Objectives: Alterations in NO/cGMP signaling have been associated with vascular dysfunction. Here, we tested whether peptides containing arginine-glycine-aspartic acid (RGD) motifs, commonly found on the binding sites of extracellular matrix to integrins, could increase the expression and function of soluble guanylate cyclase (sGC) in human mesangial cell (HMC), and human aortic smooth muscle (HASMC) cells.
Methods and results: Arginine-glycine-aspartic acid-serine (RGDS) promoted an up-regulation in the sGC beta1 subunit steady-state level, both in HMC and HASMC, in a time- and dose-dependent manner. The cellular effects of RGDS-stimulation of sGC expression was an enhanced cellular response to sodium nitroprusside, resulting in elevated cGMP levels and vasodilator-stimulated phosphoprotein (VASP) phosphorylation in both kinds of cells, and an increased NO relaxing effect on cells precontracted with H(2)O(2) or Angiotensin II. Moreover, RGDS was able to restore the sGC levels that had been previously decreased by long term exposure to NO donors. RGDS effects on sGC regulation were due to the specific interaction with alpha(5)beta(1) integrin. To investigate the intracellular mechanisms activated after RGDS cell treatment, pharmacological kinase inhibitors were used. The effect of RGDS on sGC protein content was completely abolished by treating the cells with c-Jun N-terminal kinase (JNK) inhibitors. In addition, c-fos and c-jun were found in the cell nuclei after RGDS treatment, suggesting that the RGDS effect could be mediated by the AP-1 transcription factor.
Conclusion: Results provide evidence of a mechanism able to increase the sGC protein content linked to increased activity in contractile cells, not only in basal conditions, but also after the down-regulation of the receptor by its own substrate. Elucidation of this novel mechanism provides a rationale for future pharmacotherapy in certain vascular diseases.