Submitted on July 31, 2006
Accepted on December 1, 2006
Elevated Prolactin Redirects Secretory Vesicle Traffic in Rabbit Lacrimal Acinar Cells
Yanru Wang1, Christopher T Chiu1, Tamako Nakamura1, Ameae M. Walker2, Barbara Petridou3, Melvin D Trousdale4, Sarah F. Hamm-Alvarez5, Joel E Schechter6, and Austin K Mircheff7*
1 Physiology & Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, California, United States
2 Division of Biomedical Sciences, University of California, Riverside,, California, United States
3 Endocrinologie Moléculaire, Biologie Cellulaire et Moléculaire, Institut National de Recherche Agronomique, Jouy-en-Josas, France
4 Ophthalmology, University of Southern California, Los Angeles, California, United States; Division of Biomedical Sciences, University of California Riverside, Riverside, California, United States
5 Pharmaceutical Sciences, University of Southern California, Los Angeles, California, United States; Physiology & Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, California, United States; Ophthalmology, University of Southern California, Los Angeles, California, United States
6 Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California, United States
7 Physiology & Biophysics, Keck School of Medicine, University of Southern California, Los Angeles, California, United States; Ophthalmology, University of Southern California, Los Angeles, California, United States
* To whom correspondence should be addressed. E-mail: amirchef{at}hsc.usc.edu.
During pregnancy lymphocytes infiltrating the rabbit lacrimal gland disperse to the interacinar space from their normal focal concentrations; basal fluid secretion decreases; pilocarpine-induced fluid secretion increases; and stimulated fluid protein concentration decreases. Ductal epithelial cell prolactin (PRL) content increases and redistributes from the apical to the basal-lateral cytoplasm. A replication-incompetent adenovirus vector for rabbit PRL (AdPRL) was used to test the hypothesis that increased intracrine / autocrine PRL signaling alters secretory protein traffic in an ex vivo lacrimal acinar cell model. AdPRL had no discernable influence on microtubules or actin microfilaments or their responses to carbachol (CCh). Endogenous and transduced PRLs exhibited similar, non-polarized, punctate distributions. Cells secreted PRL consititutively and at increased rate in response to CCh. In contrast, constitutive secretion of 
-hexosaminidase was negligible, suggesting that the constitutive pathway for PRL is relatively inaccessible to typical secretory proteins. AdPRL had no significant effect on total secretion of -hexosaminidase or syncollin-GFP, a chimeric secretory protein construct. However, it reversed the polarized distributions of vesicles containing rab3D and syncollin-GFP. Live-cell imaging indicated that AdPRL redirected CCh-dependent syncollin-GFP exocytosis from the apical plasma membrane to the basal-lateral membrane. Elevated concentrations of exogenous rabbit PRL in the ambient medium elicited similar changes. These observations suggest that elevated PRL, as occurs in the physiological hyperprolactinemia of pregnancy, induces lacrimal epithelial cells to express a mixed exocrine / endocrine phenotype which secretes fluid to the acinus-duct lumen but secretes proteins to the underlying tissue space. This phenotype may contribute to the pregnancy-associated immunoarchitecture.
