STYX (serine/threonine/tyrosine interacting protein) is a catalytically inactive pseudophosphatase that functions as a versatile signaling regulator despite lacking enzymatic activity 1. As a member of the protein tyrosine phosphatase family, STYX operates through multiple non-catalytic mechanisms: it competes with active phosphatases for binding to mitogen-activated protein kinases (MAPKs), particularly ERK1/ERK2, and serves as a nuclear anchor that regulates their nucleocytoplasmic shuttling, thereby modulating cell-fate decisions and migration 1. Additionally, STYX binds to the F-box domain of FBXW7, preventing assembly of the SCF E3 ubiquitin-protein ligase complex and inhibiting degradation of FBXW7 substrates 1. Beyond MAPK regulation, STYX and related pseudophosphatases (particularly MK-STYX) antagonistically regulate neurite outgrowth and participate in stress response pathways relevant to neurodegenerative diseases 2. STYX dysregulation has been implicated in various cancers and neurological disorders, establishing pseudophosphatases as emerging therapeutic targets 3. The versatility of STYX exemplifies how pseudoenzymes can exert complex regulatory functions independent of catalytic activity, expanding understanding of signal transduction beyond traditional enzymatic paradigms 1.