Knockdown of Methylenetetrahydrofolate Dehydrogenase/Cyclohydrolase 2 Promotes an Epithelial‐Like Phenotype in Canine Mammary Carcinoma Cells

In cancer cells, folate is metabolised in the cytoplasm and mitochondria. Folate metabolism mediates nucleic acid synthesis and, thereby, the growth of cancer cells. One of the enzymes within this folate metabolic pathway, methylenetetrahydrofolate dehydrogenase/cyclohydrolase 2 (MTHFD2), is rarely expressed in normal adult cells but is abundantly expressed in the mitochondria and nuclei of foetal and cancer cells in humans and mice. In this study, we examined the localisation and function of MTHFD2 in canine mammary cancer cells. MTHFD2 was expressed in the nuclei and mitochondria of canine mammary carcinoma cell lines. Short-term inhibition of MTHFD2 with an inhibitor reduced the growth of each cell line. Furthermore, long-term decreased expression, mimicked by the knockdown of MTHFD2 by RNA interference, resulted in epithelial-like cell morphology and reduced migratory ability without inducing apoptosis. Increased expression of the epithelial marker E-cadherin in MTHFD2-knock down cells suggested an enhanced epithelial-like phenotype through the inhibition of MTHFD2. To our knowledge, this is the first study to analyse the function of MTHFD2 in canine mammary carcinomas.