Incorporating robustness requirements into antiwindup design

This paper treats the problem of synthesizing antiwindup compensators that are able to handle plant uncertainty in addition to controller saturation. The uncertainty considered is of the frequency-weighted additive type, often encountered in linear robust control theory, and representative of a wide variety of uncertainty encountered in practice. The main results show how existing linear matrix inequality based antiwindup synthesis algorithms can be modified to produce compensators that accommodate uncertainty better. Embedded within these results is the ever-present performance - robustness tradeoff. A remarkable feature is that the often criticized internal model control antiwindup solution emerges as an ldquooptimally robustrdquo solution. A simple example demonstrates the effectiveness of the modified algorithms

G protein involvement in US28-mediated Tcf-Lef activation.

<p>A, HEK293T cells were co-transfected with the Tcf-Lef reporter gene construct, a US28-expressing construct or empty plasmid control (mock) and various constructs expressing Gα-proteins as indicated, Gα_q-11 shRNA construct or a construct expressing regulator of G protein signaling 2 (RGS2), known to specifically interfere with Gα_q signaling. Tcf-Lef reporter gene activation was measured 24 hr after transfection and is displayed here as the percentage of the mock control that is set at 100%. B, HEK293T cells were co-transfected with the Tcf-Lef reporter gene construct, US28-expressing construct or empty plasmid control (mock) and an shRNA construct to decrease protein levels of Gα_q. Total cell extracts were analysed on Western blot using antibodies recognizing Gα_q or actin (insert). Bars represent level of Gα_q protein level compared to the actin levels, with the ratio in non-treated mock cells set at 100%. C, HEK293T cells were co-transfected with the Tcf-Lef reporter gene construct, a US28-expressing construct or empty plasmid control (mock) and various constructs expressing Gα₁₃, a constitutive active (CA) Gα₁₃ or Lsc-RGS, encoding the RGS domain of the Rho GTPase guanine nucleotide exchange factor (Rho-GEF) Lsc, known to specifically interfere with transmembrane signaling mediated by activated Gα_12/13. Tcf-Lef reporter gene activation was measured 24 hr after transfection and is displayed here as the percentage of the mock control that is set at 100%. D, HEK293T cells co-transfected with the Tcf-Lef reporter gene construct, a US28-expressing construct or empty plasmid control (mock) were treated (overnight) with various concentrations of the ROCK inhibitor Y27632 as indicated.</p

Schematic representation of the classic Wnt signaling pathway and model of US28-mediated activation of ß-catenin signaling pathway.

<p>The left side of the model indicates components of the classic Wnt/Frizzled mediated activation of ß-catenin. In this pathway the disruption complex (Axin, APC) that enables GSK3ß- and Caseine kinase 1 (CK1)-mediated phosphorylation of ß-catenin leading to its degradation, is disrupted in a Dishevelled-mediated way upon Wnt binding to Frizzled/LRP. US28 activates ß-catenin signaling in a ligand-dependent and independent manner, involving respectively Gα_12/13 and Gα_q proteins and respective RhoGEFs, converging at RhoA/ROCK, resulting in increased Tcf-Lef transcriptional activation.</p

Classical Wnt/Frizzled/ß-catenin

<p><b>signaling is not involved in US28-mediated Tcf-Lef activation.</b> A, Western blot analysis of total cell extracts of NIH-3T3 cells, stably expressing US28 or an empty plasmid (mock) which were treated with Wnt3a- (overnight, 200 ng/ml) and vehicle-treated mock cells. The blot was probed with antibodies recognizing the non-phosphorylated (active ß-catenin, total ß-catenin and actin. A representative blot is shown and normalized quantifications of (active) ß-catenin of independent experiments are shown below the blot. B, Western blot analysis of total cell extracts of NIH-3T3 cells stably expressing US28, the non G-protein coupling US28 mutant R¹²⁹A or an empty plasmid (mock) and Wnt3a-treated mock cells. The blot was probed with antibodies recognizing Lrp6-phospho-ser¹⁴⁹⁰ and actin. A representative blot is shown and normalized quantifications of Lrp6-phospho-ser¹⁴⁹⁰ of independent experiments are shown below the blot. C, HEK293T cells co-transfected with the Tcf-Lef reporter gene construct and either US28-expressing or an empty control plasmid (mock) exposed to Wnt3a (overnight, 200 ng/ml). Luciferase activity was measured 24 hr after transfection and is displayed here as the percentage of the non-treated mock control that is set at 100%. D, HEK293T cells co- transfected with the Tcf-Lef reportergene and an US28-expressing construct or empty plasmid control (mock) were exposed to various concentrations (ON, 10–25 µM) of the COX2 inhibitor celecoxib (Cxb). Tcf-Lef reporter gene activation was measured 24 hr after transfection and is displayed here as the percentage of the mock control that is set at 100%.</p

HCMV-infected cells stimulate activation of ß-catenin in a US28 dependent manner.

<p>A. HFF cells were infected with HCMV-WT or HCMV-ΔUS28 with a M.O.I of 1 on IBIDI slides. Cells were fixed 24 hours post-infection (hpi) and stained with antibodies recognizing the HCMV immediate early antigen (IEA) and activated ß-catenin respectively. B. U373-MG cells transfected with Tcf-Lef reporter gene were either infected with HCMV-WT or HCMV-ΔUS28 with a M.O.I. of 2, or left uninfected (mock). Luciferase activity was measured 48 h post-infection.</p