Bl. Wolfe et al., INSULIN-LIKE GROWTH FACTOR-I REGULATES TRANSCRIPTION OF THE ELASTIN GENE, The Journal of biological chemistry, 268(17), 1993, pp. 2418-2426
Neonatal rat aortic smooth muscle cell cultures were used to investiga
te the mechanisms by which insulin-like growth factor-I (IGF-I) up-reg
ulates aortic elastogenesis. The addition of IGF-I (50 ng/ml) to quies
cent smooth muscle cell cultures resulted in a 5-fold increase in the
steady-state levels of tropoelastin mRNA beginning between 2 and 4 h a
nd reaching maximal levels at 8 h. Addition of cycloheximide blocked t
he effect of IGF-I. Nuclear run-on transcription analyses of nuclei is
olated from IGF-I-treated cells showed increased synthesis of new trop
oelastin transcripts indicating that transcriptional activation is a m
ajor component of IGF-I up-regulation. Transient transfections with de
letion constructs containing different portions of the elastin 5'-upst
ream region localized the IGF-I-responsive area to sequences between -
195 and -136 base pairs and further showed that this region contains a
negative element. Gel retardation assays using nuclear proteins extra
cted from control and IGF-I-treated cells demonstrated that IGF-I trea
tment results in the loss of binding complexes. Footprint analyses of
specific binding complexes affected by IGF-I show the deprotection of
two closely positioned sequences spanning positions -165 to -137 base
pairs. These results suggest that IGF-I up-regulation of elastogenesis
involves the abrogation of a negative element functionality.