Acid/bile exposure triggers TRAIL-mediated apoptosis in esophageal cancer cells by suppressing the decoy receptors and c-FLIPR.

Esophageal adenocarcinoma essentially develops from esophageal inflammation caused by chronic GERD. During GERD episodes, the lower esophageal epithelium is repeatedly exposed to stomach acid, which often contains duodenal bile salts that prompt malignant transformation. TRAIL is one of the cytokines produced in response to such insults and targets the transformed cells exclusively. In this study, we simulated GERD episodes in vitro by exposing the cancer cells to acid or acid/bile combination and found that the cancer cells lived through acid attacks by expression of the decoy receptors and c-FLIPR but died of TRAIL-mediated apoptosis when bile salts were present. Further investigation revealed that acid/bile exposure downregulated the decoy receptors and thereby facilitated TRAIL signaling; meantime, it inhibited protein kinase C activity and thus expedited c-FLIPR degradation, allowing apoptosis to take place.

Overexpression of CCN1 in Het1A cells attenuates bile-induced esophageal metaplasia through suppressing non-canonical NFκB activation.

GERD is the most common gastrointestinal diagnosis given during office visit. People who suffer from a long history of GERD eventually develop Barrett's esophagus, a premalignant intestinal metaplasia due to NFκB activation. Previous studies focused on the contribution of TNF-triggered canonical NFκB pathway to this event. In this study, we demonstrated in vitro that it was LTA, rather than TNF, initiated canonical NFκB activation at the beginning of acid/bile attacks, but later it switched to CD40-activated non-canonical pathway, which played a bigger part in esophageal metaplasia. CCN1 attenuated this cellular transformation by suppressing CD40 and its associated proteins involved in non-canonical signaling.

CCN1 induces apoptosis in esophageal adenocarcinoma through p53-dependent downregulation of survivin.

Many cancer drugs have been developed to control tumor growth by inducing cancer cell apoptosis. However, several intracellular barriers could fail this attempt. One of these barrier is high expression of survivin. Survivin can interfere caspase activation and thereby abort apoptosis. In this study, we found that CCN1 suppressed the survivin expression in tumor cells of esophageal adenocarcinoma (EAC) and thus allowed apoptosis to finish. Furthermore, we demonstrated that this downregulation was dependent on p53 phosphorylation at Ser20, and CCN1 induced EAC cell apoptosis through the activation of p53.

CCN1 sensitizes esophageal cancer cells to TRAIL-mediated apoptosis.

TRAIL is one of the best anti-cancer molecules in our body. It kills a variety of cancer cells that are resistant to conventional chemotherapy, without causing much negative impact on normal cells, because its death receptors are almost exclusively found on cancer cells. However, some cancer cells are not sensitive to TRAIL treatment, even though they express its death receptors. A second molecule is needed to help TRAIL to complete its mission. Finding such molecules now becomes a top priority in cancer research. Our study shows that CCN1 is such a molecule. CCN1 was highly expressed in the esophageal epithelium of the patients suffering from gastroesophageal reflux disease, but faded away as the situation worsened towards adenocarcinoma. Treating the tumor cells with CCN1 resulted in apoptosis, while the same treatment to the normal cells only nourished cell growth. It was TRAIL that mediated this process. Apparently, CCN1 altered the expression profile of TRAIL and its receptors in tumor cells, namely, activating TRAIL and its death receptors and shutting down its decoy receptors. CCN1 and TRAIL worked as a team to put the cancer cells to death, as elimination of either one failed apoptosis.