BRAF mutation associated with dysregulation of apoptosis in human colorectal neoplasms.
To understand the role of BRAF dysfunction in the carcinogenesis and progression/development of colorectal tumors, the authors investigated genetic alterations in the BRAF gene in human colorectal neoplasms as well as the effects of an RAS inhibitor in BRAF-mutant cells. Seven colon cancer cell lines and 116 colorectal tumors (34 adenomas and 82 adenocarcinomas) were analyzed. Genetic alterations in the BRAF and K-ras genes were examined using polymerase chain reaction-single strand conformation polymorphism and direct sequencing analyses. The growth-inhibitory and apoptosis-inducing effects of the FTI-277 RAS inhibitor in colon cancer cell lines were analyzed as well. An immunohistochemical study was also performed to investigate the correlations between the clinicopathologic parameters involved in the Ki-67 labeling index and the number of apoptotic bodies in tumor cells. FTI-277 did not suppress the proliferation of BRAF-mutant cells (WiDr and TCO), but remarkably inhibited the growth of K-ras mutant cells (LoVo). Interestingly, LoVo cells underwent apoptosis by FTI-277 in a dose-dependent manner, whereas WiDr cells were resistant to this agent. In tumor samples, BRAF mutations were found in 1 (3.0%) of 33 adenomas and 6 (7.2%) of 83 adenocarcinomas. No tumor exhibited mutations in both the BRAF and K-ras genes. Neither BRAF nor K-ras mutations correlated with the Ki-67 labeling index immunohistochemically. However, the number of apoptotic bodies was significantly decreased in the BRAF-mutant tumors. Mutation in the BRAF gene may contribute to colorectal carcinogenesis by upregulating the antiapoptotic role of the RAS/RAF/MEK/ERK pathway.
Ikehara
Nobunao
N
Division of Surgical Pathology, Department of Biomedical Informatics, Kobe University Graduate School of Medicine, Kobe, Japan.
Semba
Shuho
S
Sakashita
Masanori
M
Aoyama
Nobuo
N
Kasuga
Masato
M
Yokozaki
Hiroshi
H
D000230:Adenocarcinoma / Q000235:genetics; D000236:Adenoma / Q000235:genetics; D017209:Apoptosis / Q000235:genetics*; D001483:Base Sequence; D049109:Cell Proliferation; D015179:Colorectal Neoplasms / Q000235:genetics*; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D011905:Genes, ras; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000378:metabolism; D008297:Male; D008715:Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008875:Middle Aged; D009154:Mutation; D018807:Polymorphism, Single-Stranded Conformational; D048493:Proto-Oncogene Proteins B-raf; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; C096856:FTI 277; D019394:Ki-67 Antigen; D008715:Methionine; D048493:Proto-Oncogene Proteins B-raf