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(Circulation Research. 2005;97:427.)
© 2005 American Heart Association, Inc.

Molecular Medicine

Depletion of Serum Response Factor by RNA Interference Mimics the Mitogenic Effects of Platelet Derived Growth Factor-BB in Vascular Smooth Muscle Cells

Nihal Kaplan-Albuquerque, Vicki Van Putten, Mary C. Weiser-Evans, Raphael A. Nemenoff

From the Department of Medicine, University of Colorado Health Sciences Center, Denver.

Correspondence to Dr Raphael A. Nemenoff, Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Health Sciences Center, Box C-281, 4200 E 9th Ave, Denver, CO 80262. E-mail Raphael.Nemenoff{at}UCHSC.edu

Promoters of many smooth muscle-specific genes (SM-genes) contain multiple CArG boxes, which represent a binding site for serum response factor (SRF). Transciptional control through these regions involves interactions with SRF and specific coactivators such as myocardin. We have previously reported that suppression of SM-gene expression by platelet derived growth factor (PDGF) is associated with redistribution of SRF, leading to lower intra-nuclear levels, and a reduction in SRF transactivation. To further assess the role of SRF depletion on VSMC phenotype, the current study used RNA interference (RNAi). Two SRF-specific sequences constructed as hairpins were stably expressed in rat VSMC. Clones expressing SRF RNAi had no detectable SRF expression by immunoblotting, and showed diminished levels of SM -actin protein and promoter activity. Unexpectedly, depletion of VSMC resulted in increased rates of proliferation and migration. Several genes whose expression is increased by PDGF stimulation, including c-Jun, were similarly induced in cells lacking SRF. Effects of SRF depletion were not attributable to altered PDGF receptor activity or alterations in activation of Akt. These data indicate that loss of SRF transactivation in VSMC, in this case through suppression via RNAi, induces biological responses similar to that seen with PDGF.

Key Words: vascular smooth muscle cells • serum response factor • RNA interference • platelet derived growth factor

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