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

作者：Spaich Sebastian; Will Rainer D; Just Steffen; Spaich Saskia; Kuhn Christian; Frank Derk; Berger Ina M; Wiemann Stefan; Korn Bernhard; Koegl Manfred; Backs Johannes; Katus Hugo A; Rottbauer Wolfgang; Frey Norbert^*

来源：Circulation Research, 2012, 111(12): 1504-+.

DOI：10.1161/CIRCRESAHA.112.271007

• cardiac myocytes
• cardiomyopathy
• F-box
• ubiquitin-proteasome system

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. %26lt;br%26gt;Objective: We sought to determine whether molecules exist that control turnover of cardiac-specific proteins. %26lt;br%26gt;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 identified interactions of Fbxl22 with S-phase kinase-associated protein 1 and Cullin1, 2 critical components of SCF (Skp1/Cul1/F-box) E3-ligases. Moreover, we identified several potential substrates, including the z-disc proteins alpha-actinin and filamin C. Consistently, in vitro overexpression of Fbxl22-mediated degradation of both substrates in a dose-dependent fashion, whereas proteasome inhibition with MG-132 markedly attenuated degradation of both alpha-actinin and filamin C. Finally, targeted knockdown of Fbxl22 in rat cardiomyocytes as well as zebrafish embryos results in the accumulation of alpha-actinin associated with severely impaired contractile function and cardiomyopathy in vivo. %26lt;br%26gt;Conclusions: These findings reveal the previously uncharacterized cardiac-specific F-box protein Fbxl22 as a component of a novel cardiac E3 ligase. Fbxl22 promotes the proteasome-dependent degradation of key sarcomeric proteins, such as alpha-actinin and filamin C, and is essential for maintenance of normal contractile function in vivo. (Circ Res.2012;111:1504-1516.)

• 出版日期2012-12