Akiyoshi Fukamizu

Adipose angiotensinogen is involved in adipose tissue growth and blood pressure regulation

White adipose tissue and liver are important angiotensinogen (AGT) production sites. Until now, plasma AGT was considered to be a reflection of hepatic production. Because plasma AGT concentration has been reported to correlate with blood pressure, and to be associated with body mass index, we investigated whether adipose AGT is released locally and into the blood stream. For this purpose, we have generated transgenic mice either in which adipose AGT is overexpressed or in which AGT expression is restricted to adipose tissue. This was achieved by the use of the aP2 adipocyte‐specific promoter driving the expression of rat agt cDNA in both wild‐type and hypotensive AGT‐deficient mice. Our results show that in both genotypes, targeted expression of AGT in adipose tissue increases fat mass. Mice whose AGT expression is restricted to adipose tissue have AGT circulating in the blood stream, are normotensive, and exhibit restored renal function compared with AGT‐deficient mice. Moreover, mice that overexpress adipose AGT have increased levels of circulating AGT, compared with wild‐type mice, and are hypertensive. These animal models demonstrate that AGT produced by adipose tissue plays a role in both local adipose tissue development and in the endocrine system, which supports a role of adipose AGT in hypertensive obese patients.

Two domains of Nrf2 cooperatively bind CBP, a CREB binding protein, and synergistically activate transcription

Background Nrf2 belongs to the Cap‐N‐Collar (CNC) transcription factor family and is essential for the antioxidant responsive element (ARE)‐mediated expression of a group of detoxifying and antioxidant genes. The forced expression of Nrf2 in mammalian cells activates the expression of target genes through the ARE, with Nrf2 showing the highest transactivation activity among the CNC family of transcription factors. To elucidate the molecular mechanisms generating this potent transactivation activity, we examined the functions of the domains within Nrf2.

Angiotensinogen-Deficient Mice Exhibit Impairment of Diet-Induced Weight Gain with Alteration in Adipose Tissue Development and Increased Locomotor Activity

White adipose tissue is known to contain the components of the renin-angiotensin system, which gives rise to angiotensin II from angiotensinogen (AGT). Recent evidence obtained in vitro and ex vivo is in favor of angiotensin II acting as a trophic factor of adipose tissue development. To determine whether AGT plays a role in vivo in this process, comparative studies were performed in AGT-deficient (agt−/−) mice and control wild-type mice. The results showed that agt−/− mice gain less weight than wild-type mice in response to a chow or high fat diet. Adipose tissue mass from weaning to adulthood appeared altered rather specifically, as both the size and the weight of other organs were almost unchanged. Food intake was similar for both genotypes, suggesting a decreased metabolic efficiency in agt−/− mice. Consistent with this hypothesis, cellularity measurement indicated hypotrophy of adipocytes in agt−/− mice with a parallel decrease in the fatty acid synthase activity. Moreover, AGT-deficient mice exhibit...

Characterization of RGS5 in regulation of G protein-coupled receptor signaling.

RGS proteins (regulators of G protein signaling) serve as GTPase-activating proteins (GAPs) for G alpha subunits and negatively regulate G protein-coupled receptor signaling. In this study, we characterized biochemical properties of RGS5 and its N terminal (1-33)-deleted mutant (deltaN-RGS5). RGS5 bound to G alpha(i1), G alpha(i2), G alpha(i3), G alpha(o) and G alpha(q) but not to G alpha(s) and G alpha13 in the presence of GDP/AIF4-, and accelerated the catalytic rate of GTP hydrolysis of G alpha(i3) subunit. When expressed in 293T cells stably expressing angiotensin (Ang) AT1a receptors (AT1a-293T cells), RGS5 suppressed Ang II- and endothelin (ET)-1-induced intracellular Ca2+ transients. The effect of RGS5 was concentration-dependent, and the slope of the concentration-response relationship showed that a 10-fold increase in amounts of RGS5 induced about 20-25% reduction of the Ca2+ signaling. Furthermore, a comparison study of three sets of 293T cells with different expression levels of AT1a receptors showed that RGS5 inhibited Ang II-induced responses more effectively in 293T cells with the lower density of AT1a receptors, suggesting that the degree of inhibition by RGS proteins reflects the ratio of amounts of RGS proteins to those of activated G alpha subunits after receptor stimulation by agonists. When expressed in AT1a-293T cells, deltaN-RGS5 was localized almost exclusively in the cytosolic fraction, and exerted the inhibitory effects as potently as RGS5 which was present in both membrane and cytosolic fractions. Studies on relationship between subcellular localization and inhibitory effects of RGS5 and deltaN-RGS5 revealed that the N terminal (1-33) of RGS5 plays a role in targeting this protein to membranes, and that the N terminal region of RGS5 is not essential for exerting activities.

