Autophagy protein Ulk1 promotes mitochondrial apoptosis through reactive oxygen species

• Published in: Free radical biology & medicine 2015-12, Vol.89, p.311-321
• Main Authors: Mukhopadhyay, Subhadip, Das, Durgesh Nandini, Panda, Prashanta Kumar, Sinha, Niharika, Naik, Prajna Paramita, Bissoyi, Akalabya, Pramanik, Krishna, Bhutia, Sujit Kumar
• Format: Article
• Language: English
• Subjects: Apoptosis; ATP depletion; Autophagy; Autophagy-Related Protein-1 Homolog; Blotting, Western; Cell Proliferation; Cells, Cultured; HeLa Cells; Humans; Immunoenzyme Techniques; Immunoprecipitation; Intracellular Signaling Peptides and Proteins - metabolism; Membrane Potential, Mitochondrial; Mitochondria - metabolism; Mitochondria - pathology; Mitochondrial superoxide dismutase; Protein Serine-Threonine Kinases - metabolism; Reactive oxygen species; Reactive Oxygen Species - metabolism; Ulk1
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2015.07.159

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. [Display omitted] •Autophagy protein Ulk1 regulates cell proliferation and survivability.•Ulk1 triggers reactive oxygen species-mediated mitochondrial apoptosis.•Ulk1 inhibits mitochondrial MnSOD and induces ATP depletion.•Ulk1-induced apoptosis is promoted by inhibiting Ulk1-mediated autophagy.