Central role of SIAH inhibition in DCC-dependent cardioprotection provoked by netrin-1/NO.

Deleted in colorectal cancer (DCC), a large transmembrane receptor of netrin-1, is critical for mediating netrin-1's cardioprotective function. In the present study we investigated novel mechanisms underlying netrin-1-induced, rapid, and feed-forward up-regulation of DCC, which is believed to sustain nitric oxide (NO) production to potentiate cardioprotection. Intriguingly, NO markedly reduced expression of the E3 ubiquitin ligase seven in absentia homolog (SIAH) that is specific for regulation of protesome-dependent DCC degradation, resulting in accumulation of DCC. The two SIAH isoforms compensate for each other when one is repressed; inhibition of both SIAH1 and SIAH2 using combined siRNAs significantly reduced infarct size while improving cardiac function after ischemia/reperfusion injury of the heart. This effect was absent in DCC-deficient mice. Moreover, in vivo RNAi inhibition of SIAH1/2 further augmented netrin-1's cardioprotective function. In summary, these data identify a novel therapeutic target of SIAH in facilitating NO/netrin-1-dependent cardioprotection, using the DCC receptor. Combination of netrin-1 and SIAH RNAi may prove to be a substantially effective therapy for myocardial infarction.