The Ribosomal S6 Kinases, cAMP-responsive Element-binding, and STAT3 Proteins Are Regulated by Different Leukemia Inhibitory Factor Signaling Pathways in Mouse Embryonic Stem Cells

Abstract

Mouse embryonic stem (ES) cells remain "pluripotent"in vitro in the continuous presence of leukemia inhibitory factor (LIF). In the absence of LIF, ES cells are irreversibly committed to differentiate into various lineages. In this study we have set up an in vitro assay based on the anti-apoptotic activity of LIF to distinguish pluripotent from "differentiation-committed" ES cells. We have examined the phosphorylation profiles of known (STAT3 and ERKs) and identified new (ribosomal S6 kinases (RSKs) and cAMP-responsive element-binding protein (CREB)) LIF-regulated targets in ES and in ES-derived neuronal cells. We have demonstrated that although STAT3, a crucial player in the maintenance of ES cell pluripotency, is induced by LIF in all cell types tested, the LIF-dependent activation of RSKs is restricted to ES cells. We have shown that LIF-induced phosphorylation of RSKs in ES cells is dependent onERKs, whereas STAT3 phosphorylation is not mediated by any known MAPK activities. Our results also demonstrate that the LIF-dependent phosphorylation of CREB is partially under the control of the RSK2 kinase.

Ataxia Telangiectasia Mutated Proteins, MAPKs, and RSK2 Are Involved in the Phosphorylation of STAT3

“…ERK2) (52). Furthermore, STAT3 has been shown to be an oncogene (53) and is activated concomitant with MAPKs and RSKs following stimulation of some oncogenes by UVA or UVC (29,33,39) (reviewed in Refs. 7, 8, 49, and 54).…”

“…RSKs) of MAPKs in the phosphorylation process. Furthermore, RSKs and STAT3, as well as their upstream MAPKs, were reported to be concomitantly activated and to play a role in controlling cell development, growth, and survival (33), suggesting that a certain association existed between MAPKs/RSKs and STAT3. Here, we find that RSKs are also required for phosphorylation of STAT3 (Ser 727 ) following exposure of cells to UVA or UVC (200 -290 nm).…”

Apoptosis and differentiation commitment: novel insights revealed by gene profiling studies in mouse embryonic stem cells

“…36 Indeed, the property of ES cells to colonize blastocyst is rapidly lost upon ES cell differentiation, a process irreversibly committed two days upon LIF withdrawal. 37,38 Fluorescent ES cell clones overexpressing, EGFP alone (control), EGFP-PD-induced fusion genes (bcl2 as a positive control; 20 metallothionein 1 (met1); Annexin A3 (Ann) and calcyclin (cal)) and one EGFP-PD-repressed fusion gene (pim2), were aggregated overnight with wild-type morulas and followed for 2 days up to the formation of the blastocyst stage (Materials and Methods) ( Figure 3a). Control ES cells can colonize blastocysts with a good efficiency, when grown with LIF and serum.…”

A p38 inhibitor allows to dissociate differentiation and apoptotic processes triggered upon LIF withdrawal in mouse embryonic stem cells

“…[6][7][8] While some molecular determinants of ES cell pluripotency are well characterized, like the fibroblast growth factor-4 (FGF-4) and the signal transducer and activator of transcription 3 (STAT3), OCT-4 and NANOG transcription factors, much less is known about the intricate processes of differentiation that start within 36 h upon LIF withdrawal in ES cells. [9][10][11][12][13][14][15] Cell differentiation and apoptosis are linked and we have shown that upon LIF withdrawal, part of the cells die through apoptosis, concomitantly with an activation of the p38 mitogen-activated protein kinase (MAPK), but independently of the caspase-dependent cleavage of the poly-(ADP ribose) polymerase (PARP)-1 substrate. 16 A LIF-dependent cell survival effect on primordial germ cells has also been described, but the molecular determinants of the antiapoptotic effect of LIF have not been characterized yet.…”