scholarly journals The PRK2 kinase is a potential effector target of both Rho and Rac GTPases and regulates actin cytoskeletal organization.

1997 ◽  
Vol 17 (4) ◽  
pp. 2247-2256 ◽  
Author(s):  
S Vincent ◽  
J Settleman
Keyword(s):  
Protein Kinases ◽  
Kinase Activity ◽  
Rho Kinase ◽  
Close Relative ◽  
Rho Proteins ◽  
Cellular Processes ◽  
Rac Gtpases ◽  
Downstream Effector ◽  
Rho Family Gtpases

The Ras-related Rho family GTPases mediate signal transduction pathways that regulate a variety of cellular processes. Like Ras, the Rho proteins (which include Rho, Rac, and CDC42) interact directly with protein kinases, which are likely to serve as downstream effector targets of the activated GTPase. Activated RhoA has recently been reported to interact directly with several protein kinases, p120 PKN, p150 ROK alpha and -beta, p160 ROCK, and p164 Rho kinase. Here, we describe the purification of a novel Rho-associated kinase, p140, which appears to be the major Rho-associated kinase activity in most tissues. Peptide microsequencing revealed that p140 is probably identical to the previously reported PRK2 kinase, a close relative of PKN. However, unlike the previously described Rho-binding kinases, which are Rho specific, p140 associates with Rac as well as Rho. Moreover, the interaction of p140 with Rho in vitro is nucleotide independent, whereas the interaction with Rac is completely GTP dependent. The association of p140 with either GTPase promotes kinase activity substantially, and expression of a kinase-deficient form of p140 in microinjected fibroblasts disrupts actin stress fibers. These results indicate that p140 may be a shared kinase target of both Rho and Rac GTPases that mediates their effects on rearrangements of the actin cytoskeleton.

scholarly journals Rac GTPases in Hematological Malignancies

2018 ◽  
Vol 19 (12) ◽  
pp. 4041 ◽  
Author(s):  
Valerie Durand-Onaylı ◽  
Theresa Haslauer ◽  
Andrea Härzschel ◽  
Tanja Hartmann
Keyword(s):  
Tyrosine Kinases ◽  
Chemokine Receptors ◽  
Hematological Malignancies ◽  
Hematologic Malignancies ◽  
Cell Microenvironment ◽  
Cellular Processes ◽  
Rac Gtpases ◽  
Rho Family Gtpases ◽  
Rho Family ◽  
Specific Contribution

Emerging evidence suggests that crosstalk between hematologic tumor cells and the tumor microenvironment contributes to leukemia and lymphoma cell migration, survival, and proliferation. The supportive tumor cell-microenvironment interactions and the resulting cellular processes require adaptations and modulations of the cytoskeleton. The Rac subfamily of the Rho family GTPases includes key regulators of the cytoskeleton, with essential functions in both normal and transformed leukocytes. Rac proteins function downstream of receptor tyrosine kinases, chemokine receptors, and integrins, orchestrating a multitude of signals arising from the microenvironment. As such, it is not surprising that deregulation of Rac expression and activation plays a role in the development and progression of hematological malignancies. In this review, we will give an overview of the specific contribution of the deregulation of Rac GTPases in hematologic malignancies.

Cocaine-Induced Endothelial Dysfunction: Role of RhoA/Rho Kinase Pathway Activation.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2177-2177
Author(s):  
Jaime Pereira ◽  
Claudia G Saez ◽  
Julio Pallavicini ◽  
Karla Pereira-Flores ◽  
Camila Mendoza ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Endothelial Dysfunction ◽  
Kinase Activity ◽  
Ex Vivo ◽  
Rho Kinase ◽  
Chronic Cocaine ◽  
Cocaine Users ◽  
Rock Activity

