CAR Macrophages: a promising novel immunotherapy for solid tumors and beyond.

With the advent of adoptive cellular therapy, chimeric antigen receptor (CAR)-T cell therapy has gained widespread application in cancer treatment and has demonstrated significant efficacy against certain hematologic malignancies. However, due to the limitations of CAR-T cell therapy in treating solid tumors, other immune cells are being modified with CAR to address this issue. Macrophages have emerged as a promising option, owing to their extensive immune functions, which include antigen presentation, powerful tumor phagocytosis, and particularly active trafficking to the tumor microenvironment. Leveraging their unique advantages, CAR-macrophages (CAR-M) are expected to enhance the effectiveness of solid tumor treatments as a novel form of immunotherapy, potentially overcoming major challenges associated with CAR-T/NK therapy. This review outlines the primary mechanism underlying CAR-M and recent progressions in CAR-M therapy, while also discussing their further applications.

The translocon protein FtsHi1 is an ATP-dependent DNA/RNA helicase that prevents R-loop accumulation in chloroplasts.

R-loops, three-stranded nucleic acid structures consisting of a DNA: RNA hybrid and displaced single-stranded DNA, play critical roles in gene expression and genome stability. How R-loop homeostasis is integrated into chloroplast gene expression remains largely unknown. We found an unexpected function of FtsHi1, an inner envelope membrane-bound AAA-ATPase in chloroplast R-loop homeostasis of Arabidopsis thaliana. Previously, this protein was shown to function as a component of the import motor complex for nuclear-encoded chloroplast proteins. However, this study provides evidence that FtsHi1 is an ATP-dependent helicase that efficiently unwinds both DNA-DNA and DNA-RNA duplexes, thereby preventing R-loop accumulation. Over-accumulation of R-loops could impair chloroplast transcription but not necessarily genome integrity. The dual function of FtsHi1 in both protein import and chloroplast gene expression may be important to coordinate the biogenesis of nuclear- and chloroplast-encoded subunits of multi-protein photosynthetic complexes. This study suggests a mechanical link between protein import and R-loop homeostasis in chloroplasts of higher plants.

A Ubiquitin-Based Module Directing Protein-Protein Interactions in Chloroplasts.

A promising approach for the genetic engineering of multiprotein complexes in living cells involves designing and reconstructing the interaction between two proteins that lack native affinity. Thylakoid-embedded multiprotein complexes execute the light reaction of plant photosynthesis, but their engineering remains challenging, likely due to difficulties in accurately targeting heterologous membrane-bound proteins to various sub-compartments of thylakoids. In this study, we developed a ubiquitin-based module (Nub-Cub) capable of directing interactions in vivo between two chloroplast proteins lacking native affinities. We applied this module to genetically modify thylakoid multiprotein complexes. We demonstrated the functionality of the Nub-Cub module in the model organism Arabidopsis thaliana. Employing this system, we successfully modified the Photosystem II (PSII) complex by ectopically attaching an extrinsic subunit of PSII, PsbTn1, to CP26-a component of the antenna system of PSII. Surprisingly, this mandatory interaction between CP26 and PsbTn1 in plants impairs the efficiency of electron transport in PSII and unexpectedly results in noticeable defects in leaf development. Our study not only offers a general strategy to modify multiprotein complexes embedded in thylakoid membranes but it also sheds light on the possible interplay between two proteins without native interaction.

Efficient scavenging of reactive carbonyl species in chloroplasts is required for light acclimation and fitness of plants.

Reactive carbonyl species (RCS) derived from lipid peroxides can act as critical damage or signaling mediators downstream of reactive oxygen species by modifying target proteins. However, their biological effects and underlying mechanisms remain largely unknown in plants. Here, we have uncovered the mechanism by which the RCS 4-hydroxy-(E)-2-nonenal (HNE) participates in photosystem II (PSII) repair cycle of chloroplasts, a crucial process for maintaining PSII activity under high and changing light conditions. High Light Sensitive 1 (HLT1) is a potential NADPH-dependent reductase in chloroplasts. Deficiency of HLT1 had no impact on the growth of Arabidopsis plants under normal light conditions but increased sensitivity to high light, which resulted from a defective PSII repair cycle. In hlt1 plants, the accumulation of HNE-modified D1 subunit of PSII was observed, which did not affect D1 degradation but hampered the dimerization of repaired PSII monomers and reassembly of PSII supercomplexes on grana stacks. HLT1 is conserved in all photosynthetic organisms and has functions in overall growth and plant fitness in both Arabidopsis and rice under naturally challenging field conditions. Our work provides the mechanistic basis underlying RCS scavenging in light acclimation and suggests a potential strategy to improve plant productivity by manipulating RCS signaling in chloroplasts.

NADP+ supply adjusts the synthesis of photosystem I in Arabidopsis chloroplasts.

In oxygenic photosynthesis, NADP+ acts as the final acceptor of the photosynthetic electron transport chain and receives electrons via the thylakoid membrane complex photosystem I (PSI) to synthesize NAPDH by the enzyme ferredoxin:NADP+ oxidoreductase. The NADP+/NADPH redox couple is essential for cellular metabolism and redox homeostasis. However, how the homeostasis of these two dinucleotides is integrated into chloroplast biogenesis remains largely unknown. Here, we demonstrate the important role of NADP+ supply for the biogenesis of PSI by examining the nad kinase 2 (nadk2) mutant in Arabidopsis (Arabidopsis thaliana), which demonstrates disrupted synthesis of NADP+ from NAD+ in chloroplasts. Although the nadk2 mutant is highly sensitive to light, the reaction center of photosystem II (PSII) is only mildly and likely only secondarily affected compared to the wild-type. Our studies revealed that the primary limitation of photosynthetic electron transport, even at low light intensities, occurs at PSI rather than at PSII in the nadk2 mutant. Remarkably, this primarily impairs the de novo synthesis of the two PSI core subunits PsaA and PsaB, leading to the deficiency of the PSI complex in the nadk2 mutant. This study reveals an unexpected molecular link between NADK activity and mRNA translation of psaA/B in chloroplasts that may mediate a feedback mechanism to adjust de novo biosynthesis of the PSI complex in response to a variable NADPH demand. This adjustment may be important to protect PSI from photoinhibition under conditions that favor acceptor side limitation.