FK506 binding proteins 12 and 12.6 (FKBP12 and FKBP12.6) are intracellular receptors for the immunosuppressant drug FK506 (ref. 1). The skeletal muscle ryanodine receptor (RyR1) is isolated as a hetero-oligomer with FKBP12 (ref. 2), whereas the cardiac ryanodine receptor (RyR2) more selectively associates with FKBP12.6 (refs 3, 4, 5). FKBP12 modulates Ca2+ release from the sarcoplasmic reticulum in skeletal muscle and developmental cardiac defects have been reported in FKBP12-deficient mice, but the role of FKBP12.6 in cardiac excitation-contraction coupling remains unclear. Here we show that disruption of the FKBP12.6 gene in mice results in cardiac hypertrophy in male mice, but not in females. Female hearts are normal, despite the fact that male and female knockout mice display similar dysregulation of Ca2+ release, seen as increases in the amplitude and duration of Ca2+ sparks and calcium-induced calcium release gain. Female FKBP12.6-null mice treated with tamoxifen, an oestrogen receptor antagonist, develop cardiac hypertrophy similar to that of male mice. We conclude that FKBP12.6 modulates cardiac excitation-contraction coupling and that oestrogen plays a protective role in the hypertrophic response of the heart to Ca2+ dysregulation.

Background-The roles of angiotensin II (Ang II) in the regulation of heart function under normal and pathological conditions have been well documented.

We describe a novel signaling mechanism mediated by the G-protein-coupled receptor (GPCR) angiotensin II (Ang II) type 2 receptor (AT 2 ). Yeast two-hybrid studies and af®nity column binding assay show that the isolated AT 2 C-terminus binds to the transcription factor promyelocytic zinc ®nger protein (PLZF). Cellular studies employing confocal microscopy show that Ang II stimulation induces cytosolic PLZF to colocalize with AT 2 at the plasma membrane, then drives AT 2 and PLZF to internalize. PLZF slowly emerges in the nucleus whereas AT 2 accumulates in the perinuclear region. Nuclear PLZF binds to a consensus sequence of the phosphatidylinositol-3 kinase p85a subunit (p85a PI3K) gene. AT 2 enhances expression of p85a PI3K followed by enhanced p70 S6 kinase, essential to protein synthesis. An inactive mutant of PLZF abolishes this effect. PLZF is expressed robustly in the heart in contrast to many other tissues. This cardiac selective pathway involving AT 2 , PLZF and p85a PI3K may explain the absence of a cardiac hypertrophic response in AT 2 gene-deleted mice.

The pathophysiological roles of the angiotensin II type 2 receptor (AT 2 ) in cardiac hypertrophy remain unclear. By the targeted deletion of mouse AT 2 we were able to prevent the left ventricular hypertrophy resulting from pressure overload, while cardiac contractile functions remained normal. This implies that AT 2 is a mediator of cardiac hypertrophy in response to increased blood pressure. The effects of AT 2 deletion were independent of activation of embryonic genes for cardiac hypertrophy. However, p70 S6k , one of the key factors in cardiac hypertrophy, was markedly and specifically reduced in the ventricles of Agtr2 -/Y mice. We propose that p70 S6k plays a major role in AT 2 -mediated ventricular hypertrophy.

The (pro)renin receptor ((P)RR), which is a recently discovered molecule of the renin-angiotensin system, plays an important role in the development of cardiovascular diseases. However, the molecular properties and the subcellular distribution of (P)RR remain controversial. In this study, (P)RR-Venus in Chinese hamster ovary (CHO) cells ((P)RR-Venus-CHO) or endogenous (P)RR in human vascular smooth muscle cells (VSMC) were constitutively cleaved without any stimulation, and secretion of the aminoterminal fragment (NTF-(P)RR) into the media was determined using western blot analysis. Immunofluorescent analysis showed robust expression of (P)RR in the endoplasmic reticulum (ER) or the Golgi but not in the plasma membrane. Moreover, we identified ADAM19, which is expressed in the Golgi, as one of cleaving proteases of (P)RR. Transfected ADAM19 evoked the shedding of (P)RR, whereas transfected dominant negative ADAM19 suppressed it. Although (P)RR contains a furin cleavage site, neither the furin-deficient LoVo cells nor furin inhibitor-treated VSMC lost NTF-(P)RR in the media. The secreted NTF-(P)RR induced the renin activity of prorenin in the extracellular space. We describe that (P)RR is mainly localized in the subcellular organelles, such as the ER and Golgi, and (P)RR is cleaved by ADAM19 in the Golgi resulting in two fragments, NTF-(P)RR and CTF-(P)RR. These results may suggest that (P)RR is predominantly secreted into the extracellular space. Hypertension Research (2011) 34, 599-605; doi:10.1038/hr.2010.284; published online 27 January 2011Keywords: ADAM19; ectodomain shedding; (pro)renin receptor; renin-angiotensin system INTRODUCTION The (pro)renin receptor ((P)RR) is a recently discovered molecule of the renin-angiotensin system (RAS), which plays pivotal roles in the regulation of the cardiovascular system under normal and pathological conditions. (P)RR binds both renin and prorenin, which is the precursor form of renin. 1 Although the binding of renin to (P)RR may increase its catalytic activity, the binding affinity between (P)RR and renin is lower than that of (P)RR and prorenin. These results indicate that it may be necessary to focus on the interaction between (P)RR and prorenin. Prorenin does not display protease activity in the plasma because the enzymatic cleft is covered by the prosegment. 2 However, the binding of prorenin to (P)RR evokes the renin activity without removal of its prosegment. This nonproteolytic activation of prorenin contributes to the activation of the local RAS. In addition to the enzymatic activity, renin/prorenin has been shown to provide other (P)RR-mediated effects. 3 The binding of renin/prorenin to (P)RR induces the activation of intracellular signaling, including the p38 MAP kinase-HSP27 cascade, the PI3K pathway and the ERK 1/2 pathway; these effects occur independently of angiotensin II, which is a final product of RAS. 2,4,5 Although this evidence strongly supports (P)RR localization in the plasma membrane, the subcellular localization of (P)RR remains unknown. (P)R...