Loss of transgelin in breast and colon tumors and in RIE-1 cells by Ras deregulation of gene expression through Raf-independent pathways.
Activated Ras but not Raf can transform RIE-1 and other epithelial cells, indicating the critical importance of Raf-independent effector function in Ras transformation of epithelial cells. To elucidate the nature of these Raf-independent activities, we utilized representational difference analysis to identify genes aberrantly expressed by Ras through Raf-independent mechanisms in RIE-1 cells. We identified a total of 22 genes, both known and novel, whose expression was either activated or abolished by Ras but not Raf. The genes up-regulated encode proteins involved in protein or DNA synthesis, regulation of protease activity, or ligand binding, whereas those genes down-regulated encode actin cytoskeletal-, extracellular matrix-, and gap junction-associated proteins, and transmembrane receptor- or cytokine-like proteins. These results suggest that a key function of Raf-independent signaling involves deregulation of gene expression. We further characterized transgelin as a gene whose expression was abolished by Ras. Transgelin was identified previously as a protein whose expression was lost in virally transformed cell lines. We show that this loss is regulated at the level of gene expression and that both Raf-dependent and Raf-independent pathways are required to cause Ras down-regulation of transgelin in RIE-1 cells, whereas Raf alone is sufficient to cause its loss in NIH 3T3 fibroblasts. We also found that Ras-dependent and Ras-independent mechanisms can cause the down-regulation of transgelin in human breast and colon carcinoma cells lines and patient-derived tumor samples. We conclude that loss of transgelin gene expression may be an important early event in tumor progression and a diagnostic marker for breast and colon cancer development.
Shields
Janiel M
JM
Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295, USA. shieldsj@med.unc.edu
Rogers-Graham
Kelley
K
Der
Channing J
CJ
D016475:3T3 Cells; D000818:Animals; D015152:Blotting, Northern; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008024:Ligands; D051379:Mice; D008840:Microfilament Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D051381:Rats; D014407:Tumor Cells, Cultured; D015854:Up-Regulation; D018631:ras Proteins / Q000378:metabolism*
D018076:DNA, Complementary; D008024:Ligands; D008840:Microfilament Proteins; D009124:Muscle Proteins; C058992:Tagln protein, mouse; C051615:transgelin; D012313:RNA; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins