C/EBPbeta sustains undifferentiated state of murine embryonic stem cells as a mediator of LIF.

C/EBPbeta (also called NF-IL6) is a multifunctional transcription factor, a major function of which is the enhancement of cellular differentiation. Leukemia inhibitory factor (LIF) is a cytokine playing divergent roles in different cell types: induces differentiation in preadipocytes and, however, inhibits differentiation in pluripotent murine embryonic stem (mES) cells. However, roles of C/EBPbeta in mES cells are obscure. Here, we show for the first time that C/EBPbeta in the presence of LIF plays a role of sustaining undifferentiated state in this cell line, i.e. C/EBPbeta is a target of regulation of LIF, as described as follows. The expression of endogenous C/EBPbeta proteins in mES cells is positively correlated with the LIF added into medium. Even the exogenous C/EBPbeta proteins and their truncated form, LIP, artificially overexpressed in undifferentiated mES cells, do not enhance but inhibit ES cells' differentiation in the presence of LIF, and the long isoforms of C/EBPbeta proteins strongly enhance cell propagation. This enhancement lasts for a certain short time even after LIF removal. In the absence of LIF, C/EBPbeta and LIP induce expression of differentiation-related genes and promote mES cells' differentiation, as anticipated. With LIF, the expression levels of some differentiation-related genes regulated by C/EBPbeta and LIP were significantly lower than that without LIF. Therefore, in pluripotent mES cells C/EBPbeta is regulated by LIF and sustains undifferentiated state of those cells as a mediator of LIF.