Peritoneal dissemination is a major clinical obstacle in
gastrointestinal cancer therapy, and it accounts for the majority of
cancer-related mortality.
Calreticulin (CRT) is over-expressed in gastric
tumors and has been linked to poor prognosis. In this study, immunohistochemistry studies revealed that the up-regulation of CRT was associated with lymph node and distant
metastasis in patients with
gastric cancer specimens. CRT was significantly down-regulated in highly metastatic
gastric cancer cell lines and metastatic animal by
Honokiol-treated. Small RNA interference blocking CRT by
siRNA-CRT was translocated to the cells in the early immunogenic response to
Honokiol.
Honokiol activated endoplasmic reticulum (ER) stress and down-regulated
peroxisome proliferator-activated receptor-γ (PPARγ) activity resulting in PPARγ and CRT degradation through
calpain-II activity, which could be reversed by
siRNA-
calpain-II. The
Calpain-II/PPARγ/CRT axis and interaction evoked by
Honokiol could be blocked by gene silencing or pharmacological agents. Both
transforming growth factor (TGF)-β1 and
N-methyl-N'-nitro-N-nitrosoguanidine (
MNNG) induced cell migration, invasion and reciprocal down-regulation of epithelial marker
E-cadherin, which could be abrogated by
siRNA-CRT. Moreover,
Honokiol significantly suppressed
MNNG-induced gastrointestinal
tumor growth and over-expression of CRT in mice. Knockdown CRT in
gastric cancer cells was found to effectively reduce growth ability and
metastasis in vivo. The present study provides insight into the specific biological behavior of CRT in epithelial-to-mesenchymal transition (EMT) and
metastasis. Taken together, our results suggest that the therapeutic inhibition of CRT by
Honokiol suppresses both gastric
tumor growth and peritoneal dissemination by dictating early translocation of CRT in immunogenic cell death, activating ER stress, and blocking EMT.