Contractile proteins participate in release of erythroid growth regulators
from mononuclear cells
N Dainiak, MA Riordan, PR Strauss, L Feldman and S Kreczko
Department of Medicine, St. Elizabeth's Hospital, Boston, MA 02135.
We have investigated the role of contractile proteins of circulating
mononuclear cells in generation of membrane-associated, erythroid growth
regulatory molecules. Lymphocytes and monocytes were incubated under
serum-free conditions without and with cytochalasin B, cytochalasin D, or
colchicine, and effects on positive and negative erythropoietic activities
were determined in cell membranes and in surface membrane vesicle-rich
pellets and supernatants of dialyzed medium conditioned by the cells. In
serum-free cultures of human bone marrow, plasma membranes and exfoliated
membrane-derived vesicles from cytochalasin-treated lymphocytes lost their
capacity to support the formation of erythroid bursts, while monocyte
membrane-associated inhibitory activity was abolished by preincubation with
cytochalasin. In contrast, membrane-associated activities of
colchicine-treated cells were unaffected. Cytochalasin-induced alterations
of membrane regulatory molecules were observed in a dose-dependent fashion
over a wide range of concentrations (1 to 100 micrograms/mL) tested.
However, the capacity of membrane vesicle-free supernatants of medium
conditioned by lymphocytes or monocytes was unaffected by cytochalasins,
regardless of drug concentration used. Lysates of cytochalasin B-treated
cells inhibited the activity of deoxyribonuclease I to a greater degree
than did lysates of untreated cells, suggesting that the relative amount of
monomeric actin is increased in the cytoplasm of treated cells.
Furthermore, results of experiments with D-glucose and with cytochalasin D
suggest that cytochalasin effects are independent of alterations in glucose
metabolism. The data indicate that expression of plasma membrane-
associated regulators is sensitive to agents that block polymerization of
actin. They raise the possibility that changes in distribution of actin
between unpolymerized and filamentous pools may influence the organization
and/or function of mononuclear cell surface-associated erythroid regulatory
molecules.
Volume 72,
Issue 1,
pp. 165-171,
07/01/1988
Copyright © 1988 by The American Society of Hematology
