Protective effect of MUC2 siRNA against colon cancer growth through the induction of apoptosis

ABSTRACT

Mucinous colorectal cancers are highly aggressive phenotype presenting with more advanced disease and a poor prognosis. The biological mechanisms involved are unclear, but appear to be linked to mucin glycoprotein overexpression like MUC2. While the role of MUC2 in colon cancer metastasis is established, the biological events and molecular pathways modulated by MUC2 are still unknown. In this study, mucin expressing human colon cancer cells LS174T were grown 'in vitro' and MUC2 expression was inhibited by MUC2 small interfering RNA molecules [siRNA]. Cell culture and soft agar growth were measured to determine the overall effect on viability. Apoptosis was investigated by measuring protein level of polyADP-ribose polymerase [PARP], caspases-3 and -8. Finally, in vivo LS174T xenografts where grown in nude mice, different treatments included MUC siRNA, scramble siRNA or saline where administered, via tail vein injection, twice a week for two weeks. Results showed that upon treatment with MUC2-siRNA there was a 5-fold reduction cell culture growth and 9-fold reduction in soft agar growth in LS174T cells. A 3 to 5-fold increase in apoptosis was mediated by caspase-8 activation. Systemic administration of MUC2 siRNA markedly inhibited tumor growth in colon cancer xenografts grown in nude mice. Tumor growth inhibition was 59% by comparing MUC2 siRNA treatment and control siRNA treatments. There was no significance difference in tumor growth between control siRNA and normal saline treatment groups [p>0.05]. We conclude that MUC2 expression appears to protect LS174T colon cancer cells from apoptosis through extrinsic apoptosis pathway. We hypothesize that contrary to previous notions that MUC2 is a secreted glycoprotein involved in digestion and gastrointestinal tract lubrication, it appears to be involved in maintenance of LS174T cell viability. MUC2 may represent a therapeutic target in mucinous colorectal carcinomas