Abstract 4238: Human non-small cell lung cancer cells asymmetrically divide their template DNA strands and cell fate proteins
Authors: Pine Sharon R. , Ryan Brid M. , Varticovski Lyuba , Robles Ana I. , Harris Curtis C. 
Published: February 2011

Certain subpopulations of tumor cells are capable of both self-renewal and regeneration of phenotypically heterogeneous tumors. These observations suggest that tumor initiation and maintenance are linked to asymmetric cell divisions of tumor stem cells. However, cell progeny of symmetric divisions could adopt different cell fates, possibly through interactions between the daughter cells and their microenvironments. We set out to determine if human lung cancer primary tumor cells and cell lines asymmetrically divide their template DNA strands exclusively to only one daughter cell during cell division, and further, if the process is linked to cell fate. By performing pulse-chase experiments with halogenated thymidine analogs, we observed that 0.7-6.0% of cells within human lung cancer cell lines and 15-25% of short-term culture cells from primary lung tumor samples asymmetrically divide their template DNA strands. The data was confirmed by examination of asymmetrically dividing cells by two-color DNA analogs and visualization in real-time. Furthermore, cells that asymmetrically divide the lung cancer stem cell marker CD133 are 10-fold more likely to asymmetrically divide their labeled template DNA strands than cells that symmetrically divide CD133, and in each case, the CD133 co-segregates with the older DNA strands. The lung adenocarcinoma differentiation marker pro-surfactant protein C (SPC) is passed to the opposing daughter cell in 93% of cell divisions that asymmetrically divide both the DNA and SPC, suggesting a correlation between asymmetric division of template DNA and cell fate. To gain insight into the mechanisms regulating asymmetric cell division in lung cancer, we subjected cell lines to conditions known to enhance self-renewal. We observed that the frequency of template DNA co-segregation decreases 2- to 3-fold at lower cell densities as well as during serum deprivation and hypoxic conditions. These data indicate that a switch from asymmetric to symmetric cell divisions is one mechanism by which tumor cells increase self-renewal. Furthermore, the process requires cell-cell contact, suggesting that the niche participating in self-renewal regulation is provided by direct signaling from neighboring tumor cells. Our results demonstrate that a hierarchical cellular pattern within human lung tumors may be regulated, in part, by an orchestrated mechanism of self-renewal and differentiation involving co-segregation of template DNA and cell fate markers. An in-depth examination of intercellular and environmental response signaling pathways are needed to decipher exactly how neighboring cells and the environment influence cancer cell fate decisions. Examination of genes known to disrupt asymmetric cell division in lower organisms in human cancers could elucidate novel pathways controlling cancer maintenance and provide novel therapeutic targets.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4238.