exogenous cytoplasmic hnRNP A1. We propose that eIF2␣ phosphorylation during hypertonic stress promotes apoptosis by sequestration of specific mRNAs in SGs in a process mediated by the cytoplasmic accumulation of hnRNP A1.