One of the major unanswered questions in hypertension-is the mechanism of smooth muscle cell growth in response to an elevation of blood pressure. There is little information concerning the mechanisms which initiate the increase in smooth muscle cell mass. Recently, angiotensinogen mRNA, the precursor for angiotensin (ang) II, has been localized in the blood vessel wall. Since ang II increases smooth muscle cell growth in culture it has been suggested that it may be partially responsible for the increase in smooth muscle mass in vivo. Recently, the principal investigator has demonstrated that when ang II is added to quiescent cultures of rat aortic smooth muscle cells there is a resultant increase in the mRNA for the prootoncogenes c-fos and c-myc, followed by an increase in the mRNA for the A-chain of the platelet derived growth factor. This current proposal will examine in detail the molecular mechanisms by which ang II increases the PDGF A-chain mRNA and will also attempt to define the significance of this increase. Initially, the mechanisms by which ang II activates the PDGF A- chain gene will be studied by first performing nuclear run-off transcription assays and then mapping in detail the 5'-regulatory region of the PDGF A-chain gene to identify the element(s) that are responsive to ang II. Specific ang II induced nuclear binding proteins will be identified by a gel mobility shift assay and the binding sequence identified by a DNase protection assay. Since the c-fos protein complex can act as a transcriptional activator, and it is activated early following addition of ang II, the significance of this initial activation on the subsequent increase in PDGF A-chain will be investigated by blocking the rise in c-fos with an inducible antisense expression vector and antisense oglionucleotides. Finally, to test the significance of the rise in PDGF A-chain mRNA, this increase will be blocked with an inducible antisense expression vector. The effect of this inducible antisense plasmid on the ang II induced increase in smooth muscle cell size, DNA and protein synthesis will be evaluated. The above research should clearly elucidate the mechanisms by which ang II increases PDGF A-chain mRNA expression and ultimately PDGF A-chain release. Not only will this give us greater insight into the possible role this increase plays in hypertensive induced hypertrophy in vivo, but it will also elucidate the mechanism(s) by which ang II effects transcription.
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| Naftilan, A J; Gilliland, G K; Eldridge, C S et al. (1990) Induction of the proto-oncogene c-jun by angiotensin II. Mol Cell Biol 10:5536-40 |
