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Miihkinen, M.

Publications and source records attributed to Miihkinen, M..

12 recordsLinked to original sources

Paired activity learning supports systematic identification of mutant-selective EGFR inhibitors

Acquired resistance to epidermal growth factor receptor (EGFR) inhibitors remains a major clinical challenge in non-small cell lung cancer (NSCLC), where successive rounds of therapy with first- and third-generation EGFR inhibitors often lead to increasingly resistant EGFR variants. In particular, EGFR L858R/T790M/C797S triple mutation renders tumors resistant to earlier-generation inhibitors, while disrupting the covalent engagement required by third-generation inhibitors such as osimertinib. Here, we developed an integrated computational-experimental framework for identifying compounds with differential activity between the triple-mutant EGFR and wild-type EGFR. Matched bioactivity measurements were leveraged to train a mutant-aware paired-activity regression framework, and the predicted candidates meeting stringent potency and mutant-preference criteria were subsequently evaluated using a support vector machine classifier for triple-mutant activity. Application of this sequential screening approach to 12 million molecules identified 16 consensus hits, including several previously reported inhibitors of drug-resistant EGFR variants. Based on their predicted differential activity and degree of prior characterization, five hit compounds were prioritized for initial biochemical evaluation, and two were selected for further biochemical, cellular and structural characterization. Mutant EGFR crystal structures in complex with the best-performing compounds revealed two distinct noncovalent binding modes within the ATP-binding cleft, demonstrating the ability of the framework to identify potent inhibitors with diverse binding modes. Together, this work illustrates how incorporating mutant-selectivity into a predictive framework as paired activities support the identification of mutant EGFR inhibitors and provide insights into their potency and selectivity. The discovered complementary structures provide experimentally defined templates for optimizing potency, mutant preference and drug-like properties of these and future compounds combating drug resistant NSCLC.

bioinformatics↗

Domain-adversarial learning predicts clinically actionable drug combination synergy in leukemia patients using bulk transcriptomics data

Deep learning has gained popularity in drug combination synergy prediction; however, DL models require large training datasets from cell line pharmacogenomic screens that poorly capture the heterogeneity in transcriptomic features and phenotypic responses seen in patients. To that end, we developed a domain-adversarial neural network (DANN) for personalized drug synergy prediction that accounts for systematic differences between cell line and patient domains. In applications to AML and CLL patient samples, we demonstrate how DANN boosts prediction accuracy under realistic data constraints. The model predictions demonstrated elevated synergy among clinically used combinations, such as venetoclax-based regimens, supporting its ability to identify both pharmaceutically and clinically meaningful combinations. DANN estimates prediction uncertainty and prioritizes high-confidence combination predictions to aid clinical translation. Together, DANN provides a systematic approach to improving accuracy and reliability in cross-domain drug synergy prediction, advancing the development of methods that are aligned with the translational requirements of precision hematology.

cancer biology↗

Filopodome proteomics identifies CCT8 as a MYO10 interactor critical for filopodia functions

Cancer cells utilize filopodia to explore, adhere to, and invade their surrounding microenvironment, yet the protein networks that organize these protrusions remain incompletely defined. To uncover the molecular machinery underlying MYO10-positive filopodia, we targeted the fast biotin ligase TurboID to the filopo-dia tip-localized motor protein MYO10. Proximity biotinylation in two cell types revealed hundreds of potential MYO10 interactors. Surprisingly, there was limited overlap between the cell lines, indicating a previously unknown level of cell-type specificity in filopodia composition. A targeted microscopy and siRNA screen identified MINK1, SCRIB, CSNK1A1, and CCT8 as new regulators of filopodia formation. Focusing on one common interactor between cell lines, CCT8, known as a subunit of the chaperonin TRiC (TCP1 Ring Complex), we found that CCT8 associates with the MYO10 motor domain and regulates MYO10 filopodia independently of TRiC. Depleting CCT8 affected filopodia dynamics and impaired cell spreading, migration, and invasion in breast cancer cells. These findings establish CCT8 as a TRiC-independent regulator of MYO10 filopodia across different cancer cell types, highlight the surprising cell-type-specificity of filopodia composition, and provide a strategy and resource for studying filopodia in various biological contexts.

