SHMT1 and lung adenocarcinoma: In addition, the mRNA levels of other serine enzymes, phosphoglycerate dehydrogenase (PHGDH), phosphoserine phosphatase (PSPH), and serine hydroxymethyltransferase 1 (SHMT1), which are the up- and downstream enzymes in the serine synthesis pathway, have been found to be elevated in lung adenocarcinoma, thus negatively regulating interferon regulatory factor 1 (IRF1)77.