Opposing Roles of the Extracellular Signal-Regulated Kinase and p38 Mitogen-Activated Protein Kinase Cascades in Ras-Mediated Downregulation of Tropomyosin
Open Access
- 1 April 2002
- journal article
- Published by Informa UK Limited in Molecular and Cellular Biology
- Vol. 22 (7), 2304-2317
- https://doi.org/10.1128/mcb.22.7.2304-2317.2002
Abstract
We showed previously that activated Ras, but not Raf, causes transformation of RIE-1 epithelial cells, demonstrating the importance of Raf-independent pathways in mediating Ras transformation. To assess the mechanism by which Raf-independent effector signaling pathways contribute to Ras-mediated transformation, we recently utilized representational difference analysis to identify genes expressed in a deregulated fashion by activated Ras but not Raf. One gene identified in these analyses encodes for α-tropomyosin. Therefore, we evaluated the mechanism by which Ras causes the downregulation of tropomyosin expression. By using RIE-1 cells that harbor inducible expression of activated H-Ras(12V), we determined that the downregulation of tropomyosin expression correlated with the onset of morphological transformation. We found that the reversal of Ras transformation caused by inhibition of extracellular signal-regulated kinase activation corresponded to a restoration of tropomyosin expression. Inhibition of p38 activity in Raf-expressing RIE-1 cells caused both morphological transformation and loss of tropomyosin expression. Thus, a reduction in tropomyosin expression correlated strictly with morphological transformation of RIE-1 cells. However, forced overexpression of tropomyosin in Ras-transformed cells did not reverse morphological or growth transformation, a finding consistent with the possibility that multiple changes in gene expression contribute to Ras transformation. We also determined that tropomyosin expression was low in two human tumor cell lines, DLD-1 and HT1080, that harbor endogenous mutated alleles of ras, but high in transformation-impaired, derivative cell lines in which the mutant ras allele has been genetically deleted. Finally, treatment with azadeoxycytidine restored tropomyosin expression in Ras-transformed RIE-1, HT1080, and DLD-1 cells, suggesting a role for DNA methylation in downregulating tropomyosin expression.Keywords
This publication has 72 references indexed in Scilit:
- Oncogenic Ras Blocks Anoikis by Activation of a Novel Effector Pathway Independent of Phosphatidylinositol 3-KinaseMolecular and Cellular Biology, 2001
- NF-κB is required for H-ras oncogene induced abnormal cell proliferation and tumorigenesisOncogene, 2000
- Suppression of src-induced transformed phenotype by expression of tropomyosin-1Oncogene, 1999
- Ras, but not Src, transformation of RIE-1 epithelial cells is dependent on activation of the mitogen-activated protein kinase cascadeOncogene, 1998
- New 5′ Regions of the Murine and Human Genes for DNA (Cytosine-5)-methyltransferaseJournal of Biological Chemistry, 1996
- Restoration of microfilament bundle organization in v-raf-transformed NRK cells after transduction with tropomyosin 2 cDNACancer Letters, 1994
- Phosphatidylinositol-3-OH kinase direct target of RasNature, 1994
- Altered Growth of Human Colon Cancer Cell Lines Disrupted at Activated Ki- rasScience, 1993
- Two-dimensional electrophoretic analysis of transformation-sensitive polypeptides during chemically, spontaneously, and oncogene-induced transformation of rat liver epithelial cellsElectrophoresis, 1992
- Suppression of synthesis of tropomyosin isoform 2 in metastatic v-Ha-ras-transformed NIH3T3 cellsBiochemical and Biophysical Research Communications, 1988