Study of MAPK Signaling Using Knockout Mice
The p42 and p44 mitogen-activated protein kinases (MAPKs) (p42/p44 MAPK, Erk2 /Erk1) are activated through the small G protein Ras and sequential activation of the protein kinases Raf and MEK on stimulation of cells with a broad range of extracellular signals (1,2). This signaling pathway, conserved in evolution, controls cell fate, differentiation, proliferation, and cell survival in various invertebrates, mammalian cells, and plants (3, 4, 5, 6, 7). To understand the specific role of the commonly expressed and activated p42 and p44 MAPK isoforms in the whole animal, we generated p44 MAPK–deficient mice through homologous recombination in embryonic stem (ES) cells (8). p44 MAPK null mice are viable, fertile, and of normal size. This result indicates that p44 MAPK is dispensable and that the second isoform, p42 MAPK, can compensate for the loss of p44 MAPK. Loss of the p44 MAPK isoform does not affect expression of p42 MAPK in all the tissues tested even in the sciatic nerve, the only tissue in which p44 MAPK is expressed at higher levels than p42 MAPK (1). We previously established that p42/p44 MAPK nuclear translocation (9) and persistent activation during the G1 phase of the cell cycle is a prerequisite for growth control in fibroblasts (10). Thus, it was crucial to analyze the temporal activation of p42/p44 MAPKs and reinitiation of DNA synthesis in wild-type and p44 MAPK–deficient mouse embryo fibroblasts (MEFs). The growth rate as well as reinitiation of DNA synthesis in serum-starved MEFs is not significantly impaired by the ablation of both alleles of p44 MAPK gene (8)
Boulton, T. G., Nye, S. H., Robbins, D. J., et al. (1991) ERKs: a family of proteinserine/threonine kinases that are activated and tyrosine phosphorylated in response to insulin and NGF. Cell
, 663–675.PubMedCrossRefGoogle Scholar
Ahn, N. G., Seger, R., and Krebs, E. G. (1992) The mitogen-activated protein kinase activator. Curr. Opin. Cell Biol.
, 992–999.PubMedCrossRefGoogle Scholar
Nishida, E., and Gotoh, Y. (1993) The MAP kinase cascade is essential for diverse signal transduction pathways. Trends Biochem. Sci.
, 128–131.PubMedCrossRefGoogle Scholar
Marshall, C. J. (1995) Specificity of receptor tyrosine kinase signaling: transient versus sustained extracellular signal-regulated kinase activation. Cell
, 179–185.PubMedCrossRefGoogle Scholar
Brunet, A. and Pouyssegur, J. (1997) Mammalian MAP kinase modules: how to transduce specific signals. Essays Biochem.
, 1–16.PubMedGoogle Scholar
Ligterink, W. and Hirt, H. (2001) Mitogen-activated protein (MAP) kinase pathways in plants: versatile signaling tools. Int. Rev. Cytol.
, 209–275.PubMedCrossRefGoogle Scholar
Bent, A. F. (2001) Plant mitogen-activated protein kinase cascades: negative regulatory roles turn out positive. Proc. Natl. Acad. Sci. USA
, 784–786.PubMedCrossRefGoogle Scholar
Pagès, G., Guerin, S., Grall, D., et al. (1999) Defective thymocyte maturation in p44 MAP kinase (Erk 1) knockout mice. Science
, 1374–1377.PubMedCrossRefGoogle Scholar
Brunet, A., Roux, D., Lenormand, P., et al. (1999) Nuclear translocation of p42/p44 mitogen-activated protein kinase is required for growth factor-induced gene expression and cell cycle entry. EMBO J.
, 664–674.PubMedCrossRefGoogle Scholar
Pagès, G., Lenormand, P., L’Allemain, G., et al. (1993) Mitogen-activated protein kinases p42mapk
are required for fibroblast proliferation. Proc. Natl. Acad. Sci. USA
, 8319–8323.PubMedCrossRefGoogle Scholar
Pagès, G., Stanley, R., Legal, M., et al. (1995) The mouse p44 Mitogen-Activated Protein kinase (extracellular signal-regulated kinase 1) gene. J. Biol. Chem.
, 26,986–26,992.PubMedCrossRefGoogle Scholar
Boulton, T. G., Yancopoulos, G. D., Gregory, J. S., et al. (1990) An insulin-stimulated protein kinase similar to yeast kinases involved in cell cycle control. Science
, 64–67.PubMedCrossRefGoogle Scholar
Mansour, S. L., Thomas, K. R., and Capecchi, M. R. (1988) Disruption of the proto-oncogene int-2 in mouse embryo-derived stem cells: a general strategy for targeting mutations to non-selectable genes. Nature
, 348–352.PubMedCrossRefGoogle Scholar
McKenzie, F. R. and Pouyssegur, J. (1996) cAMP-mediated growth inhibition in fibroblasts is not mediated via mitogen-activated protein (MAP) kinase (ERK) inhibition. cAMP-dependent protein kinase induces a temporal shift in growth factor-stimulated MAP kinases. J. Biol. Chem.
, 13,476–13,483.PubMedCrossRefGoogle Scholar
Guerin, S., Mari, B., Fernandez, E., et al. (1997) CD10 is expressed on human thymic epithelial cell lines and modulates thymopentin-induced cell proliferation. FASEB J.
, 1003–1011.PubMedGoogle Scholar
te Riele, H., Maandag, E. R., and Berns, A. (1992) Highly efficient gene targeting in embryonic stem cells through homologous recombination with isogenic DNA constructs. Proc. Natl. Acad. Sci. USA
, 5128–5132.CrossRefGoogle Scholar
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