182 EXPRESSION OF THE PROANGIOGENIC FACTOR CYSTEINE-RICH PROTEIN 61 GENE IN MECHANICALLY STRAINED BLADDER SMOOTH MUSCLE CELLS REQUIRES THE COMBINED ACTIVITIES OF THE MYOCARDIN-RELATED TRANSCRIPTION FACTOR AND HISTONE ACETYL TRANSFERASE

Article Outline

• INTRODUCTION AND OBJECTIVES
• METHODS
• RESULTS
• CONCLUSIONS
• Copyright

Back to Article Outline

INTRODUCTION AND OBJECTIVES 

The cellular components of the urinary bladder elicit adaptive responses to pressure overload acutely by remodeling their cytoskeletal structures and chronically through hypertrophic growth of smooth muscle cells (SMCs). The long term responses are associated with the activation of angiogenesis to improve tissue perfusion which, otherwise, becomes impaired as a result of a mismatch between the smooth muscle mass and capillary density, leading to hypoxia/ischemia, altered muscle contractility and organ failure. Neoangiogenesis is promoted by mechano-responsive angiogenic factors such as cysteine-rich protein 61 (Cyr61) which enhances sprouting of new blood vessels and protects against oxidative stress. In this study, we examined the expression and regulation of the Cyr61 gene by mechanical forces in bladder SMCs.

Back to Article Outline

METHODS 

Cultured human bladder SMCs were subjected to cyclic mechanical stretch using a mechanical device designed to impart a biaxial strain to the cells. Partial urethral obstruction of the bladder was created in female Sprague Dawley rats by loosely tying the urethra. The expression and activation of the Cyr61 gene was examined by real-time PCR, transfection and chromatin immunoprecipitation (ChIP) assays.

Back to Article Outline

RESULTS 

Mechanical strain-dependent induction of the Cyr61 gene involves signaling cascades through RhoA-mediated actin remodeling and the p38 stress-activated protein kinase (SAPK). Actin signaling controls serum response factor (SRF) activity via SRF interaction with the myocardin-related transcriptional activator (MRTF)-A and its tethering to a single CArG-box sequence within the Cyr61 promoter. Such activity was abolished in mechanically stimulated mouse MRTF-A null cells or upon inhibition of cyclic AMP responsive element (CREB)-binding protein (CBP) histone acetyl transferase (HAT). Mechanical strain induced CBP-mediated acetylation of histones 3 and 4 at the SRF binding site. Inhibition of p38 SAPK reduced CBP HAT activity and its recruitment to the SRF-MRTF-A complex. Similarly, mechanical overload-induced Cyr61 gene expression in obstructed bladders was associated with nuclear localization of MRTF-A and enrichment of the Cyr61 promoter with both MRTF-A and acetylated histone H3.

Back to Article Outline

CONCLUSIONS 

Signal-controlled activation of SRF, MRTF-A and CBP provides a novel connection between mechanical forces and angiogenic gene expression in bladder smooth muscle.