The enigmatic role of the ankyrin repeat domain 1 gene in heart development and disease.

It has been proposed that the ankyrin repeat domain 1 (ANKRD1) factor (also known as CARP) plays a critical role in transcriptional regulation, myofibrillar assembly and stretch sensing during heart development and cardiac insults. ANKRD1/CARP has also been reported to negatively regulate cardiac gene expression in cell-based promoter-reporter assays. Consequently, rapid up-regulation of the ankrd1 gene in myocardium in response to developmental stimuli or pathological insults has tended to be interpreted in the context of the inhibitory effects of ANKRD1 on cardiomyocyte gene expression. Surprisingly, a total ankrd1 knockout resulted in a complete lack of phenotype, suggesting that ANKRD1/CARP is not crucial for regulation of cardiac gene expression in vivo. In this essay, we summarize (1) the accumulated evidence for the apparent multifunctional properties of this enigmatic protein, (2) the distinct chamber-dependent regulation of ankrd1 expression patterns in the heart, both during development and cardiac injury, and (3) ANKRD1 involvement in networks regulating adaptation of the myocardium to stress. Whenever feasible, we present the results obtained in patients together with those obtained in the relevant animal and cellular models. A close examination of the findings still fails to define ANKRD1 as a negative regulator of cardiac gene expression in vivo, but rather indicates that its augmented expression can represent an adaptive response of the myocardium to stress both during development and various heart insults.