The small GTPase Rac1 is required for smooth muscle contraction

Abstract

Key pointsr The role of the small G-protein Rac1 was investigated in smooth muscle, using a smooth muscle-specific knockout mouse and pharmacological blockers. r The results demonstrate a novel Rac1-associated signalling pathway for regulation of smooth muscle contraction. AbstractThe role of the small GTP-binding protein Rac1 in smooth muscle contraction was examined using small molecule inhibitors (EHT1864, NSC23766) and a novel smooth muscle-specific, conditional, Rac1 knockout mouse strain. EHT1864, which affects nucleotide binding and inhibits Rac1 activity, concentration-dependently inhibited the contractile responses induced by several different modes of activation (high-K + , phenylephrine, carbachol and protein kinase C activation by phorbol-12,13-dibutyrate) in several different visceral (urinary bladder, ileum) and vascular (mesenteric artery, saphenous artery, aorta) smooth muscle tissues. This contractile inhibition was associated with inhibition of the Ca 2+ transient. Knockout of Rac1 (with a 50% loss of Rac1 protein) lowered active stress in the urinary bladder and the saphenous artery consistent with a role of Rac1 in facilitating smooth muscle contraction. NSC23766, which blocks interaction between Rac1 and some guanine nucleotide exchange factors, specifically inhibited the α 1 receptor responses (phenylephrine) in vascular tissues and potentiated prostaglandin F2α and thromboxane (U46619) receptor responses. The latter potentiating effect occurred at lowered intracellular [Ca 2+ ]. These results show that Rac1 activity is required for active contraction in smooth muscle, probably via enabling an adequate Ca 2+ transient. At the same time, specific agonists recruit Rac1 signalling via upstream modulators, resulting in either a potentiation of contraction via Ca 2+ mobilization (α 1 receptor stimulation) or an attenuated contraction via inhibition of Ca 2+ sensitization (prostaglandin and thromboxane receptors).

Glucotoxicity promotes aberrant activation and mislocalization of Ras-related C3 botulinum toxin substrate 1 [Rac1] and metabolic dysfunction in pancreatic islet β-cells: reversal of such metabolic defects by metformin

“…Data from our current studies have provided evidence to suggest that Rac1 activation is upstream to CD36 expression since EHT1864, a known inhibitor of Rac1 [31, 32], attenuated HG-induced CD36 expression in INS-1 832/13 cells. Our findings are also compatible with recent observations of Elumalai and associates demonstrating regulatory roles for Rac1-Nox2 signaling axis promotes CD36 expression in INS-1 cells under the duress of glucotoxic conditions [19].…”

“…However, there was a 50% reduction in nuclear association of N17 mutant in cells under the same conditions [Figure 2; Panels A and B]. In the second approach, we utilized EHT1864, a known inhibitor of Rac1 [31, 32] to functionally inactivate endogenous Rac1 and then assessed nuclear association of Rac1 under LG and HG conditions. Data in Figure 2 [Panels C and D] demonstrate decreased localization of Rac1 in INS-1 832/13 cells exposed to EHT1864.…”

Rac1 Regulates Myosin II Phosphorylation Through Regulation of Myosin Light Chain Phosphatase

“…While this study was under preparation, Rahman et al (Rahman et al, ) reported quite recently that EHT1864 significantly inhibited both phenylephrine and high K + induced contraction of mouse saphenous artery, while NSC23766 inhibited phenylephrine but not high K + induced contraction. High concentration (100 μM) of NSC23766 completely inhibited phenylephrine induced increase in cytosolic Ca 2+ and contraction of saphenous artery, although it did not inhibit high K + induced contraction.…”

Involvement of Rho GTPases and their regulators in the pathogenesis of hypertension

“…12 Recently, Rac inhibitors (EHT1864, NSC23766) have been described to either potentiate or inhibit smooth muscle contraction depending on the vasoconstrictor used. 13 Rho GTPases and vascular NO signaling Endothelial cells are key regulators of the arterial tone by releasing vasoactive factors that modulate the contractile state of the underlying smooth muscle cells, in a great part through the regulation RhoA activity. While endothelium-derived contracting factors such as Et-1 activates RhoA, NO, the most important physiological endothelial relaxing factor, inactivates RhoA/Rock pathway.…”