ABSTRACT
We assessed the effect of angiotensin II on fibronectin biosynthesis a nd transcription factor activation in adult human mesangial cells in culture. We found that 10(-5) mol/L angiotensin II tended to increase fibronectin mRNA expression within 1 hour (1.2-fold +/- 0.3-fold of that in controls), with a significant increase after 4 hours (0.3-fold +/- 0.1-fold of that in controls, p < 0.05) and 24 hours (1.9-fold +/- 0.3-fold of that in controls, p < 0.02). In conjunction with increased fibronectin mRNA levels, angiotensin II exposure resulted in a significant elevation in immunoreactive fibronectin concentrations and the incorporation of (35S)-labeled methionine into fibronectin after 2 hours (224% +/- 23% of controls, p < 0.05). Angiotensin II also induced mesangial cell activation of the cyclic adenosine monophosphate response element binding protein (CREB) transcription factor, a DNA binding protein known to recognize specific regulatory elements present on the fibronectin gene promoter. Using the electrophoretic mobility shift assay, we showed that angiotensin II increased mesangial cell expression of the activated form of CREB after 4 hours (1.2-fold +/- 0.04-fold of that in controls, p < 0.05). To determine the importance of the CREB regulatory elements in mediating angiotensin II induction of fibronectin gene transcription, JEG-3 cells were transfected with plasmids containing fibronectin promoter-chloramphenicol acetyltransferase (CAT) reporter gene constructs with (FN510) or without (FN122) the CREB regulatory motifs. Angiotensin II resulted in a significant increase in CAT activity in FN510 transfectants (1.6-fold +/- 0.2-fold of that in controls, p < 0.05), but there was no effect of angiotensin II on FN122 transfected cells. These data demonstrate that angiotensin II stimulates fibronectin biosynthesis in adult human mesangial cells and suggest that the process may be regulated at the transcriptional level.
