Erectile Dysfunction in Young Non-Obese Type II Diabetic Goto-Kakizaki Rats is Associated with Decreased eNOS Phosphorylation at Ser1177

Introduction. Diabetes mellitus (DM) is a risk factor for erectile dysfunction (ED). Although type 2 DM is responsible for 90-95% diabetes cases, type 1 DM experimental models are commonly used to study diabetes-associated ED. Aim. Goto-Kakizaki (GK) rat model is relevant to ED studies since the great majority of patients with type 2 diabetes display mild deficits in glucose-stimulated insulin secretion, insulin resistance, and hyperglycemia. We hypothesized that GK rats display ED which is associated with decreased nitric oxide (NO) bioavailability. Methods. Wistar and GK rats were used at 10 and 18 weeks of age. Changes in the ratio of intracavernosal pressure/mean arterial pressure (ICP/MAP) after electrical stimulation of cavernosal nerve were determined in vivo. Cavernosal contractility was induced by electrical field stimulation (EFS) and phenylephrine (PE). In addition, nonadrenergic-noncholinergic (NANC)- and sodium nitroprusside (SNP)-induced relaxation were determined. Cavernosal neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS) mRNA and protein expression were also measured. Main Outcome Measure. GK diabetic rats display ED associated with decreased cavernosal expression of eNOS protein. Results. GK rats at 10 and 18 weeks demonstrated impaired erectile function represented by decreased ICP/MAP responses. Ten-week-old GK animals displayed increased PE responses and no changes in EFS-induced contraction. Conversely, contractile responses to EFS and PE were decreased in cavernosal tissue from GK rats at 18 weeks of age. Moreover, GK rats at 18 weeks of age displayed increased NANC-mediated relaxation, but not to SNP. In addition, ED was associated with decreased eNOS protein expression at both ages. Conclusion. Although GK rats display ED, they exhibit changes in cavernosal reactivity that would facilitate erectile responses. These results are in contrast to those described in other experimental diabetes models. This may be due to compensatory mechanisms in cavernosal tissue to overcome restricted pre-penile arterial blood supply or impaired veno-occlusive mechanisms. Carneiro FS, Giachini FRC, Carneiro ZN, Lima VV, Ergul A, Webb RC, and Tostes RC. Erectile dysfunction in young non-obese type II diabetic Goto-Kakizaki rats is associated with decreased eNOS phosphorylation at Ser1177. J Sex Med 2010;7:3620-3634.

Ataxia telangiectasia mutated (ATM) kinase and ATM and Rad3 related kinase mediate phosphorylation of Brca1 at distinct and overlapping sites - In vivo assessment using phospho-specific antibodies

Recent studies have provided evidence that breast cancer susceptibility gene products (Brca1 and Brca2) suppress cancer, at least in part, by participating in DNA damage signaling and DNA repair. Brca1 is hyperphosphorylated in response to DNA damage and co-localizes with Rad51, a protein involved in homologous-recombination, and Nbs1·Mre11·Rad50, a complex required for both homologous-recombination and nonhomologous end joining repair of damaged DNA. Here, we report that there is a qualitative difference in the phosphorylation states of Brca1 between ionizing radiation (IR) and UV radiation. Brca1 is phosphorylated at Ser-1423 and Ser-1524 after IR and UV; however, Ser-1387 is specifically phosphorylated after IR, and Ser-1457 is predominantly phosphorylated after UV. These results suggest that different types of DNA-damaging agents might signal to Brca1 in different ways. We also provide evidence that the rapid phosphorylation of Brca1 at Ser-1423 and Ser-1524 after IR (but not after UV) is largely ataxia telangiectasia mutated (ATM) kinase-dependent. The overexpression of catalytically inactive ATM and Rad3 related (ATR) kinase inhibited the UV-induced phosphorylation of Brca1 at these sites, indicating that ATR controls Brca1 phosphorylation in vivo after the exposure of cells to UV light. Moreover, ATR associates with Brca1; ATR and Brca1 foci co-localize both in cells synchronized in S phase and after exposure of cells to DNA-damaging agents. ATR can itself phosphorylate the region of Brca1 phosphorylated by ATM (Ser-Gln cluster in the C terminus of Brca1, amino acids 1241-1530). However, there are additional uncharacterized ATR phosphorylation site(s) between residues 521 and 757 of Brca1. Taken together, our results support a model in which ATM and ATR act in parallel but somewhat overlapping pathways of DNA damage signaling but respond primarily to different types of DNA lesion.

