The study for the mechanism and biomarkers expression of pulmonary stem/progenitor cells becoming tumor initiating cells under malignant transformation

• Main Authors: Sing-Yi Gu, 古幸宜
• Other Authors: Fu-Chuo Peng
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/00070778651905939967

博士 === 國立臺灣大學 === 毒理學研究所 === 104 === Lung cancer is the leading cause of cancer-related mortality worldwide. The overall 5-year survival rate is less than 14% and most cases are diagnosed in the late stages of the disease, which tend to exhibit chemotherapy resistance, tumor recurrence, and metastasis, resulting in poor prognoses. A number of factors may increase the risk of lung cancer, such as smoking, radon exposure, and asbestos inhalation. The lung is a highly complex organ comprised of a diversity of cell types. Recent studies suggest that stem/progenitor cells are susceptible to tumorigenic force. Thus, lung stem/progenitor cells are an important model for exploring the tumorigenesis process. Cancer initiating cells (CICs), also called cancer stem cells (CSCs), are responsible for chemotherapy resistance, tumor recurrence, and metastasis. Currently, the identification of CICs is highly dependent on surface markers. For example, lung cancer CICs are identified by CD133, CD117, or ALDH activity. However, through surface marker identification, studies have yielded conflicting results on CICs in different types of cancer. Clues to more effective treatments targeting tumorigenic cells could be developed with an accelerated understanding of tumor biology aided by characterization of CICs. Oct-4 is one of the most important transcription factors for the pluripotency of stem cells. Meanwhile, an increasing number of studies have demonstrated that aberrant expression of Oct-4 can contribute to CICs-like behavior in various somatic cancers. In previous studies, we have reported on the enrichment of mouse pulmonary stem/progenitor cells (mPSCs) by serum-free primary selection culture followed by FACS isolation using the coxsackievirus/adenovirus receptor (CAR) as the positive selection marker. In the current study, we demonstrated that overexpression of the pluripotent transcription factor Oct-4 is sufficient to induce CAR+/mPSCs transformation, the result of which we name CAR+/mPSCsOct-4_hi (C1, E9, and C7 clones). CAR+/mPSCsOct-4_hi clones exhibit a progressive cell cycle, proliferation potential, and telomerase activity. With a xenograft tumor formation assay, CAR+/mPSCsOct-4_hi clones showed cancer initiating and metastasis capacity. In further validating their CICs-like abilities, CAR+/mPSCsOct-4_hi clones express CD133, ALDH activity, as well as chemoresistance potential. Next generation sequencing (NGS) analysis of CAR+/mPSCsOct-4_hi clones revealed that angiogenesis-associated mechanisms were highly activated. CAR+/mPSCsOct-4_hi clones show remarkable expression of certain proangiogenic factors, including angiopoietins (ANGs) and VEGF, and enhanced angiogenic potential. Moreover, CAR+/mPSCsOct-4_hi actively participated in tumor blood vessel formation and triggered a novel angiogenic mechanism, the angiopoietins/Tie2 signaling pathway. The present study indicates that by overexpressing Oct-4 at high levels in a subset of pulmonary stem/progenitor cells, CAR+/mPSCs, can transform the cells such that they exhibit tumorigenic potential and CICs-like properties. The transformed cells not only showed enhanced angiogenic potential, but also actively participated in tumor blood vessel formation and activated the ANGs/Tie2 signaling pathway. This study provides critical evidence supporting a possible origin of CICs and helps elucidate the pathways responsible for CICs-mediated blood vessel formation.