Elevated prolactin redirects secretory vesicle traffic in rabbit lacrimal acinar cells

Abstract

-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, nonpolarized, punctate distributions. Cells secreted PRL consititutively and at increased rates 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 syncollingreen fluorescent protein (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 that secretes fluid to the acinus-duct lumen but secretes proteins to the underlying tissue space. This phenotype may contribute to the pregnancy-associated immunoarchitecture. ocular surface; mucosal immunity; pregnancy; Sjögren's syndrome THE OCULAR SURFACE SYSTEM maintains a thin fluid film that comprises an external milieu necessary for optimal homeostasis of its mucosal tissues and of the cornea. Disruptions of ocular surface homeostasis frequently elicit sensations of dryness, itching, or burning. These symptoms may be associated with immune system diseases, such as Sjögren's syndrome and graft vs. host disease, but most cases occur without the typical signs of autoimmune disease. They occur more frequently in women than men and are often associated with altered states of the systemic hormonal milieu: perimenopause, postmenopause, pregnancy, lactation, oral contraceptive use (39), and estrogen or estrogen-progesterone replacement therapy (35,36). Among men, the frequency increases with age (8).Aging in men is accompanied by gradual decreases in gonadal and adrenal production of androgens. The physiological states associated with altered ocular surface system homeostasis in women share one well-known common denominator, a decrease in the amount of testosterone that...

Diverse Mediators Modulate the Chloride Ion Fluxes That Drive Lacrimal Fluid Production

“…21 The decrease of lacrimal gland fluid protein concentration can be attributed to the prolactin-induced redirection of merocrine secretion from the exocrine direction to the paracrine direction. 22,52 However, the decrease of basal fluid production rates in a setting of increased rose Bengal staining and an evidently competent fluid production mechanism suggests that the sensorimotor loop that acutely regulates fluid production is altered in pregnancy.…”

“…21,22 Exposure to mediators that are not cytokines but, rather, G protein-coupled receptor agonists, can also interfere with cholinergically induced Ca 2þ elevation and exocrine b-hexosaminidase secretion. These include the muscarinic cholinergic agonist, carbachol (CCh), at a submaximal dose, 23 and the biogenic amines, histamine, and serotonin (5-HT).…”

Rab27b regulates exocytosis of secretory vesicles in acinar epithelial cells from the lacrimal gland

“…A GFP signal was detected by Western blotting, and its band intensity was measured using the Odyssey imaging software. According to previously established methods (49), secretion into culture medium was normalized to total pellet protein in each well. In previous studies, we showed that only 20 -30% of total cellular syncollin-GFP is released during a typical stimulation period with CCH (14,25).…”

Munc18/SNARE proteins’ regulation of exocytosis in guinea pig duodenal Brunner’s gland acini

“…In contrast, rabbit lacrimal acini seem to follow a similar distribution for these exocytotic proteins as those described in rat pancreatic acini [28] . In fact, like pancreatic acini [11][12][13][14] , apical exocytosis in rabbit lacrimal acini could also be redirected to the basolateral membrane surface by prolactin [29] . The distinct localization of these exocytotic proteins within the family of exocrine tissues is of fundamental importance.…”