title: 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 cross talk with apoptosis. In this study, we overexpressed Ulk1 in HeLa cells and evaluated the apoptosis-inducing potential of the 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 increased cell viability and colony number as well as mitochondrial membrane potential (MMP). Our data showed that Ulk1 on entering into mitochondria inhibits the manganese dismutase activity and intensifies the mitochondrial superoxide level. The Ulk1-triggered autophagy (particularly mitophagy) resulted in a fall in ATP; thus the nonmitophagic mitochondria overwork the electron-transport cycle to replenish energy demand and are inadvertently involved in ROS overproduction that led to apoptosis. In this present investigation, our results decipher a previously unrecognized perspective of apoptosis induction by a key autophagy protein Ulk1 that may contribute to identification of its tumor-suppressor properties through dissecting the connection among cellular bioenergetics, ROS, and MMP.
authors.affiliation: Department of Life Science, National Institute of Technology, Rourkela, Odisha, India.
authors.forename: Subhadip
authors.initials: S
authors.lastname: Mukhopadhyay
authors.affiliation: Department of Life Science, National Institute of Technology, Rourkela, Odisha, India.
authors.forename: Durgesh Nandini
authors.initials: DN
authors.lastname: Das
authors.affiliation: Department of Life Science, National Institute of Technology, Rourkela, Odisha, India.
authors.forename: Prashanta Kumar
authors.initials: PK
authors.lastname: Panda
authors.affiliation: Department of Life Science, National Institute of Technology, Rourkela, Odisha, India.
authors.forename: Niharika
authors.initials: N
authors.lastname: Sinha
authors.affiliation: Department of Life Science, National Institute of Technology, Rourkela, Odisha, India.
authors.forename: Prajna Paramita
authors.initials: PP
authors.lastname: Naik
authors.affiliation: Department of Biotechnology & Medical Engineering, National Institute of Technology, Rourkela, Odisha, India.
authors.forename: Akalabya
authors.initials: A
authors.lastname: Bissoyi
authors.affiliation: Department of Biotechnology & Medical Engineering, National Institute of Technology, Rourkela, Odisha, India.
authors.forename: Krishna
authors.initials: K
authors.lastname: Pramanik
authors.affiliation: Department of Life Science, National Institute of Technology, Rourkela, Odisha, India. Electronic address: sbhutia@nitrkl.ac.in.
authors.forename: Sujit Kumar
authors.initials: SK
authors.lastname: Bhutia
mesh_terms: D017209:Apoptosis; D001343:Autophagy; D000071189:Autophagy-Related Protein-1 Homolog; D015153:Blotting, Western; D049109:Cell Proliferation; D002478:Cells, Cultured; D006367:HeLa Cells; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D017382:Reactive Oxygen Species; D000071189:Autophagy-Related Protein-1 Homolog; D017346:Protein Serine-Threonine Kinases; C484754:ULK1 protein, human
keywords: ATP depletion; Apoptosis; Autophagy; Mitochondrial superoxide dismutase; Reactive oxygen species; Ulk1