Bone morphogenetic protein signalling is required for the anti-mitogenic effect of the proteasome inhibitor MG-132 on colon cancer cells.
OBJECTIVE
Inhibition of proteasome has been emerging as a promising approach in pathway-directed cancer therapy. Bone morphogenetic protein (BMP) signalling, which is known to be regulated by the ubiquitin-proteasome pathway in osteoblasts, plays a crucial role in the suppression of gastrointestinal carcinogenesis. Here we sought to elucidate the anti-mitogenic effect of a proteasome inhibitor in relation to BMP signalling in colon cancer.


METHODS
The effects of the proteasome inhibitor MG-132 on proliferation of SW1116 and HT-29 colon cancer cells were determined by [(3)H]-thymidine incorporation and colony-formation assay. The involvement of BMP signalling in the action of MG-132 was elucidated by western blot, real-time PCR, immunofluorescence and RNA interference.


RESULTS
MG-132 significantly suppressed the proliferation of colon cancer SW1116 and HT-29 cells. In this regard, MG-132 activated BMP signalling and this was manifested as an increase in Smad1/5/8 phosphorylation and upregulation of p21(Waf1/Cip1) and p27(Kip1) expression. Knockdown of BMP receptor II abolished Smad1/5/8 phosphorylation, the induction of p21(Waf1/Cip1) and p27(Kip1) and inhibition of cell proliferation induced by MG-132. Further analysis revealed that MG-132 upregulated the expression of BMP1 and BMP2, which are secreted members of the BMP superfamily. Moreover, the expression of Smad6, an intracellular inhibitor of BMP signalling, was suppressed by MG-132.


CONCLUSIONS
These findings suggest that inhibition of proteasome suppresses the proliferation of colon cancer cells via activation of BMP signalling. They also demonstrate a novel aspect of proteasome function in the regulation of colon cancer cell proliferation.
Wu
W K K
WK
Department of Medicine & Therapeutics, The Chinese University of Hong Kong, Hong Kong, China.
Sung
J J Y
JJ
Wu
Y C
YC
Li
Z J
ZJ
Yu
L
L
Cho
C H
CH
D000230:Adenocarcinoma / Q000188:drug therapy / Q000473:pathology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D019485:Bone Morphogenetic Proteins / Q000187:drug effects* / Q000378:metabolism; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000473:pathology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D034622:RNA Interference; D015398:Signal Transduction / Q000187:drug effects
D000970:Antineoplastic Agents; D019485:Bone Morphogenetic Proteins; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde