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Overview

Cell Biology of Salivary Protein Secretion Biology of salivary glands (BMS 513) Nisha D’Silva DDS, PhD Monday, June 3, 2002 9 - 10 am, Rm G322. Overview. 1. Review anatomy and Histology 2. Secretory pathways 3. Signaling mechanism in regulated secretion.

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Overview

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  1. Cell Biology of Salivary Protein SecretionBiology of salivary glands (BMS 513)Nisha D’Silva DDS, PhDMonday, June 3, 20029 - 10 am, Rm G322

  2. Overview 1. Review anatomy and Histology 2. Secretory pathways 3. Signaling mechanism in regulated secretion. 4. Brief discussion about drugs and saliva.

  3. Macromolecule secretion • Polypeptides and proteins are synthesized and secreted by the salivary acinar cells • Sublingual saliva -- very thick and viscous • produced by mucous acinar cells • Parotid saliva -- thin and watery • produced by serous acinar cells • mainly salivary amylase and proline-rich polypeptides • Submandibular saliva -- intermediate consistency • a mix of serous and mucous acini

  4. Regardless of the type of protein • Too large to cross the cell membrane • Must be synthesized and stored within a membrane-bound vesicle and released by exocytosis

  5. Protein synthesis and secretory pathways

  6. Protein synthesis and secretion • Genes transcribed in nucleus to make mRNA • Message is transferred to ribosomes in cytoplasm • Secretory proteins begin with signal sequence which targets developing peptide to endoplasmic reticulum • At ER, peptide is N-glycosylated and folded into correct 3D structure • Small membrane vesicles carry proteins from ER through several layers of the golgi apparatus for additional processing and packaging for export

  7. Protein synthesis and secretion (cont’d) • Proteins move by default onwards from the ER • Specific retention sequences segregate non-secreted proteins • Secretory proteins are concentrated and stored in secretory vesicles • Mature vesicles are transported to apical membrane • Secretory stimuli result in vesicle fusion with plasma membrane • Contents of vesicles are discharged outside of cell

  8. Secretory pathways • 1. Constitutive - occurs continuously • 2. Regulated • 3. Paragranular - small vesicles break-off from SGs that undergo regulated secretion and are released

  9. Constitutive exocytosis • Differs from regulated exocytosis • Proteins not concentrated into secretory vesicles awaiting exocytotic stimulus • Continuous flow of protein in small vesicles to plasma membrane • Regulation occurs at synthesis stage

  10. Regulated secretion in salivary glands

  11. Mechanism of action of G- proteins

  12. Control of protein secretion: second messengers • Each stage of secretion is regulated by phosphorylation of target proteins • Phosphorylation is carried out by a protein kinase such as cyclic adenosine monophosphate (cAMP)-dependent protein kinase (protein kinase A) or PKC • cAMP stimulates maturation and translocation of secretory vesicles to the apical membrane • cAMP stimulates exocytosis

  13. Regulated secretion in salivary glands

  14. Four stages of cAMP production • Nordrenaline (NA) binds to -adrenergic receptors • G-protein (Gs) associated with the -adrenergic receptor moves to an active GTP-bound state • The Gs-GTP stimulates adenylate cyclase to convert ATP into cAMP • cAMP activates protein kinase A which phosphorylates target proteins

  15. Regulated secretion in salivary glands

  16. Crosstalk • Fluid and protein secretion occurs by different mechanisms controlled by different nerves • Separation between control of protein and electrolytes breaks down at second messenger level • Interaction between Ca2+ and cAMP-mediated events (cross-talk) allows combination of intracellular signaling pathways into an integrated stimulus-secretion coupling mechanism.

  17. Drugs and secretion 1. Propranolol (Inderal): -blocker 2. Pilocarpine (Salagen): cholinergic agonist parasympathetic pathway 3. Atropine: (Atropisol, Sal-Tropine) anti-cholinergic.

  18. Summary

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