AJP - Cell Physiology, Vol 245, Issue 1 144-C150, Copyright © 1983 by American Physiological Society
Complex regulation of fibronectin synthesis by cells in culture
D. R. Senger, A. T. Destree and R. O. Hynes
We have studied the biosynthesis of fibronectin by NIL8 hamster embryo
cells in various stages of growth. Pulse labeling with [35S]methionine,
immunoprecipitation, electrophoresis, and autoradiography were employed to
compare fibronectin synthesis by cells in subconfluent monolayers,
confluent monolayers, and "aged" postquiescent monolayers. We have
determined that fibronectin synthesis is proportionally low while cells are
subconfluent, rises to maximal levels at confluence but just prior to
quiescence, and then declines with increasing culture age in quiescent
cultures. Furthermore, when cells are stimulated to grow, the effects on
rates of fibronectin synthesis depend on the prior history of the cells;
freshly confluent cells stimulated to grow show reductions in rate of
fibronectin synthesis, whereas aged postquiescent cultures show increases
in this rate. These results are in contrast to those on the rates of
synthesis of other proteins (including the precursor to the C3 component of
complement), which strictly correlate with quiescence and do not decline
significantly with culture age postconfluence. We have also determined that
the microheterogeneity of pulse-labeled fibronectin differs between
exponentially growing and quiescent cells and that it becomes less
heterogeneous once cells are quiescent. We conclude that the
microheterogeneity of pulse-labeled fibronectin and the proportionate
amount of total fibronectin synthesized both depend on growth state prior
to the entry of cells into quiescence and that they depend on culture age
thereafter.
