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J Thorac Oncol. 2011 Mar;6(3):423-31. doi: 10.1097/JTO.0b013e3182018ace.

p16Ink4a suppression of lung adenocarcinoma by Bmi-1 in the presence of p38 activation.

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Department of Biomedical Science, Bundang CHA Hospital, College of Medicine, CHA University, Seoul, Korea.



Because evasion of tumor suppression is a critical step in cancer development, cancer cells have developed a variety of mechanisms to circumvent the influence of tumor suppressive pathways. Thus, genes that negatively regulate tumor suppressors could be considered novel types of oncogenes such as Bmi-1 repressing p16Ink4a and inhibiting p53 and were found to be frequently up-regulated in a variety of cancers. p38 mitogen-activated protein kinase (MAPK), which reportedly plays a crucial role as a tumor suppressor, is activated in number of lung adenocarcinomas, which is seemingly at odds with its role as a tumor suppressor.


We examined 10 lung adenocarcinomas and corresponding normal tissues and determined the expression levels of a variety of tumor suppressor proteins through real-time polymerase chain reaction and immunohistochemistry and measured p38 MAPK activity by immunoblotting or immunohistochemistry analysis. In the in vitro cellular model, p38 activation by H-Ras and consequent senescence induction was achieved through retro-viral gene transduction. Similarly, the suppression of p16Ink4a by Bmi-1 after the introduction of H-Ras was achieved through transient transfection with cationic liposome.


We detected several lung adenocarcinomas that were positive for activated p38 MAPK but evidenced reduced levels of p16Ink4a expression. The suppression of p16Ink4a occurred in parallel with an increase in Bmi-1 and/or p16Ink4a promoter hypermethylation. Consistent with these observations, the H-Ras-stimulated induction of p16Ink4a was suppressed significantly through the coexpression of Bmi-1 in vitro.


These results demonstrate that the suppression of p16Ink4a by either the induction of Bmi-1 or the hypermethylation of p16Ink4 may be an important step in avoiding tumor surveillance by p38 MAPK during the development of lung cancer.

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