Ataxia telangiectasia mutated (ATM) kinase and ATM and Rad3 related kinase mediate phosphorylation of Brca1 at distinct and overlapping sites - In vivo assessment using phospho-specific antibodies

Recent studies have provided evidence that breast cancer susceptibility gene products (Brca1 and Brca2) suppress cancer, at least in part, by participating in DNA damage signaling and DNA repair. Brca1 is hyperphosphorylated in response to DNA damage and co-localizes with Rad51, a protein involved in homologous-recombination, and Nbs1.Mre11.Rad50, a complex required for both homologous-recombination and nonhomologous end joining repair of damaged DNA. Here, we report that there is a qualitative difference in the phosphorylation states of Brca1 between ionizing radiation (IR) and UV radiation. Brca1 is phosphorylated at Ser-1423 and Ser-1524 after IR and W; however, Ser-1387 is specifically phosphorylated after IR, and Ser-1457 is predominantly phosphorylated after W. These results suggest that different types of DNA-damaging agents might signal to Brca1 in different ways. We also provide evidence that the rapid phosphorylation of Brca1 at Ser-1423 and Ser-1524 after IR (but not after W) is largely ataxia telangiectasia mutated (ATM) kinase-dependent. The overexpression of catalytically inactive ATM and Rad3 related (ATR) kinase inhibited the UV-induced phosphorylation of Brca1 at these sites, indicating that ATR controls Brca1 phosphorylation in vivo after the exposure of cells to UV light. Moreover, ATR associates with Brca1; ATR and Brca1 foci co-localize both in cells synchronized in S phase and after exposure of cells to DNA-damaging agents. ATR can itself phosphorylate the region of Brca1 phosphorylated by ATM (Ser-Gln cluster in the C terminus of Brca1, amino acids 1241-1530), However, there are additional uncharacterized ATR phosphorylation site(s) between residues 521 and 757 of Brca1, Taken together, our results support a model in which ATM and ATR act in parallel but somewhat overlapping pathways of DNA damage signaling but respond primarily to different types of DNA lesion.

The role of putative phosphorylation sites in the targeting and shuttling of the aquaporin-2 water channel

In renal collecting ducts, a vasopressin-induced cAMP increase results in the phosphorylation of aquaporin-2 (AQP2) water channels at Ser-256 and its redistribution from intracellular vesicles to the apical membrane. Hormones that activate protein kinase C (PKC) proteins counteract this process. To determine the role of the putative kinase sites in the trafficking and hormonal regulation of human AQP2, three putative casein kinase II (Ser-148, Ser-229, Thr-244), one PKC (Ser-231), and one protein kinase A (Ser-256) site were altered to mimic a constitutively non-phosphorylated/phosphorylated state and were expressed in Madin-Darby canine kidney cells. Except for Ser-256 mutants, seven correctly folded AQP2 kinase mutants trafficked as wild-type AQP2 to the apical membrane via forskolin-sensitive intracellular vesicles. With or without forskolin, AQP2-Ser-256A was localized in intracellular vesicles, whereas AQP2-S256D was localized in the apical membrane. Phorbol 12-myristate 13-acetate-induced PKC activation following forskolin treatment resulted in vesicular distribution of all AQP2 kinase mutants, while all were still phosphorylated at Ser-256. Our data indicate that in collecting duct cells, AQP2 trafficking to vasopressin-sensitive vesicles is phosphorylation-independent, that phosphorylation of Ser-256 is necessary and sufficient for expression of AQP2 in the apical membrane, and that PMA-induced PKC-mediated endocytosis of AQP2 is independent of the AQP2 phosphorylation state.

Ataxia-telangiectasia-mutated (ATM) and NBS1-dependent phosphorylation of Chk1 on Ser-317 in response to ionizing radiation

