Ankyrin-repeat protein with a PEST motif and a proline-rich region (ARPP), also designated as Ankrd2, which isolated from a cDNA library of human esophageal carcinoma cell line (TE-1) is composed of 333 amino acids and contains four ankyrin-like repeat motifs in its middle portion, a PEST-like sequence and a lysine-rich sequence in the N-terminal region, and a proline-rich region in the C-terminal region. ARPP is homologous to CARP, cardiac ankyrin repeat protein (52 % identical), which is a nuclear protein and is involved in the regulation of the transcription of MLC-2s in cardiomyogenesis. In the immunohistochemical analysis of paraffin embedded sections, ARPP is found to express at a high level in almost all rhabdomyosarcomas. On the other hand in normal tissues, ARPP preferentially expresses in skeletal and cardiac muscle. Furthermore ARPP expresses in part of the distal tubule of the kidney and also expresses specifically in renal oncocytoma but barely detectable in conventional renal cell carcinoma. ARPP may have potential use as a marker for distinguishing renal oncocytoma from other renal cell carcinomas.Synonyms: ARPP, Ankyrin repeat domain-containing protein 2, Skeletal muscle ankyrin repeat protein