Abstract Abstract 2177 Background. Cocaine abuse is associated with an increased risk of cardiac and cerebrovascular events, such as myocardial infarction, sudden cardiac death, and ischemic stroke. The underlying mechanisms leading to these complications are not fully understood although intravascular thrombus formation and accelerated atherosclerosis are prominent findings. We have recently demonstrated that chronic cocaine use is associated with endothelial dysfunction (Sáez et al. Thromb Res 2011; 128: 18), a key event in the onset and progression of atherosclerosis. There is growing evidence that the RhoA/Rho kinase (ROCK) pathway has an important pathophysiological role in vascular endothelial dysfunction. Accordingly, we hypothesized that cocaine use induces activation of RhoA/ROCK pathway. Objectives. The main aim of this work was to investigate the activation of RhoA/ROCK pathway through ex vivo, in vivo and in vitro studies. Methods. Ex vivo studies. We studied 13 cocaine dependent individuals (aged 19–52 years mean age 37 years) who met DSM-IV criteria for cocaine dependence, seeking treatment for cocaine abuse and age, sex-matched healthy controls (aged 20–49 years, mean age 35 years). Samples were obtained at admission, within 72 hours of drug exposure. Endothelial cell damage was determined by enumerating circulating endothelial cells (CECs). Rho-kinase activity was assessed by the levels of phosphorylated to total myosin light chain phosphatase 1 (MYPT1-P/T) in circulating leukocytes. In vivo studies. Adult male Sprague-Dawley rats were randomly assigned to receive either cocaine (30mg/kg, provided by NIDA, USA) or saline intraperitoneally once daily for 21 days. The levels of aortic phosphorylated MYPT1 (phospho-MYPT1) were assessed by western blot in aorta extracts. In vitro experiments. Human umbilical vein endothelial cells (HUVECs) were cultured under standard conditions and supplemented for 5 hours with plasma from chronic cocaine users, normal plasma, cocaine (10μM) or vehicle. After media removal, HUVECs were either lysed for determination of ROCK activity or co-cultured with resting platelets and immunostained for von Willebrand factor (FVW). Platelet adhesion was evaluated by immunofluorescence microsocopy. Experiments were conducted in the presence or absence of ROCK inhibitors, Y-27632 (10 μM) or atorvastatin (10μM). Results. Cocaine users showed significantly elevated number of CECs compared to the controls (65 ± 6.6 vs 14 ± 3.4 cells/mL, p: 0.0002). In the control subjects, leukocyte mean MYPT1-P/T ratio was 2.2 ± 0.8 whereas in cocaine addicts were significantly increased (9.8 ± 2.8; p 0.015). ROCK activity was higher by 100% (p: 0.019) in the aortic wall of the cocaine-treated rats compared to sham animals. HUVECs supplemented with plasma from cocaine users showed an increase in ROCK activity by 25% (p: 0.039), released significantly higher amount of FVW (p<0.05) and adhered a larger number of platelets (22.6±5 vs 7.9±3 platelets/cell, respectively; p: 0.006) compared with control plasma. Cocaine exposure induced a dramatically higher number of platelets adhered to HUVEC than in vehicle-treated cells (220±73 vs 10.2±1.1 platelets/cell, respectively; p>0.001).ROCK inhibitors, atorvastatin and Y-27632 reduced the release of FVW by HUVECs exposed to plasma from cocaine users by 65% (p: 0.004) and strongly inhibited platelet adhesion (by 75% in plasma-treated cells and by 90% in HUVECs exposed to cocaine, p:< 0.006). Conclusions. We found an increase in Rho kinase activity in peripheral leukocytes of cocaine abusers, in the vessel wall of rats exposed to cocaine and a marked positive effect of ROCK inhibitors on the cellular injury induced by cocaine or plasma from cocaine consumers on endothelial cells. Collectively, these data suggest that activation of RhoA/ROCK pathway plays a key role in cocaine-induced endothelial dysfunction. Inhibition of ROCK may provide therapeutic benefits in a comprehensive treatment for cocaine addiction. Disclosures: No relevant conflicts of interest to declare.

scholarly journals DYRK1A Autophosphorylation on Serine Residue 520 Modulates Its Kinase Activity via 14-3-3 Binding

2007 ◽  
Vol 18 (4) ◽  
pp. 1167-1178 ◽  
Author(s):  
Mónica Alvarez ◽  
Xavier Altafaj ◽  
Sergi Aranda ◽  
Susana de la Luna
Keyword(s):  
Protein Kinases ◽  
Kinase Activity ◽  
Dynamic Changes ◽  
Activated T Cells ◽  
Cellular Processes ◽  
Dual Specificity ◽  
Evolutionarily Conserved ◽  
The Family ◽  
Intramolecular Mechanism

