Role of GAD peptides p217 and p290 in the repair of INS receptor in salivary tissues of type 1 diabetic mice.

Glutamate decarboxylase or glutamic acid decarboxylase (GAD) is a protein associated with autoimmune diseases, including type-1 diabetes. This disease is primarily associated with the occurrence of a specific isoform: GAD65. Conversely, some specific peptides of this protein may block autoimmunity in diabetes. In this respect, understanding the relationship between GAD and the development of diabetes is important, and it is necessary to understand the role of each GAD peptide to design effective autoimmune diabetes treatments. The purpose of the present study was to analyze the effects of treatment with GAD-derived peptides p217 and p290 on INS receptors in the salivary epithelium of nonobese diabetic (NOD) animals. Three groups of 7 mice each were studied: I, BALB/c mice (control); II, NOD mice; and III, NOD mice treated with peptides p290 and p217. Groups I and II only received buffered saline solution. Glucose levels were measured daily during the 21 days of the experiment. After the study, the animals were euthanized and the parotid and submandibular glands were removed for the analysis of INS-R by fluorescence microscopy. Therapy with two peptides together was associated with reduced glucose levels in NOD mice and intense INS-R expression in both salivary organs. Our approach of combining GAD p217 and p290 peptides contributed to hormonal balance and promoted the repair of INS-R.

Enzyme activities in parotid saliva of patients with the restrictive type of anorexia nervosa.

OBJECTIVE: In patients with anorexia nervosa (AN) specific signs may occur in the oral cavity, but there are conflicting reports about their significance, especially concerning changes in salivary composition. The aim of this clinical study was to evaluate the resting parotid flow rate (PFR) and the activity of the following enzymes in parotid saliva: amylase, aspartate amino transferase (AST), lysozyme, peroxidase, serine and acidic proteases in the acute phase of the restrictive type of AN and to compare the findings with those in healthy controls. DESIGN: Forty-one subjects participated (20 patients with AN, 21 matched healthy controls), parotid saliva was collected using a modified Lashley cap at rest. Enzyme activities were measured with fluorimetric and photometric assays. RESULTS: The unstimulated PFR was significantly lower than in the controls, lysozyme and AST activity was significantly lower, and amylase showed a high inter-individual variability. A positive correlation for amylase and lysozyme and negative ones for lysozyme and BMI, lysozyme and IBW%, serine protease and salivary flow were observed. CONCLUSIONS: The reduced PFR and enzyme activities levels suggest that AN does not only affect the quantity of the saliva but also its quality and, its biological functions. The results obtained should help to provide a better understanding of the effect of AN disease on the pathogenesis of at least some oral diseases. Further research is needed on any possible role of reduced lysozyme and transaminase activity in maintaining oral protection against external toxic agents and bacteria.

Effects of biomaterial-derived fibroblast conditioned medium on the α-amylase expression of parotid gland acinar cells.

