Biology subjects

Geissler, K.

Publications and source records attributed to Geissler, K..

6 recordsLinked to original sources

bioRxiv2026

Ubiquitin selective ribosome profiling reveals systematic principles of co-translational quality control

Protein biogenesis is a stress- and error-sensitive process that can lead to nascent protein misfolding and aggregation, challenging cellular proteostasis.1 Co-translational ubiquitination (CTU) is a critical surveillance mechanism,2,3 yet its regulatory principles remain unclear due to limited known substrates and the lack of translatome-wide methods to query CTU. Here, we introduce UbSeRP, an approach that enables ubiquitin linkage-specific, and translatome-wide mapping of CTU. Focusing on ribosome-associated quality control (RQC), we expand the known endogenous RQC substrates in S. cerevisiae from few4-7 to thousands, reveal that only a subset of all identified disomes undergoes RQC, and uncover biophysical features of nascent chains that predict RQC engagement. We also identify widespread RQC-independent ubiquitination of nascent proteins, implicating broader roles of CTU in protein complex assembly. In a chronological aging model, we show that aging remodels translation and diminishes RQC engagement, favoring RQC-independent proteasomal pathways. Our findings provide systematic insight into the determinants and adaptability of CTU in maintaining proteostasis under changing physiological conditions.

biochemistry↗

bioRxiv2026

EZH2 inactivation drives MAPK-dependent vulnerability to MEK inhibition in RAS-mutant CMML

Chronic myelomonocytic leukemia (CMML) is a heterogeneous hematologic malignancy with limited therapeutic options. Although RAS and RAS-modifying mutations (RASmut) are common and associated with poor prognosis, targeting RAS signaling has shown limited clinical success. Here, we define co-occurrence of RASmut and EZH2 inactivation (EZH2inact) as a distinct molecular subgroup of CMML characterized by aggressive disease biology. Mechanistically, RASmutEZH2inact drives selective MAPK/ERK hyperactivation in mature myeloid cells and hematopoietic stem and progenitor compartments. Transcriptomic analysis of a large independent myeloid neoplasm cohort (Beat-AML) further supports this finding, demonstrating selective activation of gene signatures of MAPK/ERK activation in RASmutEZH2inact cases. Functionally, this signaling activation promotes proliferation and myelomonocytic differentiation in human and murine models. Therapeutically, this MAPK/ERK upregulation confers increased sensitivity to MEK inhibition (MEKi). In a murine RasmutEzh2inact-driven CMML model, MEKi suppresses MAPK/ERK activity and reduces leukemic burden by impairing proliferation and myelomonocytic differentiation without inducing cell death. In primary human CMML samples ex vivo, MEKi shows stronger anti-proliferative effects in RASmutEZH2inact specimens compared with RASmut samples. Drug-sensitivity data from the Beat-AML cohort further supported this. Ultimately, these findings were confirmed in a patient-derived xenograft model, where MEKi reduced the leukemic burden by selectively inhibiting the proliferation of transplanted human RASmutEZH2inact leukemic cells. In summary, our data define RASmutEZH2inact CMML as a clinically relevant subgroup with selective MAPK/ERK hyperactivation and increased sensitivity to MEKi. They provide a mechanistic explanation for the limited efficacy of MEK inhibitors in unselected CMML and support molecularly guided use of MEK-targeted therapy in this patient population.

molecular biology↗

bioRxiv2026

How the TREX-2 complex associates with the nuclear pore

Nuclear pore complexes (NPCs) control nucleocytoplasmic transport in eukaryotes, yet their architecture remains incompletely understood. Here we report a substantially extended structure of the human NPC, obtained by combining cryo-electron tomography, crosslinking mass spectrometry, and AI-assisted integrative modeling. We resolve the molecular arrangement of TPR, NUP153, NUP50 and ZC3HC1, and reveal that five additional proteins -- TMEM209, SMPD4, GANP, Centrin-2 and ENY2 -- are incorporated into the NPC. Unexpectedly, GANP, Centrin-2 and ENY2, core members of the TREX-2 mRNA export complex, are built into the nuclear ring. This finding establishes TREX-2 not as a transiently associated factor, but as an integral NPC module, positioning it opposite of the cytoplasmic NUP214 mRNA export platform. Together, our results redefine the molecular composition of the inner ring, nuclear ring and nuclear basket. They suggest a direct structural basis that couples TREX-2-mediated mRNP remodeling to NPC-facilitated transport.

