Opposing Actions of Extracellular Signal-regulated Kinase (ERK) and Signal Transducer and Activator of Transcription 3 (STAT3) in Regulating Microtubule Stabilization during Cardiac Hypertrophy

Dominic C.H Ng,Ivan H.W Ng,Yvonne Y.C Yeap,Bahareh Badrian,Tatiana Tsoutsman,Julie R Mcmullen,Christopher Semsarian,Marie A Bogoyevitch

doi:10.1074/jbc.m110.128157

Abstract

Excessive proliferation and stabilization of the microtubule (MT) array in cardiac myocytes can accompany pathological cardiac hypertrophy, but the molecular control of these changes remains poorly characterized. In this study, we examined MT stabilization in two independent murine models of heart failure and revealed increases in the levels of post-translationally modified stable MTs, which were closely associated with STAT3 activation. To explore the molecular signaling events contributing to control of the cardiac MT network, we stimulated cardiac myocytes with an α-adrenergic agonist phenylephrine (PE), and observed increased tubulin content without changes in detyrosinated (glu-tubulin) stable MTs. In contrast, the hypertrophic interleukin-6 (IL6) family cytokines increased both the glu-tubulin content and glu-MT density. When we examined a role for ERK in regulating cardiac MTs, we showed that the MEK/ERK-inhibitor U0126 increased glu-MT density in either control cardiac myocytes or following exposure to hypertrophic agents. Conversely, expression of an activated MEK1 mutant reduced glu-tubulin levels. Thus, ERK signaling antagonizes stabilization of the cardiac MT array. In contrast, inhibiting either JAK2 with AG490, or STAT3 signaling with Stattic or siRNA knockdown, blocked cytokine-stimulated increases in glu-MT density. Furthermore, the expression of a constitutively active STAT3 mutant triggered increased glu-MT density in the absence of hypertrophic stimulation. Thus, STAT3 activation contributes substantially to cytokine-stimulated glu-MT changes. Taken together, our results highlight the opposing actions of STAT3 and ERK pathways in the regulation of MT changes associated with cardiac myocyte hypertrophy.

Highlights

In addition to well-established roles under physiological conditions, MT reorganization accompanies the development of cardiac disease [8]
When the levels of phosphorylated STAT3 were normalized against total STAT3, we found a significant increase in mice with pressure overload hypertrophy (Fig. 1D)
To evaluate the contribution of STAT3 without the complication of extracellular signal-regulated kinase (ERK) activation, we looked at MT stabilization in a double mutation (TnI-203/MHC-403) murine model of cardiomyopathy that recapitulates a rapid progression to heart failure observed in human patients [24]

Summary

Introduction

In addition to well-established roles under physiological conditions, MT reorganization accompanies the development of cardiac disease [8]. In response to pressure overload, cardiac STAT3 phosphorylation was substantially increased in mice with compensated or decompensated hypertrophy (Fig. 1A) and correlated well with the elevated levels of posttranslationally modified tubulin. After normalizing for ␣-tubulin changes, LIF- and OSM-stimulated a significant increase in glu-tubulin levels compared with control cells (Fig. 3B).

Results

Conclusion