Glucocorticoid Receptor-mediated Expression of Caldesmon Regulates Cell Migration via the Reorganization of the Actin Cytoskeleton

Kenji Sobue,Tsuyoshi Morita,Taira Mayanagi,Kentaro Fukumoto,Ken'ichiro Hayashi

doi:10.1074/jbc.m801606200

Abstract

Glucocorticoids (GCs) play important roles in numerous cellular processes, including growth, development, homeostasis, inhibition of inflammation, and immunosuppression. Here we found that GC-treated human lung carcinoma A549 cells exhibited the enhanced formation of the thick stress fibers and focal adhesions, resulting in suppression of cell migration. In a screen for GC-responsive genes encoding actin-interacting proteins, we identified caldesmon (CaD), which is specifically up-regulated in response to GCs. CaD is a regulatory protein involved in actomyosin-based contraction and the stability of actin filaments. We further demonstrated that the up-regulation of CaD expression was controlled by glucocorticoid receptor (GR). An activated form of GR directly bound to the two glucocorticoid-response element-like sequences in the human CALD1 promoter and transactivated the CALD1 gene, thereby up-regulating the CaD protein. Forced expression of CaD, without GC treatment, also enhanced the formation of thick stress fibers and focal adhesions and suppressed cell migration. Conversely, depletion of CaD abrogated the GC-induced phenotypes. The results of this study suggest that the GR-dependent up-regulation of CaD plays a pivotal role in regulating cell migration via the reorganization of the actin cytoskeleton.

Highlights

Because of their pharmacological properties, they have been widely used to treat inflammatory and autoimmune diseases [5, 6]
Two isoforms with different molecular weights (Mr), generated from a single gene by alternative splicing, have been identified as follows: high Mr CaD (h-CaD; 120 –150 kDa) and low Mr CaD (l-CaD; 70 – 80 kDa) [18, 19]. h-CaD is exclusively expressed in smooth muscle cells (SMCs), but l-CaD is widely expressed in non-muscle cells [18]. h-CaD is a component of smooth muscle thin filaments and regulates their contraction via inhibition of the actin-myosin interaction [20, 21]. l-CaD has an alternative function for stabilizing actin filaments in non-muscle cells, in addition to regulating contraction [22, 23]
These results indicate that CaD plays a pivotal role in cell migration in response to GCs, and will shed light on the mechanisms underlying the effects of GCs

Summary

Introduction

Because of their pharmacological properties, they have been widely used to treat inflammatory and autoimmune diseases [5, 6]. Rho activity as measured by a pulldown assay using RBD (Rho binding domain) beads, by examining the expression levels of the Rho downstream effectors ROCK1, ROCK2, and mDia1, or by evaluating the phosphorylation levels of cofilin and myosin light chain (MLC) (Fig. 1C), suggesting that the DEX-induced enhancement of thick stress fiber formation and focal adhesion assembly is independent of the Rho signaling pathway.

Results

Conclusion