The c‐RAF/MEK/ERK MAPK pathway regulates a class of GCN2‐independent amino acid response genes (818.6)

Abstract

During adaptation to protein/amino acid (AA) limitation, the general control non‐derepressible 2 (GCN2) serine/threonine protein kinase initiates the amino acid response (AAR) by binding uncharged tRNAs, which activates its kinase activity. Subsequently, GCN2 phosphorylates eukaryotic initiation factor 2 (eIF2) leading to suppression of general protein synthesis, but induction of translation for specific mRNA species, including that for the transcription factor ATF4. ATF4 is a major effector of AAR‐induced transcription for many genes involved in restoring homeostasis or inducing apoptosis. GCN2 is currently the only well characterized sensor for AA deficiency in mammalian cells and the GCN2‐eIF2‐ATF4 pathway is considered the predominant AAR signaling mechanism. However, evidence from several laboratories has been published suggesting that GCN2‐independent AAR signaling exists. In this study, HepG2 human hepatoma clonal cell lines, expressing shRNA against GCN2, were generated to investigate the possibility of alternative AAR signaling mechanisms. Based on previous research, the MAPK pathways were likely candidates and therefore, were screened using chemical inhibitors. Using IL‐8 as a model MAPK‐responsive and AA‐responsive gene, it was established that c‐RAF/MEK/ERK signaling contributes to GCN2‐independent regulation of a wide spectrum of genes following AA limitation. Grant Funding Source: Supported by NIH, DK092062 and DK094729