Biology subjects

Koerner, C.

Publications and source records attributed to Koerner, C..

7 recordsLinked to original sources

bioRxiv2025

GLYATL1 is associated with metabolic and epigenetic changes and with endocrine resistance in luminal breast cancer

Estrogen receptor alpha (ER)-positive luminal breast cancer is commonly treated with aromatase inhibitors (AI) to block estrogen signaling; however, resistance frequently develops, limiting therapy success. We observed that GLYATL1 (Glycine-N-Acyltransferase Like 1) expression is upregulated in AI-resistant breast cancer cell models and in patients undergoing AI therapy, correlating with poorer survival. Here we demonstrate that GLYATL1 promotes resistance to estrogen deprivation by elevating succinate levels and altering epigenetic histone marks associated with active transcription. Knockdown or knockout of GLYATL1 reverses these effects and reduces proliferation under estrogen-deprived conditions. Notably, GLYATL1 expression is positively regulated by estrogen receptor alpha signaling independently of estrogen. These findings reveal GLYATL1 as a metabolic and epigenetic mediator of endocrine therapy resistance, suggesting it as a potential target to overcome AI resistance in luminal breast cancer.

cancer biology↗

bioRxiv2025

Molecular requirements for PLK1 activation by T-loop phosphorylation

Activation of PLK1, a master mitotic kinase, requires phosphorylation of its activation segment on Thr210, within a basic consensus sequence for Aurora kinases. Aurora B-dependent phosphorylation of Thr210 has been reported, but other evidence identified a strict requirement for the Aurora A partner Bora for Thr210 phosphorylation. Here, we investigate the elusive mechanistic basis for this requirement. We show that Aurora A:Bora phosphorylates Thr210 of PLK1 in vitro, while Aurora A, other Aurora A:activator complexes, and Aurora B:INCENP fail to target T210 even at high kinase/substrate ratios. A transient interaction of Bora and PLK1, identified by structural modelling and probed mutationally, is uniquely required for Thr210 phosphorylation. Dependency on Bora for Thr210 phosphorylation is eliminated after mutating Lys208, in the Aurora consensus, into arginine. This conservative mutation turns PLK1 into an excellent substrate of nearly all tested active Aurora kinases, especially Aurora B. Collectively, these results shine a new light on the specificity of the PLK1 activation mechanism.

biochemistry↗

bioRxiv2025

PAK1 activation drives divergent resistance mechanisms to aromatase inhibition and Tamoxifen in a luminal A breast cancer model

Breast cancer is the most frequent malignancy and the second leading cause of cancer-related mortality in women worldwide, and is a heterogeneous disease regarding driver mechanisms, therapies, and outcome. Estrogen receptor-positive (ER+) tumors are treated with endocrine therapies such as Tamoxifen or aromatase inhibitors (AI), aimed at disrupting tumor-promoting estrogen signaling. While these therapies are initially effective, resident tumor cells can develop resistance, leading to relapse. The p21-activated kinase 1 (PAK1) is a key regulator of multiple oncogenic signaling pathways and has been implicated in resistance to Tamoxifen. However, it remains unclear, whether PAK1 also affects the response to other endocrine therapies. Using global phosphoproteomic profiling of endocrine resistant cell line models, we observed elevated PAK1 activity in cells resistant to Tamoxifen and to estrogen deprivation, respectively, with further increases following EGF stimulation. Pharmacological inhibition of PAK1 effectively reduced cell proliferation in both resistance models, however, with distinct effects on PAK1 downstream substrates and pathways. In the Tamoxifen resistance context, PAK1 reduces apoptosis via inhibition of the pro-apoptotic protein BAD, whereas in the AI resistance model PAK1 rather triggers proliferation via RAF1. Our findings position PAK1 as a common mediator of resistance to different endocrine therapies and offer insights into the distinct signaling networks that are involved. In summary, our results suggest that targeting PAK1 may present a novel therapeutic strategy to overcome endocrine therapy resistance in ER+ breast cancer, potentially enhancing the efficacy of both Tamoxifen and AI treatments.

