The Small GTP-binding Protein Rac1 Induces Cardiac Myocyte Hypertrophy through the Activation of Apoptosis Signal-regulating Kinase 1 and Nuclear Factor-κB

Masatsugu Hori,Toshiaki Mano,Kazunori Kashiwase,Kazuhiko Nishida,Toshihiro Takeda,Yoshiharu Higuchi,Hikaru Ueno,Hiroyuki Nakayama,Osamu Yamaguchi,Shinichi Hirotani,Yasushi Matsumura,Shungo Hikoso,Kinya Otsu,Tetsuya Watanabe

doi:10.1074/jbc.m213203200

Abstract

The small guanine nucleotide-binding protein Rac1 has emerged as an important molecule involved in cardiac myocyte hypertrophy. Recently, we reported on apoptosis signal-regulating kinase (ASK) 1 and a transcriptional factor, nuclear factor-kappaB (NF-kappaB), as novel signaling intermediates in cardiac myocyte hypertrophy. The aim of the study presented here was to clarify the role of Rac1 in the ASK1-NF-kappaB signaling pathway. Infection of isolated neonatal cardiac myocytes with an adenovirus expressing a constitutively active form of Rac1 (RacV12) enhanced the expression of a kappaB-dependent reporter gene construct and induced the degradation of IkappaBalpha. Expression of a degradation-resistant mutant of IkappaBalpha inhibited the RacV12-induced hypertrophic responses, including increases in protein synthesis and atrial natriuretic factor production and the enhancement of sarcomeric organization. An immune complex kinase assay indicated that the expression of RacV12 activated ASK1. Expression of a dominant negative mutant of ASK1 eliminated the RacV12-induced NF-kappaB activation and the biochemical and morphological hypertrophic responses, whereas expression of a dominant negative form of Rac1 attenuated phenylephrine-induced activation of ASK1 and NF-kappaB and cardiac myocyte hypertrophy. These findings suggest that Rac1 induces cardiac myocyte hypertrophy mediated through ASK1 and NF-kappaB.

Highlights

Cardiac myocyte hypertrophy is an important adaptive process in response to various extracellular stimuli such as mechanical stress, cytokines, and growth factors
We demonstrated that Rac1 induces cardiac myocyte hypertrophy via the activation of nuclear factor-␬B (NF-␬B) and that apoptosis signal-regulating kinase 1 (ASK1) is required for the activation of NF-␬B and the development of cardiac myocyte hypertrophy
We examined whether NF-␬B is involved as a transcription factor in RacV12-induced cardiac myocyte hypertrophy

Summary

Introduction

Cardiac myocyte hypertrophy is an important adaptive process in response to various extracellular stimuli such as mechanical stress, cytokines, and growth factors. Infection of isolated neonatal cardiac myocytes with an adenovirus expressing a constitutively active form of Rac1 (RacV12) enhanced the expression of a ␬B-dependent reporter gene construct and induced the degradation of I␬B␣. Expression of a dominant negative mutant of ASK1 eliminated the RacV12-induced NF-␬B activation and the biochemical and morphological hypertrophic responses, whereas expression of a dominant negative form of Rac1 attenuated phenylephrine-induced activation of ASK1 and NF-␬B and cardiac myocyte hypertrophy.

Results

Conclusion