In mammals, the ATM (ataxia-telangiectasia-mutated) and ATR (ATM and Rad3-related) protein kinases function as critical regulators of the cellular DNA damage response. The checkpoint functions of ATR and ATM are mediated, in part, by a pair of checkpoint effector kinases termed Chk1 and Chk2. In mammalian cells, evidence has been presented that Chk1 is devoted to the ATR signaling pathway and is modified by ATR in response to replication inhibition and UV-induced damage, whereas Chk2 functions primarily through ATM in response to ionizing radiation (IR), suggesting that Chk2 and Chk1 might have evolved to channel the DNA damage signal from ATM and ATR, respectively. We demonstrate here that the ATR-Chk1 and ATM-Chk2 pathways are not parallel branches of the DNA damage response pathway but instead show a high degree of cross-talk and connectivity. ATM does in fact signal to Chk1 in response to IR. Phosphorylation of Chk1 on Ser-317 in response to IR is ATM-dependent. We also show that functional NBS1 is required for phosphorylation of Chk1, indicating that NES1 might facilitate the access of Chk1 to ATM at the sites of DNA damage. Abrogation of Chk1 expression by RNA interference resulted in defects in IR-induced S and G2/M phase checkpoints; however, the overexpression of phosphorylation site mutant (S317A, S345A or S317A/S345A double mutant) Chk1 failed to interfere with these checkpoints. Surprisingly, the kinase-dead Chk1 (D130A) also failed to abrogate the S and G2 checkpoint through any obvious dominant negative effect toward endogenous Chk1. Therefore, further studies will be required to assess the contribution made by phosphorylation events to Chk1 regulation. Overall, the data presented in the study challenge the model in which Chk1 only functions downstream from ATR and indicate that ATM does signal to Chk1. In addition, this study also demonstrates that Chk1 is essential for IR-induced inhibition of DNA synthesis and the G2/M checkpoint.

Deciphering the role of Yap4 phosphorylation under stress conditions

The existence of molecular mechanisms of response, repair and adaptation, many of which are greatly conserved across nature, gives to the cell with the plasticity it requires to adjust to its ever-changing environment, a homeostatic event that is termed the stress response. In the budding yeast Saccharomyces cerevisiae there is a particular family of transcription factors, the Yap family, which has been shown to have a relevant role in yeast adaptation to several stress conditions. In particular, Yap1 is the major regulator of the transcriptional response to oxidative stress and Yap2 and Yap8 play important roles upon cadmium and arsenic exposure, respectively.(...)

Enzymatic phosphorylation of hair keratin enhances fast adsorption of cationic moieties

The current study describes the in vitro phosphorylation of a human hair keratin, using protein kinase for the first time. Phosphorylation of keratin was demonstrated by 31P NMR (Nuclear Magnetic Resonance) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) techniques. Phosphorylation induced a 2.5 fold increase of adsorption capacity in the first 10 minutes for cationic moiety like Methylene Blue (MB). Thorough description of MB adsorption process was performed by several isothermal models. Reconstructed fluorescent microscopy images depict distinct amounts of dye bound to the differently treated hair. The results of this work suggest that the enzymatic phosphorylation of keratins might have significant implications in hair shampooing and conditioning, where short application times of cationic components are of prime importance.

In vitro phosphorylation as tool for modification of silk and keratin fibrous materials

An overview is given of the recent work on in vitro enzymatic phosphorylation of silk fibroin and human hair keratin. Opposing to many chemical "conventional" approaches, enzymatic phosphorylation is in fact a mild reaction and the treatment falls within "green chemistry" approach. Silk and keratin are not phosphorylated in vivo, but in vitro. This enzyme-driven modification is a major technological breakthrough. Harsh chemical chemicals are avoided, and mild conditions make enzymatic phosphorylation a real "green chemistry" approach. The current communication presents a novel approach stating that enzyme phosphorylation may be used as a tool to modify the surface charge of biocompatible materials such as keratin and silk.

Fosforilación de lípidos señales disparada por ABA, NaCl y manitol en coleóptilos, raíces y células de aleurona de cebada (Hordeum vulgare). Lipid signaling phosphorylation triggered by ABA, NaCl and mannitol in coleoptile, roots and aleurone cells of barley (Hordeum vulgare).

