Holothurian Glycosaminoglycan (hGAG) Promoted Bim-Induced Apoptosis in Human Lung Adenocarcinoma A549 Cell Line Through Inhibition of Akt-Mediated FOXO3a Translocation

Introduction: Holothurian glycosaminoglycan (hGAG) is an extract from the body wall of sea cucumber and previous studies have proved many unique bioactivities of it, such as anti-tumor, anti-coagulation and immune regulation. Previous studies of our research group have shown hGAG promoted cell apoptosis in human lung adenocarcinoma A549 cells by upregulating Bax and caspase-3 and downregulating Bcl-2, indicating mitochondrial apoptosis pathway participated in the process. In the mitochondrial apoptosis pathway, Bim induces cell apoptosis by either direct activation of pro-apoptotic Bax/Bak or neutralization of anti-apoptotic Bcl-2 proteins. The transcription of Bim was regulated by FOXO3a. Akt, one of the most important cellular signaling molecules, regulates apoptosis through its phosphorylation. Phosphorylation of Akt results in translocation of FOXO3a from nuclear to cytoplasm. This study aimed to explore the mechanism by which hGAG induced apoptosis in A549 cells, focusing on its regulation of the Akt/FOXO3a/Bim signaling pathway. Methods: A549 cells were divided into three groups: control group, hGAG group and hGAG+SC79 (an Akt activator) group. Cell proliferation was detected by CCK-8 assay. Cell apoptosis was detected by flow cytometry. mRNA and protein expression levels were detected by Real-time Fluorescence Quantitative PCR and Western blotting assay, respectively. Protein localization was detected by immunofluorescence. Results: The results showed that hGAG induced apoptosis in A549 cells by downregulating p-Akt level, promoting FOXO3a expression, preventing FOXO3a nuclear export, and upregulating Bim expression, while SC79 reversed these effects, further demonstrating that hGAG regulated FOXO3a and Bim through inhibition of phosphorylation of Akt. Conclusion: In conclusion, our data demonstrated that hGAG promoted apoptosis in A549 cells via the Akt/FOXO3a/Bim-mediated intrinsic apoptosis pathway.