Nitric oxide represses the proliferation of Caco-2 cells by inducing S-G2/M cell cycle arrest.

Abstract

There is conflicting data regarding the ability of nitric oxide (NO) to promote or inhibit colorectal cancer cell proliferation. Furthermore, NO reacts rapidly with endogenous superoxide at a diffusion-controlled rate to give peroxynitrite (ONOO^-), a strong oxidant and nitrating agent. The aim of this study was to assess the effects of exogenous NO and ONOO^- on the proliferation of the colorectal cancer cell line Caco-2. NOR5 and SIN-1 were used as NO and ONOO^- donors, respectively. Both NOR5 and SIN-1 inhibited the proliferation of the Caco-2 cells; however, the effect of NOR5 was slightly stronger than that of SIN-1. The results also indicated that NO plays a major role in the inhibition of SIN-1-induced proliferation of Caco-2 cells. The results of a terminal deoxynucleotidyl transferase dUTP nick end labeling assay, cell cycle analysis, and p21 protein expression measurement further indicated that NO induced S-G₂/M phase arrest, but not apoptosis, in the Caco-2 cells. The results suggest that NO, rather than ONOO^-, has the potential to repress the proliferation of Caco-2 cells by inducing S-G₂/M cell cycle arrest.