SHMT1 knockdown induces apoptosis in lung cancer cells by causing uracil misincorporation

Abstract

Reprogramming of cellular metabolism towards de novo serine production fuels the growth of cancer cells, providing essential precursors such as amino acids and nucleotides and controlling the antioxidant and methylation capacities of the cell. The enzyme serine hydroxymethyltransferase (SHMT) has a key role in this metabolic shift, and directs serine carbons to one-carbon units metabolism and thymidilate synthesis. While the mitochondrial isoform of SHMT (SHMT2) has recently been identified as an important player in the control of cell proliferation in several cancer types and as a hot target for anticancer therapies, the role of the cytoplasmic isoform (SHMT1) in cancerogenesis is currently less defined. In this paper we show that SHMT1 is overexpressed in tissue samples from lung cancer patients and lung cancer cell lines, suggesting that, in this widespread type of tumor, SHMT1 plays a relevant role. We show that SHMT1 knockdown in lung cancer cells leads to cell cycle arrest and, more importantly, to p53-dependent apoptosis. Our data demonstrate that the induction of apoptosis does not depend on serine or glycine starvation, but is because of the increased uracil accumulation during DNA replication.

Oncogenic Properties of Candidate Oncogenes in Chromosome Region 17p11.2p12 in Human Osteosarcoma

“…Our functional analyses now suggest a direct stimulating effect of overexpression of SHMT1 on tumor cell proliferation. This is in accordance with the increased expression of SHMT1 that was recently found in lung cancer [Paone et al, 2014]. However, the inhibitory effect of SHMT1 overexpression on migration and invasion of the osteosarcoma cells that we noted was not expected and remains to be clarified.…”

Alterations in cellular metabolism triggered by URA7 or GLN3 inactivation cause imbalanced dNTP pools and increased mutagenesis

“…Mammalian Shmt1 also serves as a scaffold protein that facilitates the interaction with DHFR and thymidylate synthase at the nuclear lamina (77). Remarkably, inactivation of Shmt1 in mice (78,79) or its down-regulation in human lung cells (80) results in increased uracil incorporation into DNA as result of impaired de novo dTMP biosynthesis.…”

“…Supporting this hypothesis, quantitative metabolic flux analysis done in mammalian cells revealed that the C1 cycle, through oxidation of 5,10-CH 2 -THF, contributes to the production ∼40% of NADPH (82), a central cofactor in redox homeostasis. Alternatively, loss of Shm2 in S. cerevisiae, similar to inactivation of mammalian Shmt1 (78,80), might cause uracil accumulation and increased mutagenesis. However, our analysis in shm2Δ mutants did not reveal major differences in NTP/dNTP pools or signs of DDR activation.…”

Role of Cytosolic Serine Hydroxymethyl Transferase 1 (SHMT1) in Phosphate-Induced Vascular Smooth Muscle Cell Calcification

“…The reaction catalyzed by SHMT1 is an important source of glycine [14,15] and hypoglycinemia was shown to contribute to occurrence of vascular calcification and elevated cardiovascular risk in diabetes and CKD [47]. Furthermore, direct targets of SHMT1-mediated methylation [18][19][20][21] may be involved in osteoinductive signaling in VSMCs. Conversely, SHMT1 may mediate anti-calcific effects of folate-dependent pathways to protect against vascular calcification [48].…”

“…One carbon transfer is a key component in amino acid and nucleotide synthesis as well as methylation of proteins, DNA and RNA [18,19] and, thus, participating in the regulation of cell function, proliferation and growth [18,20]. SHMT1 has been associated with apoptotic pathways [21]. SHMT1 differs in targets and effects from the mitochondrial isoform SHMT2 [14,15,18].…”