PSAT1 (phosphoserine aminotransferase 1) catalyzes the second step of the phosphorylated L-serine biosynthetic pathway, converting 3-phosphohydroxypyruvate and L-glutamate to O-phosphoserine in a pyridoxal 5'-phosphate-dependent transamination reaction 1. Beyond canonical serine synthesis, PSAT1 functions as a ferroptosis inhibitor by promoting GPX4 stability through a CAMK2A-dependent phosphorylation mechanism; phosphorylated PSAT1 interacts with GPX4 and provides 2-oxoglutarate to EGLN3, enabling GPX4 hydroxylation and preventing autophagy-mediated degradation 2. In cancer contexts, PSAT1 expression is transcriptionally regulated by multiple pathways including NRF2-ATF4 signaling in non-small cell lung cancer 3, AMPK-HIF-1α signaling in glioblastoma 4, and m6A-IGF2BP3-mediated mRNA stabilization in hepatocellular carcinoma 5. PSAT1 protein stability is controlled by interplay between acetylation/deacetylation and ubiquitination in lung adenocarcinoma 6, and by AURKB-HNRNPM-mediated mRNA degradation suppression in colorectal cancer 7. Clinically, elevated PSAT1 correlates with poor prognosis across multiple cancers and contributes to chemoresistance and immunotherapy resistance 82. Germline PSAT1 mutations cause Neu-Laxova syndrome 2 and phosphoserine aminotransferase deficiency.