The Role of Serine Hydroxymethyltransferase and Methylene‐Tetrahydrofolate Dehydrogenase in Genome Stability

Abstract

The conversion of tetrahydrofolate (THF) to 5,10‐methyleneTHF is catalyzed by the isozymes serine hydroxymethyltransferase 1 and 2 (SHMT1, SHMT2) and the trifunctional enzyme methylenetetrahydrofolate dehydrogenase 1 (MTHFD1). 5,10‐methyleneTHF is a cofactor for the enzyme thymidylate synthase (TYMS) in the conversion of deoxyuridylate (dUMP) to thymidylate (dTMP) via one‐carbon metabolism. De novo dTMP synthesis is critical to prevent uracil misincoporation and double stranded breaks (DSBs). The objective of this experiment is to observe the effects of SHMT and MTHFD1 knockdown and arsenic exposure on the thymidylate biosynthesis pathway and genome stability. Reduced SHMT1, SHMT2, and MTHFD1 expression, either alone or in combination, led to a greater percentage of average nuclear area displaying the signal for γH2AX phosphorylation, indicating that knockdown of these proteins increases the extent of DSBs in DNA of affected cells. Arsenic induced uracil incorporation into DNA and increased the extent of genome instability without affecting de novo purine biosynthesis. These data indicate that both SHMT and MTHFD1 contribute to maintenance of genome stability. Supported by Public Health Services grant HD059120 to PJS.