A protocol to construct RNA-protein devices for photochemical translational regulation of synthetic mRNAs in mammalian cells

Here, we describe a protocol for the translational regulation of transfected messenger RNAs (mRNAs) using light in mammalian cells. We detail the steps for photocaged ligand synthesis, template DNA preparation, and mRNA synthesis. We describe steps for mRNA transfection, treatment of cells with a photocaged ligand followed by light irradiation, and analysis of the transgene expression. The protocol enables spatiotemporally regulated transgene expression without the risk of insertional mutagenesis

Functional visualization of NK Cell-mediated killing of metastatic single tumor cells

ナチュラルキラー（NK）細胞による転移がん細胞殺傷の可視化 --NK細胞とがん細胞の肺毛細血管上での戦いを実況中継する--. 京都大学プレスリリース. 2022-02-07.Natural killer (NK) cells lyse invading tumor cells to limit metastatic growth in the lung, but how some cancers evade this host protective mechanism to establish a growing lesion is unknown. Here we have combined ultra-sensitive bioluminescence imaging with intravital two-photon microscopy involving genetically-encoded biosensors to examine this question. NK cells eliminated disseminated tumor cells from the lung within 24 hrs of arrival, but not thereafter. Intravital dynamic imaging revealed that 50% of NK-tumor cell encounters lead to tumor cell death in the first 4 hrs after tumor cell arrival, but after 24 hrs of arrival, nearly 100% of the interactions result in the survival of the tumor cell. During this 24 hrs period, the probability of ERK activation in NK cells upon encountering the tumor cells was decreased from 68% to 8%, which correlated with the loss of the activating ligand CD155/PVR/Necl5 from the tumor cell surface. Thus, by quantitatively visualizing the NK-tumor cell interaction at the early stage of metastasis, we have revealed the crucial parameters of NK cell immune surveillance in the lung

A Dual Promoter System to Monitor IFN-γ Signaling in vivo at Single-cell Resolution

IFN-γ secreted from immune cells exerts pleiotropic effects on tumor cells, including induction of immune checkpoint and antigen presentation, growth inhibition, and apoptosis induction. We combined a dual promoter system with an IFN-γ signaling responsive promoter to generate a reporter named the interferon sensing probe (ISP), which quantitates the response to IFN-γ by means of fluorescence and bioluminescence. The integration site effect of the transgene is compensated for by the PGK promoter-driven expression of a fluorescent protein. Among five potential IFN-γ-responsive elements, we found that the interferon γ-activated sequence (GAS) exhibited the best performance. When ISP-G₅AS was introduced into four cell lines and subjected to IFN-γ stimulation, dose-dependency was observed with an EC₅₀ ranging from 0.2 to 0.9 ng/mL, indicating that ISP-GAS can be generally used as a sensitive biosensor of IFN-γ response. In a syngeneic transplantation model, the ISP-GAS-expressing cancer cells exhibited bioluminescence and fluorescence signals in an IFN-γ receptor-dependent manner. Thus, ISP-GAS could be used to quantitatively monitor the IFN-γ response both in vitro and in vivo

Native FKBP12 Engineering by Ligand-Directed Tosyl Chemistry: Labeling Properties and Application to Photo-Cross-Linking of Protein Complexes in Vitro and in Living Cells

The ability to modify target “native” (endogenous) proteins selectively in living cells with synthetic molecules should provide powerful tools for chemical biology. To this end, we recently developed a novel protein labeling technique termed ligand-directed tosyl (LDT) chemistry. This method uses labeling reagents in which a protein ligand and a synthetic probe are connected by a tosylate ester group. We previously demonstrated its applicability to the selective chemical labeling of several native proteins in living cells and mice. However, many fundamental features of this chemistry remain to be studied. In this work, we investigated the relationship between the LDT reagent structure and labeling properties by using native FK506-binding protein 12 (FKBP12) as a target protein. In vitro experiments revealed that the length and rigidity of the spacer structure linking the protein ligand and the tosylate group have significant effects on the overall labeling yield and labeling site. In addition to histidine, which we reported previously, tyrosine and glutamate residues were identified as amino acids that are modified by LDT-mediated labeling. Through the screening of various spacer structures, piperazine was found to be optimal for FKBP12 labeling in terms of labeling efficiency and site specificity. Using a piperazine-based LDT reagent containing a photoreactive probe, we successfully demonstrated the labeling and UV-induced covalent cross-linking of FKBP12 and its interacting proteins in vitro and in living cells. This study not only furthers our understanding of the basic reaction properties of LDT chemistry but also extends the applicability of this method to the investigation of biological processes in mammalian cells

Golgi Recruitment Assay for Visualizing Small-Molecule Ligand–target Engagement in Cells

The development of methods that allow detection of ligand–target engagement in cells is an important challenge in chemical biology and drug discovery. Here, we present a Golgi recruitment (G-REC) assay in which the ligand binding to the target protein can be visualized as Golgi-localized fluorescence signals. We show that the G-REC assay is applicable to the detection of various ligand–target interactions, ligand affinity comparison among distinct protein isoforms, and the monitoring of unmodified drug–target engagement in cells.</b