The effect of alternative splicing on key regulators of the integrated stress response

Abstract

The protein kinase General control non-derepressible-2 (GCN2) is a key regulator of the Integrated stress response that responds to various stress signals, including nutritional deprivation. As a result of high levels of uncharged tRNAs during amino acid depletion, GCN2 phosphorylates serine-51 of the α subunit of eukaryotic initiation factor-2 (eIF2), a translation factor that delivers initiator tRNA to ribosomes. Phosphorylation of eIF2α inhibits general translation, which conserves energy and nutrients and facilitates reprogramming of gene expression for remediation of stress damage. Phosphorylation of eIF2α also directs preferential translation of specific transcription factors, such as ATF4. ATF4 reprograms gene expression to alleviate stress damage; however, under chronic stress, ATF4 directs the transcriptional expression of CHOP, which can trigger apoptosis. Because multiple stresses can induce eIF2α phosphorylation and translational control in mammals, this pathway is referred to as the Integrated stress response. GCN2 and CHOP are subject to alternative splicing that results in multiple transcripts that differ in the 5'-end of the gene transcripts. However, the effect of the different GCN2 and CHOP isoforms on their function and regulation have not been investigated. Our data suggests that GCN2 is alternatively spliced into five different transcripts and the beta isoform of GCN2 is most abundant. Also alternative splicing of CHOP creates two CHOP transcripts with different 5'-leaders encoding inhibitory upstream open reading frames that are critical for translational control of CHOP during stress. This study suggests that alternative splicing can play an integral role in the implementation and regulation of key factors in the Integrated stress response.