cell biology↗

Off-target mapping enhances selectivity of machine learning-predicted CK2 inhibitors

A key challenge in drug development is identification of druggable targets, the modulation of which attenuates disease progression, while avoiding inhibition of proteins that lead to dose-limiting toxicities. Here, we investigate a drug target casein kinase 2 (CK2) - a serine/threonine kinase implicated in cancer, for which existing inhibitors have so far failed in clinical trials. Using molecular and pharmacoepidemiology approaches, we show that small molecules targeting cyclin-dependent kinase (CDK) family members CDK1/2/7/9, including the existing CK2 inhibitors, have a higher risk to induce adverse effects or fail in clinical trials. Based on this finding, we establish a machine learning (ML) assisted discovery pipeline to redesign more specific and allosteric lead compounds against CK2, with a more selective on-target binding and favourable off-target profile. Importantly, we show that such selective design is possible when standard molecular docking and ML algorithms are combined with an error prediction model. In conclusion, our study reports a simple yet efficient ML-powered drug discovery pipeline and novel submicromolar inhibitors targeting clinically relevant CK2 kinase with no clinically approved antagonists available. Our prediction pipeline was able to achieve a 90% hit-rate, significantly reducing the need for subsequent wet-lab validation.

pharmacology and toxicology↗

High-resolution integrative analysis allows characterization and spatial annotation of normal and cancer-associated colon fibroblasts

Fibroblasts represent key regulators of colon homeostasis, and cancer-associated fibroblasts (CAFs) play pivotal roles in colorectal cancer (CRC). Despite their critical influence, a consensus view of adult human colon fibroblast and CRC CAF heterogeneity, spatial organization, and developmental trajectories is currently lacking. Here, we address this gap by performing a comprehensive characterization of colonic fibroblasts and CRC CAFs. Using large-scale integration of single-cell RNA-sequencing datasets from normal colon and CRC we mapped the fibroblast subpopulations. Spatial transcriptomics, immunohistochemistry, and in situ hybridization were used for validation and computational analyses to predict developmental trajectories and transcription factors underlying CAF activation. Subepithelial myofibroblasts (SEMFs), mucosa-associated fibroblasts (MAFs), and submucosa-associated fibroblasts (SAFs) were identified as the main colon fibroblast subtypes, and in mice, further divided into location-based subclusters. We also identified a novel colon fibroblast subset: muscle-embedded interstitial fibroblasts (MIFs). CRCs contained normal fibroblasts as well as four cancer-specific CAF populations: inflammatory CAFs (iCAFs), matrix CAFs (mCAFs), and two precursor CAF (preCAF) subtypes. Our data suggested that iCAFs originate from SEMFs through a preCAF1 intermediate phenotype, while mCAFs derive from SAFs/MIFs via preCAF2s. Transcription factors PRRX1, MAFB, and TWIST1 were uncovered as potential regulators of CAF identity and CTHRC1 was identified as a specific and sensitive pan-CAF marker in CRC. Our study presents a detailed framework for understanding colon fibroblast and CRC CAF heterogeneity. This work lays the groundwork for future research into the roles and potential therapeutic relevance of different CRC CAF subsets.

cancer biology↗

Completeness estimation of large-scale single-cell sequencing projects

During embryonic development, cells undergo differentiation into highly specialized cell types. Capitalizing on single-cell RNA sequencing, many initiatives and substantial resources have been established for cataloguing these differentiated cell types by their transcriptomic profiles. Despite the extensive efforts to profile various organs and their cellular compositions, we lack metrics to assess the completeness of the sequencing projects. In this cellular biodiversity analysis, we leveraged the increasingly available single-cell data together with statistical methods, originally developed for assessing the species richness of ecological communities, to estimate the cellular diversity of any organ based on current data from single-cell profiling technologies. Deriving from such cellular richness estimates, we established a practical statistical framework that enables reliable assessment of the completeness of any large-scale single-cell profiling projects, after which additional sequencing efforts do not anymore reveal new insights into an organs cellular composition. Such estimates can serve as stoppage-points for the ongoing sequencing projects, hence guiding a more cost-efficient completion of the profiling of various human tissues.

