Slomiany B L, Slomiany A
Research Center, C875, Rutgers School of Dental Medicine, Rutgers, The State University of New Jersey, 110 Bergen Street, PO Box 1709, Newark, NJ, 07103-2400, USA,
Inflammopharmacology. 2015 Jun;23(2-3):111-8. doi: 10.1007/s10787-015-0235-2. Epub 2015 May 10.
A small GTPase, Rac1, is recognized as an important modulator of the inflammatory responses to bacterial lipopolysaccharide (LPS) by affecting the processes of phospholipase C activation. The activation of Rac1 involves the exchange of GDP for GTP and is catalyzed by the guanine nucleotide exchange factors (GEFs). Here, we report on the gastric mucosal GEF, Dock180, activation in response to H. pylori PS, and the hormone, ghrelin. We show that stimulation of gastric mucosal cells with the LPS leads to up-regulation in Dock180 phosphorylation on Tyr and Ser that is accompanied by a massive rise in Rac1-GTP level, while the effect of ghrelin, manifested by a drop in Dock180 phosphorylation on Ser, is associated with a decrease in Rac1-GTP formation. Furthermore, we demonstrate that phosphorylation on Tyr remains under the control of the Src family protein tyrosine kinases (SFK-PTKs), and is accompanied by Dock180 membrane translocation, while phosphorylation of the membrane-localized Dock180 on Ser represents the stimulatory contribution of protein kinase Cδ (PKCδ) to Dock180 activation. Moreover, we reveal that the interaction between Dock180 and PKCδ is dependent on Dock180 Tyr phosphorylation as well as the activity of PKCδ. Thus, our findings point to the involvement of PKCδ in the LPS-induced up-regulation of Dock180 activation, and suggest the modulatory mechanism of ghrelin influence on the gastric mucosal inflammatory responses to H. pylori.
一种小GTP酶Rac1，通过影响磷脂酶C的激活过程，被认为是对细菌脂多糖（LPS）炎症反应的重要调节因子。Rac1的激活涉及GDP与GTP的交换，由鸟嘌呤核苷酸交换因子（GEFs）催化。在此，我们报告胃黏膜GEF Dock180对幽门螺杆菌多糖（PS）和激素胃饥饿素的反应激活情况。我们发现，用LPS刺激胃黏膜细胞会导致Dock180酪氨酸（Tyr）和丝氨酸（Ser）磷酸化上调，同时伴随Rac1 - GTP水平大幅升高，而胃饥饿素的作用表现为Dock180丝氨酸磷酸化下降，这与Rac1 - GTP形成减少有关。此外，我们证明酪氨酸磷酸化仍受Src家族蛋白酪氨酸激酶（SFK - PTKs）控制，并伴随Dock180膜转位，而膜定位的Dock180丝氨酸磷酸化代表蛋白激酶Cδ（PKCδ）对Dock180激活的刺激作用。而且，我们揭示Dock180与PKCδ之间的相互作用依赖于Dock180酪氨酸磷酸化以及PKCδ的活性。因此，我们的研究结果表明PKCδ参与LPS诱导的Dock180激活上调，并提示胃饥饿素对胃黏膜幽门螺杆菌炎症反应的调节机制。
