Betanodavirus B2 protein triggers apoptosis and necroptosis in lung cancer cells that suppresses autophagy

A Mitochondrion-Targeting Protein (B2) Primes ROS/Nrf2-Mediated Stress Signals, Triggering Apoptosis and Necroptosis in Lung Cancer

The betanodavirus B2 protein targets mitochondria and triggers mitochondrion-mediated cell death signaling in lung cancer cells; however, its molecular mechanism remains unknown. In this study, we observed that B2 triggers hydrogen peroxide/Nrf2-involved stress signals in the dynamic regulation of non-small lung cancer cell (NSCLC)-programmed cell death. Here, the B2 protein works as a necrotic inducer that triggers lung cancer death via p53 upregulation and RIP3 expression, suggesting a new perspective on lung cancer therapy. We employed the B2 protein to target A549 lung cancer cells and solid tumors in NOD/SCID mice. Tumors were collected and processed for the hematoxylin and eosin staining of tissue and cell sections, and their sera were used for blood biochemistry analysis. We observed that B2 killed an A549 cell-induced solid tumor in NOD/SCID mice; however, the mutant ΔB2 did not. In NOD/SCID mice, B2 (but not ΔB2) induced both p53/Bax-mediated apoptosis and RIPK3-mediated necroptosis. Finally, immunochemistry analysis showed hydrogen peroxide /p38/Nrf2 stress strongly inhibited the production of tumor markers CD133, Thy1, and napsin, which correlate with migration and invasion in cancer cells. This B2-triggered, ROS/Nrf2-mediated stress signal triggered multiple signals via pathways that killed A549 lung cancer tumor cells in vivo. Our results provide novel insight into lung cancer management and drug therapy.

Necroptosis pathways in tumorigenesis

Necroptosis is a caspase-independent form of programmed cell death executed by the receptor interacting protein kinase 1 (RIPK1)-RIPK3-mixed lineage kinase domain-like protein (MLKL) signaling cascade, deregulation of which can cause various human diseases including cancer. Escape from programmed cell death is a hallmark of cancer, leading to uncontrolled growth and drug resistance. Therefore, it is crucial to further understand whether necroptosis plays a key role in therapeutic resistance. In this review, we summarize the recent findings of the link between necroptosis and cancer, and discuss that targeting necroptosis is a new strategy to overcome apoptosis resistance in tumor therapy.

Overexpression of Bcl2 and Bcl2L1 Can Suppress Betanodavirus-Induced Type III Cell Death and Autophagy Induction in GF-1 Cells

Betanodavirus infection induces viral nervous necrosis (VNN) in fish. However, the role of cell death and autophagy in the pathogenesis of VNN remains unknown. This study aimed to investigate the effect of red-spotted grouper nervous necrosis virus (RGNNV) infection on Bcl2 downregulation and overexpression on asymmetric interaction between cell death and autophagy. The mRFP-LC3 reporter system was used to identify autophagosome formation in GF-1 (Grouper fin-1) fish cells. We found that the RGNNV could strongly induce autophagosome formation 36 h post-infection (hpi) after autophagy inhibitor 3-MA had downregulated anti-apoptotic genes such as Bcl2 and Bcl2L1 (Bcl-xL). We proposed that the overexpression of Bcl2 and Bcl2L1 can modulate both cell death and autophagy. Then, we found that it can also reduce either type III cell death or autophagy, which are mildly correlated with reduced viral replication. Our data suggest that RGNNV-induced Bcl2 downregulation correlates with the asymmetrical interaction between cell death induction and the autophagy process, which resembles viral replication.

Necroptosis in Pulmonary Diseases: A New Therapeutic Target

In the past decades, apoptosis has been the most well-studied regulated cell death (RCD) that has essential functions in tissue homeostasis throughout life. However, a novel form of RCD called necroptosis, which requires receptor-interacting protein kinase-3 (RIPK3) and mixed-lineage kinase domain-like pseudokinase (MLKL), has recently been receiving increasing scientific attention. The phosphorylation of RIPK3 enables the recruitment and phosphorylation of MLKL, which oligomerizes and translocates to the plasma membranes, ultimately leading to plasma membrane rupture and cell death. Although apoptosis elicits no inflammatory responses, necroptosis triggers inflammation or causes an innate immune response to protect the body through the release of damage-associated molecular patterns (DAMPs). Increasing evidence now suggests that necroptosis is implicated in the pathogenesis of several human diseases such as systemic inflammation, respiratory diseases, cardiovascular diseases, neurodegenerative diseases, neurological diseases, and cancer. This review summarizes the emerging insights of necroptosis and its contribution toward the pathogenesis of lung diseases.

Attenuation of autophagy flux by 6-shogaol sensitizes human liver cancer cells to TRAIL-induced apoptosis via p53 and ROS

Tumor necrosis factor (TNF)‑related apoptosis‑inducing ligand (TRAIL) is a member of the TNF superfamily and is an antitumor drug that induces apoptosis in tumor cells with minimal or no effects on normal cells. Here, it is demonstrated that 6‑shogaol (6‑sho), a bioactive component of ginger, exerted anti‑inflammatory and anticancer properties, attenuated tumor cell propagation and induced TRAIL‑mediated cell death in liver cancer cells. The current study identified a potential pathway by revealing that TRAIL and 6‑sho or chloroquine acted together to trigger reactive oxygen species (ROS) production, to upregulate tumor‑suppressor protein 53 (p53) expression and to change the mitochondrial transmembrane potential (MTP). Treatment with N‑acetyl‑L‑cysteine reversed these effects, restoring the MTP and attenuated ROS production and p53 expression. Interestingly, treatment with 6‑sho increased p62 and microtubule‑associated proteins 1A/1B light chain 3B‑II levels, indicating an inhibited autophagy flux. In conclusion, attenuation of 6‑sho‑induced autophagy flux sensitized cells to TRAIL‑induced apoptosis via p53 and ROS, suggesting that the administration of TRAIL in combination with 6‑sho may be a suitable therapeutic method for the treatment of TRAIL‑resistant Huh7 liver cells.