Abstract
Treatment of aortic smooth muscle cells with PDGF induces the upregulation of protein tyrosine phosphatase 1B (PTP1B). PTP1B, in turn, decreases the function of several growth factor receptors, thus completing a negative feedback loop. Studies have reported that PDGF induces the downregulation of PKG as part of a repertoire of dedifferentiation of vascular smooth muscle cells. Other studies have reported that chronic nitric oxide (NO) treatment also induces the downregulation of PKG. In the present study, we tested the hypothesis that the downregulation of PKG by PDGF or NO in differentiated rat aortic smooth muscle cells can be attributed to the upregulation of PTP1B. We found that treatment with PDGF or NO induced an upregulation of PTP1B levels. Overexpression of PTP1B induced a marked downregulation of PKG mRNA and protein levels, whereas the expression of dominant negative PTP1B or short interfering RNA directed against PTP1B blocked the capacity of PDGF or NO to decrease PKG levels. We conclude that the upregulation of PTP1B by PDGF or NO is both necessary and sufficient to induce the downregulation of PKG via an effect on PKG mRNA levels.