Role of nuclear unphosphorylated STAT3 in angiotensin II type 1 receptor-induced cardiac hypertrophy.

AIMS: Cardiac hypertrophy is a risk factor independent of blood pressure; however, the mechanisms that distinguish pathological remodelling due to local cues from pressure overload are unresolved. This study was aimed at discovering a novel gene expression mechanism in heart failure.

METHODS AND

RESULTS

In angiotensin II type 1 receptor (AT1R) transgenic mice (TG), we found a significant increase of mRNA and total STAT3 (T-STAT3) protein, but not STAT3 phosphorylated at residues Y705 and S727. A net increase in nuclear accumulation of this unphosphorylated form of STAT3 (U-STAT3) correlated with the development of cardiac hypertrophy and dysfunction, which are associated with abnormal expression of osteopontin and regulator of G protein signalling 2 genes. Nuclear accumulation of U-STAT3 is induced by angiotensin II treatment in neonatal cardiac myocytes, fibroblasts, and AT1R-expressing human embryonic kidney 293 (HEK-AT1R) cells. Chromatin immunoprecipitation demonstrated that U-STAT3 binds to the target gene promoter, and siRNA-mediated knockdown of STAT3 expression significantly altered the expression of target genes in HEK-AT1R cells. T-STAT3 in TG mouse hearts and the phosphorylation-deficient Y705F mutant STAT3 in HEK-AT1R cells physically interacted with transcription co-activator p300.

CONCLUSION

Chronic activation of AT1R induces unregulated expression of the Stat3 gene, leading to nuclear accumulation of U-STAT3, which significantly correlated with progression of cardiac hypertrophy.