Dual roles of RNA helicase A in CREB-dependent transcription.

ABSTRACT RNA helicase A (RHA) is a member of an ATPase/DNA and RNA helicase family and is a homologue of Drosophila maleless protein (MLE), which regulates X-linked gene expression. RHA is also a component of holo-RNA polymerase II (Pol II) complexes and recruits Pol II to the CREB binding protein (CBP). The ATPase and/or helicase activity of RHA is required for CREB-dependent transcription. To further understand the role of RHA on gene expression, we have identified a 50-amino-acid transactivation domain that interacts with Pol II and termed it the minimal transactivation domain (MTAD). The protein sequence of this region contains six hydrophobic residues and is unique to RHA homologues and well conserved. A mutant with this region deleted from full-length RHA decreased transcriptional activity in CREB-dependent transcription. In addition, mutational analyses revealed that several tryptophan residues in MTAD are important for the interaction with Pol II and transactivation. These mutants had ATP binding and ATPase activities comparable to those of wild-type RHA. A mutant lacking ATP binding activity was still able to interact with Pol II. In CREB-dependent transcription, the transcriptional activity of each of these mutants was less than that of wild-type RHA. The activity of the double mutant lacking both functions was significantly lower than that of each mutant alone, and the double mutant had a dominant negative effect. These results suggest that RHA could independently regulate CREB-dependent transcription either through recruitment of Pol II or by ATP-dependent mechanisms.

An Essential Role of Angiotensin II Receptor Type 1a in Recipient Kidney, Not in Transplanted Peripheral Blood Leukocytes, in Progressive Immune-Mediated Renal Injury

Despite an intensive effort of elucidating the pathogenic role of angiotensin II (AII) in immune-mediated renal injury, the precise mechanisms are poorly understood. In the present study, we examined the site of AII action, peripheral blood leukocytes or resident renal cells, in immune-mediated renal injury using AII type 1a receptor (AT1a)-deficient homozygous (AT1a −/−) mice and wild-type (AT1a +/+) mice. The AT1a −/− mice showed delayed-type hypersensitivity similar to that of the AT1a +/+ mice, suggesting that the lack of AT1a does not impair a Th1-type cellular immune response of peripheral blood leukocytes involved in immune-mediated renal injury. We then generated the radiation bone marrow chimera mice, WA and AW, which have transplanted peripheral blood leukocytes from the AT1a +/+ and AT1a −/− mice into the AT1a −/− and AT1a +/+ mice, respectively. As controls, WW and AA, the AT1a +/+ and AT1a −/− mice given bone marrow cells from the AT1a +/+ and AT1a −/− mice, respectively, were generated. Seven days after induction of antiglomerular basement membrane nephritis, glomerulosclerosis observed in the WW mice was markedly ameliorated in the WA mice, but not in the AW mice. In addition, the recruitment of monocytes/macrophages and the expressions of monocyte chemoattractant protein-1 and intercellular adhesion molecule-1 in the glomeruli of the AW and WW mice was evident, but such significant phenotypes were not seen in the WA and AA mice, showing a marked amelioration of renal injury dependent on the host AT1a genotype. These results demonstrate an essential role of AT1a in intrinsic renal cells for progressive immune-mediated renal injury and indicate a beneficial effect of blocking the renin-angiotensin system in the treatment of such diseases.

PODs in the Nuclear Spot: Enigmas in the Magician's Pot

The promyelocytic leukemia (PML) nuclear body, also known as the PML oncogenic domain (POD), is implicated in the pathophysiology of PML. These nuclear subcompartments are dynamic structures. The PML protein, which undergoes a fusion event in patients with promyelocytic leukemia, is normally found in PODs. The PML protein may be a major regulator of the constituents of PODs, controlling POD organization and function. Hatta and Fukamizu describe the functions of PML and discuss how the POD structure and organization may be regulated and affect apoptosis, gene expression, and cellular transformation.