OSBP-Related Protein 8 (ORP8) Induces Apoptosis And Interacts With Homo Sapiens Sperm Associated Antigen 5

Oxysterol binding protein related protein family are characterized by their common oxysterol binding domain. Researches of ORP family have shown that their function in many aspects:integration of sterol and sphingomyelin metabolism, sterol transport, regulate lipid metabolism and so on. ORP8 is a member of the protein family. Previous study showed that ORP8 participate in cholesterol transport. However, it is still unclear how ORP8 participate in these functions. In this research, we select ORP8 as a subject and construct a plasmid of human ORP8 with the bait vector. Then use this plasmid to screening human universal cDNA library. We successfully screened proteins interacting with ORP8. In this study, we choose SPAG5 (Homo Sapiens Sperm Associated Antigen 5, SPAG5) for further functional studies.Protein interaction of ORP8 and SPAG5 were confirmed by GST pull-down assay and Co-IP assay. We found that in human hepatocarcinoma cell line HepG2, ORP8 overexpression could cause HepG2 cell apoptosis. And ORP8 overexpression could cause changes on HepG2 cell cycle. SPAG5 is known as mitotic related protein, knockdown of SPAG5 showed mitotic arrest, causing cell apoptosis. Also we found co-transfection of SPAG5 and ORP8 may reduce the apoptosis level induced by ORP8. Also we demonstrating that overexpression of ORP8 induced endoplasmic reticulum stress and led to cell apoptosis. These experiments revealed the new functions of ORP8 involved in cell cycle and apoptosis. This study shows that ORP8 involved in human hepatocarcinoma HepG2 cell apoptosis and proliferation, suggesting it possibly play a role in rapid matabolism in liver tissue. The results also provides reference for understanding the role of ORP8 in other cells and tissues.