The (pro)renin receptor [(P)RR] is crucial for cardio-renal pathophysiology. The distinct molecular mechanisms of this receptor are still incompletely understood. The (P)RR is able to interact with different signalling proteins such as promyelocytic leukemia zinc finger protein (PLZF) and Wnt receptors. Moreover, domains of the (P)RR are essential for V-ATPase activity. V-ATPase- and Wnt-mediated effects imply constitutive, i.e., (pro)renin-independent functions of the (P)RR. Regarding ligand-dependent (P)RR signalling, the role of prorenin glycosylation is currently unknown. Therefore, the aim of this study was to analyse the contribution of constitutive (P)RR activity to its cellular effects and the relevance of prorenin glycosylation on its ligand activity. We were able to demonstrate that high glucose induces (P)RR signal transduction whereas deglycosylation of prorenin abolishes its intrinsic activity in neuronal and epithelial cells. By using siRNA against (P)RR or PLZF as well as the PLZF translocation blocker genistein and the specific V-ATPase inhibitor bafilomycin, we were able to dissect three distinct sub-pathways downstream of the (P)RR. The V-ATPase function is ligand-independently associated with strong pro-proliferative effects whereas prorenin causes moderate proliferation in vitro. In contrast, PLZF per se [i.e., in the absence of (pro)renin] does not interfere with cell number.

The (pro)renin receptor ((P)RR) signaling is involved in different pathophysiologies ranging from cardiorenal end-organ damage via diabetic retinopathy to tumorigenesis. We have previously shown that the transcription factor promyelocytic leukemia zinc finger (PLZF) is an adaptor protein of the (P)RR. Furthermore, recent publications suggest that major functions of the (P)RR are mediated ligand-independently by its transmembrane and intracellular part, which acts as an accessory protein of V-ATPases. The transcriptome and recruitmentome downstream of the V-ATPase function and PLZF in the context of the (P)RR are currently unknown. Therefore, we performed a set of microarray and chromatin-immunoprecipitation (ChIP)-chip experiments using siRNA against the (P)RR, stable overexpression of PLZF, the PLZF translocation inhibitor genistein and the specific V-ATPase inhibitor bafilomycin to dissect transcriptional pathways downstream of the (P)RR. We were able to identify distinct and overlapping genetic signatures as well as novel real-time PCR-validated target genes of the different molecular functions of the (P)RR. Moreover, bioinformatic analyses of our data confirm the role of (P)RŔs signal transduction pathways in cardiovascular disease and tumorigenesis.

The Editors and publisher gratefully acknowledge the excellent work performed by our reviewers. The quality of a journal is definitely depending on the review process. The work laid down by our reviewers is essential for the increasing interest of our journal within ORL-HNS in Europe and outside. We are sure that we have a common interest to make European Archives of Oto-Rhino-Laryngology an even better journal and a leading one in ORL-HNS in Europe. At the same time we take the opportunity to wish you all a prosperous year 2013. Jan Olofsson Olivier Sterkers Jochen A. Werner

Background/Aims: Putative in vitro-in vivo correlations of pharmacokinetic (PK) parameters are regarded as a prerequisite to filter hits derived from high-throughput screening (HTS) approaches for subsequent murine in vivo PK studies. Methods: In this study, we assessed stabilities in rat and human microsomes of 121 compounds from an early, academic drug discovery programme targeting the (pro)renin receptor and correlated the respective data with single-dose, in vivo PK parameters of 22 hits administered intravenously in rats. Results: After transformation of in vitro half-lives to predicted in vivo hepatic clearances, r2 regarding in vitro-in vivo clearance correlations were 0.31 and 0.27 for the rat and human species, respectively. Conclusions: Our data concerning structurally diverse real-world compounds indicate that microsomal stability testing is not a tool to triage early compounds for in vivo PK testing.

