Relationship between cell attachment and bcr-abl cell expression heterogeneity within CML cell lines

Abstract
Chronic myelogenous leukemia (CML) is believed to occur as a consequence of the clonal expansion of leukemic stem cells and to be maintained by an expanding population of hematopoietic stem cells that have acquired a BCR-ABL fusion gene. Recent studies indicate that primitive CML cells are less responsive to tyrosine kinase inhibitors and are a reservoir for the emergence of tyrosine kinase resistant subclones. Some studies have suggested that expression of BCR-ABL may also be required for altered cell adhesion and CML progression. The bcr-abl protein modulates cell adhesion and its effects in cell lines like K562 correlate with increased adhesion to fibronectin. It also has been reported that cell adhesion mediated resistance to apoptosis induced by BCR-ABL inhibitors, suggests that bcr-abl mediated cell adhesion may be involved in post-therapy residual disease of CML. However, some reports imply that a relatively small fraction (2%–20%) of blasts from patients with acute myeloid leukemia adhere to the plastic of the cell-culture dish. In this study we test if elevated BCR-ABL expression could be specifically identified in individual cells from attached cell populations and not unattached populations. The study developed a means to utilise flow assisted cell sorting of cell lines expressing BCR-ABL to derive individual attached and unattached cell sub-populations. Using a homogenous extraction procedure, cells individually flow sorted into microtitre plates were subjected to combinations of abl and bcr-abl qRT-PCR, and revealed the existence of low and high bcr-abl expressing cell line populations. The implications of this study will be discussed.