Metastatic cell homing is a complex process mediated in part by diffusible factors secreted from immune cells found at a pre-metastatic niche. We report on connecting secretomics and TRanscriptional Activity CEll aRray (TRACER) data to identify functional paracrine interactions between immune cells and metastatic cells as novel mediators of homing. Metastatic breast cancer mouse models were used to generate a diseased splenocyte conditioned media (D-SCM) containing immune cell secreted factors. MDA-MB-231 metastatic cell activity including cell invasion, migration, transendothelial migration, and proliferation were increased in D-SCM relative to control media. Our D-SCM secretome analysis yielded 144 secreted factor candidates that contribute to increased metastatic cell activity. The functional mediators of homing were identified using MetaCore software to determine interactions between the immune cell secretome and the TRACER-identified active transcription factors within metastatic cells. Among the 5 candidate homing factors identified, haptoglobin was selected and validated in vitro and in vivo as a key mediator of homing. Our studies demonstrate a novel systems biology approach to identify functional signaling factors associated with a cellular phenotype, which provides an enabling tool that complements large-scale protein identification provided by proteomics.
Bibliographical noteFunding Information:
We thank Dr. Ji Yi for his assistance with SEM imaging, Dr. Karla Satchell for IVIS access, and Katie Aguado for illustrating the mouse image in our schematic. This research was supported by the National Institutes of Health (R01CA173745) and the Northwestern H Foundation Cancer Research Award. The content is solely the responsibility of the authors and does not necessarily represent the official views of the H Foundation. B.A.A. and G.G.B. are recipients of National Science Foundation Graduate Research Fellowships. Dr. Vincent Cryns, Dr. Andrew Mazar, and the Northwestern University Developmental Therapeutics Core developed the 231BR cells and the orthotopic tumor model. The Northwestern Flow Cytometry Facility and a Cancer Center Support Grant (NCI CA060553) supported flow cytometry work. The Northwestern University Proteomics Core Facility supported secretomics analysis. The Simpson Querrey Institute Equipment Core provided Cytation 3 access.