Abstract 1236: Upregulation of stem cell markers in senescent lung cancer cells following chemotherapy
Authors: Wang Liang-Chuan S. , Cheng Guanjun , Crisanti Maria C. , Sun Jing , Albelda Steven M. 
Published: June 2012

Abstract
Rationale: Local recurrence following chemotherapy and radiotherapy is very common and one of the current paradigms suggests that the viable and metabolically active senescent cancer cells play a role here. These cells can influence their surrounding cells by secreting tumor-promoting factors, plus they have the possibility to emerege from senescence into growth, suggesting a need to eradicate them to improve clinical outcome. Interestingly, a possible cell survival mechanism exerted by senescent lymphoma cells following DNA damage through re-activation of embryonic renewal network (OCT4 and others) has been suggested. Given that there are other known similarities between stem cells and senescent cells, such as a mesenchymal phenotype and resistance to chemotherapy, we examined if these DNA-damaged-induced senescent cells expressed any common stem cell antigens.
Experimental procedures: A series of lung cancer cell lines were treated with high dose chemotherapy (doxorubicin, cisplatin and gemcitabine) that killed 90% of entire population over three days. The remaining cells were then collected for further analyses. Genes involved in epithelial-mesenchymal transition and embryonic self renewal were analyzed with real-time PCRs and protein expression was confirmed with immunohistochemical staining (IHC) or immunoblots. The surface antigens expressed on these senescent lung cancer cells were also analyzed with flow cytometry.
Results: The cells remaining after treatment with the DNA-damaging agent doxorubicin and cisplatin (but not the nucleoside analog gemcitabine) had a flattened and enlarged morphology, and were growth arrested. Senescence was confirmed by positive SA-β-galactosidase staining. Genes involved in epithelial to mesenchymal transition (EMT), such as N-cadherin, fibronectin, vimentin, SNA/1 and SNA/2, were shown to increase. EpCAM surface expression went down, which correlates well with EMT. The expression of other stem cell surface markers, such as ABCG2 and CD24, were also increased. CD133 and integrin α6 remained unchanged. In terms of stem cell-related genes, OCT4 mRNA expression went up in the senescent cells. Interestingly, the OCT4A protein expression was localized in the cytosol of senescent cells, which was confirmed with both IHC and immunoblots. Knockdown of this cytoplasmic OCT4A with siRNA in these senescent cells caused cell death.
Conclusions: In summary, these data show that some stem cell markers are also expressed on senescent cells. This needs to be considered when cancer initiating stem cell are being identified using these known stem cell markers. Cytoplasmic OCT4A may be involved in cell survival mechanism of these senescent cells.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1236. doi:10.1158/1538-7445.AM2011-1236