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Substrate recognition is one of the hallmarks of enzyme catalysis. Enzyme conformational changes have been linked to selectivity between substrates with little direct evidence. Aldolase, a glycolytic enzyme, must distinguish between two physiologically important substrates, fructose 1-phosphate and fructose 1,6-bisphosphate, and provides an excellent model system for the study of this question. Previous work has shown that isozyme specific residues (ISRs) distant from the active site are responsible for kinetic distinction between these substrates. Notably, most of the ISRs reside in a cluster of five surface α-helices, and the carboxyl-terminal region (CTR), and cooperative interactions among these helices have been demonstrated. To test the hypothesis that conformational changes are at the root of these changes, single surface-cysteine variants were created with the cysteine located on helices of the cluster and CTR. This allowed for site-specific labeling with an environmentally sensitive fluorophore, and subsequent monitoring of conformational changes by fluorescence emission spectrophotometry. These labeled variants revealed different spectra in the presence of saturating amounts of each substrate, which suggested the occurrence of different conformations. Emission spectra collected at various substrate concentrations showed a concentration dependence of the fluorescence spectra, consistent with binding events. Lastly, stopped-flow fluorescence spectrophotometry showed that the rate of these fluorescence changes was on the same time-scale as catalysis, thus suggesting a link between the different fluorescence changes and events during catalysis. On the basis of these results, we propose that different conformational changes may be a common mechanism for dictating substrate specificity in other enzymes with multiple substrates. [ABSTRACT FROM AUTHOR]

Chromosome segregation requires the generation of force at the kinetochore-the multiprotein structure that facilitates attachment of chromosomes to spindle microtubules. This force is required both to move chromosomes and to signal the formation of proper bioriented attachments. To understand the role of force in these processes, it is critical to define how force is generated at kinetochores, the contributions of this force to chromosome movement, and how the kinetochore is structured and organized to withstand and respond to force. Classical studies and recent work provide a framework to dissect the mechanisms, functions, and consequences of force at kinetochores. [ABSTRACT FROM AUTHOR]

Various subunits of mammalian SWI/SNF chromatin remodeling complexes display loss-of-function mutations characteristic of tumor suppressors in different cancers, but an additional role for SWI/SNF supporting cell survival in distinct cancer contexts is emerging. In particular, genetic dependence on the catalytic subunit BRG1/SMARCA4 has been observed in acute myelogenous leukemia (AML), yet the feasibility of direct therapeutic targeting of SWI/SNF catalytic activity in leukemia remains unknown. Here, we evaluated the activity of dual BRG1/BRM ATPase inhibitors across a genetically diverse panel of cancer cell lines and observed that hematopoietic cancer cell lines were among the most sensitive compared with other lineages. This result was striking in comparison with data from pooled short hairpin RNA screens, which showed that only a subset of leukemia cell lines display sensitivity to BRG1 knockdown. We demonstrate that combined genetic knockdown of BRG1 and BRM is required to recapitulate the effects of dual inhibitors, suggesting that SWI/SNF dependency in human leukemia extends beyond a predominantly BRG1-driven mechanism. Through gene expression and chromatin accessibility studies, we show that the dual inhibitors act at genomic loci associated with oncogenic transcription factors, and observe a downregulation of leukemic pathway genes, including MYC, a well-established target of BRG1 activity in AML. Overall, small-molecule inhibition of BRG1/BRM induced common transcriptional responses across leukemia models resulting in a spectrum of cellular phenotypes., Implications: Our studies reveal the breadth of SWI/SNF dependency in leukemia and support targeting SWI/SNF catalytic function as a potential therapeutic strategy in AML., (©2021 American Association for Cancer Research.)

Uveal melanoma is a rare and aggressive cancer that originates in the eye. Currently, there are no approved targeted therapies and very few effective treatments for this cancer. Although activating mutations in the G protein alpha subunits, GNAQ and GNA11 , are key genetic drivers of the disease, few additional drug targets have been identified. Recently, studies have identified context-specific roles for the mammalian SWI/SNF chromatin remodeling complexes (also known as BAF/PBAF) in various cancer lineages. Here, we find evidence that the SWI/SNF complex is essential through analysis of functional genomics screens and further validation in a panel of uveal melanoma cell lines using both genetic tools and small-molecule inhibitors of SWI/SNF. In addition, we describe a functional relationship between the SWI/SNF complex and the melanocyte lineage-specific transcription factor Microphthalmia-associated Transcription Factor, suggesting that these two factors cooperate to drive a transcriptional program essential for uveal melanoma cell survival. These studies highlight a critical role for SWI/SNF in uveal melanoma, and demonstrate a novel path toward the treatment of this cancer., (©2020 American Association for Cancer Research.)

The key player in directing proper chromosome segregation is the macromolecular kinetochore complex, which mediates DNA-microtubule interactions. Previous studies testing individual kinetochore genes documented examples of their overexpression in tumors relative to normal tissue, leading to proposals that up-regulation of specific kinetochore genes may promote tumor progression. However, kinetochore components do not function in isolation, and previous studies did not comprehensively compare the expression behavior of kinetochore components. Here we analyze the expression behavior of the full range of human kinetochore components in diverse published expression compendia, including normal tissues and tumor samples. Our results demonstrate that kinetochore genes are rarely overexpressed individually. Instead, we find that core kinetochore genes are coordinately regulated with other cell division genes under virtually all conditions. This expression pattern is strongly correlated with the expression of the forkhead transcription factor FoxM1, which binds to the majority of cell division promoters. These observations suggest that kinetochore gene up-regulation in cancer reflects a general activation of the cell division program and that altered expression of individual kinetochore genes is unlikely to play a causal role in tumorigenesis., (© 2014 Thiru et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).)

Chromosome segregation requires the generation of force at the kinetochore-the multiprotein structure that facilitates attachment of chromosomes to spindle microtubules. This force is required both to move chromosomes and to signal the formation of proper bioriented attachments. To understand the role of force in these processes, it is critical to define how force is generated at kinetochores, the contributions of this force to chromosome movement, and how the kinetochore is structured and organized to withstand and respond to force. Classical studies and recent work provide a framework to dissect the mechanisms, functions, and consequences of force at kinetochores.