Effects of L. paracasei subp. paracasei X12 on cell cycle of colon cancer HT-29 cells and regulation of mTOR signalling pathway 12

• Lactobacillus X12 arrests HT-29 cell cycle at G1 phase.
• Lactobacillus X12 inhibits the expressions of cyclin E1 mRNA and cyclin D1 mRNA.
• Lactobacillus X12 induces cyclin-dependent kinases inhibitor p27.
• Lactobacillus X12 suppresses the expression of mTOR.
• mTOR/p27 takes the crucial roles in Lactobacillus X12-mediated cell cycle arrest.

L. paracasei subp. paracasei X12 1 is obtained from traditional cheese in northwestern China and exhibited effective anticancer activities in previous screening experiments. Here, its effects on colon cancer cell line HT-29 cell cycle and the roles of mammalian target of rapamycin (mTOR) signalling were investigated. Firstly, the effects of Lactobacillus X12 at different multiplicity of infection (MOI) on HT-29 cell cycle were detected by flow cytometry. In order to determine the specific regulators involved, cyclin D1, cyclin E1, the positive regulators, and p21, p16, and p27, the negative regulatory factors, were further explored by RT-PCR technique. Finally, mTOR signalling was focused to demonstrate its relationship with cell cycle arrest. Overall, the present findings suggested that Lactobacillus X12 can block HT-29 cell cycle at G1 phase through inhibiting cyclin E1, meanwhile enhancing p27, which were mediated by mTOR/4EBP12 signalling pathway. These results will provide a theoretical basis for further development of Lactobacillus.