Abstract
Recent studies demonstrated that cancer stem cells (CSCs) have higher tumorigenesis properties than those of differentiated cancer cells and that transcriptional factor-SOX2 plays a vital role in maintaining the unique properties of CSCs; however, the function and underlying mechanism of SOX2 in carcinogenesis of lung cancer are still elusive. This study applied immunohistochemistry to analyze the expression of SOX2 in human lung tissues of normal individuals as well as patients with adenocarcinoma, squamous cell carcinoma, and large cell and small cell carcinoma and demonstrated specific overexpression of SOX2 in all types of lung cancer tissues. This finding supports the notion that SOX2 contributes to the tumorigenesis of lung cancer cells and can be used as a diagnostic probe. In addition, obviously higher expression of oncogenes c-MYC, WNT1, WNT2, and NOTCH1 was detected in side population (SP) cells than in non-side population (NSP) cells of human lung adenocarcinoma cell line-A549, revealing a possible mechanism for the tenacious tumorigenic potential of CSCs. To further elucidate the function of SOX2 in tumorigenesis of cancer cells, A549 cells were established with expression of luciferase and doxycycline-inducible shRNA targeting SOX2. We found silencing of SOX2 gene reduces the tumorigenic property of A549 cells with attenuated expression of c-MYC, WNT1, WNT2, and NOTCH1 in xenografted NOD/SCID mice. By using the RNA-Seq method, an additional 246 target cancer genes of SOX2 were revealed. These results present evidence that SOX2 may regulate the expression of oncogenes in CSCs to promote the development of human lung cancer.
Highlights
Cancer stem cells (CSCs) represent a very small population of cancer cells from which tumors originates
There was a positive correlation between SOX2 and the pathological degree of human adenocarcinoma (p = 0.002), indicating that SOX2 may inhibit the differentiation of adenocarcinoma cells
We used immunohistochemistry to systemically analyze the expression of SOX2 in various types of lung cancers and found that SOX2 is predominantly overexpressed in adenocarcinoma, squamous cell carcinoma (SCC), large cell carcinomas and small cell lung cancer (SCLC) tissues, indicating that SOX2 can be used as a universal marker for the diagnosis of human lung cancer
Summary
Cancer stem cells (CSCs) represent a very small population of cancer cells from which tumors originates. Recent studies have shown that CSCs like cell subpopulations could be isolated from various cultured tumor cell lines or tissues by using the Hoechst33342 dye efflux method to separate side population (SP) cells [2] or by sorting cells expressing specific stem cell surface markers, such as CD133(+), CD44(+), CD34(+) and CD38(+) [3,4,5] et al. Lung cancer represents the most common cause of cancerrelated lethality in both men and women throughout the world with very low five-year survival rates, even after clinical therapy [6,7]. It was found that isolated SP cells show higher expression levels of stem cell genes, such as SOX2 and OCT4 and tumorigenesis properties than NSP cells [2]
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