We have examined the regulation of endothelial IGFBP-3 production by I
GF-I and TGF-P, two growth factors thought to play major roles in the
complications of diabetes mellitus. In addition, we developed a sensit
ive method for IGFBP-3 mRNA quantitation by adapting the fluorescent m
odification of the competitive PCR strategy. Our results using both No
rthern analysis and the fluorescent competitive PCR method indicate th
at: (1) IGFBP-3 mRNA is increased 2- to 10-fold by IGF-I and maximally
reduced to 20% of control by TGF-P; (2) the changes in mRNA levels co
rrelate with the levels of IGFBP-3 protein secreted into the media by
these cells; (3) the induction of IGFBP-3 mRNA and protein by IGF-I an
alogs was directly related to their ability to bind to the type I IGF
receptor, reflecting an IGF-I receptor-mediated process; and (4) stead
y state IGFBP-3 mRNA levels did not change significantly after a 6 h i
ncubation with actinomycin D in the presence or absence of the growth
factors suggesting that the observed IGF-I/TGF-beta effects occur at t
he level of gene transcription rather than mRNA stability.