A HIF-1 target, ATIA, protects cells from apoptosis by modulating the mitochondrial thioredoxin, TRX2

The regulation of apoptosis is critical for controlling tissue homeostasis and preventing tumor formation and growth. Reactive oxygen species (ROS) generation plays a key role in such regulation. Here, we describe a HIF-1 target, Vasn/ATIA (anti-TNFα-induced apoptosis), which protects cells against TNFα- and hypoxia-induced apoptosis. Through the generation of ATIA knockout mice, we show that ATIA protects cells from apoptosis through regulating the function of the mitochondrial antioxidant, thioredoxin-2, and ROS generation. ATIA is highly expressed in human glioblastoma, and ATIA knockdown in glioblastoma cells renders them sensitive to hypoxia-induced apoptosis. Therefore, ATIA is not only a HIF-1 target that regulates mitochondrial redox pathways but also a potentially diagnostic marker and therapeutic target in human glioblastoma.

Initial stages of mammary tumor virus infection are superantigen independent

Exogenous mouse mammary tumor virus (MMTV) is transmitted via the milk from infected mothers to newborn pups. Efficient MMTV transmission is dependent on proliferation of T cells with particular TCR beta-chains, which occurs upon recognition of virally encoded superantigen (SAg) bound to MHC class II molecules. It is assumed that infection of these dividing cells favors MMTV amplification. SAg is important for MMTV infection, as mice that lack SAg-cognate T cells due to expression of endogenous Mtv loci or mice that express inappropriate MHC haplotypes unable to present viral SAg efficiently were shown to be resistant to MMTV infection. However, this resistance was not absolute, as these mice developed late onset MMTV-induced mammary tumors. In this study, we show that the success of initial MMTV infection in neonates is independent of SAg function but depends on the developmentally regulated proliferation of target cells. However, SAg was absolutely required for virus spread following completion of this proliferative stage.

Subversion of the innate immune system by a retrovirus

Retroviruses evolve rapidly to avoid the immune response of the infected host. We show here that the wild-type mouse mammary tumor virus MMTV(C3H) persisted indefinitely in C3H/HeN mice. However, it was rapidly lost in mice of the closely related C3H/HeJ strain and was replaced by a virus recombinant with an endogenous Mtv provirus. Maintenance of the wild-type virus was dependent on Toll-like receptor-4 (TLR4) signaling, which triggered production of the immunosuppressive cytokine interleukin-10. In the presence of mutant TLR4 in C3H/HeJ mice, wild-type virus was eliminated by the cytotoxic immune response, promoting selection of the immune escape recombinant MMTV variants. Thus, subversion of the innate immune system is yet another survival strategy used by retroviruses.