Ankyrin Repeat, PEST sequence and Proline-rich region (ARPP), also known as Ankyrin repeat domain-containing protein 2 is a protein that in humans is encoded by the ANKRD2 gene. ARPP is a member of the muscle ankyrin repeat proteins (MARP), which also includes CARP and DARP, and is highly expressed in cardiac and skeletal muscle and in other tissues. Expression of ARPP has been shown to be altered in patients with dilated cardiomyopathy and amyotrophic lateral sclerosis. A role for Ankrd2 in tumor progression and metastases spreading has also been described. Structure Two isoforms of ARPP have been documented; a 39.8 kDa protein isoform composed of 360 amino acids and a 36.2 kDa protein isoform composed of 327 amino acids. ANKRD2 has nine exons, four of which encode ankyrin repeats in the middle region of the protein, a PEST-like and Lysine-rich sequence in the N-terminal region, and a Proline-rich sequence containing consensus sequences for phosphorylation in the C-terminal region. It has been proposed that ARPP can homo- or hetero-dimerize with other MARPs in an antiparallel fashion. ARPP is highly expressed in nuclei and I-bands in slow skeletal fibers and cardiac muscle, specifically in ventricular regions at intercalated discs; and expression in brain, pancreas and esophageal epithelium has also been documented. Though ARPP and CARP proteins show significant homology, their expression profiles in muscle cells are markedly different; CARP is expressed throughout atria and ventricles, in development and in adult myocytes, however ARPP is almost exclusively ventricular and only in adult myocytes. ARPP was also found to be expressed in rhabdomyosarcomas, exhibiting a pattern distinct from actin and desmin. Function ARPP localizes to both nuclei and sarcomeres in muscle cells. ARPP may play a role in the differentiation of myocytes, as ARPP expression was shown to be induced during the C2C12 differentiation in vitro. A role for ARPP in regulating muscle gene expression and sensing stress signals was implicated in the finding that ARPP colocalizes with the transcriptional co-activator and co-repressor PML in myoblast nuclei, and binds p53 to enhance the p21(WAFI/CIPI) promoter. It was further demonstrated that Nkx2.5 and p53 synergistically activate the ANKRD2 promoter to promote effects on myogenic differentiation. At the sarcomere, ARPP binds titin at I-bands, which is potentiated by homo-dimerization and can alter the protein kinase A/protein kinase C phosphorylation status of itself or titin. These studies demonstrate a stretch-responsive relationship between ARPP and Titin, which can