Regulation of Abro1/KIAA0157 during myocardial infarction and cell death reveals a novel cardioprotective mechanism for Lys63-specific deubiquitination

Abro1 (also known as KIAA0157) is a scaffold protein that recruits polypeptides to assemble the BRISC (BRCC36-containing isopeptidase complex) deubiquitinating (DUB) enzyme. The four subunits of BRISC enzyme include Abro1, NBA1, BRE, and BRCC36 proteins. The DUB activity of the BRISC enzyme is exclusively directed against Lys63-linked polyubiquitin that does not have a proteolytic role but regulates protein function. In this report, we identified Abro1 as a specific interactor of THAP5, a zinc finger transcription factor that is involved in G2/M control and apoptosis. Abro1 was predominantly expressed in the heart and its protein level was regulated following experimentally induced myocardial ischemia/reperfusion (MI/R) injury. Furthermore, in patients with coronary artery disease (CAD), there was a dramatic increase in Abro1 protein level in the myocardial infarction (MI) area. Increase in Abro1 leads to a significant reduction in Lys63-linked ubiquitination of specific protein targets. Reducing the Abro1 protein level exacerbated cellular damage and cell death of cardiomyocytes due to MI/R injury. Additionally, overexpression of Abro1 in a heterologous system provided significant protection against oxidative stress-induced apoptosis. In conclusion, our results demonstrate that Abro1 protein level substantially increases in myocardial injury and coronary artery disease and this up-regulation is part of a novel cardioprotective mechanism. In addition, our data suggest a potential new link between Lys63-specific ubiquitination, its modulation by the BRISC DUB enzyme, and the development and progression of heart disease.

THAP5 is a DNA-binding transcriptional repressor that is regulated in melanoma cells during DNA damage-induced cell death

THAP5 was originally isolated as a specific interactor and substrate of the mitochondrial pro-apoptotic Omi/HtrA2 protease. It is a human zinc finger protein characterized by a restricted pattern of expression and the lack of orthologs in mouse and rat. The biological function of THAP5 is unknown but our previous studies suggest it could regulate G2/M transition in kidney cells and could be involved in human cardiomyocyte cell death associated with coronary artery disease (CAD). In this report, we expanded our studies on the properties and function of THAP5 in human melanoma cells. THAP5 was expressed in primary human melanocytes as well as in all melanoma cell lines that were tested. THAP5 protein level was significantly induced by UV irradiation or cisplatin treatment, conditions known to cause DNA damage. The induction of THAP5 correlated with a significant increase in apoptotic cell death. In addition, we show that THAP5 is a nuclear protein that could recognize and bind a specific DNA motif. THAP5 could also repress the transcription of a reporter gene in a heterologous system. Our work suggests that THAP5 is a DNA-binding protein and a transcriptional repressor. Furthermore, THAP5 has a pro-apoptotic function and it was induced in melanoma cells under conditions that promoted cell death.