Targeted ablation of the histidine-rich Ca2+-binding protein (HRC) gene is associated with abnormal SR Ca2+-cycling and severe pathology under pressure-overload stress

Abstract

The histidine-rich Ca2+-binding protein (HRC) is located in the lumen of the sarcoplasmic reticulum (SR) and exhibits high capacity Ca2+ binding properties. Overexpression of HRC in the heart resulted in impaired SR Ca2+ uptake and depressed relaxation through its interaction with SERCA2a. However, the functional significance of HRC in overall regulation of calcium cycling and contractility is not currently well defined. To further elucidate the role of HRC in vivo under physiological and pathophysiological conditions, we generated and characterized HRC-knockout (KO) mice. The KO mice were morphologically and histologically normal compared to wild type (WT) mice. At the cellular level, ablation of HRC resulted in significantly enhanced contractility, Ca2+ transients, and maximal SR Ca2+ uptake rates in the heart. However, after-contractions were developed in 50% of HRC-KO cardiomyocytes, compared to 11% in WT mice under stress conditions of high frequency stimulation (5 Hz) and isoproterenol application. A parallel examination of the electrical activity revealed significant increases in the occurrence of Ca2+ spontaneous SR Ca2+ release and delayed after depolarizations (DADs) with ISO in HRC-KO, compared to WT cells. The frequency of Ca2+ sparks was also significantly higher in HRC-KO cells with ISO, consistent with the elevated SR Ca2+ load in the KO cells. Furthermore, HRC-KO cardiomyocytes showed significantly deteriorated cell contractility and Ca2+-cycling caused possibly by depressed SERCA2a expression after transverse-aortic constriction (TAC). Also HRC null mice exhibited severe cardiac hypertrophy, fibrosis, pulmonary edema and decreased survival after TAC. Our results indicate that ablation of HRC is associated with poorly regulated SR Ca2+-cycling, and severe pathology under pressure-overload stress, suggesting an essential role of HRC in maintaining the integrity of cardiac function.

The histidine-rich calcium binding protein (HRC) promotes tumor metastasis in hepatocellular carcinoma and is upregulated by SATB1

“…Recent studies demonstrated that HRC interacted with SERCA and RyR to regulate SR Ca 2+ -uptake and Ca 2+ -release in heart [6, 27], but ParK CS et al showed that poorly regulated SR Ca 2+ -cycling in HRC-KO hearts was not associated with the expressions of SERCA and RyR [17]. Consistent with previous researches [7, 28], our study also confirmed that HRC could influence intracellular calcium.…”

“…Recently, a number of known molecular players in cellular Ca 2+ homeostasis, including annexins and S100 proteins, have been implicated in tumor invasion and metastasis [14–16]. Substantial evidences suggest that HRC plays a critical role in Ca 2+ -homeostasis [17], but the role of HRC in the occurrence and development of cancer has not been investigated so far.…”

Phospholamban interactome in cardiac contractility and survival: A new vision of an old friend

“…One of them is the small anti-apoptotic HS-1 associated protein X-1 (HAX1), which interacts with PLN and regulates SR Ca-cycling and contractility [5]. The other one is the histidine-rich calcium binding protein, HRC, which interacts with SERCA2a as well as the ryanodine receptor Ca release complex [6], mediating regulation of both SR Ca-uptake and release [7]. …”

Phosphorylation of serine96 of histidine-rich calcium-binding protein by the Fam20C kinase functions to prevent cardiac arrhythmia

“…Conversely, ablation of HRC results in significantly enhanced contractility, Ca transients, and maximal SR Ca uptake rates. However, HRCdeficient cardiomyocytes develop aftercontractions at a significantly higher frequency, compared with wild-type (WT) cells under stress conditions (8). Interestingly, HRC protein levels are reduced both in animal models of heart failure and in failing human hearts (9).…”

“…We previously demonstrated that S96A-HRC and Hrc null (HRC KO) mouse cardiomyocytes increased arrhythmogenic features under stress in comparison to Ser96-HRC cardiomyocytes (8,11). The S96A-HRC cells also displayed hyperactive RyR2 activity that resulted in aftercontractions (11).…”