Salivary gland cells are surrounded by a complex stromal environment, in which fibroblasts are the main cells in proximity to the gland cells. In this study, the interaction between parotid gland acinar cells (PGACs), fibroblasts, and biomaterials was investigated. We prepared different biomaterials, including chitosan, polyvinyl alcohol (PVA), poly (ethylene-co-vinyl alcohol) (EVAL), polyvinylidene fluoride (PVDF), and tissue culture polystyrene (TCPS) to culture fibroblasts and then collect their conditioned media to culture PGACs. We observed no difference in AQP3, AQP5, and E-cadherin expression among different fibroblast conditioned medium treatments. Interestingly, α-amylase expression was obviously enhanced in PGACs cultured in the presence of conditioned medium from fibroblasts cultured on PVDF. Higher neurotrophin-4 (NT-4) expression was observed in PVDF-derived fibroblast conditioned medium using a growth factor protein array assay. In addition, directly adding NT-4 into the culture medium significantly promoted α-amylase expression by PGACs. Finally, nestin and ßIII-tubulin expression by fibroblasts cultured on PVDF was also enhanced. Together, these results suggest that PVDF could promote α-amylase expression by PGACs via the NT-4 produced by fibroblasts. STATEMENT OF SIGNIFICANCE: To date, there is no effective therapy for patients with dry mouth with persistent salivary hypofunction. The study made use of different biomaterials to culture fibroblasts and then collect their conditioned media to culture PGACs. It was found that the effect of fibroblast conditioned medium from PVDF on the α-amylase expression of PGACs was obviously enhanced and higher neurotrophin-4 (NT-4) expression was found in PVDF-derived fibroblast conditioned medium. In addition, directly adding NT-4 into the culture medium significantly promoted the expression of α-amylase by PGACs and the expression of nestin and ßIII-tubulin of fibroblasts after being cultured on PVDF was enhanced. Therefore, the present study represents the first description of the role of NT-4 in the expression of α-amylase of PGACs and the role of PVDF in the reprogramming fibroblasts into neural progenitor-like cells, indicating that PVDF could promote the expression of α-amylase by PGACs via the NT-4 produced by fibroblasts.

The long-term administration of calcineurin inhibitors decreases antioxidant enzyme activity in the rat parotid and submandibular salivary glands.

AIMS: Calcineurin inhibitors are widely used for prevention of graft rejection and treatment of autoimmune disorders, which result in increased longevity and enhanced quality of life for patients. Unfortunately, the toxic side effects of these drugs (mainly renal, hepatic and cardiac) limit their use. In this work, we studied the effects of long-term treatment of rats with the immunosuppressant cyclosporin (CsA) or tacrolimus (Tac) on salivation, saliva composition and on the major salivary glands (parotid and submandibular) in terms of histological alterations and oxidative stress, evaluated as lipoperoxidation (thiobarbituric acid reactive species--TBARS) and antioxidant enzyme activity contents (superoxide dismutase--SOD, catalase--CAT and glutathione peroxidase--GPx). MAIN METHODS: Male adult rats were treated with either CsA (10 mg/kg/day) or Tac (1 mg/kg/day) subcutaneously for 30 or 60 days. At the end of the experimental periods, pilocarpine-stimulated salivary flow rate was measured, saliva samples were collected and the salivary glands were dissected for morphological and biochemical analyses. KEY FINDINGS: After a 60-day treatment with any of the immunosuppressants, the total protein, Ca(2+) and Na(+) saliva concentrations were decreased but salivary flow rates were unaffected. In addition, both parotid and submandibular glands showed decreased SOD, CAT and GPx activities, increased TBARS contents and histomorphological alterations involving the epithelium and acini. SIGNIFICANCE: Based on these results, we suggest that the systemic long-term administration of the calcineurin inhibitor CsA or Tac induces an impairment of the antioxidant enzymatic defense in the rat major salivary glands, which may, in turn, lead to altered saliva composition.

The small GTPase Rab33A participates in regulation of amylase release from parotid acinar cells.

Amylase is released from exocrine parotid acinar cells via typical exocytosis. Exocytosis of amylase-containing granules occurs through several steps, including formation, maturation, and transport of granules. These steps are thought to be regulated by members of the small GTPase Rab family. We previously demonstrated that Rab27 and its effectors mediate amylase release from parotid acinar cells, but the functional involvement of other Rab proteins in exocrine granule exocytosis remains largely unknown. Here, we studied isoproterenol (IPR)-induced amylase release from parotid acinar cells to investigate the possible involvement of Rab33A, which was recently suggested to regulate exocytosis in hippocampal neurons and PC12 cells. Rab33A was endogenously expressed in parotid acinar cells and present in secretory granules and the Golgi body. Functional ablation of Rab33A with anti-Rab33A antibody or a dominant-negative Rab33A-T50N mutant significantly reduced IPR-induced amylase release. Our results indicated that Rab33A is a novel component of IPR-stimulated amylase secretion from parotid acinar cells.