Dual-specificity tyrosine-phosphorylated and regulated kinase (DYRK) proteins are an evolutionarily conserved family of protein kinases, with members identified from yeast to humans, that participate in a variety of cellular processes. DYRKs are serine/threonine protein kinases that are activated by autophosphorylation on a tyrosine residue in the activation loop. The family member DYRK1A has been shown to phosphorylate several cytosolic proteins and a number of splicing and transcription factors, including members of the nuclear factor of activated T cells family. In the present study, we show that DYRK1A autophosphorylates, via an intramolecular mechanism, on Ser-520, in the PEST domain of the protein. We also show that phosphorylation of this residue, which we show is subjected to dynamic changes in vivo, mediates the interaction of DYRK1A with 14-3-3β. A second 14-3-3 binding site is present within the N-terminal of the protein. In the context of the DYRK1A molecule, neither site can act independently of the other. Bacterially produced DYRK1A and the mutant DYRK1A/S520A have similar kinase activities, suggesting that Ser-520 phosphorylation does not affect the intrinsic kinase activity on its own. Instead, we demonstrate that this phosphorylation allows the binding of 14-3-3β, which in turn stimulates the catalytic activity of DYRK1A. These findings provide evidence for a novel mechanism for the regulation of DYRK1A kinase activity.

325 ACTIVITY OF MATURATION-PROMOTING FACTOR (MPF) AND MITOGEN-ACTIVATED PROTEIN KINASES DURING IN VITRO MATURATION OF BUFFALO OOCYTES (BUBALUS BUBALIS)

2006 ◽  
Vol 18 (2) ◽  
pp. 270
Author(s):  
B. Gasparrini ◽  
G. Leoni ◽  
L. Boccia ◽  
M. Galiotto ◽  
S. Ledda ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Kinases ◽  
In Vitro Maturation ◽  
Map Kinases ◽  
Kinase Activity ◽  
Buffer System ◽  
Mitogen Activated Protein Kinases ◽  
Mitogen Activated Protein ◽  
Maturation Promoting Factor

The maturation promoting factor (MPF) and mitogen-activated protein kinases (MAPK) are the key regulators of both meiotic and mitotic cell cycles. The absence of data on the activity of the major cell cycle kinases in buffalo oocytes during meiotic progression provided the bases for this study. More specifically we assayed the MPF and MAP kinase activity of buffalo oocytes during meiosis. Abattoir-derived cumulus-oocyte complexes (COCs) with a compact, non-atretic cumulus and a homogeneous cytoplasm were utilized for the study. The COCs (n = 293, over four replicates) were matured in vitro in TCM-199 supplemented with 10% fetal calf serum (FCS), 0.2 mM sodium pyruvate, 0.5 �g/mL FSH, 5 �g/mL LH, 1 �g/mL 17�-estradiol, 50 �M of cysteamine, and 50 �g/mL kanamycin (B199). In vitro maturation (IVM) was carried out at 38.5�C under a controlled gas atmosphere of 5% CO2 in humidified air. At scale times during the culture (0, 3, 6, 9, 12, 15, 18, 21, 24 h) groups of oocytes were stained with Hoechst 33342 to assess chromatin configuration and stored according to the maturation stage (GV, GVDB, MI, and MII) at -80�C pending protein analysis. SDS-polyacrylamide gel electrophoresis wase performed using Laemmli discontinuous buffer system (Laemmli 1970 Nature 227, 680) with a 12% running gel. Groups of oocytes were analyzed for MPF activity (n = 65) by histone H1 kinase activity (Naito and Toyoda 1991 J. Reprod. Fertil. 93, 467-473) and for MAPK activity (n = 48) by myelin basic protein assays (Chesnel et al. 1995 Biol. Reprod. 52, 895-902). The activity of both MPF and MAP kinases was quantified by measuring the density of the bands on the autoradiographic film with a densitometer. Differences in the levels of the kinases among groups were analyzed by ANOVA. It was assumed that the value of MPF and MAPK was 100% in metaphase II (MII) stage oocytes. The lowest levels of MPF and MAPK activities were found in the oocytes at the GV (0-6 h post-IVM: 40% and 17.2%, respectively) and at the GVBD (6-9 h post-IVM: 41.2% and 18%) stages. The activities increased at metaphase I (MI) stage (9-15 h post-IVM) and at MII (21-24 post-IVM). Interestingly, although similar levels of MAP kinases were found at MI and MII stages (95.1% vs. 100%), MPF levels were significantly lower (P < 0.01) at the MI stage compared to those detected at MII (82.8% vs. 100%). The fluctuations of the MPF levels in buffalo appear different compared to those observed in other species; in particular, no differences were recorded between the GV and the GVBD stages whereas a significant increase of the MPF levels was found at MII compared to the MI stage. It seems that MPF and MAPK could differently guide meiotic resumption and progression to the MII arrest in this species. To our knowledge, this is the first report on biochemical analysis of the cell cycle regulation in buffalo oocytes.