cell biology↗

Myosin-X recruits lamellipodin to filopodia tips

Myosin-X (MYO10), a molecular motor localizing to filopodia, is thought to transport various cargo to filopodia tips, modulating filopodia function. Yet, only a few MYO10 cargoes have been described. Here, using GFP-Trap and BioID approaches combined with mass spectrometry, we identified lamellipodin (RAPH1) as a novel MYO10 cargo. We report that the FERM domain of MYO10 is required for RAPH1 localization and accumulation at filopodia tips. Previous studies have mapped RAPH1 interaction with adhesome components to its talinbinding and Ras-association domains. Surprisingly, we find that the RAPH1 MYO10-binding site is not within these domains. Instead, it comprises an area with previously unknown functions. Functionally, RAPH1 supports MYO10 filopodia formation and stability but is not involved in regulating integrin activity in filopodia tips. Taken together, our data indicate a feed-forward mechanism whereby MYO10 filopodia are positively regulated by MYO10-mediated transport of RAPH1 to the filopodium tip.

cell biology↗

Conformational dynamics regulate SHANK3 actin and Rap1 binding

Actin-rich cellular protrusions direct versatile biological processes from cancer cell invasion to dendritic spine development. The stability, morphology and specific biological function of these protrusions are regulated by crosstalk between three main signaling axes: integrins, actin regulators and small GTPases. SHANK3 is a multifunctional scaffold protein, interacting with several actin-binding proteins, and a well-established autism risk gene. Recently, SHANK3 was demonstrated to sequester integrin-activating small GTPases Rap1 and R-Ras to inhibit integrin activity via its N-terminal SPN domain. Here, we demonstrate that SHANK3 interacts directly with actin using its SPN domain. Actin binding can be inhibited by an intramolecular closed conformation of SHANK3, where the adjacent ARR domain covers the actin-binding interface of the SPN domain. Actin and Rap1 compete with each other for binding to SHANK3 and loss of SHANK3-actin binding augments inhibition of Rap1-mediated integrin activity. This dynamic crosstalk has functional implications for filopodia formation in cancer cells, dendritic spine morphology in neurons and autism-linked phenotypes in vivo.

cell biology↗

Myosin-X is required for integrin activation at filopodia tips

Filopodia assemble unique integrin-adhesion complexes to sense the extracellular matrix. However, the mechanisms of integrin localization and regulation in filopodia are poorly defined. Here, we observed that active integrins accumulate at the tip of myosin-X(MYO10)-positive filopodia while inactive integrins are uniformly distributed. RNAi depletion of 10 integrin activity modulators identified talin as the principal integrin activator in filopodia. Deletion of the MYO10-FERM domain, or mutation of the {beta}1-integrin-binding residues within, revealed MYO10 as facilitating integrin activation but not transport in filopodia. However, MYO10-FERM alone could not activate integrins, potentially due to dual binding to both a- and {beta}-integrin tails. As swapping MYO10-FERM with talin-FERM enabled integrin activation in filopodia, our data indicate that an integrin-binding FERM domain coupled to a myosin motor is a core requirement for integrin activation in filopodia. Therefore, we propose a two-step integrin activation model in filopodia: receptor tethering by MYO10 followed by talin-mediated integrin activation.