Effects of glucose and sucrose variants of the caries-promoting Diet 2000 on the feeding patterns and parotid glands of prematurely weaned rats.

OBJECTIVE: The hypothesis of this study was that feeding glucose instead of sucrose in the cariogenic Diet 2000 to rats weaned at age 18 days would result in greater light/dark differences in feeding activity and secretion and storage of parotid salivary enzymes. DESIGN OF STUDY: Diet 2000 and a stock commercial diet (controls) were prepared in pelleted and powdered forms, as the increased mastication required by pellets has been shown to support circadian rhythms in rats. Food jars were weighed at lights on and just prior to lights off daily. Rats were euthanized at 25 days and their parotid glands removed, weighed, and analyzed for specific activities of the salivary enzymes α-amylase and deoxyribonuclease I. RESULTS: Light/dark differences in feeding activity were strong in the rats fed the pelleted stock diet and both powdered and pelleted glucose 2000 diets, moderate with the pelleted sucrose 2000 diet, and not significant with the powdered sucrose 2000 and stock diets. Light/dark differences in the parotid salivary enzymes were strong with the powdered glucose 2000 diet and the pelleted forms of the glucose and sucrose 2000 and stock diets, and not significant with the powdered stock and sucrose 2000 diets. CONCLUSION: Caries reportedly is higher in sucrose than glucose fed to rats in the standard powdered form of Diet 2000, mainly due to the colonizing advantage Streptococcus mutans gains with sucrose. These results suggest that additional factors are more feeding during lights on and less stimulation of parotid salivary secretion with the sucrose powder.

Isolation and sequencing of swine carbonic anhydrase VI, an enzyme expressed in the swine kidney.

BACKGROUND: Carbonic anhydrase VI (CA-VI) is produced by the salivary gland and is secreted into the saliva. Although CA-VI is found in the epithelial cells of distal straight tubule of swine kidneys, the exact function of CA-VI in the kidneys remains unclear. RESULTS: CA-VI was located in the epithelial cells of distal straight tubule of swine kidneys.A full-length cDNA clone of CA-VI was generated from the swine parotid gland by reverse transcription polymerase chain reaction, using degenerate primers designed based on conserved regions of the same locus in human and bovine tissues. The cDNA sequence was 1348 base pairs long and was predicted to encode a 317 amino acid polypeptide with a putative signal peptide of 17 amino acids. The deduced amino acid sequence of mature CA-VI was most similar (77.4%) to that of human CA-VI. CA-VI expression was confirmed in both normal and nephritic kidneys, as well as parotid. As the primers used in this study spanned two exons, the influence of genomic DNA was not detected. The expression of CA-VI was demonstrated in both normal and nephritic kidneys, and mRNA of CA-VI in the normal kidneys which was the normalised to an endogenous ß-actin was 0.098 ± 0.047, while it was significantly lower in the diseased kidneys (0.012 ± 0.007). The level of CA-VI mRNA in normal kidneys was 19-fold lower than that of the parotid gland (1.887). CONCLUSIONS: The localisation of CA-VI indicates that it may play a specialised role in the kidney.

Effects of isoproterenol on aquaporin 5 levels in the parotid gland of mice in vivo.

In the membrane fraction of mouse parotid gland (PG), the protein level of aquaporin 5 (AQP5), a member of the water channel family, was increased by injection (ip) of isoproterenol (IPR), a ß-adrenergic agonist, at 1 h, and stayed at high levels until 6 h; this change occurred simultaneously as amylase secretion. The AQP5 level then decreased and returned toward the original level at 12-48 h. After IPR injection, the AQP5 mRNA gradually increased and reached a maximum at 24 h. The facts suggest a rapid appearance of AQP5 at plasma membrane by IPR and subsequent degradation/metabolism by activation of proteolytic systems. Pretreatment of animals with two calpain inhibitors, N-Ac-Leu-Leu-methininal (ALLM) and calpeptin, as well as a protein synthesis inhibitor, cycloheximide (CHX), significantly suppressed the IPR-induced AQP5 degradation in the PG membrane fraction; such suppression was not observed by two proteasome inhibitors, MG132 and lactacystin, or the lysosome denaturant chloroquine, although most of these inhibitors increased AQP5 protein levels in unstimulated mice. The AQP5 protein was also degraded by µ-calpain in vitro. Furthermore, we demonstrated that µ-calpain was colocalized with AQP5 in the acinar cells by immunohistochemistry, and its activity in the PG was increased at 6 h after IPR injection. These results suggest that the calpain system was responsible for IPR-induced AQP5 degradation in the parotid gland and that such a system was coupled to the secretory-restoration cycle of amylase in the PG.

