Abstract
Differentiation of hematopoietic cells is known to be accompanied by profound changes in acetylcholinesterase (AChE) enzyme activity, yet the basic mechanisms underlying this developmental regulation remain unknown. We initiated a series of experiments to examine the molecular mechanisms involved in regulating AChE expression during hematopoiesis. Differentiation of murine erythroleukemia (MEL) cells using dimethyl sulfoxide resulted in a 5- and 10-fold increase in intracellular and secreted AChE enzyme activity, respectively. Interestingly, these increases resulted from a preferential induction of the globular molecular form G1 and a slight increase in G4 instead of an increase in the levels of the G2 membrane-bound form, a molecular form expressed in mature erythrocytes. Concomitantly, expression of the two predominant AChE transcripts (R and T, for read-through and tail, respectively) in MEL cells was induced to a similar extent with differentiation. Nuclear run-on assays performed with nuclei isolated from induced versus uninduced MEL cells revealed that in contrast to the large increases seen in the transcription of the beta-globin gene, the transcriptional activity of the AChE gene remained largely unaffected after differentiation. Determination of the half-lives of the R and T transcripts demonstrated that they both exhibited an increase in stability in induced MEL cells. Taken together, results from these studies indicate that post-transcriptional regulatory mechanisms account for the increased expression of AChE in differentiated hematopoietic cells.
Highlights
Acetylcholinesterase (AChE)1 is responsible for inactivating acetylcholine at cholinergic synapses in both central and peripheral nervous systems
To determine whether differentiation was accompanied by selective increases in the amount of specific molecular forms, we separated by velocity sedimentation using sucrose gradients aliquots of the cell extracts and growth media obtained from both uninduced and induced murine erythroleukemia (MEL) cells and measured the AChE enzyme activity in each fraction
It is well established that AChE is expressed in hematopoietic cells and that significant changes in total enzyme activity accompany the process of terminal hematopoietic differentiation
Summary
Acetylcholinesterase (AChE) is responsible for inactivating acetylcholine at cholinergic synapses in both central and peripheral nervous systems. For example, the asymmetric forms of AChE are expressed exclusively in differentiated muscle and neuronal cells, whereas glycophospholipid-linked dimers are found preferentially in tissues of hematopoietic origin Such varied patterns of expression suggest that expression of AChE involves several levels of regulatory mechanisms ranging from tissue-specific transcriptional control to highly regulated post-translational events. Deletion of the AChE locus at 7q22 has been shown to be associated with both myelodysplastic syndromes and acute myeloid leukemia, suggesting that AChE may act as a tumor suppressor gene (14, 15) In light of these recent findings, it becomes important to elucidate the cellular and molecular mechanisms presiding over AChE expression in hematopoietic cells since it may provide additional insights into its physiological function in this cell type. AChE expression during hematopoiesis because induced cells are known to express high levels of AChE compared with their uninduced counterparts (9, 17)
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