The drive toward more sustainable agriculture has raised the profile of crop plant nutrient-use efficiency. Here we show that a major rice nitrogen-use efficiency quantitative trait locus (qNGR9) is synonymous with the previously identified gene DEP1 (DENSE AND ERECT PANICLES 1). The different DEP1 alleles confer different nitrogen responses, and genetic diversity analysis suggests that DEP1 has been subjected to artificial selection during Oryza sativa spp. japonica rice domestication. The plants carrying the dominant dep1-1 allele exhibit nitrogen-insensitive vegetative growth coupled with increased nitrogen uptake and assimilation, resulting in improved harvest index and grain yield at moderate levels of nitrogen fertilization. The DEP1 protein interacts in vivo with both the Gα (RGA1) and Gβ (RGB1) subunits, and reduced RGA1 or enhanced RGB1 activity inhibits nitrogen responses. We conclude that the plant G protein complex regulates nitrogen signaling and modulation of heterotrimeric G protein activity provides a strategy for environmentally sustainable increases in rice grain yield.

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Anaplastic lymphoma kinase (ALK) activation has been associated with many types of human cancer. Significant efforts have been devoted to the development of ALK inhibitors to antagonize the kinase activity of ALK. Four ALK inhibitors have been approved by the FDA to date for treating patients with ALK-positive non-small cell lung cancers (NSCLC). However, drug resistance has been observed in the majority of patients treated with these inhibitors. New therapeutic strategies (e.g., compounds with novel mechanisms of action) are needed to overcome the drug resistance issue. The emerging PROTAC (Proteolysis Targeting Chimera) technology has been successfully applied to selective degradation of multiple protein targets, but not ALK. Since ALK protein levels are not important for viability in mammals, ALK PROTACs could lead to novel therapeutics with minimal toxicity. Here we report the design, synthesis and biological evaluation of novel PROTACs (degraders) of ALK. MS4077 (5) and MS4078 (6) potently decreased cellular levels of oncogenic active ALK fusion proteins in a concentration- and time-dependent manner in SU-DHL-1 lymphoma and NCI-H2228 lung cancer cells. The ALK protein degradation induced by compounds 5 and 6 was cereblon and proteasome dependent. In addition, compounds 5 and 6 potently inhibited proliferation of SU-DHL-1 cells. Furthermore, compound 6 displayed good plasma exposure in a mouse pharmacokinetic study, thus is suitable for in vivo efficacy studies. We also developed MS4748 (7) and MS4740 (8), very close analogs of 5 and 6 respectively, which are incapable to degrade the ALK fusion proteins, as negative controls. Compounds 5-8 are valuable chemical tools for investigating effects of ALK pharmacological degradation. Our study paved the way for developing the next generation of ALK PROTACs.

SignificancePulmonary alveolar type I (AT1) cells are essential for the gas-exchange function of lungs. AT1 cells retain their cellular plasticity during injury-induced alveolar regeneration. However, we know very little about the developmental heterogeneity of the AT1 cell population. Our study identified a robust genetic marker of postnatal AT1 cells, insulin-like growth factor-binding protein 2 (Igfbp2). We use this marker to demonstrate that the postnatal AT1 cell population actually consists of two AT1 cell subtypes (Hopx+Igfbp2+ and Hopx+Igfbp2− AT1 cells) with distinct cell fates during alveolar regeneration. The large majority of adult AT1 cells expresses Igfbp2 and cannot transdifferentiate into AT2 cells during post pneumonectomy formation of new alveoli. Therefore, Hopx+Igfbp2+ AT1 cells represent the terminally differentiated population of AT1 cells.

Glutathione plays many important roles in biological processes; however, the dynamic changes of glutathione concentrations in living cells remain largely unknown. Here, we report a reversible reaction-based fluorescent probe—designated as RealThiol (RT)—that can quantitatively monitor the real-time glutathione dynamics in living cells. Using RT, we observe enhanced antioxidant capability of activated neurons and dynamic glutathione changes during ferroptosis. RT is thus a versatile tool that can be used for both confocal microscopy and flow cytometry based high-throughput quantification of glutathione levels in single cells. We envision that this new glutathione probe will enable opportunities to study glutathione dynamics and transportation and expand our understanding of the physiological and pathological roles of glutathione in living cells.

Protein-protein interactions (PPIs) play a central role in most biological processes, and therefore represent an important class of targets for therapeutic development. However, disrupting PPIs using small-molecule inhibitors (SMIs) is challenging and often deemed as "undruggable." We developed a cell-based functional assay for highthroughput screening to identify SMIs for steroid receptor coactivator-3 (SRC-3 or AIB1), a large and mostly unstructured nuclear protein.Without any SRC-3 structural information, we identified SI-2 as a highly promising SMI for SRC-3. SI-2 meets all of the criteria of Lipinski's rule [Lipinski et al. (2001) Adv Drug Deliv Rev 46(1-3):3-26] for a drug-like molecule and has a half-life of 1 h in a pharmacokinetics study and a reasonable oral availability in mice. As a SRC-3 SMI, SI-2 can selectively reduce the transcriptional activities and the protein concentrations of SRC-3 in cells through direct physical interactions with SRC-3, and selectively induce breast cancer cell death with IC 50 values in the low nanomolar range (3-20 nM), but not affect normal cell viability. Furthermore, SI-2 can significantly inhibit primary tumor growth and reduce SRC-3 protein levels in a breast cancer mouse model. In a toxicology study, SI-2 caused minimal acute cardiotoxicity based on a hERG channel blocking assay and an unappreciable chronic toxicity to major organs based on histological analyses. We believe that this work could significantly improve breast cancer treatment through the development of "first-in-class" drugs that target oncogenic coactivators.steroid receptor coactivator | small-molecule inhibitor | breast cancer | drug development | protein-protein interactions P rotein-protein interactions (PPIs) play a central role in most biological processes, and therefore represent an important class of targets for therapeutic development (1). Biologics-based therapeutics, such as antibodies, exemplify success in PPI regulation (2). However, antibodies usually can only be applied to protein targets on cell surfaces because of their impermeability to plasma membranes (2). Although small-molecule drugs can readily cross membranes, applying small-molecule inhibitors (SMIs) to disrupt PPIs is a challenging task because ∼750-1,500 Å 2 of protein surface area is involved at the interface of PPIs (3), which is too large for SMIs to cover. In addition, these interacting protein surfaces do not have pocket-like small-molecule binding sites (2). Therefore, these PPI sites are deemed as "undruggable" targets for SMIs. The Holy Grail of drug development is to render small molecules the power of biologics to regulate PPIs.The current strategies for designing small-molecule PPI inhibitors primarily rely on the structural information of the protein targets (4). Clackson and Wells discovered that only a small set of residues at the PPI interface are critical for their interactions, known as "hot spots" (5). Therefore, current drug design for PPIs is mainly focused on small hot spots that can be covered by a dru...

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Interferon-inducible transmembrane protein IFITM3 was known to restrict the entry of a wide spectrum of viruses to the cytosol of the host. The mechanism used by the protein to restrict viral entry is unclear given the unavailability of the membrane topology and structures of the IFITM family proteins. Systematic site-directed spin labeling (SDSL) and electron paramagnetic resonance (EPR) studies of IFITM3 in detergent micelles identified a single, long transmembrane helix in the C-terminus and an intramembrane segment in the N-terminal hydrophobic region. Solution NMR studies of the same sample verified the secondary structure distribution and demonstrated two rigid regions interacting with the micellar surface. The resulting membrane topology of IFITM3 supports the mechanism of an enhanced restricted membrane hemi-fusion.