Akt Mediates Insulin-stimulated Phosphorylation of Ndrg2

Na؉ /K ؉ -ATPase, a plasma membrane protein abundantly expressed in epithelial tissues, has been identified and linked to numerous biological events, including ion transport and reabsorption. In Na ؉ /K ؉ -ATPase, the ␤-subunit plays a fundamental role in the structural integrity and functional maturation of holoenzyme. Estrogens are important circulating hormones that can regulate Na ؉ /K ؉ -ATPase abundance and activity; however, the specific molecules participating in this process are largely unknown. Here, we characterize that N-myc downstream-regulated gene 2 (NDRG2) is an estrogen up-regulated gene. 17␤-Estradiol binds with estrogen receptor ␤ but not estrogen receptor ␣ to up-regulate NDRG2 expression via transcriptional activation. We also find that NDRG2 interacts with the ␤1-subunit of Na ؉ /K ؉ -ATPase and stabilizes the ␤1-subunit by inhibiting its ubiquitination and degradation. NDRG2-induced prolongation of the ␤1-subunit protein half-life is accompanied by a similar increase in Na ؉ /K ؉ -ATPase-mediated Na ؉ transport and Na ؉ current in epithelial cells. In addition, NDRG2 silencing largely attenuates the accumulation of ␤1-subunit regulated by 17␤-estradiol. Our results demonstrate that estrogen/NDRG2/Na ؉ /K ؉ -ATPase ␤1 pathway is important in promoting Na ؉ /K ؉ -ATPase activity and suggest this novel pathway might have substantial roles in ion transport, fluid balance, and homeostasis. Na ϩ /K ϩ -ATPase, a plasma membrane ion pump, has numerous physiological functions. Of note, it is consisted of three subunits (1), ␣, ␤, and ␥, and the holoenzyme activity required by the participation of the three subunits. ␣ is the catalytic subunit of the enzyme that utilizes ATP hydrolysis to pump K ϩ into the cell in exchange for Na ϩ , which is essential for maintaining normal resting membrane potentials and facilitating the exchange of other materials needed for cellular homeostasis and activity (2-4). ␤-Subunit is responsible for the formation and integrity of the holoenzyme. In vertebrate cells, ␤-subunit may stabilize the correct folding of the ␣-subunit to facilitate its delivery to the plasma membrane (5-7). In addition, evidence showed that ␤-subunit is related to the cell motility and invasion (8, 9). At present, four ␣-isoforms known as ␣1, ␣2, ␣3, ␣4 as well as three different ␤-polypeptides termed as ␤1, ␤2, and ␤3 (3) have been identified. Among these isoforms, ␣1␤1 distributes in nearly every tissue whereas other isoforms exhibit a tissue-specific pattern of expression. ␥-Subunit, a small hydrophobic polypeptide that has only one isoform, is involved in the modulation of Na ϩ /K ϩ -ATPase function (10, 11). The ionic homeostasis maintained by the Na ϩ /K ϩ -ATPase is also critical for cell survival, differentiation, and cell apoptosis (12, 13).As an important molecule in charge of so many biological events, Na ϩ /K ϩ -ATPase is regulated by a number of hormones, including aldosterone, thyroid hormone, glucocorticoid, catecholamines, insulin, carbachol, and androgen. These circulating horm...

Section: Discussionmentioning

confidence: 98%

N-myc Downstream-regulated Gene 2, a Novel Estrogen-targeted Gene, Is Involved in the Regulation of Na+/K+-ATPase

Yang²,

Li³

et al. 2011

“…NDRG2 mRNA levels were rapidly increased in vivo within 45 min of aldosterone treatment in the kidney and distal colon of adrenalectomized adult rats and even faster after 15 min in cultured rat kidney cortical collecting duct (RCCD2) cells (20). Interestingly, NDRG2 was recently identified as a possible substrate for Sgk1 (25) and protein kinase B (Akt) (26). These findings led us to hypothesize that NDRG2 may contribute to ENaC regulation.…”

mentioning

confidence: 95%

(NDRG2) Stimulates Amiloride-sensitive Na+ Currents in Xenopus laevis Oocytes and Fisher Rat Thyroid Cells

