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Ann. N.Y. Acad. Sci. 961: 178–182 (2002). © 2002 New York Academy of Sciences.
TGF-1-Stimulated Osteoblasts Require
Intracellular Calcium Signaling for Enhanced
5 Integrin Expression
LEON J. NESTI,
a,b
E.J. CATERSON,
a
MARK WANG,
a
RICHARD CHANG,
a
FELIX CHAPOVSKY,
a
JAN B. HOEK,
b
AND ROCKY S. TUAN
a
Departments of
a
Orthopaedic Surgery and
b
Pathology, Anatomy, and Cell Biology,
Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
ABSTRACT: The osteoactive factor, transforming growth factor 1 (TGF-1),
influences osteoblast activity and bone function. We recently characterized a
Smad-independent TGF-1-induced Ca
2+
signal in human osteoblasts (HOB)
and demonstrated its importance in cell adhesion. Here, we further elucidate
the role of the TGF-1 Ca
2+
signal in the mechanics of HOB adhesion. Osteo-
blast interaction with fibronectin (FN) through 51 integrin is principally re-
sponsible for osteoblast-substrate adhesion. Our results show that the TGF-1
intracellular Ca
2+
signal is responsible, in part, for stimulation of 5 integrin
expression, but not 1 integrin or FN expression. Increased 5 integrin pro-
tein and mRNA expression was seen as early as 12 h after TGF-1 treatment,
but was inhibited by cotreatment with nifedipine, a Ca
2+
channel blocker.
TGF-1 increased both FN and 1 integrin protein production within 48 h, in-
dependent of nifedipine cotreatment. Immunofluorescence observations re-
vealed that TGF-1 increased 5 integrin staining, clustering, and
colocalization with the actin cytoskeleton, effects that were blocked by nife-
dipine. The TGF-1 Ca
2+
signal, a pathway crucial for HOB adhesion, en-
hances 5 integrin expression, focal contact formation, and cytoskeleton
reorganization. These early events are necessary for osteoblast adhesion; thus
they determine the fate of the cell and ultimately affect bone function.
KEYWORDS: TGF- signaling; orthopedic tissue engineering
INTRODUCTION
Substantial information is available indicating that the osteoactive factor, trans-
forming growth factor-β1 (TGF-β1), which is crucial for bone growth and develop-
ment, influences osteoblast adhesion, proliferation, differentiation, and maturation.
These properties are important in considering TGF-β1 for orthopedic tissue engi-
neering applications such as fracture repair, implant fixation, and structural defects.
The direct effect of TGF-β1 on osteoblast activity has been well documented; how-
ever, little is known about the mechanisms through which TGF-β1 exerts these ef-
Address for correspondence: Leon J. Nesti, Department of Orthopaedic Surgery, Thomas Jef-
ferson University, 501 Curtis Building, 1015 Walnut Street, Philadelphia, PA 19107. Voice: 215-
955-4321; fax: 215-955-4317.
leonnesti@yahoo.com