Objective    To construct a pHippy vector encoding siRNA for mitogen-activated protein kinase (MAPK) by bidirectional promoter RNA interference

and study its suppressing effect on expression of MAPK in rat vascular smooth muscle cells (VSMCs)．     Methods    Three siRNA sequences to MAPK were designed and synthesized

and then subcloned into plasmid pHippy. The plasmid expressing EGFP siRNA served as control. After restriction enzyme digestion and sequencing

the selected positive recombinant plasmid were transfected into primary isolated rat VSMCs. The mRNA and protein expressions of MAPK in VSMCs were analyzed by RT-PCR and Western blot analysis respectively．Tri

tiated thymidine (

3

H-TdR) incorporation was used to measure the proliferation of the cells

and immunoprecipitation for the activity of MAPK.     Results    Three RNA interference pHippy-MAPK vectors based on bidirectional promoter were constructed and one of them suppressed MAPK expression effectively. And it dramatically inhibited the cell proliferation and the MAPK activity.     Conclusion    One of our obtained pHippy-MAPK3 vector based on bidirectional promoter can suppress MAPK expression in VSMCs significantly

and the vector can be used as a tool to regulate MAPK pathway.