Microenvironmental modulation of asymmetric cell division in human lung cancer cells.

Normal tissue homeostasis is maintained through asymmetric cell divisions that produce daughter cells with differing self-renewal and differentiation potentials. Certain tumor cell subfractions can self-renew and repopulate the heterogeneous tumor bulk, suggestive of asymmetric cell division, but an equally plausible explanation is that daughter cells of a symmetric division subsequently adopt differing cell fates. Cosegregation of template DNA during mitosis is one mechanism by which cellular components are segregated asymmetrically during cell division in fibroblast, muscle, mammary, intestinal, and neural cells. Asymmetric cell division of template DNA in tumor cells has remained elusive, however. Through pulse-chase experiments with halogenated thymidine analogs, we determined that a small population of cells within human lung cancer cell lines and primary tumor cell cultures asymmetrically divided their template DNA, which could be visualized in single cells and in real time. Template DNA cosegregation was enhanced by cell-cell contact. Its frequency was density-dependent and modulated by environmental changes, including serum deprivation and hypoxia. In addition, we found that isolated CD133(+) lung cancer cells were capable of tumor cell repopulation. Strikingly, during cell division, CD133 cosegregated with the template DNA, whereas the differentiation markers prosurfactant protein-C and pan-cytokeratins were passed to the opposing daughter cell, demonstrating that segregation of template DNA correlates with lung cancer cell fate. Our results demonstrate that human lung tumor cell fate decisions may be regulated during the cell division process. The characterization and modulation of asymmetric cell division in lung cancer can provide insight into tumor initiation, growth, and maintenance.