bims-pimaco Biomed News
on PI3K and MAPK signalling in colorectal cancer
Issue of 2024‒03‒24
three papers selected by
Lucas B. Zeiger
  1. Top-Down Proteomic Assay to Evaluate KRAS4B-Compound Engagement.
  2. An evolutionary mechanism to assimilate new nutrient sensors into the mTORC1 pathway.
  3. Reactivating PTEN to impair glioma stem cells by inhibiting cytosolic iron-sulfur assembly.
  1. Anal Chem. 2024 Mar 18.
    Top-Down Proteomic Assay to Evaluate KRAS4B-Compound Engagement.
    Robert A D'Ippolito, Dana Rabara, Maria Abreu Blanco, Emily Alberico, Matthew R Drew, Nitya Ramakrishnan, Dara Sontan, Stephanie R T Widmeyer, Grace M Scheidemantle, Simon Messing, David Turner, Michelle Arkin, Anna E Maciag, Andrew G Stephen, Dominic Esposito, Frank McCormick, Dwight V Nissley, Caroline J DeHart.
      Development of new targeted inhibitors for oncogenic KRAS mutants may benefit from insight into how a given mutation influences the accessibility of protein residues and how compounds interact with mutant or wild-type KRAS proteins. Targeted proteomic analysis, a key validation step in the KRAS inhibitor development process, typically involves both intact mass- and peptide-based methods to confirm compound localization or quantify binding. However, these methods may not always provide a clear picture of the compound binding affinity for KRAS, how specific the compound is to the target KRAS residue, and how experimental conditions may impact these factors. To address this, we have developed a novel top-down proteomic assay to evaluate in vitro KRAS4B-compound engagement while assessing relative quantitation in parallel. We present two applications to demonstrate the capabilities of our assay: maleimide-biotin labeling of a KRAS4BG12D cysteine mutant panel and treatment of three KRAS4B proteins (WT, G12C, and G13C) with small molecule compounds. Our results show the time- or concentration-dependence of KRAS4B-compound engagement in context of the intact protein molecule while directly mapping the compound binding site.
    DOI:  https://doi.org/10.1021/acs.analchem.3c05626
  2. Nat Commun. 2024 Mar 21. 15(1): 2517
    An evolutionary mechanism to assimilate new nutrient sensors into the mTORC1 pathway.
    Grace Y Liu, Patrick Jouandin, Raymond E Bahng, Norbert Perrimon, David M Sabatini.
      Animals sense and respond to nutrient availability in their environments, a task coordinated in part by the mTOR complex 1 (mTORC1) pathway. mTORC1 regulates growth in response to nutrients and, in mammals, senses specific amino acids through specialized sensors that bind the GATOR1/2 signaling hub. Given that animals can occupy diverse niches, we hypothesized that the pathway might evolve distinct sensors in different metazoan phyla. Whether such customization occurs, and how the mTORC1 pathway might capture new inputs, is unknown. Here, we identify the Drosophila melanogaster protein Unmet expectations (CG11596) as a species-restricted methionine sensor that directly binds the fly GATOR2 complex in a fashion antagonized by S-adenosylmethionine (SAM). We find that in Dipterans GATOR2 rapidly evolved the capacity to bind Unmet and to thereby repurpose a previously independent methyltransferase as a SAM sensor. Thus, the modular architecture of the mTORC1 pathway allows it to co-opt preexisting enzymes to expand its nutrient sensing capabilities, revealing a mechanism for conferring evolvability on an otherwise conserved system.
    DOI:  https://doi.org/10.1038/s41467-024-46680-3
  3. Sci Transl Med. 2024 Mar 20. 16(739): eadg5553
    Reactivating PTEN to impair glioma stem cells by inhibiting cytosolic iron-sulfur assembly.
    Jianxing Yin, Xin Ge, Fangshu Ding, Liuguijie He, Keying Song, Zhumei Shi, Zehe Ge, Junxia Zhang, Jing Ji, Xiefeng Wang, Ningwei Zhao, Chuanjun Shu, Fan Lin, Qianghu Wang, Qigang Zhou, Yuandong Cao, Wentao Liu, Dan Ye, Jeremy N Rich, Xiuxing Wang, Yongping You, Xu Qian.
      Glioblastoma, the most lethal primary brain tumor, harbors glioma stem cells (GSCs) that not only initiate and maintain malignant phenotypes but also enhance therapeutic resistance. Although frequently mutated in glioblastomas, the function and regulation of PTEN in PTEN-intact GSCs are unknown. Here, we found that PTEN directly interacted with MMS19 and competitively disrupted MMS19-based cytosolic iron-sulfur (Fe-S) cluster assembly (CIA) machinery in differentiated glioma cells. PTEN was specifically succinated at cysteine (C) 211 in GSCs compared with matched differentiated glioma cells. Isotope tracing coupled with mass spectrometry analysis confirmed that fumarate, generated by adenylosuccinate lyase (ADSL) in the de novo purine synthesis pathway that is highly activated in GSCs, promoted PTEN C211 succination. This modification abrogated the interaction between PTEN and MMS19, reactivating the CIA machinery pathway in GSCs. Functionally, inhibiting PTEN C211 succination by reexpressing a PTEN C211S mutant, depleting ADSL by shRNAs, or consuming fumarate by the US Food and Drug Administration-approved prescription drug N-acetylcysteine (NAC) impaired GSC maintenance. Reexpressing PTEN C211S or treating with NAC sensitized GSC-derived brain tumors to temozolomide and irradiation, the standard-of-care treatments for patients with glioblastoma, by slowing CIA machinery-mediated DNA damage repair. These findings reveal an immediately practicable strategy to target GSCs to treat glioblastoma by combination therapy with repurposed NAC.
    DOI:  https://doi.org/10.1126/scitranslmed.adg5553
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