Es bien conocido que los fosfolípidos son un conjunto de moléculas capaces de funcionar como reguladores en diversos procesos celulares. Al respecto, este proyecto tiene como objetivo dilucidar la participación de los mismos, en particular ácido fosfatídico (PA) y diacilglicerol pirofosfato (DGPP) durante el efecto antagónico de ABA en la germinación y como reguladores de la respuesta al estrés salino en la plántula. Se sabe que las plantas responden de forma rápida y adecuada a una situación de estrés modificando el patrón de fosfolípidos de sus membranas, lo cual lleva a un cambio global en las actividad de lípido quinasas, fosfatasas y a la expresión/represión de genes particulares. El desarrollo de la propuesta permitiría responder dos cuestiones básicas: conocer la relación entre fosfolípidos y ABA e indagar su participación durante la señal de estrés. La relevancia de la propuesta radica en la necesidad de ampliar el conocimiento sobre una de las causas mas importantes "estrés salino" que afecta la germinación de la semilla y luego el crecimiento y desarrollo de la plántula. En principio se evaluara a nivel morfológico, bioquímico y molecular el efecto de ABA y de fosfolípidos. Se pretende indagar sobre cambios a nivel de vacuolización en protoplastos aislados, actividad de enzimas relacionadas, pH intracelular, nivel de fosfolípidos y enzimas implicadas en su metabolismo y también efectos sobre la expresión génica. Por otro lado, se analizara los niveles de fosfolípidos y enzimas relacionadas con su metabolismo en raíces y coleoptilos de semillas que germinaron bajo condiciones de estrés. Asimismo, se identificaran los cambios morfológicos provocados por el estrés en la longitud de coleóptilos y raíces. Por ultimo como indicador de una respuesta al estrés se evaluara los cambios en los niveles de prolina. La importancia del proyecto es determinar el papel que desempeñan PA y DGPP en la germinación y durante la respuesta al estrés.

Obesity does not Lead to Imbalance Between Myocardial Phospholamban Phosphorylation and Dephosphorylation

Background: The activation of the beta-adrenergic system promotes G protein stimulation that, via cyclic adenosine monophosphate (cAMP), alters the structure of protein kinase A (PKA) and leads to phospholamban (PLB) phosphorylation. This protein participates in the system that controls intracellular calcium in muscle cells, and it is the primary regulator of sarcoplasmic reticulum calcium pump activity. In obesity, the beta-adrenergic system is activated by the influence of increased leptin, therefore, resulting in higher myocardial phospholamban phosphorylation via cAMP-PKA. Objective: To investigate the involvement of proteins which regulate the degree of PLB phosphorylation due to beta-adrenergic activation in obesity. In the present study, we hypothesized that there is an imbalance between phospholamban phosphorylation and dephosphorylation, with prevalence of protein phosphorylation. Methods: Male Wistar rats were randomly distributed into two groups: control (n = 14), fed with normocaloric diet; and obese (n = 13), fed with a cycle of four unsaturated high-fat diets. Obesity was determined by the adiposity index, and protein expressions of phosphatase 1 (PP-1), PKA, PLB, phosphorylated phospholamban at serine16 (PPLB-Ser16) were assessed by Western blot. Results: Obesity caused glucose intolerance, hyperinsulinemia, hypertriglyceridemia, hyperleptinemia and did not alter the protein expression of PKA, PP-1, PLB, PPLB-Ser16. Conclusion: Obesity does not promote an imbalance between myocardial PLB phosphorylation and dephosphorylation via beta-adrenergic system.

Multisite phosphorylation in (bio-)chemical reaction networks : multistationarity and robustness

Magdeburg, Univ., Fak. für Elektro- und Informationstechnik, Diss., 2014

Brain Glucose Transport and Phosphorylation Under Acute Insulin-Induced Hypoglycemia in Mice: An 18F-FDG PET Study.

We addressed the questions of how cerebral glucose transport and phosphorylation change under acute hypoglycemia and what the underlying mechanisms of adaptation are. METHODS: Quantitative (18)F-FDG PET combined with the acquisition of real-time arterial input function was performed on mice. Hypoglycemia was induced and maintained by insulin infusion. PET data were analyzed with the 2-tissue-compartment model for (18)F-FDG, and the results were evaluated with Michaelis-Menten saturation kinetics. RESULTS: Glucose clearance from plasma to brain (K1,glc) and the phosphorylation rate constant increased with decreasing plasma glucose (Gp), in particular at a Gp of less than 2.5 mmol/L. Estimated cerebral glucose extraction ratios taking into account an increased cerebral blood flow (CBF) at a Gp of less than 2 mmol/L were between 0.14 and 0.79. CBF-normalized K1,glc values were in agreement with saturation kinetics. Phosphorylation rate constants indicated intracellular glucose depletion at a Gp of less than 2-3 mmol/L. When brain regions were compared, glucose transport under hypoglycemia was lowest in the hypothalamus. CONCLUSION: Alterations in glucose transport and phosphorylation, as well as intracellular glucose depletion, under acute hypoglycemia can be modeled by saturation kinetics taking into account an increase in CBF. Distinct transport kinetics in the hypothalamus may be involved in its glucose-sensing function.

