Genotypic and phenotypic characterization of the side population of gastric cancer cell lines

To sum up our results, we managed to isolate a reproducible SP cell fraction of human gastric carcinoma cell lines for the first time. Those cells differed from the rest of the population regarding morphology and biological behaviour. They had the ability to build a population resembling the basic tumor population and therefore performed differenziation and asymmetric cell division. SP cells expressed potential stem cell markers like musashi 1 and Cd133 and also showed a high expression of genes that encode for stem cell properties. The so identified phenotypic and genetic factors showed a variable expression in tumor samples of patient series and might be applicable as prognostic factors in the diagnosis of gastric carcinoma. Aims: The side population (SP) of tumor cell lines shares characteristics with tumor stem cells. In this study we phenotypically and genotypically characterized the SP of gastric cancer cell lines. Methods: The SP was obtained from MKN45- and AGS-gastric cancer cells using Hoechst 33342 staining and fluorescence-activated cell sorting (FACS). SP cells were subsequently studied morphologically (cytology, immunocytochemistry), on the transcriptional level (gene array) and in cell culture (recultivation assays). Genes differentially expressed in the SP cells were finally searched by immunohistochemistry in neoplastic and non-neoplastic gastric tissue from gastric cancer patients. Results: The SP was reproducibly obtained from gastric cancer cell lines. The SP cells were smaller and rounder then non-SP cells. SP cells self-renewed in re-cultivation experiments and differentiated into SP- and non-SP cells. Re-cultivated SP- and non-SP cells showed distinct phenotypes in culture regarding cell shape and colony-formation. SP cells had increased levels of the stem cell markers CD133 and Musashi 1. Transcriptional analyses demonstrated that SP cells express genes that encode for stem cell properties like FZD7, HEY1, SMO and ADAM17. Finally we detected the transcripts of these genes in tissue samples from patients with gastric cancer. Conclusions: Human gastric cancer cell lines enclose a phenotypically and genotypically distinct cell population with tumor stem cell features. Phenotypical characteristics of this distinct cell population are also present in gastric cancer tissue.