Effects of single exposure of sodium fluoride on lipid peroxidation and antioxidant enzymes in salivary glands of rats.

Many studies suggest that fluoride exposure can inhibit the activity of various enzymes and can generate free radicals, which interfere with antioxidant defence mechanisms in living systems. To further the understanding of this issue, this present study examined the effects of low-dose fluoride treatment on the activity of enzymatic antioxidant superoxide dismutase (SOD) and catalase (CAT), as well as the levels of lipid peroxidation (LPO) in the parotid (PA) and submandibular (SM) salivary glands of rats. Rats were injected with a single dose of sodium fluoride (NaF) (15 mg F(-)/kg b.w.) then euthanized at various time intervals up to 24 hours (h) following exposure. NaF exposure did not cause significant differences in SOD or CAT activity or LPO levels in PA glands compared to control. Conversely, SM glands presented increased SOD activity after 3 h and decreased SOD activity after 1, 12, and 24 h, while LPO was increased after 6, 12, and 24 h of the NaF injection. There were no significant differences in the CAT activity in the groups studied. Our results demonstrated that NaF intoxication caused oxidative stress in salivary glands few hours after administration. These changes were more pronounced in SM than in PA gland.

Laser irradiation affects enzymatic antioxidant system of streptozotocin-induced diabetic rats.

The aim of the present study was to analyze the effect of low-power laser irradiation in the antioxidant enzymatic system of submandibular (SMG) and parotid (PG) salivary glands of streptozotocin-induced diabetic rats. The animals were randomly divided into six groups: three diabetic groups (D0, D5, and D20) and three non-diabetic groups (C0, C5, and C20), according to laser dose received (0, 5, and 20 J/cm(2), respectively). Areas of approximately 1 cm(2) were demarcated in the salivary glands (each parotid and both submandibular glands) and after irradiated according to Simões et.al. (Lasers Med Sci 24:202-208, 2009). A diode laser (660 nm/100 mW) was used, with laser beam spot of 0.0177 cm(2). The group treated with 5 J/cm(2) laser dose was subjected to irradiation for 1 min and 4 s (total irradiation time) and the group treated with 20 J/cm(2) laser dose was subjected to irradiation for 4 min and 16 s. Twenty-four hours after irradiation the animals were euthanized and the salivary glands were removed for biochemical analysis. The total antioxidant values (TA), the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase enzymes were determined. SOD and CAT activities, as well as TA were higher in SMG of irradiated diabetic rats. However, in SMG of non-diabetic rats, laser irradiation decreased TA values and led to an increase in the CAT activity. In addition, there was a decrease in the activity of CAT in PG of diabetic and non-diabetic animals after laser irradiation. According to the results of the present study, low-power laser irradiation can affect the enzymatic antioxidant system of salivary glands of streptozotocin-induced diabetic rats.

Isoproterenol modulates matrix metalloproteinase-2 (MMP-2) and its tissue inhibitor-2 (TIMP-2) in rat parotid gland.