Abstract 3571: Evidence for Rho-Kinase Activation in Patients with Pulmonary Hypertension

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Zhulanqiqige Doe ◽  
Yoshihiro Fukumoto ◽  
Aya Takaki ◽  
Shunsuke Tawara ◽  
Junko Ohashi ◽  
...  
Keyword(s):  
Pulmonary Hypertension ◽  
Kinase Activity ◽  
Kinase Inhibitor ◽  
Heart Diseases ◽  
Pulmonary Arteries ◽  
Connective Tissue Diseases ◽  
Rho Kinase ◽  
Kinase Activation ◽  
And Gender

Pulmonary hypertension (PH) still remains a fatal disease characterized by hyperconstriction and remodeling of pulmonary arteries (PA). We and others have previously demonstrated that long-term inhibition of Rho-kinase is useful for treatment of PH in animal models, however, it remains to be examined whether Rho-kinase is actually activated in patients with PH. First, we examined whether Rho-kinase activity is enhanced in circulating neutrophils from 40 healthy age- and gender-matched controls and 40 PH patients with various etiologies, including idiopathic PAH (n=18), and PH associated with connective tissue diseases (n=8), congenital heart diseases (n=7), or chronic thromboembolism (n=7). We measured total and phosphorylated forms of myosin binding subunit (MBS), a substrate of Rho-kinase, by Western blotting, and defined the p-MBS/t-MBS ratio as an index of systemic Rho-kinaes activity. Next, we examined Rho-kinase activity by immunostaining in lung tissues from 5 controls and 5 IPAH obtained during lung surgery and transplantation, respectively. Finally, we examined vascular responses of isolated small PA from those subjects in vitro. Systemic Rho-kinase activity was significantly increased in the PAH patients compared with the controls (P<0.0001). Among the 4 subgroups of PH, Rho-kinase activity was significantly increased in all except for PH with thromboembolism (P<0.05). Significant correlations were noted between Rho-kinase activity and mean PA pressure, pulmonary vascular resistance, and duration of the disorder in the PH patients (all P<0.05). Rho-kinase expression in small PA and Rho-kinase activity in the lung tissue also were significantly increased in the PAH patients compared the controls (both P<0.0001). Endothelium-dependent relaxations were markedly impaired and serotonin-induced contractions were markedly enhanced in the PAH patients compared with the controls, and the hypercontractions were abolished in the presence of hydroxyfasudil, a specific Rho-kinase inhibitor (all P<0.01). These results provide the first direct evidence for Rho-kinase activation in patients with PH, confirming the therapeutic importance of Rho-kinase in the treatment of PH in humans.

Glutaredoxin AtGRXC2 catalyses inhibitory glutathionylation of Arabidopsis BRI1-associated receptor-like kinase 1 (BAK1) in vitro

2015 ◽  
Vol 467 (3) ◽  
pp. 399-413 ◽  
Author(s):  
Kyle W. Bender ◽  
Xuejun Wang ◽  
George B. Cheng ◽  
Hyoung Seok Kim ◽  
Raymond E. Zielinski ◽  
...  
Keyword(s):  
Protein Kinases ◽  
Redox Regulation ◽  
Kinase Activity ◽  
Cytoplasmic Domain ◽  
Post Translational Modification ◽  
Cysteine Oxidation ◽  
Receptor Like Kinase ◽  
Reversible Protein Phosphorylation ◽  
Two Hybrid

Reversible protein phosphorylation, catalysed by protein kinases, is the most widely studied post-translational modification (PTM), whereas the analysis of other modifications such as S-thiolation is in its relative infancy. In a yeast-two-hybrid (Y2H) screen, we identified a number of novel putative brassinosteroid insensitive 1 (BR1)-associated receptor-like kinase 1 (BAK1) interacting proteins including several proteins related to redox regulation. Glutaredoxin (GRX) C2 (AtGRXC2) was among candidate proteins identified in the Y2H screen and its interaction with recombinant Flag–BAK1 cytoplasmic domain was confirmed using an in vitro pull-down approach. We show that BAK1 peptide kinase activity is sensitive to the oxidizing agents H2O2 and diamide in vitro, suggesting that cysteine oxidation might contribute to control of BAK1 activity. Furthermore, BAK1 was glutathionylated and this reaction could occur via a thiolate-dependent reaction with GSSG or a H2O2-dependent reaction with GSH and inhibited kinase activity. Surprisingly, both reactions were catalysed by AtGRXC2 at lower concentrations of GSSG or GSH than reacted non-enzymatically. Using MALDI–TOF MS, we identified Cys353, Cys374 and Cys408 as potential sites of glutathionylation on the BAK1 cytoplasmic domain and directed mutagenesis suggests that Cys353 and Cys408 are major sites of GRXC2-mediated glutathionylation. Collectively, these results highlight the potential for redox control of BAK1 and demonstrate the ability of AtGRXC2 to catalyse protein glutathionylation, a function not previously described for any plant GRX. The present work presents a foundation for future studies of glutathionylation of plant receptor-like protein kinases (RLKs) as well as for the analysis of activities of plant GRXs.

