Ken Matsumoto

Chemical stabilization of protein–protein interactions involving intrinsically disordered phosphoproteins is an emerging yet challenging problem. Synthetic agents capable of achieving this goal are desirable for advancing understanding of the biological roles of these transient interactions and for developing new therapeutics. 12-Deoxyfusicoccin (12-dFC), a semisynthetic derivative of the phytotoxin fusicoccin A, exhibits significant antitumor activity in animal models while its parent compound and 12-hydroxyfusicoccin (12-hFC) are inactive, although the molecular mechanism underlying this differential activity has remained unclear. Here, through tandem-affinity proteomics, we identified GRB10-interacting GYF protein 2 (GIGYF2), a largely disordered scaffold protein in mRNA translational repression complexes as a 14-3-3 binding partner selectively stabilized by 12-dFC but not 12-hFC. Biochemical analyses revealed that 12-dFC promotes cooperative binding of 14-3-3 to the mode-1 consensus motif KGVpS₅₄₆IP in GIGYF2, enhancing binding affinity by approximately 50-fold. This stabilization enhanced GIGYF2’s translational repressor function, suppressing protein synthesis and inhibiting cell proliferation. We further demonstrated that activation of AMP-activated protein kinase (AMPK), the cellular energy sensor kinase, enhanced 14-3-3 binding to wild-type GIGYF2 but not the S546A mutant, indicating that AMPK mediates S₅₄₆ phosphorylation. Importantly, S₅₄₆ phosphorylation increased significantly under starvation conditions, suggesting a GIGYF2-regulated stress-responsive pathway that suppresses protein synthesis to conserve ATP through reversible 14-3-3 binding. These findings demonstrate that 12-dFC is a potent molecular glue stabilizer of 14-3-3 interactions with intrinsically disordered phosphoproteins and offers a robust chemical basis for developing synthetic agents that target 14-3-3-mediated control of metabolic homeostasis.

Montanine, an Amaryllidaceae alkaloid, has demonstrated superior antiviral activity against dengue virus (DENV), SARS-CoV-2, vesicular stomatitis Indiana virus (VSV-G), and vesicular stomatitis virus pseudotyped with Ebola virus glycoprotein (VSV-ZGP), outperforming other antiviral alkaloids tested, including lycorine, narciclasine, tetracetylnarciclasine, and pancracine. We further showed that montanine inhibits translation in mammalian cells, as evidenced by a puromycin incorporation assay. Cryo-EM analysis revealed that montanine binds to the peptidyl transferase center of the human ribosome. A chemical genomics survey indicated that the knockdown of the GCN1 complex, which senses ribosome collisions and triggers the translation quality control process, increased the cytotoxicity of montanine while reducing viral infectivity. Together, these results suggest that the antiviral activity of montanine is closely linked to its impact on translational elongation and GCN1-related stress responses, underscoring the potential of translation control as a targeted mode for RNA virus therapeutics.

Microalgae are microscopic unicellular organisms that inhabit marine, freshwater, and moist terrestrial ecosystems. The vast number and diversity of microalgal species provide a significant reservoir of biologically active compounds, highly promising for biomedical applications. Diatoms are unicellular eukaryotic algae belonging to the class Bacillariophyceae. They possess intricately structured silica-based cell walls, which contain long-chain polyamines that play important roles in the formation of silica. Long-chain polyamines are uncommon polyamines found only in organisms that produce biosilica. Diatomite, which is a marine sediment of the remains of the silica skeleton of diatoms, could be an abundant source of biogenic silica that can easily be converted to silica particles. This concise review focuses on the biofabrication of polyamine-based nanosilica from diatoms and highlights the possibility of utilizing diatom biosilica as a nanocarrier for drug and siRNA delivery, bioimaging, and bone tissue engineering. The challenges that may affect diatom production, including environmental stresses and climate change, are discussed together with the prospect of increasing diatom-based biosilica production with the desired nanostructures via genetic manipulation.

The eukaryotic translation factor eIF5A plays an important role in translation elongation, especially across stretches of prolines and charged amino acids, and in translation termination. eIF5A undergoes hypusination, a post-translational modification unique to this protein, although the role of hypusination in the function of eIF5A remains elusive. Here, we investigated the cellular defects induced by the hypusination inhibitor GC7 (N1-guanyl-1,7-diaminoheptane). Proteome, translatome, and transcriptome analyses indicated that GC7 downregulated a subset of mitochondrial proteins and DNA, causing mitochondrial stress and eliciting the integrated stress response. Chemical genomic screening using barcoded shRNA libraries identified genes encoding proteins involved in polyamine metabolism/transport and MPV17L2 , a mitochondrial disease gene homologue whose product regulates mitochondrial translation. Depletion of MPV17L2 caused hypersensitivity to GC7 and phenocopied the effects of GC7 treatment. These results suggest that eIF5A hypusination and MPV17L2 synthetically regulate mitochondrial molecular synthesis and integrity.