cell biology↗

Superresolution architecture of pluripotency guarding adhesions

Human pluripotent stem cells (hPSC) can generate almost all adult cell lineages. While it is clear that key transcriptional programmes are important elements for maintaining pluripotency, the equally essential requirement for cell adhesion to specific extracellular matrix components remains poorly defined. Our recent observation that hPSC colonies form unusually large \"cornerstone\" focal adhesions (FA), distinct from parental somatic cells, that are lost following differentiation, emphasises the potential of these atypical FA as gatekeepers of pluripotency. Here, using nanopatterns, we further demonstrate that physical restriction of adhesion size, in hPSC colonies, is sufficient to trigger differentiation. Using superresolution two-colour interfero-metric photo-activated localization microscopy (iPALM), we examined the three-dimensional architecture of these cornerstone adhesions and report vertical lamination of FA proteins with three main structural peculiarities: 1) integrin {beta}5 and talin are present at high density, at the edges of cornerstone FA, adjacent to a vertical kank-rich protein wall. 2) Vinculin localises higher than expected with respect to the substrata and displays a head-above-tail orientation, and 3) surprisingly, actin and -actinin are present in two discrete layers, a previously undescribed localisation for these proteins. Finally, we report that depletion of kanks diminishes FA patterning, and actin organisation within the colony, indicating a key role for kanks in hPSC colony architecture.

cell biology↗

Filopodome mapping identifies p130Cas as a mechanosensitive regulator of filopodia stability

Filopodia are adhesive cellular protrusions specialised in the detection of extracellular matrix (ECM)-derived cues. While ECM engagement at focal adhesions is known to trigger the recruitment of hundreds of proteins (\"adhesome\") to fine-tune cellular behaviour, the components of the filopodia adhesions remain undefined. Here, we performed a structured illumination microscopy-based screen to map the localisation of 80 target proteins, linked to cell adhesion and migration, within filopodia. We demonstrate preferential enrichment of several adhesion proteins to either filopodia tips, filopodia shafts, or shaft subdomains suggesting divergent, spatially restricted functions for these proteins. Moreover, proteins with phospho-inositide (PI) binding sites are particularly enriched in filopodia. This, together with the strong localisation of PI(3,4)P2 in filopodia tips, predicts critical roles for PIs in regulating filopodia ultra-structure and function. Our mapping further reveals that filopodia adhesions consist of a unique set of proteins, the filopodome, that are distinct from classical nascent adhesions, focal adhesions and fibrillar adhesions. Using live imaging, we observe that filopodia adhesions can give rise to nascent adhesions, which, in turn, form focal adhesions. Finally, we demonstrate that p130Cas (BCAR1) is recruited to filopodia tips via its CCHD domain and acts as a mechanosensitive regulator of filopodia stability.

cell biology↗

ProLIF: a quantitative assay for investigating integrin cytoplasmic protein interactions and synergistic membrane effects on proteoliposomes

Integrin transmembrane heterodimeric receptors control a wide range of biological interactions by triggering the assembly of large multiprotein complexes at their cytoplasmic interface. A diverse set of methods have been used to investigate cytoplasmic interactions between integrins and intracellular proteins. These predominantly consist of peptide-based pull-downs and biochemical immuno-isolations from detergent-solubilized cell lysates. However, quantitative methods to probe integrin-protein interactions in a more biologically relevant context where the integrin is embedded within a lipid bilayer have been lacking. Here we describe a technique called ProLIF (Protein-Liposome Iinenteractions by Flow cytometry) to reconstitute recombinant integrin transmembrane domain (TMD) and cytoplasmic tail (CT) fragments on liposomes as individual or {beta} subunits or as {beta} heterodimers and, using flow cytometry, to rapidly and quantitatively measure protein interactions with these membrane-embedded integrins. Importantly, the assay can analyse binding of fluorescent proteins directly from cell lysates without further purification steps. By combining integrins with membrane lipids to generate proteoliposomes, the effects of membrane composition such as PI(4,5)P2 presence on protein recruitment to the integrin CTs can be analyzed. ProLIF requires no specific instrumentation, apart from a standard flow cytometer and can be applied to measure a broad range of membrane-dependent protein-protein interactions with the potential for high-throughput/multiplex analyses.

molecular biology↗