J Biol Chem, Vol. 273, Issue 40, 25796-25803, October 2, 1998
Cardiac Fibroblasts Arrest at the G1/S Restriction
Point in Response to Interleukin (IL)-1
EVIDENCE FOR IL-1
-INDUCED HYPOPHOSPHORYLATION OF THE
RETINOBLASTOMA PROTEIN
Farid
Koudssi,
Javier E.
López,
Sonia
Villegas, and
Carlin S.
Long
From the Division of Cardiology and the Research Service, Veterans
Affairs Medical Center, San Francisco, California 94121, and the
Cardiovascular Research Institute and Department of Medicine,
University of California, San Francisco, California 94143
Although responsible for only approximately
one-third of the overall myocardial mass, the interstitial fibroblasts
of the heart serve a fundamental role in establishing the functional integrity of myocardium and are the major source of myocardial extracellular matrix production. Their importance in clinical medicine
is underscored by the observation that fibroblast numbers increase in
response to several pathologic circumstances that are associated with
an increase in extracellular matrix production, such as long standing
hypertension and myocardial injury/infarction. Up to the present time,
however, there has been little information available on either the
kinetics of the cardiac fibroblast cell cycle, or the fundamental
mechanisms that regulate its entry into and exit from the cell cycle.
Previous work from our laboratory examining the effects of interleukin
(IL)-1
on myocardial growth and gene expression in culture indicated
that cardiac fibroblasts have a diminished capacity to synthesize DNA
in response to mitogen in the presence of this cytokine. The mechanism
of IL-1
action was not clear, however, and could have resulted from
action at several different points in the cell cycle. The
investigations described in this report indicate that IL-1
exerts
its effect on the fibroblast cell cycle at multiple levels through
altering the expression of cardiac fibroblast cyclins,
cyclin-dependent kinases, and their inhibitors, which
ultimately affect the phosphorylation of the retinoblastoma gene
product.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.