Tyrosine phosphorylation is an early and specific event involved in primary keratinocyte differentiation.

Very little is known about early molecular events triggering epithelial cell differentiation. We have examined the possible role of tyrosine phosphorylation in this process, as observed in cultures of primary mouse keratinocytes after exposure to calcium or 12-O-tetradecanoylphorbol-13-acetate (TPA). Immunoblotting with phosphotyrosine-specific antibodies as well as direct phosphoamino acid analysis revealed that induction of tyrosine phosphorylation occurs as a very early and specific event in keratinocyte differentiation. Very little or no induction of tyrosine phosphorylation was observed in a keratinocyte cell line resistant to the differentiating effects of calcium. Treatment of cells with tyrosine kinase inhibitors prevented induction of tyrosine phosphorylation by calcium and TPA and interfered with the differentiative effects of these agents. These results suggest that specific activation of tyrosine kinase(s) may play an important regulatory role in keratinocyte differentiation.

Normal kinetics of intestinal glucose absorption in the absence of GLUT2: evidence for a transport pathway requiring glucose phosphorylation and transfer into the endoplasmic reticulum.

Glucose is absorbed through the intestine by a transepithelial transport system initiated at the apical membrane by the cotransporter SGLT-1; intracellular glucose is then assumed to diffuse across the basolateral membrane through GLUT2. Here, we evaluated the impact of GLUT2 gene inactivation on this transepithelial transport process. We report that the kinetics of transepithelial glucose transport, as assessed in oral glucose tolerance tests, was identical in the presence or absence of GLUT2; that the transport was transcellular because it could be inhibited by the SGLT-1 inhibitor phlorizin, and that it could not be explained by overexpression of another known glucose transporter. By using an isolated intestine perfusion system, we demonstrated that the rate of transepithelial transport was similar in control and GLUT2(-/-) intestine and that it was increased to the same extent by cAMP in both situations. However, in the absence, but not in the presence, of GLUT2, the transport was inhibited dose-dependently by the glucose-6-phosphate translocase inhibitor S4048. Furthermore, whereas transport of [(14)C]glucose proceeded with the same kinetics in control and GLUT2(-/-) intestine, [(14)C]3-O-methylglucose was transported in intestine of control but not of mutant mice. Together our data demonstrate the existence of a transepithelial glucose transport system in GLUT2(-/-) intestine that requires glucose phosphorylation and transfer of glucose-6-phosphate into the endoplasmic reticulum. Glucose may then be released out of the cells by a membrane traffic-based pathway similar to the one we previously described in GLUT2-null hepatocytes.

Heterologous desensitization of the glucagon-like peptide-1 receptor by phorbol esters requires phosphorylation of the cytoplasmic tail at four different sites.

Glucagon-like peptide-1 stimulates glucose-induced insulin secretion by binding to a specific G protein-coupled receptor that activates the adenylyl cyclase pathway. We previously demonstrated that heterologous desensitization of the receptor by protein kinase C correlated with phosphorylation in a 33-amino acid-long segment of the receptor carboxyl-terminal cytoplasmic tail. Here, we determined that the in vivo sites of phosphorylation are four serine doublets present at positions 431/432, 441/442, 444/445, and 451/452. In vitro phosphorylation of fusion proteins containing mutant receptor C-tails, however, indicated that whereas serines at position 431/432 were good substrates for protein kinase C (PKC), serines 444/445 and 451/452 were poor substrates, and serines 441/442 were not substrates. In addition, serine 416 was phosphorylated on fusion protein but not in intact cells. This indicated that in vivo a different PKC isoform or a PKC-activated kinase may phosphorylate the receptor. The role of phosphorylation on receptor desensitization was assessed using receptor mutants expressed in COS cells or Chinese hamster lung fibroblasts. Mutation of any single serine doublet to alanines reduced the extent of phorbol 12-myristate 13-acetate-induced desensitization, whereas substitution of any combination of two serine doublets suppressed it. Our data thus show that the glucagon-like peptide-1 receptor can be phosphorylated in response to phorbol 12-myristate 13-acetate on four different sites within the cytoplasmic tail. Furthermore, phosphorylation of at least three sites was required for desensitization, although maximal desensitization was only achieved when all four sites were phosphorylated.