Background: In previous studies, we provided evidence suggesting the involvement of γ-synuclein
in growth, invasion, and metastasis of colon cancer cells in vitro and in vivo. Among γ-synuclein downstream
genes, the microtubule-associated protein 1 Light Chain 3 (LC3), an autophagy gene, was screened by gene expression
profile chip analysis.
Objective: We planned to investigate the functional effects of γ-synuclein on autophagy induced by ER stress
in colon cancer cells.
Methods: We investigated the functional effects of γ-synuclein on autophagy and apoptosis induced by Thapsigargin
(TG), ER stress-inducing agent, in colon cancer cell lines using immunofluorescence staining, RT-PCR,
western blot, CCK8 test, flow cytometry analysis, and transmission electron microscopy. To further determine
how γ-synuclein regulated autophagy and apoptosis, PD98059 (ERK inhibitor), SP600125 (ERK inhibitor), anisomycin
(JNK activator), and c-Jun siRNA were used respectively in γ-synuclein siRNA transfected HCT116
cells. Then, autophagy proteins, apoptosis proteins, and pathway proteins were detected by western blot analysis.
The expression of autophagy genes was assessed by RT-PCR.
Results: Our data showed that ER stress-induced colon cancer cells autophagy mainly in the early stage (0-24h)
and apoptosis mainly in the late stage (24-48h). ER stress up-regulated γ-synuclein gene and protein expression
in colon cancer cells, accompanied by autophagy. γ-synuclein protected HCT116 cells by enhancing autophagy
in the early stage (0-24h) through activation of ERK and JNK pathway and inhibiting apoptosis in the late stage
(24-48h) through inhibition of the JNK pathway. γ-synuclein could promote autophagy via the JNK pathway activation
of ATG genes, LC3, Beclin 1, and ATG7. γ-synuclein may play a role in the transition between autophagy
and apoptosis in our model.
Conclusion: Overall, we provided the first experimental evidence to show that γ-synuclein may play an important
role in autophagy that protects colon cancer cells from ER stress. Therefore, our data suggest a new molecular
mechanism for γ-synuclein-mediated CRC progression.