Integrin-mediated adhesion to the extracellular matrix plays a fundamental role in
tumor metastasis.
Salvicine, a novel
diterpenoid quinone compound identified as a nonintercalative
topoisomerase II poison, possesses a broad range of antitumor and antimetastatic activity. Here, the mechanism underlying the antimetastatic capacity of
salvicine was investigated by exploring the effect of
salvicine on
integrin-mediated cell adhesion.
Salvicine inhibited the adhesion of human
breast cancer MDA-MB-435 cells to
fibronectin and
collagen without affecting nonspecific adhesion to poly-
l-lysine. The
fibronectin-dependent formation of focal adhesions and actin stress fibers was also inhibited by
salvicine, leading to a rounded cell morphology. Furthermore,
salvicine down-regulated beta(1)
integrin ligand affinity, clustering and signaling via dephosphorylation of
focal adhesion kinase and
paxillin. Conversely,
salvicine induced
extracellular signal-regulated kinase (ERK) and
p38 mitogen-activated protein kinase (MAPK) phosphorylation. The effect of
salvicine on beta(1)
integrin function and cell adhesion was reversed by
U0126 and
SB203580, inhibitors of
MAPK/ERK kinase 1/2 and
p38 MAPK, respectively.
Salvicine also induced the production of
reactive oxygen species (ROS) that was reversed by ROS scavenger
N-acetyl-l-cysteine.
N-acetyl-l-cysteine additionally reversed the
salvicine-induced activation of ERK and
p38 MAPK, thereby maintaining functional beta(1)
integrin activity and restoring cell adhesion and spreading. Together, this study reveals that
salvicine activates ERK and
p38 MAPK by triggering the generation of ROS, which in turn inhibits beta(1)
integrin ligand affinity. These findings contribute to a better understanding of the antimetastatic activity of
salvicine and shed new light on the complex roles of ROS and downstream signaling molecules, particularly
p38 MAPK, in the regulation of
integrin function and cell adhesion.