Aortic-preferentially-expressed gene-1 (APEG-1) and striated muscle preferentially expressed (SPEG) polypeptide, DNA sequences encoding and controlling the transcription of the APEG-1/SPEG encoding gene, methods of diagnosing vascular injury, methods of conferring smooth muscle-cell specific expression, and methods of inhibiting vascular smooth muscle cell proliferation by increasing the level of APEG-1 at the site of vascular injury.