cancer biology↗

bioRxiv2025

Molecular anatomy of PLK1 master docking motifs

The Polo-box domain (PBD) localizes Polo-like kinase 1 (PLK1) near mitotic substrates required for chromosome biorientation. Recent work on mitotic kinetochores showed PLK1 docking begins hierarchically at master docking motifs on BUB1 and CENP-U. Whether master docking motifs have common molecular features remains poorly understood. Presence on CENP-U of two neighbouring motifs generated by initial CDK1 priming and subsequent PLK1 phosphorylation led us to hypothesize PBD dimerization might be involved. Using biochemical, biophysical, and modelling approaches, we gathered strong evidence that CENP-U contains a single master docking motif. The motif is very high affinity and sufficient to form extensive interactions with the PBD, engaging multiple pockets on its surface without obvious added benefits from dimerization. Comparisons with motifs in BUB1, BUBR1, and PRC1 suggests apparent commonalities of master PLK1 docking motifs. We discuss the implications of our observations for the mechanism of PLK1 activation.

biochemistry↗

bioRxiv2022

Increased insula activity precedes the formation of subjective Gestalt

The constructive nature of human perception sometimes leads us to perceiving rather complex impressions from simple sensory input. Bistable stimuli give us a rare opportunity to study the neural mechanisms behind this process. Such stimuli can be visually interpreted as simple or as more complex on the basis of the same sensory input. Previous studies demonstrated increased activity in the superior parietal cortex when participants perceived an illusory Gestalt impression compared to a simpler interpretation of individual elements. Here we tested whether activity related to the illusory Gestalt can be detected not only during, but also prior to it, by examining the slow fluctuations of resting-state-fMRI activity before the stimulus onset. We presented 31 participants with a bistable motion stimulus, which can be perceived either as four moving dot pairs (local) or two moving illusory squares (global). This allowed us to isolate the specific neural mechanisms that accompany the experience of an illusion under matched sensory input. fMRI was used to measure brain activity in a sparse event-related design. We observed stronger IPS and putamen responses to the stimulus when participants perceived the global interpretation compared to local, confirming the previously reported role of these areas in perceptual grouping. Most importantly, we also observed that the global stimulus interpretation was preceded by an increased activity of the bilateral dorsal insula, which is known to process saliency and gate information for conscious access. Our data suggest an important role of the dorsal insula in shaping an internally generated illusory Gestalt percept.

neuroscience↗

bioRxiv2021

Reconstitution and use of highly active human CDK1:Cyclin-B:CKS1 complexes

As dividing cells transition into mitosis, hundreds of proteins are phosphorylated by a complex of cyclin-dependent kinase 1 (CDK1) and Cyclin-B, often at multiple sites. CDK1:Cyclin-B phosphorylation patterns alter conformations, interaction partners, and enzymatic activities and need to be recapitulated in vitro for the structural and functional characterization of the mitotic protein machinery. This requires a pure and active recombinant kinase complex. The kinase activity of CDK1 critically depends on the phosphorylation of a Threonine residue in its activation loop by a CDK1 activating kinase (CAK). We developed protocols to activate CDK1:Cyclin-B either in vitro with purified CDK1 activating kinases (CAK) or in insect cells through CDK-CAK co-expression. To boost kinase processivity, we reconstituted a tripartite complex consisting of CDK1, Cyclin-B, and CKS1. In this work, we provide and compare detailed protocols to obtain and use highly active CDK1:Cyclin-B (CC) and CDK1:Cyclin-B:CKS1 (CCC).

biochemistry↗

bioRxiv2018

Kinetochore recruitment of CENP-F illustrates how paralog divergence shapes kinetochore composition and function

The metazoan proteins CENP-E and CENP-F are components of a fibrous layer of mitotic kinetochores named the corona. Several features suggest that CENP-E and CENP-F are paralogs: they are very large (approximately 2700 and 3200 residues, respectively), rich in predicted coiled-coil structure, C-terminally prenylated, and endowed with microtubule-binding sites at their termini. In addition, CENP-E contains an ATP-hydrolyzing motor domain that promotes microtubule plus-end directed motion. Here, we show that CENP-E and CENP- F are recruited to mitotic kinetochores independently of the Rod-Zwilch-ZW10 (RZZ) complex, the main corona constituent. We identify selective interactions of CENP-E and CENP-F respectively with BubR1 and Bub1, paralogous proteins involved in mitotic checkpoint control and chromosome alignment. While BubR1 is dispensable for kinetochore localization of CENP-E, Bub1 is stringently required for CENP-F localization. Through biochemical reconstitution, we demonstrate that the CENP-E:BubR1 and CENP-F:Bub1 interactions are direct and require similar determinants, a dimeric coiled-coil in CENP-E or CENP-F and a kinase domain in BubR1 or Bub1. Our findings are consistent with the existence of pseudo-symmetric, paralogous Bub1:CENP-F and BubR1:CENP-E axes, supporting evolutionary relatedness of CENP-E and CENP-F.

cell biology↗