Thioredoxin-Interacting Protein (TXNIP) is a Biomechanical Regulator of Src Activity: Key Role in Endothelial Cell Stress Fiber Formation
Rationale: Fluid shear stress (FSS) differentially regulates endothelial cell (EC) stress fiber formation with decreased stress fibers in areas of disturbed-flow (d-flow) compared to steady-flow (s-flow) areas. Importantly, stress fibers are critical for several EC functions including cell shape, mechano-signal transduction, and EC cell-cell junction integrity. A key mediator of s-flow induced stress fiber formation is Src, which regulates downstream signaling mediators such as phosphorylation of cortactin, activity of focal adhesion kinase and small GTPases.
Objective: Previously we showed that thioredoxin-interacting protein (TXNIP, also VDUP1 and TBP-2) was regulated by FSS; TXNIP expression was increased in d-flow compared to s-flow areas. While TXNIP was originally characterized for its role in redox and metabolic cellular functions, recent reports show important scaffold functions related to its α-arrestin structure. Based on these findings, we hypothesized that TXNIP acts as a biomechanical sensor that regulates Src kinase activity and stress fiber formation.
Methods and Results: Using en face immunohistochemistry of the aorta and cultured EC, we show inverse relationship between TXNIP expression and Src activity. Specifically, s-flow increased Src activity and stress fiber formation, while it decreased TXNIP expression. In contrast, d-flow had opposite effects. We studied the role of TXNIP in regulating SHP2 plasma membrane localization and VE-cadherin binding, because SHP2 indirectly regulates dephosphorylation of Src tyrosine 527 that inhibits Src activity. Using immunohistochemistry and immunoprecipitation we found that TXNIP prevented SHP2-VE-cadherin interaction.
Conclusions:In summary, these data characterize a FSS mediated mechanism for stress fiber formation that involves a TXNIP-dependent VE-cadherin-SHP2-Src pathway.
- Received March 11, 2013.
- Revision received February 6, 2014.
- Accepted February 10, 2014.