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

Hsuan-Wen Chiu,Jiann-Ruey Hong,Yu-Chin Su

doi:10.18632/oncotarget.21588

Abstract

The betanodavirus B2 protein targets the mitochondria and acts as a “death factor”, but its effect on lung cancer cells is unknown. We examined the effect of the B2 protein on triggering apoptosis or necroptosis via P53-dependent and P53-independent pathways and increased in suppression of autophagy. The B2 protein targets the mitochondria of A549 (P53+/+) and H1299 (P53—/—) lung cancer cells due to a specific signal sequence (41RTFVISAHAA50). This triggers generation of reactive oxygen species within the mitochondria, and a minor stress response in A549 cells, but a strong stress response in H1299 cells. We examined the molecular mechanism of this cell death pathway, and found that B2 protein induces the P53/Bax-mediated apoptotic pathway in A549 cells, and that a P53 specific inhibitor (pifithrin-α) switches this response to RIP3-mediated necroptosis. On the other hand, B2 induces RIP3-mediated necroptosis pathway in H1299 cells, and a necroptosis inhibitor (necrostatin-1) switches this response to the apoptotic pathway. Both types of cell death signals inhibited autophagy via a tightly increased balance of beclin-1 and Bcl-2. Thus, B2 protein triggers P53-dependent apoptosis in A549 cells and ROS/RIP3-mediated necroptosis in H1299 cells, and crosstalk of these pathways limits initiation of autophagy. These findings provide new insights into the possible control and treatment of lung cancer.

Highlights

Betanodaviruses are the causative agents of viral nervous necrosis (VNN) in fish, an infectious neuropathological condition characterized by necrosis of the central nervous system, including the brain and retina [1]
The results show green fluorescence in the mitochondria of cells transfected with the full-length enhanced yellow fluorescent protein (EYFP)-B2 (Figure 1A and 1Ag-1Ai: A549 cells; p-r: H1299 cells)
These results confirm that B2 targets the mitochondria in A549 and H1299 cells that were transfected with the fulllength EYFP-B2, but not in cells of the other groups

Summary

Introduction

Betanodaviruses are the causative agents of viral nervous necrosis (VNN) in fish, an infectious neuropathological condition characterized by necrosis of the central nervous system, including the brain and retina [1]. RNA1 encodes a nonstructural protein of approximately 110 kDa, designated RNA-dependent RNA polymerase or protein A that is vital for replication of the viral genome. RNA2 encodes a 42-kDa capsid protein [4, 5] that may induce post-apoptotic necrotic cell death through a pathway mediated by cytochrome c release [6]. In RNA replication, betanodaviruses synthesize a sub-genomic RNA3 from the 3’ terminus of RNA1 that encodes two proteins, B1 and B2 [1, 7, 8]. The B2 protein can induce oxidative stressmediated cell death via mitochondrial targeting in vitro and in vivo [13]

Methods

Results

Conclusion