Graphlet eigencentralities capture novel central roles of genes in pathways

Motivation Graphlet adjacency extends regular node adjacency in a network by considering a pair of nodes being adjacent if they participate in a given graphlet (small, connected, induced subgraph). Graphlet adjacencies captured by different graphlets were shown to contain complementary biological functions and cancer mechanisms. To further investigate the relationships between the topological features of genes participating in molecular networks, as captured by graphlet adjacencies, and their biological functions, we build more descriptive pathway-based approaches. Contribution We introduce a new graphlet-based definition of eigencentrality of genes in a pathway, graphlet eigencentrality, to identify pathways and cancer mechanisms described by a given graphlet adjacency. We compute the centrality of genes in a pathway either from the local perspective of the pathway or from the global perspective of the entire network. Results We show that in molecular networks of human and yeast, different local graphlet adjacencies describe different pathways (i.e., all the genes that are functionally important in a pathway are also considered topologically important by their local graphlet eigencentrality). Pathways described by the same graphlet adjacency are functionally similar, suggesting that each graphlet adjacency captures different pathway topology and function relationships. Additionally, we show that different graphlet eigencentralities describe different cancer driver genes that play central roles in pathways, or in the crosstalk between them (i.e. we can predict cancer driver genes participating in a pathway by their local or global graphlet eigencentrality). This result suggests that by considering different graphlet eigencentralities, we can capture different functional roles of genes in and between pathwaysThis study received support from the following sources: The European Research Council (ERC) Consolidator Grant 770827 (awarded to NP); The Spanish State Research Agency AEI 10.13039/501100011033 grant number PID2019-105500GB-I00 (awarded to NP); and University College London Computer Science (awarded to SW). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer ReviewedPostprint (published version

Identifying cellular cancer mechanisms through pathway-driven data integration

Abstract Motivation Cancer is a genetic disease in which accumulated mutations of driver genes induce a functional reorganization of the cell by reprogramming cellular pathways. Current approaches identify cancer pathways as those most internally perturbed by gene expression changes. However, driver genes characteristically perform hub roles between pathways. Therefore, we hypothesize that cancer pathways should be identified by changes in their pathway–pathway relationships. Results To learn an embedding space that captures the relationships between pathways in a healthy cell, we propose pathway-driven non-negative matrix tri-factorization. In this space, we determine condition-specific (i.e. diseased and healthy) embeddings of pathways and genes. Based on these embeddings, we define our ‘NMTF centrality’ to measure a pathway’s or gene’s functional importance, and our ‘moving distance’, to measure the change in its functional relationships. We combine both measures to predict 15 genes and pathways involved in four major cancers, predicting 60 gene–cancer associations in total, covering 28 unique genes. To further exploit driver genes’ tendency to perform hub roles, we model our network data using graphlet adjacency, which considers nodes adjacent if their interaction patterns form specific shapes (e.g. paths or triangles). We find that the predicted genes rewire pathway–pathway interactions in the immune system and provide literary evidence that many are druggable (15/28) and implicated in the associated cancers (47/60). We predict six druggable cancer-specific drug targets.This work was supported by the European Research Council (ERC) Consolidator Grant 770827 and the Spanish State Research Agency AEI 10.13039/501100011033 [grant number PID2019-105500GB-I00].Peer ReviewedPostprint (published version

Graphlet laplacians for topology-function and topology-disease relationships

Motivation Laplacian matrices capture the global structure of networks and are widely used to study biological networks. However, the local structure of the network around a node can also capture biological information. Local wiring patterns are typically quantified by counting how often a node touches different graphlets (small, connected, induced sub-graphs). Currently available graphlet-based methods do not consider whether nodes are in the same network neighbourhood. To combine graphlet-based topological information and membership of nodes to the same network neighbourhood, we generalize the Laplacian to the Graphlet Laplacian, by considering a pair of nodes to be ‘adjacent’ if they simultaneously touch a given graphlet. Results We utilize Graphlet Laplacians to generalize spectral embedding, spectral clustering and network diffusion. Applying Graphlet Laplacian-based spectral embedding, we visually demonstrate that Graphlet Laplacians capture biological functions. This result is quantified by applying Graphlet Laplacian-based spectral clustering, which uncovers clusters enriched in biological functions dependent on the underlying graphlet. We explain the complementarity of biological functions captured by different Graphlet Laplacians by showing that they capture different local topologies. Finally, diffusing pan-cancer gene mutation scores based on different Graphlet Laplacians, we find complementary sets of cancer-related genes. Hence, we demonstrate that Graphlet Laplacians capture topology-function and topology-disease relationships in biological networks.This work was supported by the European Research Council (ERC) Starting Independent Researcher [Grant 278212]; the European Research Council (ERC) Consolidator [Grant 770827]; the Serbian Ministry of Education and Science [Project III44006]; the Slovenian Research Agency [project J1-8155]; the Prostate Project and UCL Computer Science departmental funds.Peer ReviewedPostprint (author's final draft

Towards a data-integrated cell

We are increasingly accumulating molecular data about a cell. The challenge is how to integrate them within a unified conceptual and computational framework enabling new discoveries. Hence, we propose a novel, data-driven concept of an integrated cell, iCell. Also, we introduce a computational prototype of an iCell, which integrates three omics, tissue-specific molecular interaction network types. We construct iCells of four cancers and the corresponding tissue controls and identify the most rewired genes in cancer. Many of them are of unknown function and cannot be identified as different in cancer in any specific molecular network. We biologically validate that they have a role in cancer by knockdown experiments followed by cell viability assays. We find additional support through Kaplan-Meier survival curves of thousands of patients. Finally, we extend this analysis to uncover pan-cancer genes. Our methodology is universal and enables integrative comparisons of diverse omics data over cells and tissues.Človeštvo vse bolj kopiči molekularne podatke o celicah, pri tem pa nastaja vedno večji izziv, kako jih vključiti v enoten konceptualni in računalniški okvir, ki bi omogočil nova odkritja. V članku predlagamo nov, na podatkih temelječ koncept integrirane celice, iCell. Prav tako uvajamo računski prototip take celice, ki združuje tri vrste omičnih podatkov, ki so tkivno specifični in se nanašajo na omrežja molekulskih povezav. Predstavimo konstrukcijo iCell na osnovi tkiv štirih vrst raka in ustreznih zdravih tkiv za potrebe kontrolnih skupin in identificiramo gene, ki so pri raku najbolj povezani z drugimi geni. Mnogi od njih imajo neznane funkcije v celici in jih v nobenem posamičnem molekularnem omrežju ni mogoče opredeliti kot statistično izstopajoče pri rakavih obolenjih. Njihovo vlogo pri raku biološko potrdimo s t.i. knockdown poskusi, ki jim sledijo še testi sposobnosti preživetja celic. Dodatno podporo našim ugotovitvam najdemo tudi v Kaplan-Meierjeve krivuljah preživetja več tisoč bolnikov. Na koncu analizo razširimo na iskanje pomembnih genov, ki so skupni več rakavim obolenjem. Naša metodologija je univerzalna in omogoča integrativne primerjave različnih omičnih podatkovnih virov preko celic in tkiv