F-Box and Leucine-Rich Repeat Protein 22 Is a Cardiac-Enriched F-Box Protein That Regulates Sarcomeric Protein Turnover and Is Essential for Maintenance of Contractile Function In Vivo

Rationale:The emerging role of the ubiquitin–proteasome system in cardiomyocyte function and homeostasis implies the necessity of tight regulation of protein degradation. However, little is known about cardiac components of this machinery. Objective:We sought to determine whether molecules exist that control turnover of cardiac-specific proteins. Methods and Results:Using a bioinformatic approach to identify novel cardiac-enriched sarcomere proteins, we identified F-box and leucine-rich repeat protein 22 (Fbxl22). Tissue-specific expression was confirmed by multiple tissue Northern and Western Blot analyses as well as quantitative reverse-transcriptase polymerase chain reaction on a human cDNA library. Immunocolocalization experiments in neonatal and adult rat ventricular cardiomyocytes as well as murine heart tissue located Fbxl22 to the sarcomeric z-disc. To detect cardiac protein interaction partners, we performed a yeast 2-hybrid screen using Fbxl22 as bait. Coimmunoprecipitation confirmed the identif...