Expression of tumor-related Rac1b antagonizes B-Raf-induced senescence in colorectal cells.
Mutations in the BRAF oncogene have been identified as a tumor-initiating genetic event in mainly melanoma, thyroid and colon cancer, resulting in an initial proliferative stimulus that is followed by a growth arrest period known as oncogene-induced senescence (OIS). It remains unknown what triggers subsequent escape from OIS to allow further tumor progression. A previous analysis revealed that around 80% of colorectal tumors carrying a mutation in BRAF also overexpress splice variant Rac1b. We used normal NCM460 colonocytes as a model to express oncogenic B-Raf-V600E in the presence or absence of co-transfected Rac1b and then analyzed the effect on expression of senescence markers. When oncogenic B-Raf-V600E was expressed we observed the induction of the senescence-associated β-galactosidase and of the cell-cycle inhibitors p14, p15 and p21 whereas proliferation marker Ki67 was suppressed. Upon co-expression of splice variant Rac1b, but not of Rac1, the B-Raf-induced senescence phenotype was reverted and expression of the cell-cycle inhibitors downregulated in a reactive oxygen-species dependent manner. We thus provide evidence that co-expression of splice variant Rac1b counteracts B-Raf-induced senescence, indicating the selection for increased Rac1b expression as one potential mechanism by which colorectal tumor cells can escape from B-Raf-induced OIS.
Department of Human Genetics, National Health Institute Dr. Ricardo Jorge, Lisbon, Portugal; BioISI - Biosystems and Integrative Sciences Institute, Faculty of Sciences, University of Lisbon, Lisbon, Portugal.
Andreia F A
AF
Henriques
Department of Human Genetics, National Health Institute Dr. Ricardo Jorge, Lisbon, Portugal; BioISI - Biosystems and Integrative Sciences Institute, Faculty of Sciences, University of Lisbon, Lisbon, Portugal.
Patrícia
P
Barros
INCELL Corporation, San Antonio, TX, USA.
Mary Pat
MP
Moyer
BioISI - Biosystems and Integrative Sciences Institute, Faculty of Sciences, University of Lisbon, Lisbon, Portugal; Department of Chemistry and Biochemistry, Faculty of Sciences, University of Lisbon, Lisbon, Portugal.
Paulo
P
Matos
Department of Human Genetics, National Health Institute Dr. Ricardo Jorge, Lisbon, Portugal; BioISI - Biosystems and Integrative Sciences Institute, Faculty of Sciences, University of Lisbon, Lisbon, Portugal. Electronic address: peter.jordan@insa.min-saude.pt.
Peter
P
Jordan
D045744:Cell Line, Tumor; D016922:Cellular Senescence; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D018450:Disease Progression; D006801:Humans; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D015398:Signal Transduction; D014162:Transfection; D020830:rac1 GTP-Binding Protein / Q000235:genetics* / Q000378:metabolism
D048493:Proto-Oncogene Proteins B-raf; D020830:rac1 GTP-Binding Protein
B-Raf; Colorectal cancer; Oncogene-induced senescence; Rac1b; Tumor progression