Background & aims: Epidemiological evidence suggests that statins prevent colorectal cancer (CRC), but the biological mechanism remains obscure. Statins induce bone morphogenetic protein (BMP) expression in bone cells. We have previously shown that BMPs act as tumor suppressors in CRC. We hypothesized that the action of statins in CRC involves the induction of BMPs.
Methods: We investigated the effects of statins on CRC cell lines using immunoblotting, measurements of apoptosis and cell proliferation, and luciferase reporter assays. The effect of statins was confirmed in a xenograft mouse model.
Results: CRC cell lines show widely differing sensitivities to statin treatment. Sensitive cell lines show induction of BMP2 protein levels and a BMP2 reporter construct, activation of the BMP pathway, and induction of the BMP target gene ID-2, whereas resistant cell lines do not. The addition of the specific inhibitor of BMPs, noggin, completely prevents lovastatin-induced apoptosis in sensitive cells. Sensitive cell lines express the central BMP pathway element SMAD4, whereas the resistant cell lines do not. Targeted knockout of SMAD4 leads to the loss of statin sensitivity and reconstitution with SMAD4, to the restoration of statin sensitivity. In a xenograft mouse model, tumors from sensitive and insensitive cell lines were treated with oral simvastatin. Significant inhibition of tumor growth using sensitive cells but increased tumor growth when using insensitive cells was observed.
Conclusions: Statins induce apoptosis in CRC cells through induction of BMP2. Statin therapy may only be effective in SMAD4-expressing CRCs and may have adverse effects in SMAD4-negative tumors.