Doenjang hexane fraction-induced G1 arrest is associated with the inhibition of pRB phosphorylation and induction of Cdk inhibitor p21 in human breast carcinoma MCF-7 cells

Doenjang (fermented soy paste) is a Korean traditional fermented food. In p revious studies, we demonstrated that Doenjang extracts exhibited anti-muta genic and anti-carcinogenic activities. Here we investigated the effects of Doenjang hexane fraction (DHF) on cell cycle progression in the human brea st carcinoma MCF-7 cells. Treatment of DHF to MCF-7 cells induced a GI phas e arrest of the cell cycle, which correlated with the accumulation of the h ypophosphorylated form of the retinoblastoma protein (pRB) and enhanced ass ociation of pRB with the transcription factor E2F-1. After DHF treatment, t he expression of D-type cyclins was decreased in a time-dependent manner, b ut DHF did not affect the levels of cyclin-dependent kinases (Cdks), cyclin E and cyclin A protein. However, the activity of Cdk2 and cyclin E-associa ted kinase was decreased in a time-dependent manner. The tumor suppressor p 53 and Cdk inhibitor p21, a known downstream effector of the p53, and assoc iation of p21 with Cdk2 were markedly induced in DHF-treated cells. Taken t ogether, the present results indicate that treatment of MCF-7 cells with DH F induces a significant inhibition of pRB phosphorylation and increase of C dk inhibitor p21 that appear to be responsible for the observed G1 arrest.