OBJECTIVE: Chronic isoproterenol treatment causes hypertrophy and hyperplasia of rodent salivary glands. Cell-extracellular matrix interactions play a critical role in salivary gland proliferation and matrix metalloproteinases (MMPs) are known to be involved in cell proliferation. The present study was undertaken to investigate the expression of MMP-2 and the tissue inhibitor metalloproteinase (TIMP)-2 in rat parotid gland following isoproterenol treatment. DESIGN: Female Wistar rats were daily treated with isoproterenol (25mg/kg body weight) for 0, 1, 3, and 7 days. Expression of parotid gland MMP-2 and its tissue inhibitor TIMP-2 was analysed by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. RESULTS: Our results suggest that isoproterenol modulates expression of MMP-2 and TIMP-2 mRNAs, as well as their protein expression levels in a time dependent-manner. Interestingly, at day 1 of treatment, MMP-2 and TIMP-2 expression were higher in comparison to untreated gland. At days 3 and 7, we can observe a gradual decrease of mRNA and protein levels of MMP-2 and TIMP-2. CONCLUSIONS: Our results suggest the presence of a isoproterenol-dependent modulation of extracellular matrix components. Such a modulation seems to be associated with ß-adrenergic agonist-induced hyperplasy, occurring during the first 24h of agonist treatment, and hypertrophy of the parotid gland.

[Effect of sijunzi decoction on salivary amylase secretion disorder and VIP-cAMP signaling pathway in splenasthenic rats].

OBJECTIVE: To observe the effect of Sijunzi Decoction on secretion disorder of salivary amylase in splenasthenic rat and its mechanism. METHODS: The model group rats received reserpine 0.5 mg/kg through subcutaneous injection while the control group rats received the same volume of saline for 8 days. After being modeled, the model group were divided into treatment group and model control group, treatment group were given orally Sijunzi Decoction, model control group and normal group were fed the same amount of distilled water for 4 weeks. The animal were anaesthetized and the left parotid was removed, the wounds were sutured. When the animals were awake but drowsy, 20 microL 10% glacial acetic acid was applied on the apex of the tongue once a minute for 30 minutes, removed the right parotid gland of the animals. The samples were frozen and amylase activity and VIP, cyclic adenosine monophosphate (cAMP) content and VAMP-8, SNAP-23 protein expression in the parotid glands were detected. RESULTS: Change of sAA in parotid acinar was not significantly different between treatment group and normal groups, but higher in model control groups after acid stimulation. The VIP and PKA contents were not significantly different among three groups. VIP, cAMP content and PKA activity increased significantly in normal group while VIP increased slightly, cAMP and PKA activity decreased in model control groups, which returned to some degrees in treatment group after acid stimulation. Expression of VAMP-8 protein was not significantly different between treatment group and model control groups, while expression of SNAP-23 was lower in model control groups, expression of VAMP-8 and SNAP-23 was higher in treatment group than which in model control groups. CONCLUSION: Sijunzi Decoction has a certain effect on secretion disorder of salivary amylase in splenasthenic rat, which mechanism may be related to recover changes of VIP-cAMP signal pathway in the splenasthenic rat's parotid gland cells,including increase VIP content and expression of VAMP-8 and SNAP-23.

Effects of extracorporeal shock-wave lithotripsy directed at the parotid gland on oxidative stress parameters and some trace element levels in facial nerve of rats.

INTRODUCTION: This study was designed to assess the effect of extracorporeal shock-wave lithotripsy (ESWL) exposure of the parotid gland on oxidative stress and some trace element levels in the facial nerves of rats. METHODS: Twelve male Wistar albino rats were divided into two groups, each consisting of 6 animals. The rats in the first group served as controls. The left parotid glands of animals in the second group were treated with 1000 18-kV shock waves while anesthetized with ketamine. The animals in both groups were euthanized 72 h after the ESWL treatment, and the right facial nerve was harvested for determination of oxidant/antioxidant status and trace element levels. RESULTS: Lipid peroxidation product malondialdehyde (MDA) and antioxidant glutathione (GSH) levels increased, and the activities of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), decreased in the facial nerves of ESWL-treated rats. The levels of iron, lead, manganese, and cobalt increased, and magnesium, cadmium, and copper levels decreased. CONCLUSIONS: ESWL treatment of the parotid gland may increase lipid peroxidation and decrease antioxidant enzyme activity in adjacent tissues such as the facial nerve. It also causes a decrease or increase in many mineral levels of the facial nerve, which is an undesirable condition for normal physiological function.

