The Journal of Cell Biology, Vol 106, 161-170, Copyright © 1988
by The Rockefeller University Press
Microfilament modification by dihydrocytochalasin B causes
retinoic acid-modulated chondrocytes to reexpress the
differentiated collagen phenotype without a change in shape
PD Benya, PD Brown and SR Padilla
Department of Orthopedics, Orthopedic Hospital, University of
Southern California, Los Angeles 90007-2697.
Primary monolayers of rabbit articular chondrocytes
synthesize high levels of type II collagen and proteoglycan.
This capacity was used as a marker for the expression of the
differentiated phenotype. Such cells were treated with 1
microgram/ml retinoic acid (RA) for 10 d to produce a modulated
collagen phenotype devoid of type II and consisting of
predominantly type I trimer and type III collagen. After
transfer to secondary culture in the presence of RA, the
stability of the RA- modulated phenotype was investigated by
culture in the absence of RA. Little reexpression of type II
collagen synthesis occurred in this period unless cultures were
treated with 3 X 10(-6) M dihydrocytochalasin B to modify
microfilament structures. Reexpression of the differentiated
phenotype began between days 6-8 and was essentially complete by
day 14. Substantial reexpression occurred by day 8 without a
detectable increase in cell rounding. Colony formation,
characteristic of primary chondrocytes, was infrequent even
after reexpression was complete. These data suggest that the
integrity of microfilament cytoskeletal structures can be a
source of regulatory signals that mechanistically appear to be
more proximal to phenotypic change than the overt changes in
cell shape that accompany reexpression of subculture-modulated
chondrocytes in agarose culture.
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