Genetic characterization of different tumor cell lines isolated from lung tumors of c-myc and c-raf transgenic mice

We recently reported isolation of various cancer progenitor cells of transgenic c-Myc and c-Raf mouse lung tumors [Reamon-Buettner SM and Borlak J, 2008]. As lung tumors can arise following dysregulation of signalling pathways normally activated during lung development we were particularly interested in investigating the genetic heterogeneity of these cancer cell lines. By whole genome expression analysis we identified two cell lines (A2C12, cRAF_cMYC) to be very different from the remaining tumor cells. Specifically the A2C12 and cRAF_cMYC cell lines expressed various stem cell markers, most notably CD34, CD44, Pdpn and Dlg7. Likewise, the A2C12 and cRAF_cMYC expressed the ATP-binding cassette (ABC) transporters Abcc1 and Abcg2 at different level when compared to other established cell lines. Furthermore, a genome wide expression profiling displayed differential gene expression pattern between and within progenitor cell lines. That provided important clues on heterogeneity in the signalling pathways amongst the cancer cell lines. We also knock down CD44 using a retroviral delivery system and observed an increased G1 peak and apoptosis as determined by flow cytometry. Finally, we analyzed promoters of regulated genes and identified overrepresented 18 transcription factor binding sites (TFBS) in common regulated genes, 10 unique TFBS in A2C12 and 9 unique TFBS in cRaf_cMyc. These data indicates that our tumor cell lines are suitable models to study the biology of lung cancer progenitor cell. Most importantly, we show that our tumor cell lines do not represent a homogeneous population of tumor-initiating cells. Understanding heterogeneity in tumors will lead to new diagnostic and therapeutic approaches.

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