The University of Toledo

B.A. 1991, Korea University
Master’s 1998, Medical University of South Carolina
Ph.D. 2003, Johns Hopkins University

Characterization of molecular mechanisms governing peptidergic vesicle transport and exocytosis in hippocampus and hypothalamus-pituitary-adrenal gland (HPA) axis

Post-Golgi transport of peptidergic secretory vesicles to the release site for activity-dependent secretion of neuropeptides, neurotrophins, and peptide hormones is key to normal neuronal and endocrine function. Obliteration of regulated secretion of neuropeptides, neurotrophins, and hormones leads to disorders, such as diabetes and obesity, deficits in neural development, memory and learning, and neurodegenerative diseases, such as Alzheimer's disease and Huntington's disease. Thus, elucidation of the mechanism for secretory vesicle transport in the regulated secretory pathway will facilitate developing a cure for such diseases.

My previous studies revealed that the cytoplasmic tail of vesicular membrane carboxypeptidase E (CPE) is required for post-Golgi transport of vesicles containing pro-opiomelanocortin-derived peptides, (e.g. adrenocorticotropin (ACTH), b-endorphin, a- melanocyte stimulating hormone, involved in stress, opiate activity, caloric homeostasis); and brain-derived neurotrophic factor (BDNF, involved in learning and memory), in anterior pituitary cells and hippocampal neurons, respectively. In this CPE-directed transport mechanism, ACTH and BDNF secretory vesicles are anchored to microtubules via the CPE cytoplasmic tail for their movement along processes to the release site for activity-dependent secretion.

My primary research goal is to uncover in neurons and endocrine cells, 1) the molecular machinery that govern the anterograde transport of neuropeptide-, neurotrophin-, and peptide hormone-containing vesicles along processes/neurites in the regulated secretory pathway; and 2) the machinery and mechanism that tethers/capture these vesicles at the terminals upon stimulation and moves them to the release site for activity-dependent secretion of their cargo for higher physiological function.

 In my preliminary studies, I have found that snapin directly interacts with the cytoplasmic tail of CPE, and that snapin is involved in transport of ACTH-containing secretory vesicles and CPE. Moreover, snapin appears to modulate binding of microtubule-based motors to the CPE tail in corroboration with other cytoplasmic proteins, suggesting the existence of a complex that controls snapin-CPE-motor interaction. My specific aim 1 is to identify the complex necessary for post-Golgi transport of ACTH and BDNF vesicles. After proteins that interact with snapin-CPE-motor are pulled down and purified by multi-step chromatography in combination with an in vitro motor-binding assay, they will be examined by in vivo Q-Dot-based immunocytochemstry and live cell imaging to determine their physiological crosstalk with snapin-CPE-motor. MS-MS peptide sequencing will be used to identify the proteins that are essential for modulation of ACTH and BDNF vesicle transport in the regulated secretory pathway in pituitary corticotrophs and hippocampal neurons, respectively.  In specific aim 2, I will address the role of CPE-snapin and their associated proteins in tethering peptidergic vesicles to the actin network at the terminals or cortical zone of the plasma membrane for activity-dependent secretion.

In preliminary studies, I have found that both CPE tail and snapin interact with actins, and that disruption of actin filaments prevents arrival of ACTH vesicles at the proximity of plasma membrane. I plan to search for proteins that enhance binding of CPE tail to F-actin after stimulation using an in vitro actin-binding assay and chromatography. Q-Dots will be used to select a pool of proteins that become tethered to actin cortex upon stimulation. Identification of such proteins will likely yield novel players involved in the capture of secretory vesicles at the actin cortex in an activity-dependent manner.
The proposed studies will provide a fundamental understanding of the machinery required for microtubule-based transport of neuropeptide/hormone vesicles from the synthesis site in the cell body along processes, and the actin-based capture and transport of such vesicles at the terminal for activity-dependent secretion in neurons and endocrine cells.  

