{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nRPS6KA1, which encodes the p90 ribosomal S6 kinase 1 (RSK1), is a central serine/threonine kinase acting downstream of the ERK/MAPK cascade. It is rapidly activated by various extracellular stimuli—ranging from growth factors to stress signals—and in turn phosphorylates numerous substrates to regulate diverse cellular processes including protein translation, cell survival, and apoptosis. For example, RSK1 is activated in response to agents such as SDF‐1α and growth factors, a reaction that contributes to enhanced cell survival and altered gene expression profiles through the regulation of downstream effectors and transcription factors."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "6"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn addition to its roles in survival signaling, RSK1 mediates key aspects of cell cycle progression and motility. Its phosphorylation of substrates such as p27 at threonine 198 fosters cytoplasmic retention, which is directly linked to enhanced cell migration and invasive capacities. RSK1 also contributes to the activation of transcriptional programs that promote mesenchymal motility, thereby linking ERK pathway activation to changes in the cellular cytoskeleton and metastatic behavior."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nRSK1 orchestrates complex regulatory feedback loops by phosphorylating a variety of substrates that modulate other critical signaling proteins. Its activity has been shown to affect insulin signaling via phosphorylation of IRS-1, to restrain apoptosis by modifying proteins such as Apaf-1, and to control cell cycle checkpoints through phosphorylation of Chk1. Moreover, genetic variation in RPS6KA1 has been implicated in colon cancer risk, while viral proteins such as KSHV ORF45 exploit RSK1 binding to sustain prolonged kinase activation. RSK1 also influences the stability of proteins like P-glycoprotein through indirect mechanisms involving ubiquitination regulators, and pharmacological studies have underscored the importance of precisely controlling RSK activity."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "9", "end_ref": "14"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nFurthermore, the regulatory dynamics of RSK1 are modulated by its own phosphorylation status and interactions with other proteins. The formation of intramolecular phosphoswitches within its disordered C-terminal tail regulates its binding to adaptors such as 14-3-3 proteins, thereby fine-tuning its subcellular localization and substrate specificity. RSK1-dependent phosphorylation events not only contribute to oncogenic processes but also appear to have relevance in therapeutic contexts—where agents such as melatonin can modulate its activity to enhance drug-induced apoptosis—and may play roles in cardiovascular pathophysiology and chaperonin regulation."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "15", "end_ref": "18"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Younghee Lee, Akihiko Gotoh, Hyung-Joo Kwon, et al. 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