Exocyst subunits are involved in isoproterenol-induced amylase release from rat parotid acinar cells.

Exocytosis of secretory granules in parotid acinar cells requires multiple events: tethering, docking, priming, and fusion with a luminal plasma membrane. The exocyst complex, which is composed of eight subunits (Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84) that are conserved in yeast and mammalian cells, is thought to participate in the exocytotic pathway. However, to date, no exocyst subunit has been identified in salivary glands. In the present study, we investigated the expression and function of exocyst subunits in rat parotid acinar cells. The expression of mRNA for all eight exocyst subunits was detected in parotid acinar cells by RT-PCR, and Sec6 and Sec8 proteins were localized on the luminal plasma membrane. Sec6 interacted with Sec8 after 5 min of stimulation with isoproterenol. In addition, antibodies to-Sec6 and Sec8 inhibited isoproterenol-induced amylase release from streptolysin O-permeabilized parotid acinar cells. These results suggest that an exocyst complex of eight subunits is required for amylase release from parotid acinar cells.

Chitinase expression in parotid glands of non-obese diabetic mice.

OBJECTIVE: This investigation was a basal study that used a mouse model of xerostomia to identify protein biomarkers of xerostomia in saliva. We identified genes expressed differently in parotid glands from non-obese diabetic mice with diabetes and those from control mice; subsequently, we investigated expression of the proteins encoded by these genes in parotid glands and saliva. MATERIALS AND METHODS: DNA microarray and real-time PCR analyses were performed to detect differences between NOD/ShiJcl and C57BL/6JJcl (control) female mice in gene expression from parotid glands or parotid acinar cells. Subsequently, protein expression was assessed using immunoblotting and immunohistochemistry. Similarly, enzyme activity in saliva was assessed using zymography. RESULTS: Based on gene expression analyses, Chia expression was higher in diabetic mice than non-diabetic mice and control mice; similarly, expression of chitinase, the protein encoded by Chia, was higher in diabetic mice. Saliva from NOD/ShiJcl mice had more chitinase than saliva from control mice. CONCLUSIONS: Chitinase was highly expressed in parotid acinar cells from diabetic mice compared with non-diabetic and control mice. Increased chitinase expression and enzyme activity may characterize the autoimmune diabetes in mice; however, further investigation is required to assess its use as a biomarker of xerostomia in humans.

Immunogold labeling of carbonic anhydrase isozyme (CA-VI) in secretory granules of human parotid glands.

Serous granules in the human parotid gland have a well-defined substructure, consisting of a dense spherule suspended in a moderately dense matrix. Immunogold labeling with an antibody against carbonic anhydrase VI revealed that this enzyme is localized within the matrix and is absent from the spherule. This location matches that of a number of other salivary gland proteins. Cell organelles involved in the secretory pathway are devoid of label. Labeling was not observed in any ductular component of the gland.

Enhancement of carbachol-induced amylase secretion in parotid glands from rats with experimental periodontitis.

OBJECTIVE: In a previous study we observed that parotid glands from rats with experimental periodontitis showed an increase in basal amylase release as a result of an increase in cAMP accumulation induced by PGE(2) production. The aim of this work was to study whether this change in amylase release influences the secretory effect of carbachol. DESIGN: Experimental periodontitis was induced through placing a black thread around the cervix of the two lower first molars. Experiments were done 22 days after ligature induced periodontitis. Amylase release was evaluated in vitro and determined using a colorimetric method which uses starch as substrate. RESULTS: The effect of carbachol was increased in parotid glands from periodontitis rats. The effect of 10(-6)M carbachol was inhibited by 4-DAMP (10(-6)M), U-73122 (5 × 10(-6)M) and trifluoperazine (5 × 10(-6)M) in both groups. No changes were observed in the binding sites and affinity in parotid membranes from rats with experimental periodontitis. The inhibition of the adenylyl cyclase and the cyclooxygenase induced a right shift of the carbachol concentration-response curve in periodontitis group whilst the opposite effect was observed in control group in the presence of db-cAMP and PGE(2). CONCLUSIONS: Parotid glands from rats with experimental periodontitis release more amylase in response to carbachol suggesting an interaction between Ca(2+) and cAMP in the fusion/exocytosis step of secretory vesicles.

