HTS assays using a disease-relevant cell model for interrogating the MAP kinase pathway initiated by multiple receptors.

In this article we describe the validation of a beta-lactamase reporter assay for high-throughput interrogation of the mitogen-activated protein kinase (MAPK) signaling pathway initiated by multiple receptors. Activation of cell surface receptors, such as epidermal growth factor receptor (EGFR) and cMET, upon ligand binding, leads to the activation of the downstream MAPK signaling pathway and transcription factor, activator protein 1 (AP1), which then induce the expression of genes that are important for cell growth and proliferation. Our MAPK pathway reporter cell line, AP1-bla ME-180, expresses multiple endogenous cell surface receptors. We demonstrate that this reporter assay can be used to monitor the MAPK pathway initiated by cell surface receptors, including EGFR, cMET, and tumor necrosis factor receptor. Our results from Stealth (Invitrogen Corp., Carlsbad, CA) RNA interference and small molecule inhibitor studies suggest that activation of individual kinases of the MAPK pathway is regulated in a ligand-specific manner. The AP1-bla ME-180 reporter cell line can therefore be used to screen for compounds with desired selectivity profiles.

Basic fibroblast growth factor support of human embryonic stem cell self-renewal.

Human embryonic stem (ES) cells have most commonly been cultured in the presence of basic fibroblast growth factor (FGF2) either on fibroblast feeder layers or in fibroblast-conditioned medium. It has recently been reported that elevated concentrations of FGF2 permit the culture of human ES cells in the absence of fibroblasts or fibroblast-conditioned medium. Herein we compare the ability of unconditioned medium (UM) supplemented with 4, 24, 40, 80, 100, and 250 ng/ml FGF2 to sustain low-density human ES cell cultures through multiple passages. In these stringent culture conditions, 4, 24, and 40 ng/ml FGF2 failed to sustain human ES cells through three passages, but 100 ng/ml sustained human ES cells with an effectiveness comparable to conditioned medium (CM). Two human ES cell lines (H1 and H9) were maintained for up to 164 population doublings (7 and 4 months) in UM supplemented with 100 ng/ml FGF2. After prolonged culture, the cells formed teratomas when injected into severe combined immunodeficient beige mice and expressed markers characteristic of undifferentiated human ES cells. We also demonstrate that FGF2 is degraded more rapidly in UM than in CM, partly explaining the need for higher concentrations of FGF2 in UM. These results further facilitate the large-scale, routine culture of human ES cells and suggest that fibroblasts and fibro-blast-conditioned medium sustain human ES cells in part by stabilizing FGF signaling above a critical threshold.