Objective

Secreted proteins regulate human physiology by transducing signals from the extracellular environment into cells and regulating different cellular phenotypes. The human secretome represents a small (~2200 proteins) and biologically relevant screening library that can be used in phenotypic assays. Here, we have used a high-throughput mammalian cell factory approach to generate separately purified and quality assured human secreted proteins. A sample storage and handling process has been established to enable screening of the proteins, at known concentrations, in different cell-based assays. Screening 1000 proteins from the human secretome we show that the FGF9 subfamily, FGF9 and FGF16, are strong proliferators of cardiac progenitor cells. Using the library, we demonstrate that the effect of FGF16 is specific to the cardiac progenitor cells, with no observed effect on cardiac fibroblast proliferation. Additional biophysical binding experiments, using cardiac fibroblasts and cardiac progenitor cells immobilized on a biosensor surface, showed that the interaction of FGF16 and FGF9 with cells on the surface was additive. This suggests that the proteins are signaling through different receptors. Altogether, the data demonstrates how a secretome library can be used across a panel of assays to uncover novel functional information and to aid the discovery of novel signaling pathways and targets relevant to drug discovery.