Evidence for amylase release by cyclin-dependent kinase 5 in the rat parotid.

Cyclin-dependent kinase 5 (Cdk5) plays no apparent role in cell cycle regulation, and Cdk5 is not activated by cyclins but only p35 or p39. Although the enzymatic activity of Cdk5 is highest in the central nervous system, recent reports indicate that it also has important functions in non-neuronal cells. In the present study, we investigated whether Cdk5 and its activators are expressed in rat parotid acinar cells, whether a ß-adrenergic agonist enhances the expression of Cdk5, and whether Cdk5 mediates amylase release. We found that Cdk5 and its activator, cyclin I, were expressed in rat parotid acinar cells, and that the expression of Cdk5 was enhanced by treatment of the cells with isoproterenol. Amylase release stimulated by isoproterenol was depressed by the addition of olomoucine, a Cdk5 inhibitor, or by the introduction of an anti-Cdk5 antibody. Cdk5 activity was enhanced by treatment with isoproterenol and this enhanced activity was attenuated by the addition of olomoucine. Olomoucine also attenuated both phosphorylation of Munc18c and translocation of Munc18c from the plasma membrane induced by isoproterenol. These results indicated that ß-stimulation of rat parotid acinar cells enhanced the expression of Cdk5, and that this Cdk5 activation may mediate amylase release through phosphorylation of Munc18c.

Regulation and identification of Na,K-ATPase alpha1 subunit phosphorylation in rat parotid acinar cells.

The stimulation of fluid and electrolyte secretion in salivary cells results in ionic changes that promote rapid increases in the activity of the Na,K-ATPase. In many cell systems, there are conflicting findings concerning the regulation of the phosphorylation of the Na,K-ATPase α subunit, which is the catalytic moiety. Initially, we investigated the phosphorylation sites on the α1 subunit in native rat parotid acinar cells using tandem mass spectrometry and identified two new phosphorylation sites (Ser(222), Ser(407)), three sites (Ser(217), Tyr(260), Ser(47)) previously found from large scale proteomic screens, and two sites (Ser(23), Ser(16)) known to be phosphorylated by PKC. Subsequently, we used phospho-specific antibodies to examine the regulation of phosphorylation on Ser(23) and Ser(16) and measured changes in ERK phosphorylation in parallel. The G-protein-coupled muscarinic receptor mimetic carbachol, the phorbol ester phorbol 12-myristate 13-acetate, the Ca(2+) ionophore ionomycin, and the serine/threonine phosphatase inhibitor calyculin A increased Ser(23) α1 phosphorylation. Inhibition of classical PKC proteins blocked carbachol-stimulated Ser(23) α1 subunit phosphorylation but not ERK phosphorylation, which was blocked by an inhibitor of novel PKC proteins. The carbachol-initiated phosphorylation of Ser(23) α1 subunit was not modified by ERK or PKA activity. The Na,K-ATPase inhibitor ouabain reduced and enhanced the carbachol-promoted phosphorylation of Ser(23) and Ser(16), respectively, the latter because ouabain itself increased Ser(16) phosphorylation; thus, both sites display conformational-dependent phosphorylation changes. Ouabain-initiated phosphorylation of Ser(16) α1 was not blocked by PKC inhibitors, unlike carbachol- or phorbol 12-myristate 13-acetate-initiated phosphorylations, suggesting that this site was also a substrate for a kinase other than PKC.