WNK1 is a serine-threonine kinase, the expression of which is affected in pseudohypoaldosteronism type II, a Mendelian form of arterial hypertension. We characterized human WNK1 transcripts to determine the molecular mechanisms governing WNK1 expression. We report the presence of two promoters generating two WNK1 isoforms with a complete kinase domain. Further variations are achieved by the use of two polyadenylation sites and tissue-specific splicing. We also determined the structure of a kidney-specific isoform regulated by a third promoter and starting at a novel exon. This transcript is kinase defective and has a predominant expression in the kidney compared to the other WNK1 isoforms, with, furthermore, a highly restricted expression profile in the distal convoluted tubule. We confirmed that the ubiquitous and kidneyspecific promoters are functional in several cells lines and identified core promoters and regulatory elements. In particular, a strong enhancer element upstream from the kidney-specific exon seems specific to renal epithelial cells. Thus, control of human WNK1 gene expression of kinase-active or -deficient isoforms is mediated predominantly through the use of multiple transcription initiation sites and tissue-specific regulatory elements.A new family of serine-threonine kinases was recently described. The members of this family lack a lysine at a usually invariant position in the active site and are therefore known as With No Lysine (WNK) protein kinases (17,20). Rat WNK1 was the first member of this family to be characterized; it has a cysteine in place of the conserved lysine residue in subdomain II of the catalytic domain (20). The active lysine is itself located in subdomain I in both rats and humans. In both species, WNK1 is expressed in a wide variety of tissues, and two major transcripts have been identified. One is produced mainly in heart, muscle, and brain, and the other, shorter transcript is produced mainly in kidney (18,20). The substrates of WNK1 are unknown, but WNK1 is capable of autophosphorylation on serine residues, an activity that is increased in vitro by increasing the salt concentration (20). Like many other protein kinases, WNK1 enzymes contain an autoinhibitory domain outside the catalytic domain, which is capable of abolishing kinase activity in vitro (21). There is also evidence that the autophosphorylation sites detected in the activation loop of WNK1 may control kinase activity (21).Mutations in the genes encoding WNK1 and WNK4, two of the other four members of the human WNK family (17), are responsible for pseudohypoaldosteronism type II (PHA2), also known as Gordon syndrome, an autosomal dominant form of human arterial hypertension associated with hyperkalaemia and metabolic acidosis with hyperchloraemia (5). The mutations in the WNK4 gene are missense mutations clustering in highly conserved domains close to those encoding the coiled-coil domains (18). The location and nature of these mutations suggest that they may result in changes in interactions with as-yet-u...

Recent studies have shown that angiotensin II has a trophic action on the heart. The presence of two types of angiotensin II receptors, type 1 (AT1) and type 2 (AT2), has been reported in the rat heart. This in situ hybridization study describes the tissue and cell location of AT2 receptor mRNA in the developing rat cardiopulmonary system, from 15 days of gestation to adulthood. Expression of AT1A receptor mRNA was studied in parallel for direct comparison. The aortic arch and pulmonary artery expressed high levels of AT2 receptor mRNA from 15 days of gestation up until 15 days postpartum, whereas expression of this mRNA was observed only just before and after birth in the coronary arteries. AT2 receptor mRNA was not detected in any cardiac muscle of the fetus, neonate, or adult. The annulus of all four heart valves expressed AT2 mRNA from 21 days of gestation until 10 days postpartum, but no labeling was seen in the valve leaflets. The subendocardial atrial tissue showed a high level of AT2 receptor mRNA expression during the early postnatal period, but no expression was observed in the atrial myocytes from fetal stages to adulthood. The bronchi and trachea, but not the lung parenchyma, showed a high level of AT2 receptor mRNA expression starting from 17 days of gestation until 10 days postpartum. AT2 receptor mRNA expression in the cardiopulmonary system is therefore transient, developmentally regulated, and mostly located in vascular structures. By these three characteristics, its expression contrasts with that of AT1A, which is continuously expressed in the cardiac muscle to adulthood. This spatiotemporal pattern of expression of angiotensin II receptor mRNAs during development suggests a possible role for angiotensin II in organogenesis.

Increased angiotensinogen (AGT) production by white adipose tissue has been related to not only obesity but also hypertension. Several studies have highlighted the importance of the angiotensin II type 2 receptor (AT2) in the regulation of blood pressure and fat mass, but the relevance of this transporter in a physiopathological model of increased AGT production, as it occurs in obesity, has not yet been investigated. We used transgenic mice that display either a deletion of AT2 (AT2 KO), an overexpression of AGT (OVEX), or both compound mutants (KOVEX). Results demonstrated that adipocyte hypertrophy and increased lipogenic gene expression induced by adipose AGT overproduction was rescued by deletion of AT2. In line with AGT overexpression, KOVEX and OVEX mice have similar increased plasma AGT levels. However, KOVEX mice display a higher blood pressure than OVEX mice. In kidney, renin expression was clearly reduced in OVEX mice, and its expression was normalized in KOVEX mice. Taken together, we demonstrated that the loss of AT2 expression was sufficient to rescue obesity induced by adipose tissue AGT overexpression and confirmed the necessary role of AT2 for the onset of obesity in this model. Furthermore, despite a reduction of adipose mass in KOVEX, AT2 deficiency caused increased renin production, further worsening the hypertension caused by AGT overexpression.