Low Dietary Folate Initiates Intestinal Tumors in Mice, with Altered Expression of G2-M Checkpoint Regulators Polo-Like Kinase 1 and Cell Division Cycle 25c

Abstract

mice developed tumors; mice on control diets were negative. Dietary and genotype effects on tumor development were significant. To investigate mechanisms of folate-dependent tumorigenesis, we examined levels of DNA damage and gene expression of two genes involved in DNA damage response and G 2 -M checkpoint regulation, polo-like kinase 1 (Plk1) and cell division cycle 25c (Cdc25c). Folate deficiency increased DNA damage and decreased expression of both genes (assessed by quantitative reverse transcription-PCR and immunofluorescence) in normal intestine compared with levels in mice on control diets. An immunofluorescence assay for CDC25c activity (phosphorylated CDC2) also found CDC25c activity to be decreased in folate-deficient normal intestine. In tumors, however, Plk1 and Cdc25c mRNA were found to be higher (11-and 3-fold, respectively) compared with normal intestine from folate-deficient mice; immunofluorescence studies of PLK1, CDC25c, and phosphorylated CDC2 supported these findings. Our data suggest that folate deficiency can initiate tumor development, that Mthfr mutation can enhance this phenomenon, and that altered expression of Plk1 and Cdc25c may contribute to folate-dependent intestinal tumorigenesis. (Cancer Res 2006; 66(21): 10349-56)

Genes with Aberrant Expression in Murine Preneoplastic Intestine Show Epigenetic and Expression Changes in Normal Mucosa of Colon Cancer Patients

“…After weaning, BALB/c Mthfr þ/þ and Mthfr þ/À mice were fed CD (2 mg folate/kg diet) or FD diets (0.3 mg folate/kg diet) for one year. Incidence of neoplasia was consistent with our previous reports (8,15).…”

“…However, there are limited data on differential methylation in normal colonic mucosa between controls and patients with colorectal cancer (5, 6 and our own recent report (7)). To identify protumorigenic changes in normal human colonic mucosa, we began with the identification of candidate genes in our mouse model that had previously been shown to develop intestinal tumors after administration of low folate diets (8). Since folates generate methyl groups for DNA methylation, we predicted that there would be genetic/epigenetic changes in preneoplastic intestine in our mouse model and that some of these changes might be similar to those seen in human colonic mucosa.…”

“…BALB/c and C57BL/ 6 mice were fed folate-deficient (FD) or control diets (CD) for one year. Tumors were only observed in BALB/c mice fed FD (8,12); a single functional copy of the Mthfr gene increased the number of FD mice with tumors (8). Several tumor-predisposing candidate genes involved in cell-cycle control, cell survival, and DNA repair were identified by comparing expression profiles of tumor tissue with normal tissue (13).…”

The effects of methyl-donor deficiency on mutation induction and transgenerational instability in mice

“…Age might play a critical role, as uracil misincorporation due to folate deficiency was found to be enhanced in the colon of older rats (Choi et al, 2003). Uracil misincorporation can also be affected by genetic factors such as folate-related single nucleotide polymorphisms (SNPs), like the MTHFR 667 C->T variant (Knock et al, 2006;Knock et al, 2008;De Vos et al, 2008). Additionally, folate fortification (Hazra et al, 2010) and vitamin B 12 levels (Fenech 1998;Kapiszewska et al, 2005) could play an important role to the level of uracil misincorporation in the cells (Christensen et al, 2011).…”

Génétique moléculaire deMTHFR

“…Ces faits concordent avec les résultats d'études suggérant que le génotype 677T et/ou un apport insuffisant en folates favorisent des complications de la grossesse ainsi que des anomalies congénitales. Finalement, les souris développent des tumeurs intestinales quand on les soumet à un régime alimentaire pauvre en folates [29]. Le nombre de tumeurs est plus élevé si les souris montrent de manière concomitante une déficience légère en MTHFR : ce phénomène suggère que les deux facteurs concourent à accroître le risque d'apparition de tumeurs intestinales.…”