Regulation of apoptosis in human cancer cells

Abstract

Nitric oxide is postulated to protect cancer cells from the death-inducing effects of tumour necrosis factor alpha by S-nitrosating the active site cysteines, inhibiting cleavage of caspase-9. We aimed to test this hypothesis and to determine its validity across cancer cell types. In addition, we hoped to explain the involvement of certain kinases in nitric oxide-induced apoptosis. The experimental setup involved stimulating human colorectal cancer cells, HT-29 and HCT- 116, and human prostate cancer cells, LNCaP, with cytokines in order to induce cell death. Then, we observed the effects of NO inhibitors, kinase inhibitors, and activation of Akt, a kinase up-stream of the caspase cascade, following transfection of a DNA sequence that was proven to protect cells against apoptosis induction. In our series of experiments, inhibition of the nitric oxide synthases removes nitric oxide protection from apoptosis, but inhibition of only the inducible synthase has opposite effects with prostate and colon cancer cells that are considered insignificant, and its effects on the two types of colon cancer cells are in discord. Transformation and transfection of ARK5 into the colorectal cancer cell line, HT-29 did not prove beneficial. Similarly, glucosamine showed no clear pattern of reducing apoptosis in the cells. Therefore, we propose further exploration of the inhibition of constitutive nitric oxide synthases as a potential therapy.