Regulation of Ras–MAPK pathway mitogenic activity by restricting nuclear entry of activated MAPK in endoderm differentiation of embryonic carcinoma and stem cells

Abstract

In response to retinoic acid, embryonic stem and carcinoma cells undergo differentiation to embryonic primitive endoderm cells, accompanied by a reduction in cell proliferation. Differentiation does not reduce the activation of cellular MAPK/Erk, but does uncouple mitogen-activated protein kinase (MAPK) activation from phosphorylation/activation of Elk-1 and results in inhibition of c-Fos expression, whereas phosphorylation of the cytoplasmic substrate p90RSK remains unaltered. Cell fractionation and confocal immunofluorescence microscopy demonstrated that activated MAPK is restricted to the cytoplasmic compartment after differentiation. An intact actin and microtubule cytoskeleton appears to be required for the restriction of MAPK nuclear entry induced by retinoic acid treatment because the cytoskeletal disrupting agents nocodazole, colchicine, and cytochalasin D are able to revert the suppression of c-Fos expression. Thus, suppression of cell proliferation after retinoic acid–induced endoderm differentiation of embryonic stem and carcinoma cells is achieved by restricting nuclear entry of activated MAPK, and an intact cytoskeleton is required for the restraint.

Regulation of CXCR4-Mediated Nuclear Translocation of Extracellular Signal-Related Kinases 1 and 2

“…Finally cytoskeletal disruption can even have the opposite effect. In retinoic acid-treated cells, an intact cytoskeleton is required to restrict activated ERK1/2 to the cytoplasm, and actindisrupting agents lead to increased nuclear ERK1/2 activation (Smith et al, 2004). The role of the cytoskeleton in nuclear translocation of ERK1/2 clearly needs further investigation.…”

“…Cellular distribution of CXCR4-GFP, Alexa 568-stained phospho-ERK1/2, and DAPI-stained nuclei are shown in singlechannel and overlay images. duce senescence (Gaumont-Leclerc et al, 2004) and differentiation (Smith et al, 2004). This ERK activation in the nucleus seems of particular significance in the case of CXCR4, because this receptor is expressed by a variety of metastatic cancer cell.…”

Catecholaminergic Control of Mitogen-Activated Protein Kinase Signaling in Paraventricular Neuroendocrine NeuronsIn VivoandIn Vitro: A Proposed Role during Glycemic Challenges

“…Growing evidence indicates that, on stimulation, ERK1/2 can translocate from the cytoplasm to the nucleus (Cobb and Goldsmith, 2000;Pouysségur and Lenormand, 2003), where it can influence gene expression (Kim and Kahn, 1997;Brunet et al, 1999;Smith et al, 2004). Because, in the single-plane images we acquired, phospho-ERK1/2 immunoreactivity appeared to be mainly in the cytosol, we evaluated whether immunostained cell bodies displayed colocalized signal throughout the entire volume of their cytoplasmic compartment.…”

Activated Ras induces lens epithelial cell hyperplasia but not premature differentiation

“…In many cell types, Ras activation can stimulate proliferation. In some situations, Ras is involved in cellular differentiation (Raucci et al, 2004;Smith et al, 2004). In the present study, we first examined whether specific Ras genes are expressed in the mouse lens during development.…”