scholarly journals Evidence for modification of protein phosphorylation by cytokinins

1972 ◽  
Vol 130 (4) ◽  
pp. 901-911 ◽  
Author(s):  
R. K. Ralph ◽  
P. J. A. McCombs ◽  
G. Tener ◽  
S. J. Wojcik
Keyword(s):  
Protein Phosphorylation ◽  
Chinese Cabbage ◽  
Kinase Activity ◽  
Protein Kinase Activity ◽  
Secondary Phloem ◽  
Phloem Tissue ◽  
Cyclic Monophosphate ◽  
Cellular Processes ◽  
Ylacetic Acid

Kinetin stimulated phosphorylation of protein in floated Chinese-cabbage leaf discs, but inhibited protein phosphorylation in nuclei+chloroplast extracts from Chinese-cabbage or tobacco leaves. Kinetin also inhibited protein phosphorylation in isolated tobacco nuclei or nuclei from carrot secondary-phloem tissue. Purified Chinese-cabbage leaf ribosomes exhibited protein kinase activity which was inhibited by kinetin and zeatin. The ribosome-associated kinase responded to kinetin and zeatin differently from that associated with nuclei+chloroplast preparations. Protein phosphorylation in vitro was not affected by adenosine 3′:5′-cyclic monophosphate, indol-3-ylacetic acid or gibberellic acid. It was only inhibited by N9-unsubstituted purines, among which the known cytokinins were the most effective inhibitors. The results are discussed in relation to possible similarities between the effects of cytokinins in plant tissues and the effects of adenosine 3′:5′-cyclic monophosphate in animal tissues. Both compounds appear to modify the activity of protein kinases and both affect many different cellular processes.

scholarly journals Chronic intrauterine pulmonary hypertension increases endothelial cell Rho kinase activity and impairs angiogenesis in vitro

2008 ◽  
Vol 295 (4) ◽  
pp. L680-L687 ◽  
Author(s):  
Jason Gien ◽  
Gregory J. Seedorf ◽  
Vivek Balasubramaniam ◽  
Nancy Tseng ◽  
Neil Markham ◽  
...  
Keyword(s):  
Pulmonary Hypertension ◽  
Kinase Activity ◽  
Ductus Arteriosus ◽  
Rho Kinase ◽  
Tube Formation ◽  
Normal Lung ◽  
No Production ◽  
Fetal Sheep ◽  
Enos Protein

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by endothelial dysfunction and decreased vascular growth. The role of Rho kinase activity in modulating endothelial function and regulating angiogenesis during normal lung development and in PPHN is unknown. We hypothesized that PPHN increases Rho kinase activity in fetal pulmonary artery endothelial cells (PAECs) and impairs angiogenesis in vitro. Proximal PAECs were harvested from fetal sheep with partial ligation of the ductus arteriosus in utero (PPHN) and age-matched controls. Rho kinase activity was measured by RhoA, Rho GTP, and phosphorylated MYPT-1 protein content. The effects of Rho kinase activity on angiogenesis, endothelial nitric oxide (NO) synthase (eNOS) protein expression, and NO production were determined in normal and PPHN PAECs. Angiogenesis was assessed by tube formation in vitro with/without Y-27632 (a Rho kinase inhibitor) and calpeptin (a Rho kinase activator) in the presence/absence of N-nitro-l-arginine (l-NA, an NOS inhibitor). RhoA, Rho GTP, and phosphorylated MYPT-1 protein were increased in PPHN PAECs. Tube formation was reduced 29% in PPHN PAECs ( P < 0.001) and increased with Y-27632 treatment in normal and PPHN PAECs, with PPHN PAECs achieving levels similar to those of normal PAECs. l-NA inhibited the Y-27632-induced increase in tube formation in normal, but not PPHN, PAECs. Calpeptin reduced tube formation in normal and PPHN PAECs. eNOS expression was reduced 42% in PPHN PAECs ( P < 0.01). Y-27632 increased eNOS protein and NO production in normal and PPHN PAECs. Calpeptin decreased eNOS protein only in normal PAECs but reduced NO production in normal and PPHN PAECs. We conclude that Rho kinase activity is increased in PPHN PAECs and impairs angiogenesis and downregulates eNOS protein and NO production in vitro.

