A Folate- and Vitamin B12-Deficient Diet Decreases the Latency and Increases the Incidence of Mammary Tumors in MMTV-ErbB2 Transgenic Mice

Abstract

There has been controversy regarding folate- and vitamin B12-deficient diet (FVD)-induced hyperhomocysteinemia (HHcy) associated with breast cancer risk in most published epidemiological studies. Thus, the present study designed experiments to assess the causal association between FVD-induced HHcy and mammary tumor risk, as well as to identify the relative underlying mechanism. In this study, mammary tumor development was examined in mouse mammary tumor virus (MMTV)-erb-b2 receptor tyrosine kinase 2 (ErbB2) mice fed with a control AIN-93G diet or a FVD diet. MMTV-ErbB2 mice fed with the FVD diet displayed elevated blood levels of the amino acid homocysteine, a shorter tumor latency and an increased tumor multiplicity compared with the controls. The expression levels of key markers in the receptor tyrosine kinase and estrogen receptor (ER) signaling pathways, including phosphorylated (p)-Akt, p-Erk, p-ERα and Cyclin D1, were elevated in mammary tissues from MMTV-ErbB2 mice fed the FVD diet compared with mice fed with control diet. These data suggested that FVD-induced HHcy may promote mammary tumor development and decrease tumor latency, possibly by activating the epidermal growth factor receptor/ErbB2 and ERα signaling pathways. Therefore, examining the signaling mechanisms and identifying the relative metabolic pathways underlying mammary tumor promotion following FVD-induced HHcy may provide a novel strategy for breast cancer prevention and treatment.