cell biology↗

bioRxiv2025

The vault associates with membranes in situ

The eukaryotic vault particle is a giant ribonucleoprotein complex that assembles into an iconic barrel-like cage. Its cellular function has remained elusive despite extensive characterization. Using cryo-electron tomography of Dictyostelium discoideum cells, we define the distribution, structural states and interaction landscape of vault particles in situ. Surprisingly, we detect a subpopulation of vault particles associated with the endoplasmic reticulum (ER) and nuclear envelope membranes. This association occurs at a defined barrel height of the vault particle and at patches of reduced membrane bilayer thickness and altered curvature. We further find that a substantial fraction of vaults encloses 80S ribosomes in highly ordered orientations. These structural findings are further corroborated by proximity labeling experiments which identify ER-resident proteins and numerous ribosomal components as vault particle interactors. The membrane-bound and ribosome-encapsulating vault populations that we uncover will direct future studies towards revealing vault function.

cell biology↗

bioRxiv2023

High-confidence 3D template matching for cryo-electron tomography

Cryo-electron tomography (CryoET) resolves individual macromolecules inside living cells. However, the complex composition and high density of cells challenge the faithful identification of features in tomograms. Here, we capitalize on recent advances in electron tomography and demonstrate that 3D template matching (TM) localizes a wide range of structures inside crowded eukaryotic cells with confidence 10 to 100-fold above the noise level. We establish a TM pipeline with systematically tuned parameters for automated, objective and comprehensive feature identification. High-fidelity and high-confidence localizations of nuclear pore complexes, vaults, ribosomes, proteasomes, lipid membranes and microtubules, and individual subunits, demonstrate that TM is generic. We resolve [~]100-kDa proteins, connect the functional states of complexes to their cellular localization, and capture vaults carrying ribosomal cargo in situ. By capturing individual molecular events inside living cells with defined statistical confidence, high-confidence TM greatly speeds up the CryoET workflow and sets the stage for visual proteomics.

molecular biology↗

bioRxiv2019

RAS mutations drive proliferative chronic myelomonocytic leukemia via activation of a novel KMT2A-PLK1 axis

ABSTRACTChronic myelomonocytic leukemia (CMML) is an aggressive hematological malignancy with limited treatment options. Whole exome (WES) and targeted sequencing of several independent cohorts of CMML patients, comparing dysplastic (dCMML) to proliferative (pCMML) CMML, as well as paired chronic phase disease and acute leukemic transformation (LT), associate acquisition of oncogenic RAS pathway mutations, the most common being NRASG12D, with aggressive disease and with disease progression. Using patient derived progenitor colony assays and a NRASG12D-Vav-Cre mouse model, we further demonstrate the role of mutant RAS signaling in driving and maintaining pCMML phenotype. RNA-sequencing links RAS pathway mutations with an increased expression of genes encoding the mitotic checkpoint kinases PLK1 and WEE1. Further, we dmeoinstrated that non-mutated lysine methyltransferase KMT2A (MLL1) acts as mediator of NRAS-induced PLK1 and WEE1 expression. Finally, we demonstrate the translational value of our findings by showing that pharmacological PLK1 inhibition decreases monocytosis and hepatosplenomegaly while improving hematopoiesis in RAS mutant patient-derived xenografts. Hence, we define severe CMML as oncogenic RAS pathway-enriched malignancies, with a unique gene expression profile regulated by KMT2A, amenable to therapeutic intervention.

cancer biology↗