Pao-Li Wang

Utilization of the non-obese diabetic (NOD) mouse as an animal model for the study of secondary Sjögren's syndrome.

Sjogren’s syndrome (S.S.) in the human patient population is an autoimmune inflammatory disease presenting clinical symptoms of xerophthalmia and xerostomia1. This condition predominantly affects women. Most diagnoses of S.S. is made in association with autoimmune connective tissue diseases such as rheumatoid arthritis or systemic lupus erythematosus.2 However, it can also be obseved as an isolated phenomenon, described as primary S.S.

Detection of insulin and insulin-like growth factors I and II in saliva and potential synthesis in the salivary glands of mice: Effects of type 1 diabetes mellitus

The salivary glands of mammals synthesize and secrete a number of peptide growth factors that play important roles in cell/tissue homeostasis and embryonic development. Using a radioimmunoassay, insulin, insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II) were detected in saliva from mice. Unlike epidermal growth factor (EGF), there was no sexual dimorphism in the concentrations of the insulin growth factor family. Immunohistochemical localization of IGF-I and IGF-II was confined to the duct cells of both the parotid and the submandibular glands. Reverse transcriptase-polymerase chain reaction amplification of total RNA from parotid and submandibular glands confirmed the presence of all three hormone/growth factor mRNAs in both glands. The levels of insulin and IGF-I were higher in saliva from an animal model for autoimmune type 1 diabetes, the non-obese diabetic (NOD) mouse, than in a second inbred strain, BALB/c. In contrast, the IGF-II levels were decreased relative to the BALB/c strain. With the onset of diabetes in NOD mice, insulin levels declined, while IGF-I and IGF-II levels showed trends toward lower levels of these growth factors when compared with non-diabetic animals. These changes were reflected in the concentrations from parotid and submandibular gland cell lysates.

Alterations in the subcellular distribution of p21ras-GTPase activating protein in proliferating rat acinar cells

Rat parotid acinar cells undergo transient proliferation in response to chronic administration of the beta-adrenergic agonist isoproterenol or epidermal growth factor (EGF). Treatment with these agents caused an increase in tyrosine phosphorylation of p21ras-GTPase activating protein (GAP). This phosphorylation event was accompanied by a redistribution of the protein from the plasma membrane to internal membrane compartments. Separation of subcellular membranes revealed increased GAP associated with a low density population of vesicles concomitant with growth stimulation as well as to the nuclear membrane, but not the nucleoplasm. Upon cessation of hyperplasia induced by isoproterenol, phosphorylated GAP present in the plasma membrane returned to control cell levels.

Effect of EGF on rat parotid gland secretory function.

The present study reports changes in saliva composition from the rat parotid gland in response to single and repeated administration of epidermal growth factor (EGF). Treatment of rats with EGF (10 micrograms/kg, i.p., twice daily for 3 days) caused an increase in amylase activity in saliva collected from cannulated parotid duct, following stimulation of secretion with pilocarpine, with a corresponding decrease in enzyme activity in the gland. Analysis of parotid gland RNA by reverse transcriptase-PCR generated a single predicted amylase-derived cDNA product of 576 bp. The steady-state levels of mRNA for amylase from EGF-treated parotid total RNA showed a 1.8-fold increase compared to untreated controls. A single dose of EGF (15 min following i.p. injection) elicited an activation of both protein kinase A and protein kinase C activities. While the activation of protein kinase A was still maintained under the chronic EGF regimen, the activity levels of protein kinase C showed down-regulation to untreated control values.

Effect of chronic insulin administration on mouse parotid and submandibular gland function.

Abstract Chronic (six-day) injection of insulin (im, 50 μM/animal) into BALB/c mice resulted in changes in secretory function, hypertrophy and hyperplasia of the parotid and submandibular glands. There were no significant changes in the flow rate or concentrations of proline-rich proteins, TGFα, or amylase in saliva when measured against constant protein levels. However, amylase enzyme activity and total saliva protein content were reduced when measured against constant saliva volume. In contrast, EGF synthesis and secretion from the submandibular gland was increased. Both the parotid and submandibular gland showed evidence of gland hypertrophy and increased rates of DNA synthesis as indicated by [3H]-thymidine incorporation in response to insulin treatment. Chronic injection of insulin did not effect the level of receptor in the plasma membrane of either gland.

Effect of vanadate on amylase secretion and protein tyrosine phosphatase activity in the rat parotid gland

Treatment of rat parotid acinar cells with sodium orthovanadate (an inhibitor of protein tyrosine phosphatase) caused a dose-dependent inhibition of phosphatase activity as measured by the hydrolysis of para nitrophenylphosphate (pNPP). Inclusion of 50 μM sodium orthovanadate inin vitro gland cultures prevented the amylase secretion from both untreated control and isoproterenol-stimulated parotid acinar cells. Four different tyrosine-phosphorylated proteins with Mr 40, 45, 70 and 95 kDa, respectively, were identified in secretory granule preparations from rat parotid glands by immunoblot using a monospecific antibody for phosphotyrosine. An increase in the phosphorylation levels of these phosphoproteins was noted in the presence of 50 μM sodium orthovanadate, suggesting that a protein tyrosine phosphatase (PTPase) is involved in parotid gland protein dephosphorylation reactions. Using antibody to Syp (a PTPase belonging to class 1D), a major fraction of subcellular activity was found to be associated with secretory granule membranes. These results suggest the possible involvement of a PTPase (Syp) in parotid gland secretory mechanisms.

Characterization of an SH2 containing protein tyrosine phosphatase in rat parotid gland acinar cells

Rat parotid glands were shown to possess protein phosphatase activity capable of catalyzing the dephosphorylation of several model phosphatase substrates, including p-nitrophenyl phosphate, tyrosine phosphorylated myelin basic protein and serine phosphorylated casein. A portion of this activity closely resembled dephosphorylation patterns of known protein tyrosine phosphatases. The reaction showed sensitivity to sodium orthovanadate, proceeded efficiently in the presence of metal chelators and favored acidic pH for optimum activity. Cell lysates from EGF- or isoproterenol-stimulated parotid glands, when immuno-precipitated with anti-Syp antibody, showed the induction of protein tyrosine phosphatase activity significantly higher than the unstimulated controls. The protein of M(r) = 65kDa also had elevated levels of tyrosine phosphorylation following isolation from cells treated to undergo proliferation. Thus parotid gland acinar cells possess protein tyrosine phosphatase activity of the PTPase 1D class associated with inducible cell growth, in addition to other phosphatases.

Activation of SH2-Containing Proteins by Insulin in Proliferating Mouse Parotid Gland Acinar Cells:

Abstract Chronic treatment of mice with insulin results in hypertrophy and hyperplasia of the parotid and submandibular glands (Wang et al.: 1994, Proc Soc Exp Biol Med 205:353–361). Hyperplasia of the parotid gland is mediated by the elevation of tyrosine phosphorylation of phospholipase Cγ, p21ras-GTPase activating protein (p21ras-GAP) and phosphatidylinositol 3-kinase. These proteins were found to be associated with the insulin receptor substrate-1 most likely through src homology (SH2) domains of these proteins. There was also a transient increase in intracellular cAMP and protein kinase A during the first day of treatment which declined by Day 3 to near control values. Protein kinase C activity, on the other hand, remained elevated for the 3-day injection regimen. Thus, acinar cell proliferation induced by insulin requires activation of many of the same signaling components as other tyrosine kinase possessing growth factor receptors.