Acetylcholinesterase in murine erythroleukemia (Friend) cells: evidence for
megakaryocyte-like expression and potential growth-regulatory role of
enzyme activity
F Paoletti, A Mocali and AM Vannucchi
Istituto di Patologia Generale, Universita di Firenze, Italy.
Features of true acetylcholinesterase (AChE) regulation during growth and
differentiation of Friend murine erythroleukemia cells (MELC) have been
investigated with respect to other erythroid and nonerythroid murine
elements. Enzyme levels of uninduced MELC were in between the very low AChE
contents of erythroid cells and the huge amounts of activity exhibited by
megakaryocytes and platelets. After MELC commitment to terminal division,
the enzyme-specific activity increased largely, approaching values that
were much closer to those of thrombocytic than of normal erythroid
elements. The bulk of AChE activity in MELC, megakaryocytes, and platelets
was found to be located in the cytosol as a free-soluble form. Moreover,
during incubation, MELC actively released large amounts of AChE into the
medium, like it occurs in murine thrombocytes. Conversely, the enzyme of
the erythroid elements was mainly associated with the membranes and was not
released extracellularly. Experiments with inducers showed that changes in
AChE- specific activity of MELC correlated directly with the arrest of cell
proliferation rather than with the activation of differentiated erythroid
functions. The inverse relationship existing between MELC growth rates and
AChE levels was further supported by the relative enzyme activities of the
slow- and fast-growing subclones. We conclude that uninduced MELC
potentially share properties of both the erythroid and megakaryoblastic
phenotype. The latter might be revealed by typical regulation of AChE
activity according to a thrombocytic-like program activated upon MELC
commitment to terminal division. Eventually, the inhibition of MELC growth
by exogenous pure bovine AChE suggested that the secreted murine enzyme
might serve as a potential negative signal of cellular replication.
Volume 79,
Issue 11,
pp. 2873-2879,
06/01/1992
Copyright © 1992 by The American Society of Hematology
