Lysyl-tRNA synthetase produces diadenosine tetraphosphate to curb STING-dependent inflammation

Inflammation is an essential part of immunity against pathogens and tumors but can promote disease if not tightly regulated. Self and non-self-nucleic acids can trigger inflammation, through recognition by the cyclic GMP-AMP (cGAMP) synthetase (cGAS) and subsequent activation of the stimulator of interferon genes (STING) protein. Here, we show that RNA:DNA hybrids can be detected by cGAS and that the Lysyl-tRNA synthetase (LysRS) inhibits STING activation through two complementary mechanisms. First, LysRS interacts with RNA:DNA hybrids, delaying recognition by cGAS and impeding cGAMP production. Second, RNA:DNA hybrids stimulate LysRS-dependent production of diadenosine tetraphosphate (Ap4A) that in turn attenuates STING-dependent signaling. We propose a model whereby these mechanisms cooperate to buffer STING activation. Consequently, modulation of the LysRS-Ap4A axis in vitro or in vivo interferes with inflammatory responses. Thus, altogether, we establish LysRS and Ap4A as pharmacological targets to control STING signaling and treat inflammatory diseases.

[Effect of regulator protein Nef on the viral activity of human immunodeficiency virus]

Despite 25 years of research on human immunodeficiency virus (HIV), the functions of some viral proteins are not fully understood. The role of Nef in the evolution of HIV-1 infection towards immunodeficiency is undeniable; however, the mechanisms involved in this function of Nef remain elusive. The interaction of Nef with a large number of cellular partners disrupts the metabolism of infected cells, including the endocytic pathway, in favor of viral spread. Down-regulation of cell-surface major histocompatibility complex (MHC) molecules by Nef enables infected cells to escape immune surveillance. Nef-induced down-regulation of CD4 increases the infectivity of virions by increasing the incorporation of the envelope glycoproteins into the viral membrane. In addition, Nef increases viral infectivity through a mechanism that is independent of MHC and CD4 down-regulation that nonetheless requires the ability of Nef to interfere with the endocytic process. Overall, these properties promote viral spread in the infected host.