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Molecular and Cellular Biology, September 1999, p. 6229-6239, Vol. 19, No. 9
1Department of Animal Sciences,
Received 23 July 1998/Returned for modification 27 April
1999/Accepted 28 May 1999
Cyclin-dependent kinase inhibitors such as p27KIP1 have
recently been shown to lead to cellular differentiation by causing cell cycle arrest, but it is unknown whether similar events occur in differentiating promyeloid cells. Hematopoietic progenitor cells undergo lineage-restricted differentiation, which is accompanied by
expression of distinct maturation markers. Here we show that the
classical growth factor insulin-like growth factor I (IGF-I) potently
promotes vitamin D3-induced macrophage differentiation of
promyeloid cells, as assessed by measurement of a coordinate increase
in expression of the integrin
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Elevated Cyclin E Levels, Inactive Retinoblastoma
Protein, and Suppression of the p27KIP1 Inhibitor
Characterize Early Development of Promyeloid Cells into
Macrophages
subunit CD11b, the CD14 lipopolysaccharide receptor, and the macrophage-specific esterase,
-naphthyl acetate esterase, as early as 24 h following
initiation of terminal differentiation. Addition of IGF-I to cells
undergoing vitamin D3-induced differentiation also leads to
an early increase in expression of cyclin E, phosphorylation of the
retinoblastoma tumor suppressor protein, and a doubling of the cell
number. Early expression of CD11b (24 h) is simultaneously accompanied
by inhibition in the expression of p27KIP1. Cell cycle
analysis with propidium iodide revealed that CD11b expression at
24 h following initiation of differentiation occurs at all phases
of the cell cycle instead of only those cells arrested in
G0/G1. Similarly, development of a novel
double-labeling intra- and extracellular flow-cytometric technique
demonstrated that single cells expressing the mature leukocyte
differentiation antigen CD11b can also incorporate the thymidine analog
bromodeoxyuridine. Likewise, expression of the intracellular DNA
polymerase
cofactor/proliferating-cell nuclear antigen at 24 h
is also simultaneously expressed with the surface marker CD11b,
indicating that these cells continue to proliferate early in their
differentiation program. Finally, at 24 h following induction of
differentiation, IGF-I promoted a fourfold increase in the uptake of
[3H]thymidine by purified populations of CD11b-expressing
cells. Taken together, these data demonstrate that the initial steps associated with terminal macrophage differentiation occur concomitantly with progression through the cell cycle and that these very early differentiation events do not require the accumulation of
p27KIP1.
*
Corresponding author. Mailing address: Laboratory of
Immunophysiology, University of Illinois, 207 Edward R. Madigan
Laboratory, 1201 West Gregory Dr., Urbana, IL 61801. Phone: (217)
333-5141. Fax: (217) 244-5617. E-mail: kwkelley{at}uiuc.edu.
Molecular and Cellular Biology, September 1999, p. 6229-6239, Vol. 19, No. 9
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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