Differential contributions of ERK and PI3-kinase to the regulation of cyclin D1 expression and to the control of the G1/S transition in mouse embryonic stem cells

Abstract

Mouse embryonic stem (ES) cells are known to express D-type cyclins at very low levels and these levels increase dramatically during in vitro and in vivo differentiation. Here, we investigate some of the signalling pathways regulating expression of cyclin D1 and progression to S phase, the Ras/Extracellular signal-regulated protein kinase (ERK) pathway and the phosphatidylinositol 3-kinase (PI3-kinase) pathway. We demonstrate that ERK phosphorylation is fully dispensable for the regulation of cyclin D1 level and for the progression from G1 to S phase in ES cells. By contrast, PI3-kinase activity is required for both. Differentiation induced by retinoic acid results in the gain of ERK-dependent control of cyclin D1 expression and of S phase progression. Differentiation is also paralleled by an increase in PI3-kinase activity. This leads (a) to an increase in the p70 S6 kinase-dependent regulation of the steady-state level of cyclin D1, and (b) to a concomitant decrease in the GSK3b-dependent rate of cyclin D1 degradation. Altogether, these multiple pathways account for the dramatic increase in the level of cyclin D1 protein which parallels ES cell differentiation. Our studies suggest that PI3-kinase is an important regulator of the ES cell cycle and that its activity is not regulated by mitogen stimulation.

MRP-1/CD9 gene transduction downregulates Wnt signal pathways

“…However, the present study has not shown any significant change in expression in either of these genes. These results might be partly explained by the choice of cell type in the present study, and partly due of the activity of other signal pathways, such as the Ras and ERK pathway for cyclin D1 regulation (Pruitt and Der, 2001;Jirmanova et al, 2002), TGF-b and hepatocyte growth factor for CD44 regulation (Miyazaki et al, 2002;Mine et al, 2003).…”

Regulation of Nanog Expression by Phosphoinositide 3-Kinase-dependent Signaling in Murine Embryonic Stem Cells

“…Maintenance of murine ES cell self-renewal and proliferation are intimately linked, and PI3Ks have been implicated not only in maintenance of self-renewal of ES cells (11,31) but also in regulation of mES cell proliferation (27,29,30,44) and more recently the survival (54) and pluripotency of hES cells (33,54). Our initial report on the role of PI3Ks in self-renewal implicated enhanced activation of ERKs in this response (11), consistent with the view that the balance between STAT3 and ERK signals was key to determining ES cell fate (13).…”

“…PI3K-mediated signaling has been implicated in an array of physiological processes, notably proliferation, cell survival, cell migration, and trafficking (25,26). As observed in many somatic cells, PI3Ks have been reported to control proliferation of mES cells (27)(28)(29)(30), whereas we (11) and others (31,32) have reported that PI3K-mediated signaling is important for maintenance of mES cell pluripotency and very recently that of hES cells (33). Here we have examined the mechanisms regulated by PI3Ks that contribute to maintenance of mES cell self-renewal.…”

Self-renewal of teratocarcinoma and embryonic stem cells

“…Consistent with a prodifferentiative effect of the MAPK pathway, homozygous mutant SHP2 ES cells have enhanced sensitivity to LIF (Qu and Feng, 1998 (Sun et al, 1999) and with the incidence of testicular teratocarcinomas in PTEN À/À mice (Kimura et al, 2003). However, while the PI3K inhibitor LY294002 increases the fraction of ES cells that are in G0/G1 phase of the cell cycle (Jirmanova et al, 2002), the cell cycle status of Eras À cells appears unchanged. This suggests that PI3K may have a cell cycle-independent effect on cell growth and could indicate that LY294002 has an additional effect upon ES cells that alters the cell cycle.…”