Spectrin-Based Complex for Regulation of Signal Transducer and Activator of Transcription 3 Signaling and Heart Function
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Date
2016-05
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The Ohio State University
Abstract
Maladaptive cardiac remodeling is an important step in the progression of heart failure and is characterized by changes in cardiac chamber size, structure, and performance induced by a constellation of cell- and tissue-level factors. While great strides have been made in identifying membrane receptors, signaling molecules, and transcription factors involved in the remodeling process, fundamental questions remain about the molecular pathways linking extracellular stress cues to cellular reprogramming underlying progression of disease. Signal Transducer and Activator of Transcription 3 (STAT3) is a multifunctional transcription factor which regulates expression of gene programs important for inflammation, cell survival, and hypertrophy. While STAT3 signaling modulates cardiomyocyte function in response to ischemia and biomechanical stress, the molecular pathways that coordinate STAT3 activity is unclear. We hypothesized that βIV-spectrin, an actin associated cytoskeletal protein, coordinates a macromolecular complex with CaMKII and STAT3 to promote phosphorylation/activation of STAT3 at the cardiomyocyte submembrane. We believe that dysfunction of βIV-spectrin will induce cardiac malfunction downstream of STAT3. To understand the interaction between STAT3 and βIV-spectrin, novel mouse models expressing truncated βIV-spectrin protein lacking the validated CaMKII binding domain (qv3J), a cardiac-selective knockout (cKO) of βIV-spectrin, and wildtype littermates were used. Cardiac function was assessed by echocardiography at baseline and post Transverse Aortic Constriction (TAC). Levels of total and phosphorylated STAT3 and CaMKII were assessed in whole heart lysates by western blot, pull-down, and co-immunoprecipitation assays to measure relevant protein concentrations and interactions. Permeabilized cardiomyocytes were immunostained for βIV-spectrin, CaMKII, and STAT3 and protein localization was assessed by confocal microscopy to study the activation and localization of STAT3. βIV-spectrin cKO mice showed decreased heart function while qv3J mice displayed normal cardiac function at baseline and post TAC, compared to wildtype. Mice lacking βIV-spectrin/CaMKII/STAT3 interaction demonstrated abnormal STAT3 regulation and response to biomechanical stress. This study indicates the presence of a novel complex between βIV-spectrin and STAT3, thereby regulating the localization of STAT3 in cardiomyocytes. Future studies will address the specific role of STAT3 in pathology associated with spectrin-deficiency.
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Keywords
Beta IV Spectrin, STAT3, Heart Function