Cystathionine-ß-synthase is essential for AKT-induced senescence and suppresses the development of gastric cancers with PI3K/AKT activation.

Hyperactivation of oncogenic pathways downstream of RAS and PI3K/AKT in normal cells induces a senescence-like phenotype that acts as a tumor-suppressive mechanism that must be overcome during transformation. We previously demonstrated that AKT-induced senescence (AIS) is associated with profound transcriptional and metabolic changes. Here, we demonstrate that human fibroblasts undergoing AIS display upregulated cystathionine-ß-synthase (CBS) expression and enhanced uptake of exogenous cysteine, which lead to increased hydrogen sulfide (H2S) and glutathione (GSH) production, consequently protecting senescent cells from oxidative stress-induced cell death. CBS depletion allows AIS cells to escape senescence and re-enter the cell cycle, indicating the importance of CBS activity in maintaining AIS. Mechanistically, we show this restoration of proliferation is mediated through suppressing mitochondrial respiration and reactive oxygen species (ROS) production by reducing mitochondrial localized CBS while retaining antioxidant capacity of transsulfuration pathway. These findings implicate a potential tumor-suppressive role for CBS in cells with aberrant PI3K/AKT pathway activation. Consistent with this concept, in human gastric cancer cells with activated PI3K/AKT signaling, we demonstrate that CBS expression is suppressed due to promoter hypermethylation. CBS loss cooperates with activated PI3K/AKT signaling in promoting anchorage-independent growth of gastric epithelial cells, while CBS restoration suppresses the growth of gastric tumors in vivo. Taken together, we find that CBS is a novel regulator of AIS and a potential tumor suppressor in PI3K/AKT-driven gastric cancers, providing a new exploitable metabolic vulnerability in these cancers.

Enterotoxins can support CAR T cells against solid tumors.

Responses of solid tumors to chimeric antigen receptor (CAR) T cell therapy are often minimal. This is potentially due to a lack of sustained activation and proliferation of CAR T cells when encountering antigen in a profoundly immunosuppressive tumor microenvironment. In this study, we investigate if inducing an interaction between CAR T cells and antigen-presenting cells (APCs) in lymphoid tissue, away from an immunosuppressive microenvironment, could enhance solid-tumor responses. We combined CAR T cell transfer with the bacterial enterotoxin staphylococcal enterotoxin-B (SEB), which naturally links a proportion of T cell receptor (TCR) Vß subtypes to MHC-II, present on APCs. CAR T cell proliferation and function was significantly enhanced by SEB. Solid tumor-growth inhibition in mice was increased when CAR T cells were administered in combination with SEB. CAR T cell expansion in lymphoid tissue was demonstrated, and inhibition of lymphocyte egress from lymph nodes using FTY720 abrogated the benefit of SEB. We also demonstrate that a bispecific antibody, targeting a c-Myc tag on CAR T cells and cluster of differentiation 40 (CD40), could also enhance CAR T cell activity and mediate increased antitumor activity of CAR T cells. These model systems serve as proof-of-principle that facilitating the interaction of CAR T cells with APCs can enhance their ability to mediate antitumor activity.

Neurotoxicity of Prion Peptides on Cultured Cerebellar Neurons.

Prion neurotoxicity has been modeled in vitro using synthetic peptides derived from the PrPC sequence. The major region of neurotoxicity has been localized to the hydrophobic domain located in the middle of the PrP protein. Neurotoxicity assays are typically performed on cultured mouse cerebellar neurons derived from neonatal pups, and cell viability can be monitored by assays including MTT or MTS, cell death by LDH release, or apoptosis by caspase cleavage assays. These neurotoxicity studies have been useful in identifying cofactors, such as PrPC and metals, as modulators of PrP peptide-mediated neurotoxicity. Given the biosafety issues associated with handling and purifying infectious prions, the use of synthetic peptides, which display a dependence upon PrPC expression for toxicity, as per the PrPSc agent for infectivity, supports the relevance of using these synthetic peptides for understanding PrP-mediated neurotoxicity.

Oligomeric Amyloid-ß Toxicity Can Be Inhibited by Blocking Its Cellular Binding in Cortical Neuronal Cultures with Addition of the Triphenylmethane Dye Brilliant Blue G.

Accumulation of soluble amyloid ß (Aß) oligomers in the brain has been suggested to cause neurodegeneration associated with Alzheimer's disease (AD). Our previous findings showed that the binding of Aß trimer and tetramer to neurons is significantly correlated with Aß-induced neuronal cell death. We propose blocking of neuronal binding of these neurotoxic Aß oligomers as a therapeutic strategy for preventing this disease. To test this, a nontoxic triphenylmethane dye, Brilliant Blue G (BBG), which has been reported to modulate Aß aggregation and neurotoxicity, was investigated using mouse primary cortical neuronal cultures treated with photoinduced cross-linked toxic Aß40 oligomers as well as soluble Aß40 and Aß42 peptides. We found that the BBG-induced decrease in Aß binding resulted in a significant decrease in its neurotoxicity. These findings support our hypothesis that disruption of cellular Aß binding is a promising therapeutic strategy for combating AD.

Membrane-bound tetramer and trimer Aß oligomeric species correlate with toxicity towards cultured neurons.

Amyloid beta (Aß) peptide is the major constituent of the extracellular amyloid plaques deposited in the brains of Alzheimer's disease patients and is central to the pathogenic pathway causing this disease. The identity of the neurotoxic Aß species remains elusive. We previously reported that Aß toxicity correlates strongly with its neuronal cell binding leading us to hypothesize that neuronal cell death is caused by the binding of a specific oligomeric Aß species. To identify the specific oligomeric Aß species that is associated with cell death, we treated mouse cortical neuronal cultures with synthetic Aß40 and Aß42 peptides and identified that the cellular Aß binding and neurotoxicity were time and concentration dependent. We found a significant correlation between the amount of trimer and tetramer species bound to neurons with increasing neurotoxicity. We prepared Aß40 oligomers (up to tetramers) using photo-induced cross-linking of unmodified peptides to confirm this oligomer-specific neurotoxic activity. Our results identify the Aß tetramer, followed by the trimer, as the most toxic low-order oligomers Aß species. Our findings suggested that binding of amyloid-ß (Aß) tetramer and trimer, not monomer or dimer, to neurons is critical to induce neuronal cell death associated with Alzheimer's Disease. We proposed that Aß trimer and tetramer are the potential neurotoxic Aß species. This would provide more specific therapeutic target for Alzheimer's Disease.