Objective: The underlying mechanism by which nitric-oxide synthase (iNOS) gene transfer inhibits hypoxia-induced PASMCs proliferation remains unknown. The aim of this study is to investigate if iNOS gene transfer to PASMCs during hypoxia has any effect on cell cycle progression.
Methods: Using the cationic liposome mediation method, we transfected a recombinant pLNCX/Inos vector into rat PASMCs. The instantaneous transgenic expression and the function of the recombinant protein were detected. Cell cycle analysis was performed by flow cytometry and cell proliferation assay by [(3)H] thymidine incorporation. The proteins involved in cell cycle control (P27 and P21) were determined by RT-PCR and flow cytometry.
Results: iNOS expression was detected in the transfected PASMCs. NO(2)(-) levels were increased in iNOS-transfected cells as compared to the untransfected cells. Expression of iNOS in rat PASMCs under hypoxia resulted in a delay in inhibition of DNA synthesis and cell cycle progression. The incorporation of [(3)H] thymidine in iNOS-transfected group (15,145 +/- 1,514) dpm was significantly lower than those in the hypoxia group (18,011 +/- 2,521) dpm (P < 0.01). The G(0)/G(1) cell cycle arrest rate in the iNOS-transfected group (67.8%) was significantly higher than those in the hypoxia group (46.8%) (P < 0.01). The protein level of P27 was down-regulated by hypoxia but not in iNOS-transfected cells under hypoxia, and the level of the latter was similar to that under normoxia.
Conclusions: Pre-transfer of iNOS gene to PASMCs under hypoxia inhibits cell proliferation via blocking P27 down-regulation, which is an important mechanism for the delay of cell cycle progression.