Cyclic AMP-Receptor Proteins in Human Salivary Glands

Abstract

In mammalian species, cyclic AMP receptor proteins (cARP) are the regulatory (R) subunits of cyclic AMP-dependent protein kinase (PKA), the cellular effector of cyclic AMP-mediated signal transduction. An isoform of the PKA type II R subunit (RII), cARP, is a polyfunctional protein, present in most tissues and cells. It is expressed in salivary and other glands of rodents, and secreted into the saliva of rats and Man. The aim of the present study was to determine the expression of cARP in human salivary glands using immunoelectron microscopy. Thin sections of normal salivary glands embedded in LR Gold resin were labeled with anti-cARP primary antibody, then with gold-conjugated secondary antibody. Labeling was present in the secretory granules and cytoplasm of parotid, submandibular (SMG) and sublingual gland serous cells. Quantitative analysis showed considerable variability in granule labeling from sample to sample, indicating shifts in expression and cellular location of cARP. Unlike rodent salivary glands, the granules of intercalated and striated duct cells also were labeled. The cytoplasm and granules of mucous cells of the SMG and sublingual glands were unlabeled, while the Golgi complex and filamentous bodies in these cells showed moderate reactivity. Mitochondria and nuclei of both serous and mucous cells were unlabeled. Labeling also was present in the connective tissue adjacent to the epithelial cells. The results indicate that serous cells of the parotid and SMG are the major source of salivary cARP. They also reveal significant species differences in the glandular distribution of RII. RII binds to cytoskeletal and nuclear proteins, and may function to regulate extracellular cyclic AMP levels. Thus, the tissue and cellular distribution of RII may serve as an index of regulation of gene expression and cell differentiation.

Localization of cystic fibrosis transmembrane conductance regulator signaling complexes in human salivary gland striated duct cells

“…The presence of PKA RII and C subunits in several cytoplasmic regions of striated duct cells presumably reflects binding to other AKAPs and their role in a variety of cellular functions. We previously demonstrated that PKA RII subunits are present in the secretory granules of human salivary gland acinar cells (23) and are secreted into saliva (47). The results of the present study confirm that PKA RII subunits are associated with small secretory granules and vesicles in the apical cytoplasm of human striated duct cells (23), as well as with the apical cell membrane.…”

“…We previously demonstrated that PKA RII subunits are present in the secretory granules of human salivary gland acinar cells (23) and are secreted into saliva (47). The results of the present study confirm that PKA RII subunits are associated with small secretory granules and vesicles in the apical cytoplasm of human striated duct cells (23), as well as with the apical cell membrane. We now show that PKA C subunits also are associated with these small granules and vesicles.…”

“…Increased labeling intensity was frequently seen along the luminal membrane. In acinar cells, RII subunit reactivity was strongest in the apical region; previous studies have shown that this reactivity is associated with secretory granules (23). Reactivity for the C subunits of PKA was observed along the luminal membrane of striated duct cells (Fig.…”

Immunocytochemical Localization of Histatins in Human Salivary Glands

“…Amylase and salivary agglutinin [recently demonstrated to be identical to the lung scavenger receptor cysteine-rich protein gp-340 (Prakobphol et al 2000)] are present in the rER, Golgi complex, and in forming and mature granules of parotid and submandibular serous cells (Takano et al 1991(Takano et al ,1993. Acidic proline-rich proteins and the proline-rich polypeptide P-C also are present in the secretory granules of these cells (Takano et al 1993;Kimura et al 1998), and lysozyme and cyclic AMP receptor proteins are present in the serous granules of all three major salivary glands (Machino et al 1986;Miyazaki et al 2001;Piludu et al 2002). In many species, including humans, the secretory granules of serous salivary gland cells display a variety of substructures (reviewed in Tandler and Phillips 1993).…”

Redistribution of Gαs in mouse salivary glands following β-adrenergic stimulation

“…Norepinephrine and vasoactive intestinal peptide stimulate cAMP production in rabbit SMG striated ducts (30), and sympathetic nerve stimulation depletes apical secretory granules in cat SMG striated ducts (31). We have shown that the regulatory and catalytic subunits of type II PKA are associated with the luminal membrane and the small apical secretory vesicles in human striated duct cells (32; Zinn et al, manuscript in preparation). Activation of Gα s and local generation of cAMP could activate PKA, leading to granule exocytosis and/or electrolyte reabsorption, e.g., involving the cystic fibrosis transmembrane conductance regulator (CFTR; 33), by striated duct cells.…”