The (pro)renin receptor ((P)RR) and Wnt signalling are both involved in different diseases ranging from cardiac and renal end-organ damage to cancer. (P)RR function involves signalling via the transcription factor promyelocytic leukemia zinc finger protein (PLZF) as well as the furin-mediated generation of vacuolar proton-translocating ATPase (V-ATPase)-associated and soluble (P)RR isoforms. Recently, the (P)RR was described as adaptor protein of Wnt (co)receptors. The aim of this study was to analyse the contribution of these distinct (P)RR functions to Wnt signalling. Using Tcf/Lef reporter gene systems in HEK293T and HepG2 cells and quantification of endogenous axin2 mRNA and protein levels in HEK293T cells we were able to demonstrate that full-length (P)RR acts as a repressor of Wnt signalling in a system preactivated either by Wnt3a stimulation or by constitutively active β-catenin. These repressive effects are mediated by Dvl but are independent of the mutation status of β-catenin. Furthermore, the V-ATPase complex, but not PLZF translocation or renin enzymatic activity, is necessary for the induction of Tcf/Lef-responsive genes by Wnt3a. Our data indicate interference of (P)RR and Wnt cascades, a fact that has to be considered concerning pathophysiology of cardio-renal and oncological entities as well as in drug development programs targeting (P)RR or Wnt pathways.

Genetic factors strongly contribute to the pathogenesis of sporadic Alzheimer's disease (AD). Nevertheless, genome-wide association studies only yielded single nucleotide polymorphism loci of moderate importance. In contrast, microsatellite repeats are functionally less characterized structures within our genomes. Previous work has shown that endothelin-converting enzyme-1 (ECE-1) is able to reduce amyloid β content. Here we demonstrate that a CpG-CA repeat within the human ECE-1c promoter is highly polymorphic, harbors transcriptional start sites, is able to recruit the transcription factors poly(ADP-ribose) polymerase-1 and splicing factor proline and glutamine-rich, and is functional regarding haplotype-specific promoter activity. Furthermore, genotyping of 403 AD patients and 444 controls for CpG-CA repeat length indicated shifted allelic frequency distributions. Sequencing of 245 haplotype clones demonstrated that the overall CpG-CA repeat composition of AD patients and controls is distinct. Finally, we show that human and chimpanzee [CpG]m–[CA]n ECE-1c promoter repeats are genetically and functionally distinct. Our data indicate that a short genomic repeat structure constitutes a novel core promoter element, coincides with human evolution, and contributes to the pathogenesis of AD.

Stroke is one of the major medical burdens in industrialized countries. Animal experiments indicate that blockade of the angiotensin AT1 receptor (AT1R) improves neurological outcome after cerebral ischemia. These protective effects are partially mediated by the angiotensin AT2 receptor (AT2R). The transcription factor promyelocytic leukemia zinc finger (PLZF) was identified as a direct adapter protein of the AT2R. Furthermore, our group was able to demonstrate that PLZF also directly binds and mediates the effects of the human (pro)renin receptor [(P)RR] which is involved in brain development. Therefore, we hypothesized that PLZF is involved in neuroprotection. Here we show that PLZF and its receptors (P)RR and AT2R exhibited an ubiquitous expression pattern in different brain regions. Furthermore, stable PLZF overexpression in human neuronal cells was able to mediate neuroprotection in a glutamate toxicity model in vitro. Consistently, PLZF mRNA and protein were downregulated on the ipsilateral side in a stroke model in vivo, whereas the neurodetrimental PLZF target genes cyclin A2 and BID were upregulated under this condition. Further analyses indicated that the neuroprotective AT2R is upregulated upon stable PLZF overexpression in cultured neuronal cells. Finally, reporter gene assays demonstrated the functionality of (P)RR promoter polymorphisms regarding basal and PLZF-induced activity.

The (pro)renin receptor ((P)RR) not only represents a novel component of the renin–angiotensin system but is also a promising novel drug target because of its crucial involvement in the pathogenesis of renal and cardiac end-organ damage. This review discusses the signal transduction of the (P)RR with its adapter protein promyelocytic zinc-finger protein, the impact of this receptor, especially on cardiovascular disease, and its putative interaction with renin inhibitors such as aliskiren. Furthermore, the increasing complexity regarding the cellular function of the (P)RR is addressed, which arises by the intimate link with proton pumps and the phosphatase PRL-1, as well as by the presence of different subcellular localizations and of a soluble isoform of the (P)RR. Finally, the rationale and strategy for the development of small-molecule antagonists of the (P)RR, called renin/prorenin receptor blockers, are presented.