To meet cellular bioenergetic and biosynthetic demands, cancer cells remodel their metabolism to increase glycolytic flux, a phenomenon known as the Warburg effect and believed to contribute to cancer malignancy. Among glycolytic enzymes, phosphofructokinase‐1 (PFK1) has been shown to act as a rate‐limiting enzyme and to facilitate the Warburg effect in cancer cells. In this study, however, we found that decreased PFK1 activity did not affect cell survival or proliferation in cancer cells. This raised a question regarding the importance of PFK1 in malignancy. To gain insights into the role of PFK1 in cancer metabolism and the possibility of adopting it as a novel anticancer therapeutic target, we screened for genes that caused lethality when they were knocked down in the presence of tryptolinamide (TLAM), a PFK1 inhibitor. The screen revealed a synthetic chemical–genetic interaction between genes encoding subunits of ATP synthase (complex V) and TLAM. Indeed, after TLAM treatment, the sensitivity of HeLa cells to oligomycin A (OMA), an ATP synthase inhibitor, was 13,000 times higher than that of untreated cells. Furthermore, this sensitivity potentiation by TLAM treatment was recapitulated by genetic mutations of PFK1. By contrast, TLAM did not potentiate the sensitivity of normal fibroblast cell lines to OMA, possibly due to their reduced energy demands compared to cancer cells. We also showed that the PFK1‐mediated glycolytic pathway can act as an energy reservoir. Selective potentiation of the efficacy of ATP synthase inhibitors by PFK1 inhibition may serve as a foundation for novel anticancer therapeutic strategies.

Breast carcinoma is the most prevalent cancer in women globally, with complex genetic and molecular mechanisms that underlie its development and progression. Several challenges such as metastasis and drug resistance limit the prognosis of breast cancer, and hence a constant search for better treatment regimes, including novel molecular therapeutic targets is necessary. Complement component 1, q subcomponent binding protein (C1QBP), a promising molecular target, has been implicated in breast carcinogenesis. In this study, the role of C1QBP in breast cancer progression, in particular cancer cell growth, was determined in triple negative MDA-MB-231 breast cancer cells. Depletion of C1QBP decreased cell proliferation, whereas the opposite effect was observed when C1QBP was overexpressed in MDA-MB-231 cells. Furthermore, gene expression profiling and pathway analysis in C1QBP depleted cells revealed that C1QBP regulates several signaling pathways crucial for cell growth and survival. Taken together, these findings provide a deeper comprehension of the role of C1QBP in triple negative breast cancer, and could possibly pave the way for future advancement of C1QBP-targeted breast cancer therapy.

The step of identifying target molecules and elucidating the mode of action of bioactive compounds is a major bottleneck for drug discovery from phenotypic screening. Genetic screening for genes that affect drug sensitivity or phenotypes of mammalian cultured cells is a powerful tool to obtain clues to their modes of action. Chemical genomic screening systems for comprehensively identifying such genes or genetic pathways have been established using shRNA libraries for RNA interference‐mediated mRNA knockdown or sgRNA libraries for CRISPR/Cas9‐mediated gene knockout. The combination of chemical genomic screening in mammalian cells with other approaches such as biochemical searches for target molecules, phenotypic profiling, and yeast genetics provides a systematic way to elucidate the mode of action by converging various pieces of information regarding target molecules, target pathways, and synthetic lethal pathways.

The complement component 1, q subcomponent binding protein (C1QBP/gC1q-R/p32/HABP1/TAP/YBAP1), is a ubiquitous, multifunctional protein. C1QBP localizes mainly to mitochondria due to its N-terminal mitochondrial localization signal, but it can also be found in different subcellular compartments including the cell surface, nucleus, cytoplasm, and extracellular space. C1QBP has been reported to interact with a variety of proteins that have apparently unrelated functions. C1QBP has also been observed to interact with hyaluronic acid and RNA. These findings suggest that C1QBP has both mitochondrial and extramitochondrial functions. The C1QBP binding sites of many partner proteins are located within basic and intrinsically disordered regions of these molecules, consistent with the hypothesis that C1QBP functions as a molecular chaperone. C1QBP expression is elevated in various types of human cancers, including breast cancer. Moreover, it has been implicated in the development, progression, and metastasis of cancer cells based on loss-of-function and gain-of-function studies using cancer cell lines and xenograft models. Hence C1QBP could be a molecular target in breast cancer therapy. Studies using antibodies, tumor homing peptides such as LyP-1, and small molecules that target C1QBP warrant further investigation as C1QBP is a potential therapeutic target.

舌癌に対する広範囲切除・再建後の構音・嚥下機能障害は，患者のQOLに大きな影響を与える。当科で2010年以降に根治切除・遊離皮弁再建手術を施行した舌癌症例58例を対象に術後会話機能および嚥下機能の評価を行った。 会話機能評価基準，MTFスコア，FOSSの中央値はそれぞれ9点，12点，1点であった。会話機能評価基準において社会的な言語活動が困難とされる4点以下の症例は舌全摘術を行った1例のみであった。手術時の年齢や原発巣の切除範囲が術後の会話機能・嚥下機能に有意に影響を与えていた。また，術後放射線療法の有無によって治療後の会話・嚥下機能に統計学的有意差を認めなかった。

Thioviridamide, prethioviridamide, and JBIR-140, which are ribosomally synthesized and post-translationally modified peptides (RiPPs) possessing five thioamide bonds, induce selective apoptosis in various cancer cells, especially those expressing the adenovirus oncogene E1A. However, the target protein of this unique family of bioactive compounds was previously unknown. To investigate the mechanism of action, we adopted a combined approach of genome-wide shRNA library screening, transcriptome profiling, and biochemical identification of prethioviridamide-binding proteins. An shRNA screen identified 63 genes involved in cell sensitivity to prethioviridamide, which included translation initiation factors, aminoacyl tRNA synthetases, and mitochondrial proteins. Transcriptome profiling and subsequent analysis revealed that prethioviridamide induces the integrated stress response (ISR) through the GCN2-ATF4 pathway, which is likely to cause cell death. Furthermore, we found that prethioviridamide binds and inhibits respiratory chain complex V (F₁Fo-ATP synthase) in mitochondria, suggesting that inhibition of complex V leads to activation of the GCN2-ATF4 pathway. These results imply that the members of a unique family of RiPPs with polythioamide structure target mitochondria to induce the ISR.