Transformation of immortalized colorectal crypt cells by microcystin involving constitutive activation of Akt and MAPK cascade.
It has been shown by epidemiological and animal studies that microcystin is an important exogenous factor involved in the carcinogenesis of colorectal cancer (CRC). However, details of the mechanism remain unclear. Transformation of colorectal cells is an important initial step in carcinogenesis. Whether microcystin is capable of transforming immortalized colorectal crypt cells, and what the mechanism might be, was investigated. In the present study, we demonstrated that immortalized colorectal crypt cells could be transformed by microcystin. Transformed colorectal crypt cells showed an anchorage-independent growth phenotype, and the proliferation activities of microcystin-transformed cells were also greater than that of immortalized colorectal crypt cells. The Akt and the p38, JNK of mitogen-activated protein kinase (MAPK) pathways in microcystin-transformed cells were found to be constitutively activated. In microcystin-transformed cells, PI3K, MAPKAPK2, Akt, cyclin D1 and cyclin D3 in the Akt pathway; IQGAP-2, RabGTPase, Rap1GAP, RasGAP, R-Ras, Krev-1 and TC21 of the Ras GTP/GDP protein family; and A-Raf, B-Raf and PAK in the Ras/MAPK pathway were all markedly upregulated. However, in positive control cells, dimethylhydrazine-transformed cells, only the Akt pathway was activated by PI3K, and no evidence of alteration of any molecules of the Ras superfamily was observed. Inhibition of Akt, p38 and JNK activation led to a reduced proliferation of microcystin-transformed cells. This implies that the constitutive activation of Akt and the p38, JNK of MAPK pathways in microcystin-transformed cells may be the mechanism by which this important external factor acts in the carcinogenesis of CRC.
Zhu
Yongliang
Y
Department of Gastroenterology and Cancer Institute, Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, Zhejiang Province, China.
Zhong
Xian
X
Zheng
Shu
S
Ge
Zhen
Z
Du
Qin
Q
Zhang
Suzhang
S
D018929:Cell Culture Techniques; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D003106:Colon / Q000166:cytology; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000503:physiopathology*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D048670:MAP Kinase Kinase 4; D052998:Microcystins; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000494:pharmacology*; D011230:Precancerous Conditions; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D012007:Rectum / Q000166:cytology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D052998:Microcystins; D010456:Peptides, Cyclic; D011518:Proto-Oncogene Proteins; C078588:microcystin; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases