Intestinal obstructions lead to a variety of motility disorders. Small intestine smooth muscles undergo dramatic phenotypic changes in response to obstruction, but the underlying molecular mechanisms are unknown. Using RT-PCR, ChIP, Re-ChIP, and Western blots, we examined the effect of small bowel mechanical obstruction on smooth muscle gene expression. Obstruction caused a transient
hyperplasia, followed by a prolonged hypertrophic response of small intestine smooth muscle cells. Smooth muscle
myosin heavy chain (MHC),
alpha-actin, and
gamma-actin expression decreased initially, and then increased as
hypertrophy developed.
Myocardin expression decreased initially and then increased, while
kruppel-like factors (KLF)4 and KLF5 expression increased initially, and then decreased.
Serum response factor (SRF) expression decreased initially, and then recovered to
sham-operated levels as
hypertrophy developed. SRF binding to smooth muscle MHC and
alpha-actin promoters decreased initially, but then increased above
sham-operated levels as
hypertrophy developed. Elk-1 binding to smooth muscle
myosin heavy chain and
alpha-actin promoters increased initially, and then decreased to
sham-operated levels as
hypertrophy developed. c-fos expression increased initially, which was associated with increased SRF/Elk-1 binding to the c-fos promoter. The Elk-1 phosphorylation inhibitor
U-0126 inhibited the increase in c-fos expression. These findings indicate a dynamic response of small intestine smooth muscles to bowel obstruction involving switching between differentiated, proliferative, and hypertrophic phenotypes. These results suggest that changes in the expression and interactions between SRF,
myocardin, Elk-1, and c-fos play key roles in the phenotypic switching of small intestine smooth muscles in response to mechanical obstruction.