Wielpütz

Lee

Dinudom

et al. 2007

Regulation of the epithelial sodium channel (ENaC) is highly complex and may involve several aldosterone-induced regulatory proteins. The N-Myc downstream-regulated gene 2 (NDRG2) has been identified as an early aldosterone-induced gene. Therefore, we hypothesized that NDRG2 may affect ENaC function. To test this hypothesis we measured the amiloridesensitive (2 M) whole cell current (⌬I ami ) in Xenopus laevis oocytes expressing ENaC alone or co-expressing ENaC and NDRG2. Co-expression of NDRG2 significantly increased ⌬I ami in some, but not, all batches of oocytes tested. An inhibitory effect of NDRG2 was never observed. Using a chemiluminescence assay we demonstrated that the NDRG2-induced increase in ENaC currents was accompanied by a similar increase in channel surface expression. The stimulatory effect of NDRG2 was preserved in oocytes maintained in a low sodium bath solution to prevent sodium feedback inhibition. These findings suggest that the stimulatory effect of NDRG2 is independent of sodium feedback regulation. Furthermore, the stimulatory effect of NDRG2 on ENaC was at least in part additive to that of Sgk1. A short isoform of NDRG2 also stimulated ⌬I ami . Overexpression of NDRG2 and ENaC in Fisher rat thyroid cells confirmed the stimulatory effect of NDRG2 on ENaC-mediated short-circuit current (I SC-ami ). In addition, small interference RNA against NDRG2 largely reduced I SC-ami in Fisher rat thyroid cells. Our results indicate that NDRG2 is a likely candidate to contribute to aldosterone-mediated ENaC regulation.The epithelial sodium channel (ENaC) 2 consists of three subunits (␣, ␤, and ␥) and is localized in the apical membranes of sodium absorbing epithelia like the aldosterone-sensitive distal nephron, respiratory epithelia, distal colon, sweat, and salivary ducts. It is the rate-limiting step for sodium absorption in these epithelia and plays a major role in the maintenance of body sodium balance (1, 2). The appropriate regulation of ENaC is critically important for the long term control of arterial blood pressure (3). This is evidenced by gain-of-function mutations of ENaC causing Liddle syndrome (pseudohyperaldosteronism), a hereditary form of severe arterial hypertension (4). In contrast, loss-of-function mutations of ENaC cause pseudohypoaldosteronism type 1, a salt-wasting syndrome with low blood pressure (5).The main hormonal regulator of ENaC is aldosterone (1, 2). It is well accepted that aldosterone increases ENaC expression in the apical membrane of principal cells in the aldosteronesensitive distal nephron (6 -9). In addition an increase in channel open probability and the activation of near-silent channels are mechanisms involved in ENaC activation by aldosterone (1, 10). The aldosterone response has a characteristic time course. During the so-called "early response" (1.5-3 h) the predominant effect is an activation of pre-existing Na ϩ channels and pumps. This is followed by a "late response" (6 -24 h) characterized by the transcriptional and translational up-regulation of the...

“…NDRG2 expression is upregulated in cortical pyramidal neurons, senile plaques, and the cellular process of dystrophic neurons in the Alzheimer's brain, whereas expression is decreased in the rat frontal cortex after antidepressant treatment and electroconvulsive therapy (11). NDRG2 also plays a role in aldosterone-mediated epithelial sodium channel function (12), dendritic cell differentiation (13), and insulin action (14). NDRG3, on the other hand, may play a role in spermatogenesis because it is found in the outer layers of the seminiferous epithelium (3).…”

Section: N-myc Downstream-regulated Gene (Ndrg)mentioning

confidence: 99%

NDRG4 Protein-deficient Mice Exhibit Spatial Learning Deficits and Vulnerabilities to Cerebral Ischemia

Yamamoto

Kokame

Okuda

et al. 2011

Self Cite

The N-myc downstream-regulated gene (NDRG) family consists of four related proteins, NDRG1-NDRG4, in mammals. We previously generated NDRG1-deficient mice that were unable to maintain myelin sheaths in peripheral nerves. This condition was consistent with human hereditary motor and sensory neuropathy, Charcot-Marie-Tooth disease type 4D, caused by a nonsense mutation of NDRG1. In contrast, the effects of genetic defects of the other NDRG members remain unknown. In this study, we focused on NDRG4, which is specifically expressed in the brain and heart. In situ mRNA hybridization on the brain revealed that NDRG4 was expressed in neurons of various areas. We generated NDRG4-deficient mice that were born normally with the expected Mendelian frequency. Immunochemical analysis demonstrated that the cortex of the NDRG4-deficient mice contained decreased levels of brain-derived neurotrophic factor (BDNF) and normal levels of glial cell line-derived neurotrophic factor, NGF, neurotrophin-3, and TGF-␤1. Consistent with BDNF reduction, NDRG4-deficient mice had impaired spatial learning and memory but normal motor function in the Morris water maze test. When temporary focal ischemia of the brain was induced, the sizes of the infarct lesions were larger, and the neurological deficits were more severe in NDRG4-deficient mice compared with the control mice. These findings indicate that NDRG4 contributes to the maintenance of intracerebral BDNF levels within the normal range, which is necessary for the preservation of spatial learning and the resistance to neuronal cell death caused by ischemic stress. N-myc downstream-regulated gene (NDRG)3 family members NDRG1-NDRG4 are intracellular proteins, consist of 340 -394 amino acid residues, and share 53-65% sequence identity with each other. Furthermore, accumulating evidence implicates their roles in development, cancer metastasis, and the immune system (1-5).We originally identified RTP (NDRG1) as a homocysteineresponsive gene in human umbilical vein endothelial cells (6), which is also called DRG1, Cap43, Rit42, Ndr1, and PROXY-1. NDRG1 expression is induced by a number of conditions, such as DNA damage, hypoxia, and intracellular calcium ion elevation (4). Overexpression of NDRG1 suppresses the metastatic potency of some types of cancer cells (4) and enhances the degranulation of mast cells in response to various stimuli (7). A nonsense mutation of NDRG1 causes hereditary motor and sensory neuropathy, Charcot-Marie-Tooth disease type 4D, which presents as distal muscle wasting and atrophy, foot and hand deformities, tendon areflexia, sensory loss, and deafness in afflicted individuals (8). We previously generated NDRG1-deficient mice and revealed the essential role of NDRG1 in the cytoplasm of Schwann cells for the maintenance of myelin sheaths in peripheral nerves (9). A frame shift deletion of Ndrg1 in Greyhounds also causes polyneuropathy (10).Similar to NDRG1, the expression of NDRG2 is induced by stress conditions such as hypoxia (1). NDRG2 expression is upregulated in cort...