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Published online 23 February 2004. doi:10.1083/jcb.200312028
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 164, Number 5, 689-699
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*COLCHICINE
*CYTOCHALASIN D
*TRANS-RETINOIC ACID
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Article

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

Elizabeth R. Smith, Jennifer L. Smedberg, Malgorzata E. Rula, and Xiang-Xi Xu

Ovarian Cancer and Tumor Cell Biology Programs, Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, PA 19111

Address correspondence to Xiang-Xi Xu, Ovarian Cancer and Tumor Cell Biology Programs, Dept. of Medical Oncology, Medical Science Division, Fox Chase Cancer Center, 7701 Burholme Ave., Philadelphia, PA 19111. Tel.: (215) 728-2188. Fax: (215) 728-2741. email: X_Xu{at}fccc.edu

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.

Key Words: retinoic acid; c-Fos; Elk-1; cytoskeleton; nucleocytoplasmic translocation


Abbreviations used in this paper: EC, embryonic carcinoma; Erk, extracellular signal–regulated kinase; ES, embryonic stem; LIF, leukocyte inhibitory factor; MEK, MAPK kinase; pErk, phosphorylated MAPK/Erk; PI, propidium iodide; RA, retinoic acid.


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