TRPM2 is a member of the transient receptor potential melastatin-related (TRPM) family of cation channels, which possesses both ion channel and ADP-ribose hydrolase functions. TRPM2 has been shown to gate in response to oxidative and nitrosative stresses, but the mechanism through which TRPM2 gating is induced by these types of stimuli is not clear. Here we show through structure-guided mutagenesis that TRPM2 gating by ADP-ribose and both oxidative and nitrosative stresses requires an intact ADP-ribose binding cleft in the Cterminal nudix domain. We also show that oxidative/ nitrosative stress-induced gating can be inhibited by pharmacological reagents predicted to inhibit NAD hydrolysis to ADP-ribose and by suppression of ADP-ribose accumulation by cytosolic or mitochondrial overexpression of an enzyme that specifically hydrolyzes ADP-ribose. Overall, our data are most consistent with a model of oxidative and nitrosative stress-induced TRPM2 activation in which mitochondria are induced to produce free ADP-ribose and release it to the cytosol, where its subsequent accumulation induces TRPM2 gating via interaction within a binding cleft in the C-terminal NUDT9-H domain of TRPM2.Eukaryotic cells have been shown to react and adapt to conditions of oxidative stress produced by disulfide-inducing chemicals, reactive oxygen species (ROS), 1 or reactive nitrogen species (RNS) through a variety of redox-sensitive signaling pathways (variously reviewed in Refs. 1-12). Recently, the TRPM2 cation channel has been shown to undergo gating in response to oxidative or nitrosative stress occurring upon ROS or RNS exposure (13,14). As TRPM2 is a novel dual function protein that possesses both ion channel and ADP-ribose hydrolase functions (15, 16), there has been great interest in understanding the molecular mechanisms through which oxidative and nitrosative stress activate TRPM2 channels, as well as the physiological role(s) of TRPM2-mediated ion fluxes and enzymatic activity in the context of cellular exposure to ROS and RNS.TRPM2 is classified as a member of the transient receptor potential melastatin-related (TRPM) ion channel family based on the homology of its Ϸ600 amino acid N-terminal domain and Ϸ300 amino acid channel-forming domain to corresponding regions of other TRPM family members. The enzymatic function of TRPM is encoded by a C-terminal domain, designated the NUDT9-homology (NUDT9-H) domain, which is homologous to the NUDT9 ADP-ribose hydrolase (15,17). In vitro studies of TRPM2 channel function using patch clamp techniques have suggested that ADP-ribose and NAD are both able to directly induce gating of full-length TRPM2 channels (14,15,18), and in vitro studies of the NUDT9-H domain demonstrate that it has a low level of ADP-ribose hydrolase activity and the apparent capacity to interact with NAD through its nudix hydrolase enzymatic motif (14, 15). However, there is a significant gap in understanding how the in vitro data on TRPM2 function relate to oxidative/nitrosative stress-induced TRPM2 gating in intact c...

Cyclic-di-GMP and cyclic-di-AMP are second messengers produced by bacteria and influence bacterial cell survival, differentiation, colonization, biofilm formation, virulence, and bacteria-host interactions. Here, we show that in both RAW264.7 macrophage cells and primary bone-marrow–derived macrophages (BMM) the production of IFNβ and IL-6, but not TNF, in response to cyclic-di-AMP and cyclic-di-GMP requires MPYS (also known as STING, MITA, and TMEM173). Furthermore, expression of MPYS was required for interferon response factor (IRF)-3 but not nuclear factor κB (NFκB) activation in response to these bacterial metabolites. We also confirm that MPYS is required for type I IFN production by cultured macrophages infected with the intracellular pathogens Listeria monocytogenes and Francisella tularensis. However, during systemic infection with either pathogen, MPYS deficiency did not impact bacterial burdens in infected spleens. Serum IFNβ and IL-6 concentrations in the infected control and MPYS−/− mice were also similar at 24 hpi, suggesting that these pathogens stimulate MPYS-independent cytokine production during in vivo infection. Our findings indicate that bifurcating MPYS-dependent and -independent pathways mediate sensing of cytosolic bacterial infections.

The generation of reactive oxygen species (ROS) is inherent to immune responses. ROS are crucially involved in host defense against pathogens by promoting bacterial killing, but also as signaling agents coordinating the production of cytokines. Transient Receptor Potential Melastatin 2 (TRPM2) is a Ca 2+ -permeable channel gated via binding of ADP-ribose, a metabolite formed under conditions of cellular exposure to ROS. Here, we show that TRPM2-deficient mice are extremely susceptible to infection with Listeria monocytogenes (Lm ), exhibiting an inefficient innate immune response. In a comparison with IFNγR-deficient mice, TRPM2 −/− mice shared similar features of uncontrolled bacterial replication and reduced levels of inducible (i)NOS-expressing monocytes, but had intact IFNγ responsiveness. In contrast, we found that levels of cytokines IL-12 and IFNγ were diminished in TRPM2 −/− mice following Lm infection, which correlated with their reduced innate activation. Moreover, TRPM2 −/− mice displayed a higher degree of susceptibility than IL-12–unresponsive mice, and supplementation with recombinant IFNγ was sufficient to reverse the unrestrained bacterial growth and ultimately the lethal phenotype of Lm -infected TRPM2 −/− mice. The severity of listeriosis we observed in TRPM2 −/− mice has not been reported for any other ion channel. These findings establish an unsuspected role for ADP-ribose and ROS-mediated cation flux for innate immunity, opening up unique possibilities for immunomodulatory intervention through TRPM2.

TRPM2 (transient receptor potential melastatin 2) is the unique fusion of a Ca(2+)-permeable pore with an enzymatic domain that binds the NAD(+)-metabolite ADP-ribose (ADPR), resulting in channel opening. ADPR formation is a metabolic corollary of cellular stress, but can also be elicited enzymatically through NAD glycohydrolases like CD38. TRPM2 thus functions as a metabolic and oxidative stress sensor and translates this information into ion fluxes that can affect Ca(2+) signaling and the membrane potential. TRPM2 is strongly represented in immune cells of the phagocytic lineage, themselves professional generators of oxidants. The recent characterization of TRPM2-deficient mouse models has revealed the involvement of this channel in various aspects of immunity. Monocytes lacking TRPM2 show reduced production of the CXCL2 chemokine, resulting in diminished neutrophilic influx to the colon in chemically induced colitis, and thus protection against tissue ulceration in TRPM2(-/-) mice. However, the insufficient production of proinflammatory cytokines leads to high morbidity and lethality of the TRPM2(-/-) mice following infection with the bacterial pathogen Listeria monocytogenes. In the context of endotoxin-induced pulmonary inflammation, TRPM2's absence was found to promote inflammation and ROS production. TRPM2 acts thereby as a negative feedback loop by interfering through membrane depolarization with ROS generation by NADPH oxidases. In dendritic cells, TRPM2 is a lysosomal Ca(2+)-release channel that promotes chemokine responsiveness and cell migration, which is reminiscent of CD38-mediated functions. The discovery of TRPM2 has unveiled an unsuspected signaling pathway and established ADPR as a novel second messenger. Understanding TRPM2's complex involvement in inflammation is crucial to evaluating the potential of manipulating TRPM2 activity and ADPR metabolism for therapeutic intervention.