Autophagy Protein Ulk1 Promotes Mitochondrial Apoptosis Through Reactive Oxygen Species

Abstract

Regardless of rapid progression in the field of autophagy, it remains a challenging task to understand the crosstalk with apoptosis. In this study, we overexpressed Ulk1 in HeLa cells and evaluated the apoptosis inducing potential of Ulk1 gene in the presence of cisplatin. The gain of function of Ulk1 gene showed a decline in cell viability and colony formation in HeLa cells. The Ulk1 overexpressing cells showed higher apoptotic attributes by an increase in the percentage of annexin V, escalated expression of Bax/Bcl2 ratio and caspase-9,-3/7 activities. Further, reactive oxygen species (ROS) generation was found to be much higher in HeLa-Ulk1 than in the mock group. Scavenging the ROS by N-acetyl-L-cysteine (NAC) increased cell viability, colony number as well as mitochondrial membrane permeabilization (MMP). Our data showed that Ulk1 upon entering into mitochondria inhibits the manganese dismutase (MnSOD) activity and intensifies the mitochondrial superoxide level. The Ulk1 triggered autophagy (particularly mitophagy) resulted in a fall in ATP, which meant the nonmitophagic mitochondria to overwork the electron-transport cycle to replenish energy demand and inadvertently involve in over ROS production that followed to apoptosis. In this present investigation, our results decipher a previously unrecognised perspective of apoptosis induction by a key autophagy protein Ulk1 that may contribute to identify its tumorsuppressor properties through dissecting the connection between cellular bioenergetics, ROS and MMP.