A Milk Protein, Casein, as a Proliferation Promoting Factor in Prostate Cancer Cells

Purpose: Despite most epidemiologic studies reporting that an increase in milk intake affects the growth of prostate cancer, the results of experimental studies are not consistent. In this study, we investigated the proliferation of prostate cancer cells treated with casein, the main protein in milk. Materials and Methods: Prostate cancer cells (LNCaP and PC3), lung cancer cells (A459), stomach cancer cells (SNU484), breast cancer cells (MCF7), immortalized human embryonic kidney cells (HEK293), and immortalized normal prostate cells (RWPE1) were treated with either 0.1 or 1 mg/mL of alpha-casein and total casein extracted from bovine milk. Treatments were carried out in serum-free media for 72 hours. The proliferation of each cell line was evaluated by an 3-(4,5-Dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Results: alpha-Casein and total casein did not affect the proliferations of RWPE1, HEK293, A459, SNU484, MCF7, HEK293, or RWPE1 cells. However, PC3 cells treated with 1 mg/mL of alpha-casein and casein showed increased proliferation (228% and 166%, respectively), and the proliferation of LNCaP cells was also enhanced by 134% and 142%, respectively. The proliferation mechanism of alpha-casein in PC3 and LNCaP cells did not appear to be related to the induction of Insulin-like growth factor-1 (IGF-1), since the level of IGF-1 did not change upon the supplementation of casein. Conclusions: The milk protein, casein, promotes the proliferation of prostate cancer cells such as PC3 and LNCaP.