Inhibition of GSK-3β enhances reovirus-induced apoptosis in colon cancer cells

Reovirus functions as an oncolytic agent for many types of cancer including colon cancer. Although most studies have emphasized the role of activated Ras signaling in enhancing reoviral oncolysis in susceptible cells, we note that many colon cancers also display elevated beta -catenin. Thus, it is possible that enhanced beta -catenin may augment reoviral susceptibility in colon cancer cells. To explore this hypothesis, HEK293 cells were treated with the glycogen synthase kinase (GSK)-3 beta inhibitor LiCl, thereby inducing beta -catenin, followed by reoviral infection. Co-administration with LiCl indeed enhanced cell death compared to reovirus infection alone, but this was not associated with elevated reoviral replication. Similarly, HEK293 cells expressing the Frizzled-1 receptor in Wnt3a-conditioned medium also showed reovirus replication equivalent to that in cells in control medium, further suggesting that up-regulation of beta -catenin does not enhance the replication of reovirus. Instead, we observed that inhibition of GSK-3 beta with LiCl decreased reovirus-induced NF-?B activation, leading to accelerated apoptosis via caspase 8 activation. We further found that colon cancer HCT116 cells were sensitized to apoptosis by co-treatment with reovirus and a GSK-3 beta inhibitor, AR-A014418. Finally, we identified that inhibition of NF-?B sensitized apoptosis of HEK293 or HCT 116 cells during reovirus infection. Taken together, we propose that inhibition of GSK-3 beta sensitizes reovirus-induced apoptosis of colon cancer cells by down-regulation of NF-?B activity, offering a potentially improved therapeutic strategy for the treatment of colon cancer.