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"The redox-sensitive regulation of Guanylyl Cyclase activity is mediated by Thioredoxin (Trx1)"

Can Huang
Pharmacology and Physiology Program
B.S. 2010, Wuhan University, China

Thesis Advisor: Annie V. Beuve, Ph.D.
Department of Pharmacology, Physiology and Neuroscience

Tuesday, May 30, 2017
1:00 P.M., MSB Room H609


Nitric oxide (NO) modulates physiologic events through two distinct signaling pathways: the classical cGMP-dependent pathway and the newly established cGMP-independent pathway. NO stimulates its receptor, the NO-sensitive Guanylyl Cyclase (GC1), to produce cGMP, which activates protein kinase G (PKG) signaling cascade. In particular, the cGMP/PKG pathway plays an important role in mediating the endothelium-dependent vasorelaxation, which is disrupted under oxidative conditions. Evidence suggests that NO signal can be transduced independent of cGMP through S-nitrosation (SNO). S-nitrosation is a post-translational modification, reversibly modifying protein activity, localization, and conformation.
Previous study in the lab has shown that GC1 S-nitrosation (SNO-GC1) is responsible for its desensitization to NO stimulation. Diminished NO sensitivity of GC1 decreases the activity of cGMP/PKG signaling, thus impairing the vascular reactivity and vessel tone. GC1 desensitization and S-nitrosation have been characterized in tissues subjected to oxidative stress, suggesting that GC1 is a redox sensor. Thioredoxin-1 (Trx1) catalyzes thiol reductions to regulate cellular redox homeostasis, such as disulfide reduction, denitrosation, and transnitrosation. Hence, we hypothesized that Trx1 modulates NO sensitivity of GC1 by exerting its oxidoreductase activity.

We demonstrated that inhibition or depletion of the Trx system reduces NO-stimulated activity of GC1. Conversely, the overexpression of Trx1 enhanced GC1 activity. Biochemical studies indicate a direct interaction between GC1 and Trx1, which is enhanced by protein S-nitrosation. Further, we showed that Trx1 protects GC1 NO sensitivity from SNO-induced desensitization, suggesting that Trx1 is involved in the regulation of GC1 activity.

We then characterized a newly identified function of GC1 as a transnitrosating enzyme, in particular under conditions of nitrosative stress. SNO-GC1 can transfer its NO moiety to oxidized Trx1 (oTrx1, without reductase activity). Proteomic analyses of S-nitrosated peptides, isolated from cells with manipulated levels of GC1, suggest that GC1 could directly or through oTrx1 transnitrosate several proteins that modulate cell cycle progression, apoptosis and vascular reactivity.

Taken together, we proposed that 1) reduced Trx1 modulates GC1 activity by catalyzing its denitrosation to restore NO sensitivity; 2) when Trx1 predominantly exists in its oxidized form, GC1 transduces NO signal through transnitrosation. The oTrx1 may act as a mediator in GC1-dependent transnitrosation. Our findings in this thesis will provide insights into a better understanding of the mechanism for preserving and/or restoring NO signal transduction, which plays an essential role in cardiovascular physiology and pathology.

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