Studying the Role of Apoptosis Inhibitor5 (Api5) in Replication Stress

Abstract

In cancer biology, apoptosis and its inhibition have gained much attention. Apoptosis, a natural process known to maintain tissue homeostasis, is found to be compromised in case of cancer. One such factor named Apoptosis Inhibitor 5 (Api5) is a 55kDa protein localised in the nucleus that can interact with other proteins to mediate processes such as inhibition of apoptosis, chemotherapy resistance, breast tumorigenesis, cell cycle regulation etc. The protein also can bind replication-related proteins like Replication Protein A (RPA), Minichromosome Maintenance Complex (MCM), Cell Division Cycle 5L (CDC5L), etc. Some of these proteins are affected during replication stress, leading to genome instability, a hallmark of cancer. Replication stress (RS), caused by the impediments in DNA replication, includes stalling and collapse of DNA replication forks, which can be caused by depletion of the dNTP pool. This project aims to study if Api5 is involved during replication stress. To achieve the same, levels of replication proteins along with Api5 were checked at different time points post- Hydroxyurea (HU) treatment. Sequential salt extraction procedure was performed to gain insights into the changes in chromatin binding properties of these proteins between normal growth conditions and during RS. The results suggested that replication stress might increase the levels of Api5 and change its chromatin binding. Also, the binding pattern of MCM2 followed the same trend as Api5, which suggested some level of similarity in their function. Hence, Api5 might have a role in replication-related functions, which can be revealed by further studies that will help determine Api5 as a therapeutic target.