Effect of Lactobacillus acidophilus CICC 6074 S-Layer Protein on Colon Cancer HT-29 Cell Proliferation and Apoptosis

The objective of this research was to investigate the effects of Lactobacillus acidophilus CICC 6074 S-layer protein on the viability, adhesion, cell cycle, and apoptosis of human colon cancer HT-29 cells and to explore their molecular mechanism of tumor suppression. The S-layer protein at doses of 0, 25, 50, and 100 mg/L significantly suppressed the proliferation of HT-29 cells. The S-layer protein exerts its cytotoxic activities against colon cancer HT-29 cells by arresting the cell cycle in the G1 phase through upregulating the expression of p53, p21, and p16 and downregulating the expression of CDK1 (cyclin-dependent kinases) and cyclin B. Morphological changes were further observed by transmission electron microscopy, and the cells treated with the S-layer protein showed obvious characteristic changes of apoptosis including chromatin condensation, nuclear fragmentation, vacuoles, and so on. Furthermore, our mechanism studies indicated that the S-layer protein may induce HT-29 cell apoptosis through the death receptor apoptotic pathway and mitochondrial pathway and impede cell invasion by inhibiting the synthesis of the PI3K/AKT pathway and FasL. These results demonstrated that the L. acidophilus CICC 6074 S-layer protein may be a potential anticarcinogenic agent.