beta1-integrin-ligand disengagement induces in vitro capillary tube disruption mediated by p38 MAPK activity

Celastrol acts as a potent antimetastatic agent targeting beta1 integrin and inhibiting cell-extracellular matrix adhesion, in part via the p38 mitogen-activated protein kinase pathway

Malignant tumors remain a significant health threat, with death often occurring as a result of metastasis. Cell adhesion is a crucial step in the metastatic cascade of tumor cells, and interruption of this step is considered to be a logical strategy for prevention and treatment of tumor metastasis. Celastrol [3-hydroxy-24-nor-2-oxo-1(10),3,5,7-friedelatetraen-29-oic acid], a quinone methide triterpene from the medicinal plant Tripterygium wilfordii, possesses antitumor activities, whereas the underlying mechanism(s) remains elusive. Here, we found that celastrol inhibited cell-extracellular matrix (ECM) adhesion of human lung cancer 95-D and mouse melanoma B16F10 cells. This inhibition was achieved through suppressing beta1 integrin ligand affinity and focal adhesion formation, accompanied by the reduced phosphorylation of focal adhesion kinase (FAK). In understanding the underlying mechanisms, we found that celastrol activated p38 mitogen-activated protein kinase (MAPK) by phosphorylation before the decrement of phosphorylated FAK and that this action was independent of the presence of fibronectin. Using 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580), a specific inhibitor of p38 MAPK, the effects of celastrol on beta1 integrin function, cell-ECM adhesion, and phosphorylation of FAK were partially attenuated. In addition, focal adhesion-dependent cell migration and invasion were both inhibited by treatment with celastrol. Finally, the antimetastatic activity of celastrol was examined in vivo using the B16F10-green fluorescent protein-injected C57BL/6 mouse model, as indicated by decreased pulmonary metastases in celastrol-administrated mice. Taken together, these data demonstrate for the first time that celastrol exerts potent antimetastatic activity both in vitro and in vivo, and they provide new evidence for the critical roles of p38 MAPK in the regulation of integrin function and cell adhesion.

Salvicine inactivates beta 1 integrin and inhibits adhesion of MDA-MB-435 cells to fibronectin via reactive oxygen species signaling

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.