Abstract
Cancer cells display abnormal redox metabolism. Autophagy, anoikis and reactive oxygen species (ROS) play a regulatory role during metastasis. LC3 is a well-known essential molecule for autophagy. Therefore, we wanted to explore the molecular interplay between autophagy, anoikis, and ROS in relation to LC3B. We observed enhanced LC3B level along with increased expression of p62 and modulation of other autophagy-related molecules (Atg 3, 5, 7, 12, 16L1 and Beclin1) by inducing oxidative-stress in ovarian cancer cells using a ROS-producing pro-oxidant molecule. Surprisingly, enhanced LC3B was unable to induce autophagosome formation rather promoted anoikis. ROS-induced inhibition of autophagosome-formation is possibly due to the instability of autophagy initiator, ULK1 complex. Moreover, such upregulation of LC3B via ROS enhanced several apoptotic molecules. Silencing LC3B reduced these apoptotic molecules and increased when overexpressed, suggesting its role in apoptosis. Furthermore, LC3B-dependent apoptosis was decreased by inhibiting ROS, indicating a possible link between ROS, LC3B, and apoptosis. Additionally, ROS-induced enhanced LC3B promoted detachment-induced cell death (anoikis). This was further reflected by reduced cell adhesion molecules (integrin-β3 and focal adhesion kinase) and mesenchymal markers (snail and slug). Our in vitro experimental data was further confirmed in primary tumors developed in syngeneic mice, which also showed ROS-mediated LC3B enhancement along with reduced autophagosomes, integrin-β3 and focal adhesion kinase ultimately leading to the decreased tumor mass. Additionally, primary cells from high-grade serous carcinoma patient’s ascites exhibited LC3B enhancement and autophagy inhibition through ROS which provided a clinical relevance of our study. Taken together, this is the first evidence for a non-canonical role of LC3B in promoting anoikis in contrast to autophagy and may, therefore, consider as a potential therapeutic target molecule in ovarian cancer. Taken together, autophagy-inhibition may be an alternative approach to induce apoptosis/anoikis in cancer.
Highlights
Autophagy is the lysosomal degradation process of cellular components for renewal of energy needed for cellAnoikis is a process of detachment-induced programmed cell death in anchorage-dependent cells[3]
LC3B mediates enhanced apoptosis through reactive oxygen species (ROS) Since ROS-induced enhanced-LC3B did not exhibit any role in autophagy, we investigated its relationship with apoptosis
The main achievement of our study is to demonstrate a non-canonical role of LC3B in detachment-induced cell death instead of canonical involvement in autophagy, induced by ROS in ovarian cancer (OC)
Summary
Autophagy is the lysosomal degradation process of cellular components for renewal of energy needed for cellAnoikis is a process of detachment-induced programmed cell death in anchorage-dependent cells[3]. Autophagy is the lysosomal degradation process of cellular components for renewal of energy needed for cell. EMT is a complex dynamic reversible-process, where cancer cells acquire mesenchymal characteristics, the hallmark of anoikis-resistance, crucial for metastasis[3,4,5]. Satyavarapu et al Cell Death and Disease (2018)9:934 adhesion molecules are correlated with anoikisresistance[6]. Enhanced anoikis-resistance and autophagy are coupled cellular processes crucial for metastasis[7]. The molecular-interplay between all major processes related to autophagy and anoikis has not fully deciphered, which might help to discover the specifictarget. Considering the vital importance of autophagy and anoikis in metastasis, we explored the possible role and molecular mechanism of LC3 in anoikis using ovarian cancer (OC) as a model system. The major task is to search the molecule(s) that could kill a primary tumor and target the metastasized-cells
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