The overall aim of this research is to understand how regulatory neurotransmitters and gastrointestinal hormones act through changes in intracellular free Ca2+ to bring about digestive enzyme secretion by pancreatic acinar cells. This proposal focuses on the mechanisms involved in the terminal steps in secretion culminating in exocytosis. Using a proteomics discovery strategy, we have identified a number of small GTP binding proteins on the zymogen granule including RabSD, Rab6, Rab11, Rab27B and Rap1. Since Rabs are believed to regulate vesicular trafficking by organizing and regulating effector proteins the focus of this work includes two of these Rab molecules, RabSD and Rab27B as well as Rap1.Two other small G proteins, Rho and Rac which regulate the actin cytoskeleton will also be studied. The overall goal is to determine the role of each of these G proteins in the series of sequential processes by which zymogen granules are brought to the apical membrane, become fusion competent and undergo exocytosis.
Specific aims of this proposal include: 1) What is the extent of activation (GTPliganded form) of Rab27B andRap1 on zymogen granules and is it increased by secretagogues such as cholecystokinin (CCK) and acetylcholine? Is Rap1important for secretion as has been shown for RabSD and 27B? Does Rap1 activation mediate the secretory stimulation by cyclic AMP? 2) What are the GEFs or other regulatory protein involved in activating the three granule small G proteins, Rho and Rac? Are they activated by specific heterotrimeric G proteins and/or by intracellular messengers such as Ca2+? Is a cyclic AMP activated GEF (Epac) involved in activating Rap1? 3) What are the downstream effector proteins for RabSD, Rab27B and Rap1? Are linker proteins of the Sip or Slac families involved? Is there a relation of specific small G proteins to myosin Vc? to Noc2? Which small G proteins directly or indirectly regulate SNARE complexes? This work will lead to better molecular understanding of the regulation of digestive enzyme secretion in acinar cells and potential sites for the pathological regulation that occurs in experimental pancreatitis. Relevance to public health: the pancreas is the major organ that secretes digestive breakdown of food and assimilation of nutrients. If these enzymes are not inflammatory disease pancreatitis can result. The present work is directed at understanding of the proteins involved in normal digestive enzyme secretion.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Method to Extend Research in Time (MERIT) Award (R37)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1-DIG-C (02))
Program Officer
Serrano, Jose
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Michigan Ann Arbor
Schools of Medicine
Ann Arbor
United States
Zip Code
Khoriaty, Rami; Vogel, Nancy; Hoenerhoff, Mark J et al. (2017) SEC23B is required for pancreatic acinar cell function in adult mice. Mol Biol Cell 28:2146-2154
Hou, Yanan; Ernst, Stephen A; Heidenreich, Kaeli et al. (2016) Glucagon-like peptide-1 receptor is present in pancreatic acinar cells and regulates amylase secretion through cAMP. Am J Physiol Gastrointest Liver Physiol 310:G26-33
Hou, Yanan; Ernst, Stephen A; Lentz, Stephen I et al. (2016) Genetic deletion of Rab27B in pancreatic acinar cells affects granules size and has inhibitory effects on amylase secretion. Biochem Biophys Res Commun 471:610-5
Hou, Yanan; Ernst, Stephen A; Stuenkel, Edward L et al. (2015) Rab27A Is Present in Mouse Pancreatic Acinar Cells and Is Required for Digestive Enzyme Secretion. PLoS One 10:e0125596
Fleuchot, Betty; Guillot, Alain; M├ęzange, Christine et al. (2013) Rgg-associated SHP signaling peptides mediate cross-talk in Streptococci. PLoS One 8:e66042
Hou, Yanan; Chen, Xuequn; Tolmachova, Tatyana et al. (2013) EPI64B acts as a GTPase-activating protein for Rab27B in pancreatic acinar cells. J Biol Chem 288:19548-57
Williams, John A (2013) Proteomics as a systems approach to pancreatitis. Pancreas 42:905-11
Sabbatini, Maria Eugenia; Williams, John A (2013) Cholecystokinin-mediated RhoGDI phosphorylation via PKC? promotes both RhoA and Rac1 signaling. PLoS One 8:e66029
Muili, Kamaldeen A; Wang, Dong; Orabi, Abrahim I et al. (2013) Bile acids induce pancreatic acinar cell injury and pancreatitis by activating calcineurin. J Biol Chem 288:570-80
Sabbatini, Maria E; D'Alecy, Louis; Lentz, Stephen I et al. (2013) Adenylyl cyclase 6 mediates the action of cyclic AMP-dependent secretagogues in mouse pancreatic exocrine cells via protein kinase A pathway activation. J Physiol 591:3693-707

Showing the most recent 10 out of 21 publications