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.

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The Bfl-1 gene, which was isolated from human fetal liver and only recently described, is a member of the Bcl-2 gene family. Reverse transcriptase-polymerase chain reaction was performed on RNA drawn from 30 breast cancer tissues to compare the expression of the Bfl-1 gene with other prognostic factors. The median relative ratio was 3.0 (range, 0.12-26.83) and the Bfl-1 gene expression rate was 36.7% (11/30). There was no statistically significant relationship between the clinicopathologic parameters of patients and the expression value of Bfl-1 gene. The level of Bfl-1 gene expression was higher in more advanced breast cancers than in early cancers. There was no significant relationship between the expression values and currently acknowledged prognostic factors, but a higher expression pattern was noticed in the groups of positive hormone receptors and negative p53 and negative c-erbB2, albeit statistically not significant. It seems that the increased expression of the Bfl-1 gene serves as a contributory factor in breast cancer, in the same way that another group of genes, the Bcl-2 family, contributes to apoptosis.