Abstract 170: Dissecting components of intercellular communication in a heterogeneous tumor
Authors: Santhanam Balaji , Cheung Yee Him , Agrawal Vartika , Volyanskyy Konstantin , Dimitrova Nevenka 
Published: July 2016

Abstract
Background: Recent advancements in single-cell sequencing technologies have enabled the study of complex biological systems such as tumors. They provide quantification of the extent and nature of the underlying heterogeneity and its impact on the disparate levels of response to therapy. The roles of receptor-ligand signaling in intercellular communication during embryogenesis and, in multicellular development and function is fairly well understood. Intercellular communication within the heterogeneous tumor mass, may proceed through the coordinated action of ligands and their cognate receptors. However, this phenomenon has not been explored in detail, especially in the context of tumor heterogeneity. We propose that a systems-level understanding of ligand- and receptor-states would shed novel insight in to dysregulated pathways in tumorigenesis and perhaps treatment.
Data: By performing single-cell RNA sequencing (RNA-seq) on freshly resected and dissociated primary glioblastomas (GBMs), Bradley Bernstein and colleagues (Patel AP et al, Science 2014) provided novel insights into the underlying heterogeneity at the molecular level. We used the data obtained from 430 cells analyzed by single-cell RNA-seq from five patient samples. The data were mean-centered, log-transformed and included about 6000 genes.
Methods: For our analysis we relied on a comprehensive list of ligand-receptor pairs from Ramilowski JA et al (Nature Communications 2015) and used 137 pairs for which data was available. Based on levels of their expression, we quantized ligand-receptor states and categorized each pair into one of four states. We adopted an unsupervised approach using hierarchical clustering to identify tightly grouped clusters. In order to test for the robustness of the clustering, we used multiscale bootstrapping and identified groups with ITGB1, LRP1, CD44, EGFR as high confidence clusters. We performed these analyses both globally and on individual samples to account for patient genotype differences.
Results: We observed that most of the tightly grouped clusters were ligand-receptor pairs that shared the same receptor. Global clustering revealed enrichment of receptors (ITGB1, ITGA5, EGFR and FGFR1) in pathways relating to signal transduction of L1 and L1CAM interactions. LRP1 and ITGB1 clusters were found in all five samples and pathways relating to hemostasis and extracellular matrix organization, respectively, were enriched.
Discussion: Bernstein et al observed that several receptors and ligands associated with GBM showed mosaic expression even among cells within a given patient sample. We broadened the scope and specifically posed the hypothesis that networks of ligands and receptors are involved in intercellular communication critical to tumor progression and pathogenesis. These molecules may also serve as good therapy targets and more detailed analyses is required to explore this possibility.
Citation Format: Balaji Santhanam, Yee Him Cheung, Vartika Agrawal, Konstantin Volyanskyy, Nevenka Dimitrova. Dissecting components of intercellular communication in a heterogeneous tumor. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 170.