The serine hydroxymethyltransferase-2 (SHMT2) initiates lymphoma development through epigenetic tumor suppressor silencing

Cancer cells are thought to adapt their metabolic activities to support growth and proliferation. However, increased activity of metabolic enzymes is not usually considered an initiating event in the malignant process. Here we show that the enzyme serine hydroxymethyltransferase-2 (SHMT2) is sufficient to initiate lymphoma development through a surprising epigenetic mechanism. This is relevant because SHMT2 localizes to the most frequent region of copy number gains Chr12q14.1 in lymphoma and other cancers. Physiologically, SHMT2 catalyzes the conversion of serine to glycine which yields activated methyl groups in the form of S-adenosyl methionine (SAM). A modest increase in the enzyme's physiological function is both sufficient and required for lymphoma development. SHMT2 acts as a tumor initiator by inducing changes in DNA and histone methylation patterns. In particular, we observe promoter silencing of previously uncharacterized tumor suppressor genes that are also mutational targets in lymphoma, such as the scaffold protein SASH1 and the tyrosine phosphatase PTPRM. Together, our findings reveal that amplification of the wild type SHMT2 enzyme initiates lymphoma development through epigenetic tumor suppressor silencing. Overall design: RNAseq, ChIPseq, and ERRBS data for B220+ cells transfected with VavPBcl2;vector or VavPBcl2;SHMT2 tumors.