ROCKII Ser1366 phosphorylation reflects the activation status

2012 ◽  
Vol 443 (1) ◽  
pp. 145-151 ◽  
Author(s):  
Hsiang-Hao Chuang ◽  
Chih-Hsuan Yang ◽  
Yeou-Guang Tsay ◽  
Chih-Yi Hsu ◽  
Ling-Ming Tseng ◽  
...  
Keyword(s):  
Phosphorylation Site ◽  
Human Breast ◽  
New Approach ◽  
Cellular Processes ◽  
Downstream Effector ◽  
Conserved Residue ◽  
Major Phosphorylation Site ◽  
Activation Status ◽  
In Cells

ROCK (Rho-associated protein kinase), a downstream effector of RhoA, plays an important role in many cellular processes. Accumulating evidence has shown the involvement of ROCK activation in the pathogenesis of many diseases. However, a reagent capable of detecting ROCK activation directly is lacking. In the present study, we show autophosphorylation of ROCKII in an in vitro kinase reaction. The phosphorylation sites were identified by MS, and the major phosphorylation site was found to be at the highly conserved residue Ser1366. A phospho-specific antibody was generated that can specifically recognize ROCKII Ser1366 phosphorylation. We found that the extent of Ser1366 phosphorylation of endogenous ROCKII is correlated with that of myosin light chain phosphorylation in cells in response to RhoA stimulation, showing that Ser1366 phosphorylation reflects its kinase activity. In addition, ROCKII Ser1366 phosphorylation could be detected in human breast tumours by immunohistochemical staining. The present study provides a new approach for revealing the ROCKII activation status by probing ROCKII Ser1366 phosphorylation directly in cells or tissues.

NH2 terminus of serum and glucocorticoid-regulated kinase 1 binds to phosphoinositides and is essential for isoform-specific physiological functions

2007 ◽  
Vol 292 (6) ◽  
pp. F1741-F1750 ◽  
Author(s):  
Alan C. Pao ◽  
James A. McCormick ◽  
Hongyan Li ◽  
John Siu ◽  
Cedric Govaerts ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Kinase Activity ◽  
Regulatory Protein ◽  
Forkhead Transcription Factor ◽  
Cellular Processes ◽  
Cellular Compartments ◽  
Stimulation Of

Serum and glucocorticoid regulated kinase 1 (SGK1) has been identified as a key regulatory protein that controls a diverse set of cellular processes including sodium (Na+) homeostasis, osmoregulation, cell survival, and cell proliferation. Two other SGK isoforms, SGK2 and SGK3, have been identified, which differ most markedly from SGK1 in their NH2-terminal domains. We found that SGK1 and SGK3 are potent stimulators of epithelial Na+ channel (ENaC)-dependent Na+ transport, while SGK2, which has a short NH2 terminus, is a weak stimulator of ENaC. Further characterization of the role of the SGK1 NH2 terminus revealed that its deletion does not affect in vitro kinase activity but profoundly limits the ability of SGK1 either to stimulate ENaC-dependent Na+ transport or inhibit Forkhead-dependent gene transcription. The NH2 terminus of SGK1, which shares sequence homology with the phosphoinositide 3-phosphate [PI( 3 )P] binding domain of SGK3, binds phosphoinositides in protein lipid overlay assays, interacting specifically with PI( 3 )P, PI( 4 )P, and PI( 5 )P, but not with PI( 3 , 4 , 5 )P3. Moreover, a point mutation that reduces phosphoinositide binding to the NH2 terminus also reduces SGK1 effects on Na+ transport and Forkhead activity. These data suggest that the NH2 terminus, although not required for PI 3-kinase-dependent modulation of SGK1 catalytic activity, is required for multiple SGK1 functions, including stimulation of ENaC and inhibition of the proapoptotic Forkhead transcription factor. Together, these observations support the idea that the NH2-terminal domain acts downstream of PI 3-kinase-dependent activation to target the kinase to specific cellular compartments and/or substrates, possibly through its interactions with a subset of phosphoinositides.

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