Salidroside induces cell apoptosis and inhibits the invasiveness of HT29 colorectal cells by regulating protein kinase R, NF-κB and STAT3

BACKGROUND: Protein kinase R (PKR) can suppress various types of solid tumors by inducing cellular oxidative stress and apoptosis. Likewise, Slaidorside, a plant flavonoid, was shown to have anti-tumorigenesis in many solid tumors. OBJECTIVE: This study evaluated anti-tumorigenesis of Salidroside in HT29 colorectal cancer and investigated if the underlying mechanism involves activation of PKR. METHODS: Control or PKR deficient cells were cultured in DMEM media treated with 100 mu M Salidroside and cell survival, apoptosis, and other biochemical-related markers were evaluated. RESULTS: Salidroside significantly reduced cell survival and proliferation and increased the release of lactate dehydrogenase (LDH) and levels of single-stranded DNA (ssDNA). It also increased the protein levels of caspases 3 and 8. Concomitantly, Salidroside increased the protein level and activity of PKR and increased the expression of its downstream targets, p-eIE2 alpha (Ser(51)), p53 MAPK, and p53. On the contrary, it inhibited the nuclear activation of STAT-3 and NF-kappa B p65. In PKR deficient cells, the partial effects of Salidroside on cell survival, proliferation, and apoptotic markers were observed coincided with no effects on the expression of eIE-2 alpha, and JNK, p53, p38 MAPK, and caspase 8 but with a significant decrease in the nuclear activities of STAT3 and NF-kappa B. CONCLUSION: Salidroside suppresses the tumorigenesis of HT29 CRC by increasing activation of eIF-2 alpha and JNK and upregulation of p53, p38 MAPK, and caspase-8 through upregulating and activation of PKR. However, the tumor suppressor effect of Salidroside requires also inhibition of STAT3 and NF-kappa B in a PKR-independent mechanism.