Reprogramming erythroleukemia cells into terminal differentiation: Role of cell cycle regulatory proteins

Abstract

Terminal differentiation involves the irreversible commitment to a developmental program that culminates in phenotypic maturation and terminal cell division. Dysregulation of the processes controlling entry of cells into terminal differentiation can lead to tumorigenesis. Not much is known about the block to differentiation that occurs in tumor cells and/or the events required to reverse them. A key aspect in accomplishing these goals is to develop an understanding of the relationship between the factors controlling differentiation and the regulators of cell proliferation.;Using the in vitro differentiation of murine erythroleukemia (MEL) cells, which recapitulates the erythroid terminal differentiation program, we assessed the contributions of specific cell cycle regulators to the differentiation program, as well as the relationship between cell cycle control and terminal differentiation by preparing MEL cell transfectants that inducibly express key cell cycle regulatory proteins. The results show that the decision of the tumor cells to differentiate is coupled to the activities of certain cell cycle regulators. We also provide evidence for the mechanisms by which control of the cell cycle and differentiation are coupled.;We have also examined the question of coupling of cell cycle regulation and differentiation during the later stages of differentiation. Once the tumor cells are reprogrammed into terminal differentiation they undergo phenotypic maturation and terminal cell division. We show that the onset of terminal cell division can be either greatly accelerated or greatly delayed without affecting phenotypic maturation (hemoglobin synthesis). The results demonstrate the plasticity of terminal cell division in differentiated cells and show that fully differentiated cells can be made to proliferate far beyond their normal capacity to divide and suggest the existence of a highly regulated program of changes in the role of cyclin D-dependent kinases during erythroid cell differentiation. We further suggest that CDK6 (along with CDK2) may be responsible for driving proliferation in early erythroid progenitors and that later in differentiating cells the cell cycle engine is driven by CDK4 (along with CDK2).;In conclusion, this thesis has addressed the relationship between regulators of proliferation and regulators of differentiation in malignant erythroid cells and the reprogramming of these cells into terminal differentiation. We have identified the contributions of individual cell cycle regulators to the differentiation program, the relationship between the control of the cell cycle and the control of various stages of differentiation, as well as the association between lineage specific transcription factors and cell cycle regulators. (Abstract shortened by UMI.).