1. 1997-1998: Predoctoral Fellowship, EPSCOR, National Science Foundation Training Program
2. 1998-2003: Predoctoral Fellowship, NIH Training Program at Johns Hopkins University
3. 2003-2009: IRTA Fellowship from NICHD
4. 2006: NIH Fellows Award for Research Excellence 2006
5. 2006: Young Investigator Award of the Summer joint US-European Neuropeptide Conference, 2006
6. 2007: NICHD Transition Career Development Award (K22)
7. 2008: NIH Fellows Award for Research Excellence 2008
8. 2009: American Recovery and Reinvestment Act (ARRA)

1. Ella, K.M., Qi, C., McNair, A.F., Park, J.H., Wisehart-Johnson, A.E., and Meier, K.E. (1997). Phospholipase D activity in PC12 cells. Journal of Biological Chemistry, 272(20):12909-12912.

2. Qi, C., Park, J.H., Shirley, D.W., Bradshaw, C.D., Ella, K.M., and Meier, K.E. (1998). Lysophosphatidic acid stimulates phospholipase D activity and cell proliferation in PC-3 human prostate cancer cells. Journal of Cellular Physiology, 174(2):261-272.

3. Miliaras, N., Park, J.H., and Wendland, B. (2004). The function of the endocytic scaffold protein Pan1p depends on multiple domains. Traffic, 5(12):963-978.

4. Park,J.J., Cawley N.W., and Loh, Y.P. (2008). Carboxypeptidase E cytoplasmic tail anchors hormone vesicles to microtubule motors for transport and activity – dependent secretion. Molecular Endocrinology, 22(4): 989-1005.

5. Park,J.J., Cawley N.W., and Loh, Y.P. (2008). Carboxypeptidase E cytoplasmic tail anchors BDNF vesicles to microtubule motors for transport and activity-dependent secretion. Molecular and Cellular Neuroscience, 39(1): 63-73.

6. Park,J.J. and Loh, Y.P. (2008). How Peptide Hormone Vesicles are Transported to the Secretion Site for Exocytosis. Molecular Endocrinology, 22(12): 2583-95.

7. Park, J.J., Koshimizu, H., and Loh, Y.P. (2009). Biogenesis and Transport of Secretory Granules to Release Site In Neuroendocrine cells. Journal of Molecular Neuroscience, 37(2): 151-9.

8. Lou, H., Park, J.J., Sarcon, A., Adams, T., Cawley, N.X., and Loh, Y.P. (2010). Carboxypeptidase E Cytoplasmic Tail Mediates Localization of Synaptic Vesicles to the Pre-Active Zone in Hypothalamic Nerve Terminals. (as a co-author) Journal of Neurochemistry, 114(3): 886-96.

9. Hensley, K., Venkova, K., Christov, A., Gunning, W., and Park, J.J. (2011). Collapsin response mediator protein-2: An emerging pathologic feature and therapeutic target for neurodisease indications. Molecular Neurobiology, 43(3): 180-91.

10. Park, J.J., Gondre-Lewis, M., Kim, T., and Loh, Y.P. (2011). A distinct trans Golgi network subcompartment for sorting of synaptic and granule proteins in neuroendocrine cells. Journal of Cell Science, 124 (5): 735-44.

11. Park,J.J. and Loh, Y.P. (2011). Visualization of Peptide Secretory Vesicles in Living Nerve Cells. Methods in Molecular Biology, 789:137-45.

12. Cawley, N.X., Wetsel, W.C., Murthy, S.R.K., Park, J.J., Pacak, K., and Loh, Y.P. (2012). New Roles of Carboxypeptidase E in Endocrine and Neural Function and Cancer. Endocrine Reviews 33:216-253

13. Park, J.J., Rubio, M.V., Zhang, Z., Um, T., Xie, Y., Knoepp, S.M., Snider, A.J., Gibbs, T.C., and Meier, K.E. (2012). Effects of lysophosphatidic acid on calpain-mediated proteolysis of focal adhesion kinase in human prostate cancer cells. Prostate, Epub ahead of print

14. Lou, H., Park, J.J., Phillips, A., and Loh, Y.P. (2012). g-Adducin Promotes Process Outgrowth and Secretory Protein Exit from the Golgi Apparatus. (as a co-author) Journal of Molecular Neuroscience, Epub ahead of print.

15. Gondré-Lewis M.C., Park, J.J., and Loh, Y.P. (2012). Cellular mechanisms for the biogenesis and transport of synaptic and dense-core vesicles. International Review of Cell and Molecular Biology, Accepted.