Abstract 2667: NF-κB(p65) Inhibits Myocardin-induced Cardiomyocyte Differentiation: Linking Inflammatory And Developmental Transcription Through Serum Response Factor
Background Myocardial and vessel injury is associated with an elaborate repair process including invading progenitor cells, dedifferentiating native cells, and re-expression of quiescent developmental genes. Serum response factor (SRF) is a central transcriptional regulator of cellular growth and differentiation. Toggling of these pathways is dependent upon its association with myocardin, a novel cofactor that induces SRF-dependent cellular differentiation. We have previously demonstrated that the transcription factor, nuclear factor kappa B (NF-κB), promotes cellular proliferation. The interaction between these key mediators of development and inflammation is unknown. We hypothesized that NF-κB would promote SRF-dependent growth by inhibiting the effects of myocardin on SRF.
Methods Myocardin and p65 NF-κB were delivered to cos-7 and rat neonatal cardiomyocytes co- transfected with reporter constructs for the differentiation genes, smooth muscle 22α (SM22α) and atrial natiuretic factor (ANF). Physical interactions between SRF, myocardin, and NF-κB were also determined.
Results Myocardin strongly induced expression of both SM22α and ANF that was abrogated in a dose-dependent manner by concurrent delivery of NF-κB. Additionally, cotransfection with an IκBα superrepressor augmented myocardin-induced differentiation. Gel shift analysis revealed that NF-κB decreased myocardin binding to SRF. Furthermore, co-immunoprecipitation and GST-fusion protein pull-down experiments demonstrate that p65 directly interacted with myocardin and disrupted the myocardin/SRF/CArG box ternary complex.
Conclusions NF-κB is an important cofactor for SRF-dependent transcription and potently inhibits myocardin-induced cellular differentiation. Furthermore, NF-κB may act as an endogenous brake on differentiation. These results define an important link between inflammatory and developmental gene regulation and suggest that targeting NF-κB signaling may be useful to manipulate cellular phenotypes important in cardiovascular repair.