Mapping signaling pathway cross-talk in Drosophila cells

Significance A key challenge in understanding cell communication is to characterize the coordinated activity of signaling pathways. A number of studies suggest that signaling pathways can regulate each other by direct control of ligand and receptor expression levels, triggering sequential signaling events in cells. To address the extent of sequential signaling, we profiled the transcriptional responses of ligand and receptor genes to single and combinatorial signaling pathway inductions in cell lines. Our analysis revealed that transcriptional regulation of genes encoding pathway components is a major level of signaling cross-talk, especially in the context of costimulation of signaling pathways. During development and homeostasis, cells integrate multiple signals originating either from neighboring cells or systemically. In turn, responding cells can produce signals that act in an autocrine, paracrine, or endocrine manner. Although the nature of the signals and pathways used in cell–cell communication are well characterized, we lack, in most cases, an integrative view of signaling describing the spatial and temporal interactions between pathways (e.g., whether the signals are processed sequentially or concomitantly when two pathways are required for a specific outcome). To address the extent of cross-talk between the major metazoan signaling pathways, we characterized immediate transcriptional responses to either single- or multiple pathway stimulations in homogeneous Drosophila cell lines. Our study, focusing on seven core pathways, epidermal growth factor receptor (EGFR), bone morphogenetic protein (BMP), Jun kinase (JNK), JAK/STAT, Notch, Insulin, and Wnt, revealed that many ligands and receptors are primary targets of signaling pathways, highlighting that transcriptional regulation of genes encoding pathway components is a major level of signaling cross-talk. In addition, we found that ligands and receptors can integrate multiple pathway activities and adjust their transcriptional responses accordingly.