Phenotypic screening of signaling motifs that efficiently induce cell proliferation.

Since cell proliferation is one of the fundamental cell fates, artificial control of cell proliferation based on a receptor-engineering approach is increasingly important in therapeutic and industrial applications. Since the signal transduction properties of cytokine receptors are greatly influenced by the amino acid sequence of tyrosine motifs, here we develop a phenotypic screening approach that can directly select cell proliferation-inducing tyrosine motifs from a synthetic library. In the tyrosine motif library, amino acid sequences around the tyrosine are randomized to attain diverse binding patterns of signaling molecules. Theoretically, engineered receptors with distinct tyrosine motifs would activate signaling molecules in diverse patterns. Thus, we investigated whether tyrosine motif sequences capable of inducing cell proliferation could be selected from the cellular library expressing the motif-engineered receptors. Consequently, the selected motifs induced similar levels of cell proliferation compared to the cytoplasmic signaling domain of a native receptor. The motif-screening system was applicable to cells that may differentiate or proliferate depending on cytokine signals. To our best knowledge, this is the first report demonstrating phenotypic screening of tyrosine motifs in living cells. Our approach would open up new possibilities in the field of artificial control of cell fate based on signal transduction engineering.