Serine Hydroxymethyltransferase Anchors de Novo Thymidylate Synthesis Pathway to Nuclear Lamina for DNA Synthesis

Abstract

The de novo thymidylate biosynthetic pathway in mammalian cells translocates to the nucleus for DNA replication and repair and consists of the enzymes serine hydroxymethyltransferase 1 and 2α (SHMT1 and SHMT2α), thymidylate synthase, and dihydrofolate reductase. In this study, we demonstrate that this pathway forms a multienzyme complex that is associated with the nuclear lamina. SHMT1 or SHMT2α is required for co-localization of dihydrofolate reductase, SHMT, and thymidylate synthase to the nuclear lamina, indicating that SHMT serves as scaffold protein that is essential for complex formation. The metabolic complex is enriched at sites of DNA replication initiation and associated with proliferating cell nuclear antigen and other components of the DNA replication machinery. These data provide a mechanism for previous studies demonstrating that SHMT expression is rate-limiting for de novo thymidylate synthesis and indicate that de novo thymidylate biosynthesis occurs at replication forks.

Arsenic trioxide targets MTHFD1 and SUMO-dependent nuclear de novo thymidylate biosynthesis

“…4 E and F). SHMT1 is an essential scaffold protein for assembly of the nuclear de novo dTMP biosynthesis complex (12). Cells cultured in folate-depleted medium and 1 μM As 2 O 3 , alone or in combination, resulted in an increase in DNA damage, as measured by phosphorylated histone H2AX (γH2AX) immunostaining in HeLa cells (Fig.…”

“…5,10-methyleneTHF can be regenerated either from serine and THF through the activity of serine hydroxymethyltransferase (SHMT1 or SHMT2α) or from formate, ATP, NADPH, and THF by the activity of methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) (4)(5)(6). SHMT1, DHFR, and TYMS are small ubiquitin-like modifier (SUMO)-ylated and translocate to the nucleus at the G1/S boundary (7)(8)(9)(10)(11)(12)(13)(14)(15)(16). During S-phase of the cell cycle, the nuclear de novo dTMP synthesis pathway assembles as a lamin-associated multienzyme complex that consists of SHMT, MTHFD1, TYMS, DHFR, and other components of the replication machinery (12,13).…”

“…1) (4,15,18). However, SHMT1 is critical for nuclear de novo dTMP synthesis by serving as a scaffold for the assembly of the multienzyme complex (12). De novo dTMP synthesis maintains a pool of deoxythymidine triphosphate nucleotides available for DNA replication and repair, and perturbations in this pathway lead to uracil incorporation into DNA, resulting from increased dUTP levels.…”

cMyc-mediated activation of serine biosynthesis pathway is critical for cancer progression under nutrient deprivation conditions

“…Serine and glycine synthesis is accompanied by the production of GSH, a tripeptide that is comprised of glycine, glutamate and cysteine, contributing to the redox balance in cells as reactive oxygen species (ROS) scavenger [20][21][22][23]. Serine and glycine are also involved in nucleotide synthesis, thus entering into one-carbon metabolism and promoting cancer cell proliferation [14,18,24]. It was reported recently that, upon serine starvation, p53 activates p21 to promote GSH production to combat ROS [25,26].…”

The contribution of CMP kinase to the efficiency of DNA repair

“…17 In addition, the enzymes of de novo thymidylate synthesis pathway form a scaffolded multienzyme complex at replication sites in the nucleus. 18 These studies demonstrated that site-specific synthesis of dNTPs provides an efficient way to ensure sufficient building blocks for DNA synthesis during repair and replication. In this study, we present evidence that CMPK forms a complex with Tip60/RNR, and is recruited to DNA damage sites.…”