Cell Stem Cell 10, 171–182 (2012)

Although some extracellular ligands or intracellular regulators are known to affect pluripotency, the mechanisms that govern self-renewal in embryonic stem cells are not well understood. To investigate the relationship among known pathways, Li et al. evaluated the phosphorylation of ERK (pERK) in response to BMP4 or LIF, noting that sustained BMP4 treatment with or without LIF decreased pERK levels and that this response was specific to stem cells. To elucidate the connection between BMP4 signaling and pERK, the authors evaluated both the kinetics and the magnitude of the pERK response in the presence of the translational inhibitor cyclohexamide, demonstrating that new protein synthesis was required and occurred on a time frame consistent with new transcription. Previous chromatin immunoprecipitation sequencing studies had revealed transcriptional effectors downstream of BMP4 localized to the promoter of the Dusp9 gene, which encodes an ERK-specific phosphatase. In stem cells, Dusp9 expression increased in response to BMP4 but not other related ligands. Overexpression of Dusp9 attenuated pERK, whereas expression of a dominant-negative Dusp9 or RNA interference–mediated knockdown of Dusp9 but not Dusp7 enhanced pERK. Dusp9 or small-molecule inhibitors of kinases upstream of ERK substituted for BMP4 to maintain ESC self-renewal. Taken together, these data suggest that, in combination with LIF, Dusp9 mediates BMP4 signaling to attenuate pERK and sustain pluripotency.