Autosis is a Na+,K+-ATPase–regulated form of cell death triggered by autophagy-inducing peptides, starvation, and hypoxia–ischemia

A long-standing controversy is whether autophagy is a bona fide cause of mammalian cell death. We used a cell-penetrating autophagy-inducing peptide, Tat-Beclin 1, derived from the autophagy protein Beclin 1, to investigate whether high levels of autophagy result in cell death by autophagy. Here we show that Tat-Beclin 1 induces dose-dependent death that is blocked by pharmacological or genetic inhibition of autophagy, but not of apoptosis or necroptosis. This death, termed “autosis,” has unique morphological features, including increased autophagosomes/autolysosomes and nuclear convolution at early stages, and focal swelling of the perinuclear space at late stages. We also observed autotic death in cells during stress conditions, including in a subpopulation of nutrient-starved cells in vitro and in hippocampal neurons of neonatal rats subjected to cerebral hypoxia–ischemia in vivo. A chemical screen of ∼5,000 known bioactive compounds revealed that cardiac glycosides, antagonists of Na⁺,K⁺-ATPase, inhibit autotic cell death in vitro and in vivo. Furthermore, genetic knockdown of the Na⁺,K⁺-ATPase α1 subunit blocks peptide and starvation-induced autosis in vitro. Thus, we have identified a unique form of autophagy-dependent cell death, a Food and Drug Administration-approved class of compounds that inhibit such death, and a crucial role for Na⁺,K⁺-ATPase in its regulation. These findings have implications for understanding how cells die during certain stress conditions and how such cell death might be prevented.

Activation of Human Herpesvirus Replication by Apoptosis.

 A central feature of herpesvirus biology is the ability of herpesviruses to remain latent within host cells. Classically, exposure to inducing agents like activating cytokines or phorbol esters that stimulate host cell signal transduction events, and epigenetic agents (e.g. butyrate) were thought to end latency. We recently showed that Kaposi's Sarcoma-associated Herpesvirus (KSHV, or Human herpesvirus-8, HHV-8) has another, alternative emergency escape replication pathway that is triggered when KSHV's host cell undergoes apoptosis, characterized by the lack of a requirement for the RTA transcriptional activator, accelerated late gene kinetics, and production of virus with decreased infectivity. Caspase-3 is necessary and sufficient to initiate the alternative replication program. HSV-1 was also recently shown to initiate replication in response to host cell apoptosis. These observations suggested that an alternative apoptosis-triggered replication program might be a general feature of herpesvirus biology and that apoptosis-initiated herpesvirus replication may have clinical implications, particularly for herpesviruses that almost universally infect humans. To explore whether an alternative apoptosis-initiated replication program is a common feature of herpesvirus biology we studied cell lines latently infected with Epstein-Barr Virus/HHV-4, HHV-6A, HHV-6B, HHV-7, and KSHV. We found that apoptosis triggers replication for each HHV studied, with caspase-3 being necessary and sufficient for HHV replication. An alternative apoptosis-initiated replication program appears to be a common feature of HHV biology. We also found that commonly used cytotoxic chemotherapeutic agents activate HHV replication, suggesting that treatments that promote apoptosis may lead to activation of latent herpesviruses, with potential clinical significance.