Viral FLICE Inhibitory Protein of Rhesus Monkey Rhadinovirus Inhibits Apoptosis by Enhancing Autophagosome Formation

Abstract

Rhesus monkey rhadinovirus (RRV) is a gamma-2 herpesvirus closely related to human herpesvirus 8 (HHV8). RRV encodes viral FLICE inhibitory protein (vFLIP), which has death effector domains. Little is known about RRV vFLIP. This study intended to examine its function in apoptosis. Here we found that RRV vFLIP inhibits apoptosis induced by tumor necrosis factor-α (TNF-α) and cycloheximide. In HeLa cells with vFLIP expression, the cleavage of poly [ADP-ribose] polymerase 1 (PARP-1) and activities of caspase 3, 7, and 9 were much lower than those in controls. Cell viability of HeLa cells with vFLIP expression was significantly higher than control cells after apoptosis induction. However, RRV vFLIP appears unable to induce NF-κB signaling when tested in NF-κB reporter assay. RRV vFLIP was able to enhance cell survival under starved conditions or apoptosis induction. At early time points after apoptosis induction, autophagosome formation was enhanced and LC3-II level was elevated in cells with vFLIP and, when autophagy was blocked with chemical inhibitors, these cells underwent apoptosis. Moreover, RRV latent infection of BJAB B-lymphoblastoid cells protects the cells against apoptosis by enhancing autophagy to maintain cell survival. Knockdown of vFLIP expression in the RRV-infected BJAB cells with siRNA abolished the protection against apoptosis. These results indicate that vFLIP protects cells against apoptosis by enhancing autophagosome formation to extend cell survival. The finding of vFLIP’s inhibition of apoptosis via the autophagy pathway provides insights of vFLIP in RRV pathogenesis.

Inhibition of human 67-kDa laminin receptor sensitizes multidrug resistance colon cancer cell line SW480 for apoptosis induction

“…The RNA interference (RNAi) procedure was carried out by transfection of in vitro transcribed dsRNA as previously described with modifications [11]. Briefly, three expressed sequence tag (EST) fragments from 67LR ORF were selected and amplified by PCR with primers containing T7 promoter at the both ends ( Table 1).…”

“…Doxorubicin, a commonly used chemotherapeutic drug had been used in here to induce the apoptosis in SW480 cell. The cleavage of PARP-1, a hall marker of cell apoptosis [11], had been used to monitor the cell status. Compared with the scramble siRNA-transfected cell, the 67LR siRNA-transfected cell had a minimum effect on apoptosis induction (Fig.…”

Herpesvirus and Autophagy: “All Right, Everybody Be Cool, This Is a Robbery!”

“…An anti-apoptotic protein of Rhesus monkey rhadinovirus (RRV) stimulates autophagy during latent infection in order to prevent cell death. Autophagy induction has also a positive effect during the latency of RRV, a virus that naturally infects rhesus monkeys and is closely related to HHV8 [ 98 ]. During latency, this virus encodes a homolog of cellular FLIP (FLICE-like inhibitory protein), vFLIP, which activates autophagy ( Figure 3 ).…”

The Role of Sex Differences in Autophagy in the Heart During Coxsackievirus B3-Induced Myocarditis

“…FLIP over-expression represses cell death by autophagy, as induced by rapamycin, an mammalian Target of rapamycin (mTor) inhibitor [43]. In contrast, c-FLIP S was also shown to possess anti-apoptotic properties during viral infection by enhancing autophagosome formation in an effort to clear virus and to extend cell survival [52]. This observation is supported by the demonstration that nitrosylation of FLIP inhibits Fas-ligand induced activation of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) under physiological condition [53], and endogenous nitric oxide production was shown to promote autophagy [54].…”